1. States of matter + 2. Atoms, elements and compounds Flashcards
Diffusion
The automatic mixing of liquids and gases as a result of the random motion of their particles
What sort of particles diffuse the quickest?
Small, light ones.
Does diffusion take place faster in a liquid or a gas?
Gas, move around faster, more chance of a collision.
Elements
Substances made up of only one type of atom.
Compound
A substance made out of two or more elements chemically bonded together.
Mixture
When substances are mixed together and intermingle but do not react.
A mixture is not a pure substance.
Atomic no.
No. of protons.
BOTTOM NUMBER
Atomic Mass no.
No. of protons plus neutrons.
TOP NUMBER
No. of Protons =
No. of electrons.
What does the number of electrons on the outer shell of an element tell us?
What group it is in, and how it reacts.
Why does the relative atomic mass only count protons and neutrons?
Because electrons weigh 1/2000 of what protons and neutrons weigh, so are generally discounted.
Isotopes
Atoms of the same element with different numbers of neutrons.
Describe the attractive forces in solids
Strong forces of attraction between particles, particles are packed very closely together in a fixed and regular pattern
Describe the attractive forces in liquids
Weaker attractive forces in liquids than in solids, particles are close together in an irregular, unfixed pattern
Describe the attractive forces in gases
No intermolecular forces, particles are in random movement and so there is no defined pattern
Describe the movement in solids
Atoms vibrate in position but can’t change position or move
Describe the movement in liquids
Particles can move and slide past each other which is why liquids adopt the shape of the container they’re in and also why they are able to flow
Describe the movement in gases
Particles are far apart and move quickly (around 500 m/s) in all directions, they collide with each other and with the sides of the container (this is how pressure is created inside a can of gas)
Describe the fixed volume and density in solids
solids have a fixed volume, shape and high density
Describe the fixed volume and density in liquids
Liquids have a fixed volume but not a fixed shape and have a moderate to high density
Describe the fixed volume and density in gases
No fixed volume, since there is a lot of space between the particles, gases can be compressed into a much smaller volume. Gases have low density
What change occurs during melting?
Melting is when a solid changes into a liquid
What does melting require?
Requires heat energy which transforms into kinetic energy, allowing the particles to move
When does melting occur?
Occurs at a specific temperature known as the melting point (m.p.) which is unique to each pure solid
What change occurs during boiling?
Boiling is when a liquid changes into a gas
What does boiling require?
Requires heat which causes bubbles of gas to form below the surface of a liquid, allowing for liquid particles to escape from the surface and within the liquid
When does boiling occur?
Occurs at a specific temperature known as the boiling point (b.p.) which is unique to each pure liquid
What change occurs during freezing?
Freezing is when a liquid changes into a solid
When does freezing occur?
This is the reverse of melting and occurs at exactly the same temperature as melting, hence the melting point and freezing point of a pure substance are the same. Water for example freezes and melts at 0ºC
What does freezing require?
Requires a significant decrease in temperature (or loss of thermal energy) and occurs at a specific temperature which is unique for each pure substance
What change occurs during evaporation?
When a liquid changes into a gas.
What is the difference between boiling and evaporation?
Evaporation occurs only at the surface of liquids where high energy particles can escape from the liquid’s surface at low temperatures, below the b.p. of the liquid
What increases the rate of evaporation?
The larger the surface area and the warmer the liquid/surface, the more quickly a liquid can evaporate
What is required for evaporation? (if anything)
No energy is required for evaporation to occur and it takes place over a range of temperatures
What change occurs during condensation?
When a gas changes into a liquid, usually on cooling
How does condensation occur (in terms of particles)?
When a gas is cooled its particles lose energy and when they bump into each other they lack the energy to bounce away again, instead they group together to form a liquid
What is required for condensation? (if anything)
No energy is required for condensation to occur and it takes place over a range of temperatures
What change occurs during sublimation?
When a solid changes directly into a gas
What example of solids can undergo sublimation?
This happens to only a few solids such as iodine or solid carbon dioxide
What is the reverse reaction of sublimation?
The reverse reaction also happens and is also called sublimation (sometimes called deposition or desublimation)
When does sublimation occurr?
Sublimation occurs at a specific temperature which is unique for a pure substance
In what type of motion are gaseous particles in?
Gaseous particles are in constant and random motion
What happens to gaseous particles when there is an increase in temperature?
An increase in temperature increases the kinetic energy of each particle, as the thermal energy is transformed to kinetic energy, so they move faster
What causes pressure in a container?
The pressure that a gas creates inside a closed container is produced by the gaseous particles hitting the inside walls of the container.
What is the effect of increasing temperature on pressure?
As the temperature increases, the particles in the gas move faster, impacting the container’s walls more frequently
Therefore an increase in temperature causes an increase in pressure
Brownian Motion definition
Brownian motion is defined as the random movement of particles in a liquid or a gas produced by large numbers of collisions with smaller, often invisible particles
What does the observation of brownian motion prove?
the correctness of the kinetic particle theory
Diffusion definition
This is the process by which different gases or different liquids mix and is due to the random motion of their particles
From where to where do diffusing particles move?
