Flashcards in Topic 1: Atomic Structure and the Periodic Table Deck (132):
What are all substances made from?
What do atoms contain? 3
Where is the nucleus and what does it contain?
It is found in the middle of the atom.
Protons and Neutrons.
What charge does the nucleus have and why?
Positive- because of the protons.
Where is almost the whole mass of the atom concentrated?
Where specifically do electrons move around the nucleus?
In electron shells.
What charge do electrons have?
What are tiny and cover a lot of space?
What determines the volume of electron orbit?
The size of the atom
What part of the atom has virtually no mass?
The number of protons equals what? And why?
The number of electrons (exception of ions).
Because the charge on the electrons is the same size as the charge on the protons, but opposite- so the positive and negative charges cancel out.
Why do ions have an overall charge?
The number of protons doesn't equal the number of electrons.
What does an ion with charge -2 mean?
It has two more electrons than protons.
What does the atomic number tell you?
How many protons there are.
What does the mass number tell you?
The total number of protons and neutrons in the atom.
How do you get the number of neutrons?
Subtract the atomic number from the mass number
Give the definition of an element
An element is a substance made up of atoms that all have the same number of protons in their nucleus.
What number of what describes what type of atom it is?
The number of protons
How many elements are there on the Periodic Table?
118 (roughly 100)
What are isotopes?
They are different forms of the same element, which have the same number of protons but a different number of neutrons.
Isotopes have the same atomic number but a different...
Give an example of a pair of isotopes
Carbon-12 (6 PROTONS, 6 electrons, 6 NEUTRONS)
Carbon-13 (6 PROTONS, 6 electrons, 7 NEUTRONS)
Because elements can exist as a number of different isotopes, what is used instead of mass number when referring to the element as a whole?
The relative atomic mass
What is the relative atomic mass?
An average mass taking into account the different masses and abundances (amounts) of all the isotopes that make up the element.
Formula for working out the relative atomic mass of an element
relative atomic mass= sum of (isotope abundance x isotope mass number) / sum of abundance of all the isotopes
Copper has two stable isotopes. Cu-63 has an abundance of 69.2% and Cu-65 has an abundance of 30.8%. Calculate the relative atomic mass of copper to 1 decimal place.
Relative atomic mass =
(69.2 x 63) + (30.8 x 65) / 69.2 + 30.8
= 4359.6 + 2002 / 100
= 6361.6 / 100
What happens when elements chemically react?
Atoms combine to other atoms to form compounds.
Give the definition of a compound
Compounds are substances formed from two or more elements chemically combined
Atoms of each element are in fixed proportions throughout the compound, held together by?
What does making bonds involve?
Atoms giving away, taking away or sharing electrons. Only the electrons are involved- the nuclei of the atoms aren't affected at all when the bond is made
In a compound, is it easy or difficult to seperate the original elements?
Difficult- a chemical reaction is needed to do it.
During a chemical reaction, at least one new substance is made. What two changes can you always measure?
Change in temperature
Change in energy
What does a compound consist of when it is formed from a metal and non metal?
What is ionic bonding?
The metal atom lose electrons to form positive ions and the non metal atoms gain electrons to form negative ions.
The opposite charges (positive and negative) of the ions mean that they're strongly attracted to each other.
Give an example of compounds that are bonded ionically
What does a compound consist of formed from non metals?
What is covalent bonding?
Each atom sharing an electron(s) with another atom
Give an example of a compound that are bonded covalently
Hydrogen chloride gas
The properties of a compound are usually totally (different of similar) from the properties of the original elements
For example if iron (lustrous magnetic metal) and sulfur (yellow powder) react, the compound formed (iron sulfide) is a dull grey solid lump and doesn't behave anything like iron or sulfur.
Just as elements can be represented by symbols, compounds can be represented by...
What are these compound formulas made up of?
Elemental symbols in the same proportion that elements can be found in the compound
Example of covalent compound formulas
Sulfuric acid: H#2SO#4
Each molecule contains 2 hydrogen atoms, 1 sulfur atom and 4 oxygen atoms.
Calcium hydroxide: Ca(OH)#2
Each molecule contains 1 calcium atom, 2 oxygen and 2 hydrogen atoms.
What do the brackets mean in a formula?
The little number outside the bracket applies to everything INSIDE the bracket
What are chemical changes shown using?
Chemical equations; word or symbol equations
Points on balancing equations
-There must always be the same number of atoms on both sides
-You balance the equation by putting numbers in front of the formulas where needed
-You can't change formulas, you can only put numbers in front of them
Are there chemical bonds between the different parts of a mixture?
The parts of a mixture are either elements or compounds and they can be separated by PHYSICAL methods such as: (5)
What is air a mixture of and can it be separated easily?
Mixture of gases, mainly nitrogen, oxygen, carbon dioxide and argon
Can be separated fairly easily
What is crude oil a mixture of?
Different length hydrocarbon molecules
Being part of a mixture, what is not affected?
The chemical properties of a substance
Filtration and crystallisation are used to separate...
solids from liquids
At the start of the 19th century John Dalton described atoms as what?