Diffusing particles move from an area of high concentration to an area of low concentration, till the concentration of particles is even
Does diffusion require energy?
NO
Diffusion happens on its own and no energy input is required although it occurs faster at higher temperatures
What is the basis of the kinetic theory of matter?
When substances are heated, the particles absorb thermal energy which is converted into kinetic energy
What happens when you heat a solid?
Heating a solid causes its particles to vibrate more and as the temperature increases, they vibrate so much that the solid expands until the structure breaks and the solid melts
What happens when you heat a liquid?
On further heating, the now liquid substance expands more and some particles at the surface gain sufficient energy to overcome the intermolecular forces and evaporate
What happens when the b.p. temperature is reached in a liquid?
When the b.p. temperature is reached, all the particles gain enough energy to escape and the liquids boils
What type of graph can be used to show how changes in temperature affect changes in state?
A heating curve - solid to gas
A cooling curve - gas to solid
What is an example of Brownian Motion?
An example of Brownian motion is the observed jerky and erratic motion of smoke particles as they are hit by the unseen molecules in the air which can be seen under a microscope
What is the basic condition needed to show the Brownian process is occurring?
In all cases, larger and visible particles are caused to move by the random bombardment of smaller, invisible particles
In what state does diffusion happen the fastest?
Diffusion occurs much faster in gases than in liquids as gaseous particles move much quicker than liquid particles
Do gases diffuse at different rates at the same temperature?
YES
- At the same temperature, different gases do not diffuse at the same rate.
What causes the difference in the rate of diffusion in gases?
This is due to the difference in their relative molecular masses
At what relative molecular mass do gas particles diffuse the fastest?
Lighter gas particles can travel faster and hence further, therefore the lower its relative mass the faster a gas will diffuse
What are the three states of matter?
Solids
Liquids
Gases
What state you get depends on what?
How strong the forces of attraction are between the particles of the material
How strong the forces are depends on what three things?
The material
The temperature
The pressure
Describe the formation of solids (attraction? shape? movement?)
Strong forces of attraction between particles holding them together in a fixed position to form a very regular lattice arrangement.
The particles don’t move from position so keep a definite shape and volume.
The particles vibrate about their position - the hotter the solid becomes the more it vibrates (causes them the expand slightly)
Describe the formation of liquids (attraction? shape? movement?)
Weak forces of attraction between the particles. Randomly arranged and free to move past each other - stick close together
Have a definite volume but don’t keep a definite shape- flow to fill container
Particles are constantly moving with random motion. The hotter the liquid gets the faster it moves causes them to expand slightly
Describe the formation of gases (attraction? shape? movement?)
No forces of attraction between particles (very weak if any) Free to move and are far apart. Particles travel in straight lines
Don’t keep a definite shape or volume and will always fill container
Particles move constantly with random motion. The hotter it gets the faster they move . They expand when heated and pressure increases.
What is a physical change?
When the particles don’t change just their arrangement or energy
Solid - Liquid
Melting
Liquid - Gas
Evaporating
Gas - Liquid
Condensing
Liquid - Solid
Freezing
Solid - Gas
Subliming
What do melting and evaporating and subliming have in common?
Heat energy is supplied between the state
What do freezing and condensing have in common?
Heat energy is given out between the states
Describe the energy of the particles from a solid to a liquid
When the solid is heated its particles gain more energy. This makes them vibrate more which weakens the forces of attraction holding the solid together making the solid expand.
At a certain temperature the particles have enough energy to break free from their positions. This is melting (solid - liquid)
Describe the energy of the particles from a liquid to a gas
When a liquid is heated the particles have more energy. The energy makes the particles move faster weakening and breaking the bonds holding the liquid together.
At a a certain temperature the particles have enough energy to break their bonds. This is evaporating (liquid - gas)
What three experiments can be used to show the movement of particles?
Potassium Manganate(Vll) and water
Ammonia and Hydrogen Chloride
Bromine gas and air
Define the process evident in all three experiments
Diffusion - the movement of particles through a liquid or gas from an area of high concentration to an area of lower concentration until a uniform concentration is achieved
Describe the potassium manganate experiment with water
1) Get a beaker of water and place some potassium manganate at the bottom
2) Watch as the purple colour of the potassium manganate slowly spreads to fill the beaker - this is diffusion as the particles are diffusing out among the water particles
What causes the particles in the potassium manganate to eventually spread out evenly?
The random motion of particles in a liquid
What happens if you add more water to the final solution of the potassium manganate?
The potassium manganate would spread out even further apart and the solution would be less purple because of dilution
What does aqueous ammonia and hydrochloric acid give off?
Aqueous ammonia - ammonia gas
Hydrochloric acid - Hydrogen chloride gas
How should you set up the experiment with ammonia and hydrogen chloride?
In a glass tube have a cotton wool soaked in aqueous ammonia at one end and at the other, cotton wool soaked in hydrochloric acid.
What happens in the ammonia and hydrogen chloride experiment?
The ammonia gas diffuses from one end of the tube and the hydrochloric acid diffuses from the other. When they meet they react to form ammonium chloride (a white ring in the glass tube)
Describe the experiment using bromine gas?
Fill half a gas jar with bromide gas and the other with air - separate with gases with a glass plate. When you remove the glass plate watch how the bromide gas slowly diffuses through the air.
What is bromine?
A brown gas that is very smelly
What causes the bromine to eventually diffuse right through the air?
The random motion of the particles
Why doesn’t the ring of ammonium chloride form in the middle?
If forms closest to the end of the tube where the hydrochloric acid was because the particles of ammonia are smaller and lighter than the hydrogen chloride, so diffuse through the air more quickly
What is a atom?
The smallest particle of a chemical element that can exist - all substances are made up of atoms
What is a molecule?
A group of atoms bonded together by covalent bonds (can be made up of one element or more than one element)
What is an element?
Substances that consist of one type of atom that cannot be broken down any simpler by use of heat or electricity
Give an example of an element
Copper (any element in the period table)
What is a compound?
Substances made up of two or more different elements which are chemically joined together
Give an example of a compound and how it is formed
Carbon dioxide - One carbon atom has boned with two oxygen atoms to form a molecule of carbon dioxide, with the formula CO2
Why is it very difficult to separate two original elements after they have been chemically combined? Give an example
The properties of the compound are often totally different from the properties of the original element.
For example a mixture of iron and sulphur is heated and react togetehr to form iron sulphide. Iron sulphide isn’t like iron (not attracted to a magnet) nor like sulphur (not yellow)
What is a mixture?
Molecules of elements and mixtures simply mixed together without chemical bonds
Give two examples of a mixture
1) Air - is a mixture of gases mainly nitrogen, oxygen, carbon dioxide and argon
2) Crude oil - mixture of different lengths hydrocarbon molecules
Can you separate mixtures easily and if so, with what methods?
Yes - there are no chemical bonds between the different parts of a mixture so can be separated by the following physical methods;
Distillation
Fractional
Filtration
Crystallisation
Paper chromatography
What is a solvent?
The liquid in which a solute dissolves
What is a solute?
The substance that dissolves in a liquid to form a solution
What does soluble mean?
A substance that can dissolve
What does insoluble mean?
What does insoluble mean?
A substance that cannot dissolve
What is filtration used to separate?
Insoluble solids from a liquid (and purification)
What is crystallisation used for?
What is crystallisation used for?
Separating soluble solids from a solution
What is the method for crystallising a product?
Pour solution in evaporating dish
Slowly heat until crystals start to form then stop *solvent evaporates solution making it more concentrated
Remove dish from heat and put in warm place *rest of solvent will evaporate
Dry the product (either in a drying oven or desiccator)
What does a desiccator contain?
Chemicals that remove water from the surroundings
What can you separate using both filtration and crystallisation!
Rock salt
What is rock salt and what is it about their physical properties that make them easy to separate?
Rock salt is a mixture of salt and sand. Salt and sand are both compounds but salt dissolves in water and sand doesn’t
Give the four steps for separating rock salt
1) Grinding - grind rock and salt with a pestle and mortar
2) Dissolve - dissolve in beaker and stir
3) Filtering - filter through filter paper in a funnel
4) Crystallisation - evaporate in a evaporating dish
Why does sand collect in the filter paper?
It is insoluble (doesn’t dissolve), so stays as big grains. These wont fit through the tiny holes in the filter paper
Why does salt go through the filter paper?
It is soluble and dissolved in the solution - when water is evaporated from it, the salt forms a crystal in the evaporating dish
What is chromatography in particular paper chromatography?
Another method for separating out mixtures - paper chromatography separates out dyes
What happens in the ammonia and hydrogen chloride experiment?
The ammonia gas diffuses from one end of the tube and the hydrochloric acid diffuses from the other. When they meet they react to form ammonium chloride (a white ring in the glass tube)
Go through the method of chromatography
1) Draw a line near the bottom of the filer paper (in pencil)
2) Add spots of different dyes to the line in regular intervals
3) Attach a lollipop stick to the top of the sheet and dip a tiny bit of the paper into beaker of solvent
4) The solvent seeps up the paper carrying the dyes with it
5) Each dyes moves up at different rates and forms spots
6) The end result is called chromatogram.
Why should you draw the line with pencil not pen?
Pencil marks are insoluble and wont react with the solvent
Why does chromatography seperate mixtures?
It works because different dyes move up the paper at different rates. Some stick to the paper and others will dissolve more readily in the solvent and travel more.
When you dip the paper in the solvent why should you make sure that the dyes aren’t touching the solvent?
So they don’t dissolve in it
When you dip the paper in the solvent why should you make sure that the dyes aren’t touching the solvent?