Atoms as solid spheres and said that spheres made up the different elements
In 1897, J J Thomson concluded what?
Atoms weren't solid spheres
Atom must contain even smaller, negatively charged particles called electrons (after measurements of charge and mass)
JJ Thomson created the theory known as the what after he felt Dalton's theory of the 'solid sphere' idea of the atomic structure had to be changed?
The plum pudding model
What did the plum pudding model show?
The atom as a ball of positive charge with electrons stuck in it
In 1909, Ernest Rutherford and his student Ernest Marsden conducted what?
The famous alpha particle scattering experiments.
What did Rutherford and Marsden fire at an extremely thin sheet of gold?
Positively charged alpha particles
From the plum pudding model, what were Marsden and Rutherford expecting?
The particles to pass staright through the sheet or be very slightly deflected at most
because the positive charge of each atom was thought to be very spread out through the 'pudding' of the atom.
Were Marsden and Rutherford's expectations proved wrong? How?
While most of the particles did go straight through the gold sheet, some were deflected more than expected and a small number were even deflected backwards.
The plum pudding could not be right.
What did Rutherford produce to explain the new evidence?
The nuclear model of the atom: there's a tiny, positively charged nucleus at the center where most of the mass is concentrated.
A 'cloud' of negative electrons surround the nucleus- so most of the atom is empty space.
When alpha particles came near the concentrated, positive charge of the nucleus, they were deflected. If they were fired directly at the nucleus they deflected backwards. Otherwise, they passed through empty space.
Scientists realised that electrons in a 'cloud' around the nucleus of an atom would be attracted to the nucleus, causing the atom to collapse. What did Niels Bohr's nuclear model of the atom suggest?
Electrons were contained in shells
Electrons orbit the nucleus in these fixed shells and aren't anywhere in between.
Each shell is a fixed distance from the nucleus.
Was Bohr's theory of atomic structure supported by many experiments and help to explain lots of other scientist's observations at the time?
What did further experiments by Rutherford show?
The nucleus can be divided into smaller particles, which each have the same charge as a hydrogen nucleus.
These particles = protons.
20 years after scientists accepted that atoms have a nucleus, who carried out an experiment which provided evidence for what?
Evidence for neutral particles in the nucleus which are now called neutrons
The discovery of the neutrons resulted in a modern day accepted model of the atom called what?
The nuclear model
Electron shell rules:
-Electrons always occupy shells (sometimes called energy levels)
-The lowest shells are always filled first- ones closest to the nucleus
-Only a certain number of electrons are allowed in each shell:
1st shell = 2
2nd shell = 8
3rd shell = 8
-Atoms are much happier when they have full electron shells- like the noble gases in group 0
-In most atoms, the outer shell is not full and this makes the atom want to react to fill it.
Until recently, there were two ways to catgeorise elements:
Their physical and chemical properties
Their relative atomic mass
What did scientists have no idea of until the 20th century?
Elements used to be arranged in order of atomic mass. Why?
The only thing that could be measured was relative atomic mass.
When it was arranged in order of atomic mass, a periodic pattern was noticed in the properties of the elements.
Why were early periodic tables not complete?
Some elements were placed in the wrong group because elements were ordered in the order of relative atomic mass and did not take into account their properties.
Some elements had not yet been discovered.
In 1869, who overcame some of the problems of the early periodic tables by taking 50 unknown elements and arranging them into his Table of Elements- with various gaps?
What did order did Mendeleev switch after taking properties into account? Give an example of this on his table
Order of atomic mass
Te and I- iodine has a smaller relative atomic mass but it is placed after tellurium as it has similar properties to the elements in that group.
Why were gaps left in the periodic table?
To make sure that elements with similar properties stayed in the same groups. Some of these gaps indicated the existence of undiscovered elements and allow Mendeleev to predict what their properties may be.
When the elemental gaps in Mendeleev's table were found what happened?
They fitted the table and helped to confirm Mendeleev's ideas.
For example, Mendeleev made really good predictions about the chemical and physical properties of an element he called ekasilicon, which is known as germanium.
In the periodic table, the elements are laid out in order of increasing...
atomic (proton) number
What does arranging the elements in order of increasing atomic number allow?
Repeating patterns in the properties of the elements to be grouped together (roughly).
Where are metals found on the periodic table?
On the left
Where are non metals found on the periodic table?
On the right
Elements with horizontal similar properties form?
Vertical columns are called?
What does the group number tell you?
How many electrons there are in the outer shell.
If you know the properties of one element what can you predict?
The properties of other elements in that group and
About trends in reactivity e.g. in group 7, reactivity decreases as you go down the group, whereas in group 1 the elements react more vigorously as you go down the group.
What are rows called and what do each new one represent?
Periods and each new period represents another full shell of electrons.
What type of ions are formed when metals react?
Where are the non metals on the periodic table?
At the far right and top of the periodic table
What doesn't generally form positive ions when they react?
Atoms generally react to form what?
Full outer shells; they do this via losing, gaining or sharing electrons
Metals where on the periodic table don't have many electrons to remove?