So they don’t dissolve in it
The distance the dyes travel up the paper depend on what?
The solvent and the paper used
How can chromatography help identify dyes?
You can work out dyes that are present in an unknown substance by making chromatograms of the unknown substance and for some reference materials (dyes you think are in it)
You then compare the chromatograms - spots on the chromatograms roe the unknown that match the spots on the chromatograms of the reference materials means the dyes are the same
What happens in the ammonia and hydrogen chloride experiment?
The ammonia gas diffuses from one end of the tube and the hydrochloric acid diffuses from the other. When they meet they react to form ammonium chloride (a white ring in the glass tube)
When you dip the paper in the solvent why should you make sure that the dyes aren’t touching the solvent?
So they don’t dissolve in it
The distance the dyes travel up the paper depend on what?
The solvent and the paper used
What are the two types of distillation called?
Simple and fractional
How can chromatography help identify dyes?
You can work out dyes that are present in an unknown substance by making chromatograms of the unknown substance and for some reference materials (dyes you think are in it)
You then compare the chromatograms - spots on the chromatograms roe the unknown that match the spots on the chromatograms of the reference materials means the dyes are the same
When you dip the paper in the solvent why should you make sure that the dyes aren’t touching the solvent?
So they don’t dissolve in it
Describe what happens in simple distillation
1) The solution is heated - the part with the lowest bp evaporates
2) The vapour is then cooled, condenses (turns back to a liquid) and collected
3) The rest of the solution is left behind in the flask
Give an example of a solution you could seperate in simple distillation
Pure water from seawater - you’ll end up with salt left in the flask
What is the problem with simple distillation which makes fractional distillation better?
You can only separate things with very different bp in simple distillation
Give an example of a solution you could seperate in simple distillation
Pure water from seawater - you’ll end up with salt left in the flask
When you dip the paper in the solvent why should you make sure that the dyes aren’t touching the solvent?
So they don’t dissolve in it
Why does chromatography seperate mixtures?
It works because different dyes move up the paper at different rates. Some stick to the paper and others will dissolve more readily in the solvent and travel more.
The distance the dyes travel up the paper depend on what?
The solvent and the paper used
How can chromatography help identify dyes?
You can work out dyes that are present in an unknown substance by making chromatograms of the unknown substance and for some reference materials (dyes you think are in it)
You then compare the chromatograms - spots on the chromatograms roe the unknown that match the spots on the chromatograms of the reference materials means the dyes are the same
What are the two types of distillation called?
Simple and fractional
Describe what happens in simple distillation
1) The solution is heated - the part with the lowest bp evaporates
2) The vapour is then cooled, condenses (turns back to a liquid) and collected
3) The rest of the solution is left behind in the flask
Give an example of a solution you could seperate in simple distillation
Pure water from seawater - you’ll end up with salt left in the flask
What is the problem with simple distillation which makes fractional distillation better?
You can only separate things with very different bp in simple distillation
Describe what happens in fractional distillation
1) You put your mixture in a flask then stick a fractionating column on top - heat it
2) The liquid with the lowest bp evaporates first (when the temp on the thermometer matches the bp it reaches the top of the column)
3) Liquids with the highest bp might also evaporate (only bet part of the way before condensing because column is cooler
4) When the first liquid has collected you raises the temperature until the next one reaches the top
What is simple distillation used to seperate out?
Solutions - liquids
What do atoms consist of?
A central nucleus, composed of protons and neutrons, surrounded by electrons, orbiting in shells
What makes the nucleus have a positive charge? Why is almost the whole mass of the atom concentrated in the nucleus?
The protons are heavy and positively charged
Describe a neutron and electron
Neutrons are heavy and have a neutral charge
- Protons are tiny and light and have a negative charge
What is the relative mass and charge of protons, neutrons and electrons?
Proton - mass 1, charge +1
Neutron - mass 1, charge 0
Electron - mass 1/2000, charge -1
What is the atomic number?
The number of protons
Where does the mass number next to the symbol of the element?
Top left hand corner
Where does the atomic number go next to the symbol of the element?
Bottom left hand corner
What is the mass number?
The number of protons and neutrons
How do you work out the number of neutrons?
Subtract the atomic number from the mass number
Atoms of the same element all have what the same?
The number of protons
Atoms of different elements will have different what?
Number of protons
What is the relative atomic mass?
A measure of the mass of one atom of the element compared with the mass of an atom of C-12 (mass is exactly 12) - the average mass of all isotopes of an element
What two things do you need to know to work out the relative atomic mass?
Relative mass of each isotope and its relative abundance
What does the relative abundance mean?
How much there is of the each isotope compared to the total amount of the element in the world
What is the equation for working out the relative atomic mass?
(% of isotope 1 × mass of isotope 1) + (% of isotope 2 × mass of isotope 2) ÷ 100
What is an isotope?
Atoms that have the same number of protons and electrons but different number of neutrons
same proton number
different mass numbers
Give an example of an isotope
C-12 and C-14 (used in carbon dating)
What does the period table show?