Metals on the left
Metals towards the bottom of the periodic table have what kind of electrons in relation to the nucleus?
They have electrons which are a long way from the nucleus so feel a weaker attraction
What do metals on the left and the bottom of the periodic table not need energy wise?
They do not need much energy to remove the electrons so it is feasible for the elements to react to form positive ions with full outer shells.
Why do non metals find it difficult to form positive ions?
It is because they are either at the right of the periodic table- where they have lots of electrons to remove to get a full outer shell, or towards the top- where the outer electrons are close to the nucleus so feel a strong attraction.
For non metals, what is most feasible for them to get a full outer shell?
To share or gain electrons
All metals have metallic bonding which causes them to have similar basic physical properties:
-they are strong, but can be bent or hammered into different shapes (malleable)
-they're great at conducting heat and electricity
-they have high melting and boiling points
As non-metals don't have metallic bonding, they don't tend to exhibit the same properties as metals:
-aren't always solids at room temp
-don't generally conduct electricity
-often have a lower density
Where are transition metals on the periodic table?
At the centre
Transition metals are typical metals and have the properties you would expect of a metal:
-good conductors of heat and electricity
What group of metal can have more than one ion?
e.g. copper forms Cu+ and Cu2+ ions
What are transition metal ions like?
Often coloured, and so compounds that contain them are colourful.
e.g. potassium chromate(VI) is yellow and potassium(VII) is purple
What group of metal's compounds often make good catalysts?
e.g. a nickel based catalyst is used in the hydrogenation of alkenes and an iron catalyst is used in the Haber process for making ammonia
Group 1 elements are known as what?
The alkali metals
What are the alkali metals?
Alkali metals have one electron in their outer shell meaning...?
They are very reactive and have similar properities
What group of metals are soft and have low density?
Give the trends for the alkali metals as you go down Group 1:
-Increasing reactivity- the outer electron is more easily lost as the attraction between the nucleus and electron decreases, because the electron is further away from the nucleus the further down the group you go.
-Lower melting and boiling points
-Higher relative atomic mass
The group 1 elements don't need much energy to lose their one outer electron to form a full outer shell, so they ready form what plus ions?
Alkali metals can lose their outer electron so easy that they only ever react to form...
What are alkali metal ionic compounds like?
They are generally white solids that dissolve in water to form colourless solutions
How do the alkali metals react with water?
They react vigorously to produce hydrogen gas and metal hydroxide- salts that dissolve in water to form alkaline solutions.
The more reactive (lower down in the group) an alkali metal is, the more violent the reaction.
The amount of energy given out by the reaction increases down the group- the reaction with potassium release enough energy to ignite hydrogen.
How do the alkali metals react with chlorine?
They act vigorously when heated in chlorine gas to form white metal chloride salts.
As you go down the group, reactivity increases so the reaction with chlorine gets more vigorous.
How do the alkali metals react with oxygen?
They can react with oxygen to form a metal oxide.
Different types of oxide will form depending on the group 1 metal:
e.g. lithium reacts to form lithium oxide
sodium reacts to make a mixture of sodium oxide and sodium peroxide
potassium reacts to form a mixture of potassium peroxide and potassium superoxide
What metals are less dense, strong and hard and have much lower boiling points in comparison to the transition metals?
Group 1 alkali metals
e.g. manganese melts at 2000C, sodium melts at 98C
What are the group 7 elements known as?
What are the Halogens?
Non metals with coloured vapours
Give three characteristics of Fluorine
Very reactive, poisonous, yellow gas
Give three characteristics of Chlorine
Fairly reactive, poisonous, dense green gas
Give three characteristics of Bromine
Dense, poisonous, red-brown volatile liquid
Give three characteristics of Iodine
Dark grey, crystalline solid, purple vapour
All the halogens exist as molecules meaning...?
They exist in pairs (of atoms)
As you go down group 7, what happens?
-become LESS REACTIVE- it's harder to gain an extra electron because the outer shell's further away from the nucleus
-have a higher melting and boiling points
-have higher relative atomic masses
Why do group 7 elements react in similar ways?
Because they all have 7 outer electrons.
Halogens can also share electrons to achieve a full outer shell- via what? Give an example
Via covalent bonding
What is similar about all compounds that form when halogens react with non metals?
They all have similar molecular structures
What do halogens form when they bond with metals?
1- ions called halides (F-, Cl-, Br-, I-)
Halides have what structures?
When can a displacement reaction occur in Halogens?
It can occur between a more reactive halogen and the salt of a less reactive one.
e.g. chlorine can displace bromine and iodine from an aqueous solution of its salt (a bromide or iodide). Bromine will also displace iodine because of the trend in reactivity.
What are elements in group 0 known as?
The noble gases
How many outer shell electrons do the group 0 elements have?
8, apart from helium which has 2
Why are Group 0 halogens not reactive?
As their outer shell is energetically stable they don't need to give up or gain electrons to become more stable, meaning they are inert
What do group 0 exist as as the single gases are NOT bonded to each other?
What colour are group 0 elements at room temperature?
Group 0 elements are inert- what does this mean about their flammability?
They are non flammable, they won't set on fire