Elements put in order of increasing atomic number
How is the period table laid out?
Elements with similar properties are put in the same column (group)
What group the elements are put into corresponds to what?
The number of electrons the elements have on their outer shell (group 1 have 1, group 2 have 2…) This is why there properties are similar
What are the five electron shell rules?
1) Electrons always occupy shells (energy levels)
2) Lowest energy levels are always filled first - closest to the nucleus
3) Only a certain number of electrons are allowed in each shell
4) Atoms are happy when they have full electron shells - like the noble gases
5) In most atoms the outer shell is not full making the atom want to react
What are the certain number of electrons allowed in each shell?
1st shell = 2
2nd shell = 8
3rd shell = 8 (still filling)
What is the electronic configuration?
The distribution of electrons in an atom
How do you work out the electronic configuration?
Use your period table and the electron shell rule (atomic number = protons and the no. of protons = no. of electrons)
What are the electronic configurations of the first 20 elements?
Atomic numbers;
H - 1
He - 2
Li - 3
Be - 4
B - 5
C - 6
N - 7
O - 8
F - 9
Ne - 10
Na - 11
Mg - 12
Al - 13
Si - 14
P - 15
S - 16
Cl - 17
Ar - 18
K - 19
Ca - 20
H - 1
He - 2
Li - 2.1
Be - 2.2
B - 2.3
C - 2.4
N - 2.5
O - 2.6
F - 2.7
Ne - 2.8
Na - 2.8.1
Mg - 2.8.2
Al - 2.8.3
Si - 2.8.4
P - 2.8.5
S - 2.8.6
Cl - 2.8.7
Ar - 2.8.8
K - 2.8.8.1
Ca - 2.8.8.2
What is the number of outer electrons in each of the following groups?
Group 1
Group 2
Group 3
Group 4
Group 5
Group 6
Group 7
Group 0
Group 1 - 1
Group 2 - 2
Group 3 - 3
Group 4 - 4
Group 5 - 5
Group 6 - 6
Group 7 - 7
Group 0 - 0
What is diffusion?
the movement of particles from a region of high concentration to a region of lower concentration
What is Brownian motion?
random molecular bombardment of large visible particles by molecules, atoms or ions
Where is evidence for Brownian motion?
Observations of the motion of tiny visible particles suspended in liquids or gases
Why is rate of diffusion dependent on molecular mass?
Greater the molecular mass => heavier the molecule
Molecules with lower mass move faster than those with higher mass
Lighter molecules diffuse faster than heavier molecules
What is the kinetic theory? (3)
All matter consists of particles
There are forces of attraction between the particles
Particles possess kinetic energy to vibrate and move
What is the relative charge of a proton?
+1
What is the relative charge of a neutron?
no charge
What is the relative charge of an electron?
-1
What is the relative mass of a proton?
1
What is the relative mass of a neutron?
1
What is the relative mass of an electron?
0.00054 (1/2000)
What is a proton number?
number of protons in the nucleus of an atom
What is a nucleon (mass) number?
total number of protons and neutrons in the nucleus of an atom
What are isotopes?
atoms of the same element which have the same proton number but a different nucleon number
Why do isotopes have the same properties?
they have the same number of electrons in their outer shell
What are the two types of isotopes?
radioactive
non radioactive
What is a medical use of radioisotopes?
Sterilizing equipment
Cancer treatment
What is an industrial use of radioisotopes?
Checking for oil leaks in pipelines
What is an element?
A substance made of one type of atom
What is a mixture?
substance contains two or more elements or compounds that are not chemically bonded together
What is an alloy?
a mixture of a metal with other elements
What is an ion?
Electrically charged particle
How are ions formed?
Electron loss/gain
What is a compound?
substance made up of two or more different types of atoms joined together by chemical bonds
What is an ionic bond?
Attraction between positive ions and negative ions
What is an ionic bond between?
Metals + non-metals
How are ionic bonds formed?
Ions transfer electrons from one atom to another
An ionic lattice has + & - ions and is held together by
strong electrostatic bonds
What are 4 properties of ionic compounds?
High fixed points
Poor conductors as solid
Hard
Soluble in water
Why do ionic compounds have high fixed points?
(ionic bonds strong)
◆ Lots of energy required to overcome electrostatic attraction
Why are ionic compounds poor conductors as solids?
no moving/free electrons
Why are ionic compounds good conductors as liquids?
Conducts electricity as liquid (charged ions free to move)
When is a covalent bond formed?
when atoms share a pair of electrons
What is an covalent bond between?
Non-metals + Non-metals
What are molecules?
a group of atoms held together by COVALENT bonds
What are 3 properties of covalent compounds?
Low fixed points
Do not conduct electricity
Insoluble in water, but dissolve in organic solvents
Why don’t covalent compounds conduct electricity?
atoms not charged
Why do covalent compounds have low fixed points?
the weak intermolecular attractive forces
What are elements made out of?
Elements are made of tiny particles of matter called atoms
What are atoms made out of?
Each atom is made of subatomic particles called protons, neutrons and electrons
Why can’t we use conventional units e.g kg to compare the masses of atoms?
Their size is so tiny that we can’t really compare their masses in conventional units such as kilograms or grams
What unit is used to show the mass of an atom?
a unit called the relative atomic mass is used
What is one relative atomic mass unit equal to?
One relative atomic mass unit is equal to the mass of a carbon-12 atom.
Why does the relative atomic mass not have units?
All other elements are measured relative to the mass of a carbon-12 atom and since these are ratios, the relative atomic mass has no units
What is the relative mass of a proton?
1
What is the relative mass of a neutron?
1
What is the relative mass of an electron?
1/1840
What is the charge of a proton?
+1
What is the charge of a neutron?
0 (neutral)
What is the charge of an electron?
-1
What is the atomic number?
The atomic number (or proton number) is the number of protons in the nucleus of an atom.
What is the symbol for the atomic number?
Z
What does the atomic number also show? (apart from number of protons)
What does this determine?
It is also the number of electrons present in an atom and determines the position of the element on the Periodic Table
What is the nucleon number?
Nucleon number (or mass number) is the total number of protons and neutrons in the nucleus of an atom
What is the symbol for the nucleon number?
A
How can you calculate the number of neutrons using the nucleon and proton number?
The nucleon number minus the proton number gives you the number of neutrons of an atom
What are nucleons?
protons and neutrons can collectively be called nucleons.
What do electrons move around in?
They move in orbital paths called shells
Where is the mass of an atom contained and why?
The mass of the electron is negligible, hence the mass of an atom is contained within the nucleus where the neutron and proton reside
How are elements arranged on the periodic table?
Elements are arranged on the Periodic table in order of increasing atomic number where each element has one proton more than the element preceding it
What are the vertical columns in the periodic table called?
The table is arranged in vertical columns called Groups numbered I – VIII
What are the rows in the periodic table called?
Periods
What do elements in the same group have?
Elements in the same group have the same amount of electrons in their outer shell, which gives them similar chemical properties
Isotope definition
Isotopes are atoms of the same element that contain the same number of protons and electrons but a different number of neutrons.
What is the symbol for an isotope?
The symbol for an isotope is the chemical symbol (or word) followed by a dash and then the mass number.
Into what two categories can isotopes be divided?
radioactive and non-radioactive
Why are radioisotopes unstable?
Radioactive isotopes (radioisotopes) are unstable due to the imbalance of neutrons and protons
What does the imbalance of neutrons and protons in radioisotopes lead to?
causes the nucleus to decay over time through nuclear fission and emit radiation
What are examples of radioisotopes?
tritium and carbon-14
Does decay occur at the same rate for each isotope?
NO
Decay occurs at a different rate for each isotope
What is half-life?
the time taken for the radioactivity of an isotope to decrease by 50% is constant for that particular isotope and is known as the half-life
What are the properties of non-radioactive isotopes?
Non-radioactive isotopes are stable atoms which really only differ in their mass
What are the 3 medical uses for radioisotopes?
to treat cancer
medical tracers
to sterilise medical instruments
How are radioisotopes used to treat cancer?
Radiation is extremely harmful and kills cells so isotopes are used to treat cancer. The isotope cobalt-60 is frequently used for this purpose
How are radioisotopes used as medical tracers?
Medical tracers as certain parts of the body absorb isotopes and others do not. In this way an isotope can be injected into the blood and its path through the body traced with a radioactive detecting camera, revealing the flow of blood through bodily systems
How are radioisotopes used to sterilise medical equipment?
Medical instruments and materials are routinely sterilised by exposure to radiation, which kills any bacteria present
What are 3 industrial uses of radioisotopes?
radioactive dating
to detect leaks
to power power plants
How are radioisotopes used in radioactive dating?
Radioactive dating uses the carbon-14 isotope to date carbon-containing materials such as organic matter, rocks and other artefacts
How are radioisotopes used in detecting leaks?
Similar to medical use, radioactive tracers are deployed to detect leaks in gas or oil pipes
How are radioisotopes used to power power plants?
The radioactive isotope uranium-235 is used as nuclear in power plants in controlled fission reactions
Do isotopes of the same element display the same chemical characteristics?
Yes
Why do isotopes of the same element display the same chemical characteristics?
This is because they have the same number of electrons in their outer shells and this is what determines an atom’s chemistry
The difference between isotopes is the neutrons which are neutral particles within the nucleus and add mass only
How can we represent the structure of an atom?
using diagrams called electron shell diagrams
- by writing out a special notation called the electronic configuration
What is the correlation between the distance of the shell away from the nucleus and its energy?
The further away from the nucleus then the more energy a shell has.
What is the outermost shell called?
The outermost shell of an atom is called the valence shell
Why is it important for an atom to try and gain a full valence shell?
an atom is much more stable if it can manage to completely fill this shell with electrons
What does the last notation in the electronic configuration show?
The last notation shows the number of outer electrons the atom has, showing the Group that element is in
What do elements in the same group have in common?
Elements in the same Group have the same number of outer shell electrons
What property do all the noble gases share?
All of the noble gases are unreactive as they have full outer shells and are thus very stable
Element definition
A substance made of atoms that all contain the same number of protons (one type of atom) and cannot be split into anything simpler
Compound definition
A pure substance made up of two or more elements chemically combined
Can compounds be separated into their elements by physical means?
no
Mixture definition
A combination of two or more substances (elements and/or compounds) that are not chemically combined
Can mixtures be separated by physical methods?
YES
Mixtures can be separated by physical methods such as filtration or evaporation
What two broad types can elements be divided into?
They can be divided into two broad types: metals and nonmetals
What is a metalloid?
small number of elements display properties of both types (metal and non-metal)
What are the 6 key properties of metals?
Conduct heat and electricity
Are malleable and ductile (can be hammered and pulled into different shapes)
Tend to be lustrous (shiny)
Have high density and usually have high melting points
Form positive ions through electron loss
Form basic oxides
What are the 6 key properties of non-metals?
Do not conduct heat and electricity
Are brittle and delicate when solid and easily break up
Tend to be dull and non-reflective
Have low density and low melting points (many are gases at room temperature)
Form negative ions through electron gain (except for hydrogen)
Form acidic oxides
What are alloys?
Alloys are mixtures of metals, where the metals are mixed together but are not chemically combined
What can alloys be made out of?
They can be made from metals mixed with nonmetals such as carbon
Why are alloys preferable over pure metals?
Alloys often have properties that can be very different to the metals they contain, for example they can have more strength, hardness or resistance to corrosion or extreme temperatures
How are alloys stronger than pure metals?
Alloys contain atoms of different sizes, which distorts the regular arrangements of atoms
This makes it more difficult for the layers to slide over each other, so they are usually much harder than the pure metal
What is an example of an alloy?
Brass is a common example of an alloy which contains 70% copper and 30% zinc
Ion definition
An ion is an electrically charged atom or group of atoms formed by the loss or gain of electrons
Why do ions gain/loose electrons?
This loss or gain of electrons takes place to gain a full outer shell of electrons
What is the electronic structure of an ion the same as?
The electronic structure of an ion will be the same as that of a noble gas – such as helium, neon and argon
Do metals lose or gain electrons to form ions?
All metals lose electrons to other atoms to become positively charged ions
Do non-metals lose or gain electrons to form ions?
All non-metals gain electrons from other atoms to become negatively charged ions
How are ionic compounds held together?
The positive and negative charges are held together by the strong electrostatic forces of attraction between opposite charges.
What does the lattice structure refer to?
Lattice structure refers to the arrangement of the atoms of a substance in 3D space
How are atoms arranged in a lattice structure?
In lattice structures, the atoms are arranged in an ordered and repeating fashion
How is a lattice formed?
The lattices formed by ionic compounds consist of a regular arrangement of alternating positive and negative ions
How are covalent compounds formed?
Covalent compounds are formed when electrons are shared between atoms
What type of elements can participate in covalent bonding?
Only non-metal elements
What is similar between ionic and covalent bonding?
As in ionic bonding, each atom gains a full outer shell of electrons
What are molecules?
When two or more atoms are chemically bonded together, we describe them as ‘molecules’
Look at covalent compound diagrams 3.3
yes ;)
What is the difference in melting and boiling points in ionic and covalent compounds?
I - Have high melting and boiling points so ionic compounds are usually solid at room temperature
C - Have low melting and boiling points so covalent compounds are usually liquids or gases at room temperature
What is the difference in volatility in ionic and covalent compounds?
I - Not volatile so they don’t evaporate easily
C - Usually volatile which is why many covalent organic compounds have distinct aromas
What is the difference in water solubility in ionic and covalent compounds?
I - Usually water-soluble as both ionic compounds and water are polar
C - Usually not water-soluble as covalent compounds tend to be non-polar but can dissolve in organic solvents
What is the difference in ability to conduct electricity in ionic and covalent compounds?
I - Conduct electricity in molten state or in solution as they have ions that can move and carry a charge
C - Cannot conduct electricity as all electrons are involved in bonding so there are no free electrons or ions to carry the charge
Why do ionic compounds have high melting and boiling points?
This is because the oppositely charged ions in the lattice structure are attracted to each other by strong electrostatic forces which hold them firmly in place
Large amounts of energy are needed to overcome these forces so the m.p. and b.p. are high
Why do covalent compounds have lower melting and boiling points?
Simple covalent substances, such as carbon dioxide and methane, have very strong covalent bonds between the atoms in each molecule, but much weaker intermolecular forces between individual molecules
When one of these substances melts or boils, it is these weak intermolecular forces that break, not the strong covalent bonds
Less energy is needed to break the molecules apart, so they have lower m.p. and b.p. than ionic compounds
What is an allotrope?
Different atomic or molecular arrangements of the same element in the same physical state
What are diamond and graphite?
allotropes of carbon which have giant covalent structures
What do giant covalent structures look like?
This class of substances contains a lot of non-metal atoms, each joined to adjacent atoms by covalent bonds forming a giant lattice structure
Do giant covalent structures have high or low melting and boiling points? Why?
Giant covalent structures have HIGH melting and boiling points as they have many strong covalent bonds that need to be broken down
What is the structure of diamond?
Each carbon atom bonds with four other carbons, forming a tetrahedron
Describe the bonds in diamond
All the covalent bonds are identical and strong with no weak intermolecular forces
3 properties of diamond
Does not conduct electricity
Has a very high melting point
Is extremely hard and dense (3.51 g/cm3)
In what two ways can diamond be used?
Diamond is used in jewellery and as cutting tools
What is the structure of graphite?
Each carbon atom is bonded to three others forming layers of hexagonal-shaped forms, leaving one free electron per carbon atom
How can graphite conduct electricity?
These free electrons exist in between the layers and are free to move and carry charge, hence graphite can conduct electricity
Describe the bonds in graphite
The covalent bonds within the layers are very strong but the layers are connected to each other by weak intermolecular forces only, hence the layers can slide over each other making graphite slippery and smooth
3 properties of graphite
Conducts electricity
Has a very high melting point
Is soft and slippery, less dense than diamond (2.25 g/cm3)
What are 3 uses of graphite?
used in pencils
used s an industrial lubricant, in engines and in locks
used to make non-reactive electrodes for electrolysis
What type of compound is SiO2?
macromolecular compound
In what forms can SiO2 occur naturally?
sand and quartz
Describe the bonds in silicon dioxide
Each oxygen atom forms covalent bonds with 2 silicon atoms and each silicon atom in turn forms covalent bonds with 4 oxygen atoms
What shape is formed in the structure of SiO2?
A tetrahedron is formed with one silicon atom and four oxygen atoms, similar as in diamond
What giant covalent structure does SiO2 have similar properties to? Why?
SiO2 has lots of very strong covalent bonds and no intermolecular forces so it has similar properties to diamond
Properties of SiO2
It is very hard, has a very high boiling point, is insoluble in water and does not conduct electricity
What is SiO2 used for?
SiO2 is cheap since it is available naturally and is used to make sandpaper and to line the inside of furnaces
How are metal atoms held together?
Metal atoms are held together strongly by metallic bonding
How do metal ions become positively charged in a metallic lattice?
Within the metal lattice, the atoms lose their valence electrons and become positively charged
What are the electrons in a metallic lattice called and why?
The valence electrons no longer belong to any metal atom and are said to be delocalised
They move freely between the positive metal ions like a sea of electrons
Why are metallic bonds so strong?
Metallic bonds are strong and are a result of the attraction between the positive metal ions and the negatively charged delocalised electrons
What is the link between metallic bonding and the high melting and boiling points of metals?
There are many strong metallic bonds in giant metallic structures
A lot of heat energy is needed to overcome forces and break these bonds
What is the link between metallic bonding and the ability to conduct electricity of metals?
There are free electrons available to move and carry charge
Electrons entering one end of the metal cause a delocalised electron to displace itself from the other end
Hence electrons can flow so electricity is conducted
What is the link between metallic bonding and metals being malleable and ductile?
Layers of positive ions can slide over one another and take up different positions
Metallic bonding is not disrupted as the valence electrons do not belong to any particular metal atom so the delocalised electrons will move with them
Metallic bonds are thus not broken and as a result metals are strong but flexible
They can be hammered and bent into different shapes without breaking
Covalent Bonding vs Ionic Bonding
Sharing electrons vs transferring electrons.
Giant Ionic Lattice
A huge 3D network of ions, held together by electrostatic attraction (ionic bonding).
Group 1 Ionic Charge
1+
Group 2 Ionic Charge
2+
Group 3 Ionic Charge
3+
Group 4 Ionic Charge
Group 4 don’t form Ions.
Group 5 Ionic Charge
3-
Group 6 Ionic Charge
2-
Group 7 Ionic Charge
1-
Group 0 Ionic Charge
Group 0 never form ions.
Electrostatic Attraction
The force of attraction between positively and negatively charged ions. Act in all directions.
Giant Ionic Structure Facts.
Held together by strong electrostatic attraction.
Very high melting and boiling points because of this.
What happens when an ionic solid melts and becomes a liquid?
The ions are free to move anywhere in the liquid.
Attracted to oppositely charged electrodes dipped into the liquid.
Therefore, they carry their electrical charge through the liquid.
Conduct Electricity.
Water also separates many ionic solids and allows them to conduct electricity.The ions are free to move anywhere in the liquid.
Attracted to oppositely charged electrodes dipped into the liquid.
Therefore, they carry their electrical charge through the liquid.
Conduct Electricity.
Water also separates many ionic solids and allows them to conduct electricity.
