What does the mass number of an element tell us?
The total number of protons and neutrons in an atom of that element
What is the atomic number of an element?
The number of protons in one atom of that element.
How can you find out the number of neutrons in an element?
Subtract the atomic number from the mass numbe
When are compounds formed?
Compounds are made when atoms of two or more elements are chemically combined together. For example, carbon dioxide is a compound formed from a chemical reaction between carbon and oxygen.
What is meant by the term ‘isotope’?
Isotopes are different atomic forms of the same element, which have the same number of protons but a different number of neutrons. (They have the same atomic number but different mass numbers).
Name the three different types of bonding and which types of elements they occur between?
- Metallic - a metal and a metal
- Covalent - a non metal and a non metal
- Ionic - a metal and a non metal
What is an ion?
An atom that has lost or gained electrons
Ionic compounds have a regular ………… structure.
Ionic compounds have a regular lattice structure.
What happens in ionic bonding?
Atoms lose or gain electrons to form charged particles (called ions), which are then strongly attracted to one another.
Give 4 features of ionic compounds
- Strong attractions between ions
- High melting and boiling point
- Once melted, they’ll carry an electrical current
- They dissolve easily - the ions will separate and are free to move in the solution so they’ll carry electrical current.
Which groups of elements are most likely to form ions? Why?
Groups 1, 2, 6 and 7
Because the small number of electrons in the outer shells of Group 1 and 2 elements are easily lost (making them very reactive). Similarly, elements in Groups 6 and 7 only have 1/2 electrons to gain to make their outer energy levels full.
What happens to the atoms when sodium and chlorine are reacted with one another?
Na becomes Na + because the electron is lost from it’s outer shell
Cl becomes Cl- because it gains an electron from the sodium.
Draw the electronic structure of Sodium Chloride and Magnesium Oxide
How do atoms form covalent bonds?
When they share electrons with one another to fill their outer energy levels
List 7 important examples of covalent bonding
H2 - Hydrogen
Cl2 - Chlorine
CH4 - Methane
HCl - Hydrogen Chloride
NH3 - Ammonia
H2O - Water
O2 - Oxygen
Draw the electronic structures of each of these covalent bonds.
Atoms form …. …… covalent bonds, which make small ………. of several atoms. By contrast, the forces of attraction between these ……….. are …. ……
Atoms form very strong covalent bonds, which make small molecules of several atoms. By contrast, the forces of attraction between these molecules are very weak.
List four features of simple molecular covalent bonds
- Weak intermolecular forces
- Low melting and boiling points
- Most molecular substances are gases or liquids ar room temperature, but they can be solid
- They don’t conduct electricity because there are no ions available to act as current carriers.
Give three examples of giant covalent structures.
What is the alterative term used to describe them?
- Silicon Dioxide
Why is diamond the hardest natural substance to exist?
Each carbon atom forms 4 covalent bonds, creating an extremely rigid structure.
Give 3 properties of graphite and draw its atomic structure
- Each carbon atoms forms three covalent bonds, creating layers which are free to slide over one another (makng it soft and slippery)
- The layers are able to rub off (this is how a pencil works) due to weak intermolecular forces
- Graphite is the only non metal which is a good conductor of heat and electricity because each carbon atom has one delocalised electron.
What is sand made of? Draw this substance’s giant covalent structure
Sand is made of silicon and oxygen atoms
What is the most important part of metallic bonding and which properties of metals do they create?
The sea of delocalised electrons that come from the outer shell of every metal atom in the structure.
- They are free to move, anad therefore make metals good conductors of heat/electricity
- They hold the atoms together in a regular structure because there are strong forces of electrostatic attraction between positive metal ions and negative electrons.
- They allow layers of atoms to slide over one another, allowing metals to be bent and shaped.
Why are metal alloys harder than pure metals?
Different elements have different sized atoms, meaning when two metals are mixed together, the neat layers are distorted and it is more difficult for them to slide over each other.
Smart materials …… ……….. depending on the ……… eg. temperature
Smart materials behave differently, depending on the conditions eg. temperature
Give one example of a smart material, describe it’s properties and what it is used for
Nitinol (half nickel, half titanium) is a “shape memory alloy”. When it’s cool you can bend it and twist it (until you bend it too far, at which point it stays). If you heat it above a certain temperature it will go back to its “remembered” shape.
- Used for glasses frames (if bent, you can place them into a bowl of hot water and they’ll return to their shape)
- Dental braces (warms in the mouth and tries to return to its shape, gently pulling the teeth with it)
Describe the atomic makeup of nanoparticles and what fuellerenes/nano tubes are
- Nano particles contain roughly a few hundred atoms
- They include fuellerenes - these are molecules of carbon shaped like hollow balls or closed tubes, they are arranged in haxagonal rings. Different fuellerenes contain different numbers of carbon numbers.
- Fuellerenes can be joined to make hollow carbon tubes (a few nanometres across). All those covalent bonds make nano tubes very strong.
List some (possible) uses of nanomaterials and nanoscience (7 in total)
- High surface area to volume ratio so could make new industrial catalysts.
- Nanoparticles can be used to make sensors to detect one type of molecule - specific sensors of this kind are already being used to test water purity.
- Nanotubes can make stronger, lighter building materials
- New cosmetics (eg. sun cream & deodrant) have been made using nano particles which don’t leave white marks on the skin.
- Nanomedicine could deliver drugs straight into the cells where they’re needed because tiny fuellerenes are absorbed more easily by the body
- New lubricant coatings are being developed using fuellerenes, they reduce friction (like ball bearings) and could be used in anything from artificial joints to gears.
- Nanotubes conduct electricity so can be used in tiny electrical circuits for computer chips.
Strong ………. bonds hold the atoms together in …….. ……. but it’s the bonds between the different ………. ……….. that determine the properties of plastics.
Strong covalent bonds hold the atoms together in long chains but it’s the bonds between the different molecule chains that determine the properties of plastics.
Draw a quick diagram of the molecular arrangement of thermosoftening and thermosetting polymers
Thermosoftening polymers don’t have links between chains, explain how this changes the property of the material
- The individual tangled chains of polymers, held together by weak intermolecular forces, are free to slide over one another.
- The forces are easy to overcome so the plastic will melt easily, when it cools it will harden into a new shape. These materials can be remoulded over and over again.
What are plastics with strong intermolecular forces (crosslinks) between the polymer chains called?
Why don’t thermosetting polymers soften when heated?
Their crosslinks hold them together in a solid, hard and rigid structure.
The starting materials and reaction conditions of will affect the properties of a polymer. Outline the difference between the processes that make low and high density polythene.
- Low density: heating ethene to 200° C under high pressure - it’s flexible and used for bags and bottles.
- High density: made at a lower temperature with a catalyst. It’s more rigid and used for water tanks/drainpipes
What do Ar and Mr stand for?
Ar = Relative atomic mass
Mr = Relative formula mass
How can you identify the atomic mass of an element from the periodic table?
The relative atomic mass is usually the same as the mass number.
How is the relative atomic mass of an element with more than one stable isotope identified?
The mean average of all the different isotopes is calculated.
How do you calculate the relative formula mass of a compound?
What is the Mr for MgCl2?
You have to add up all the relative atomic masses (Ar) in the compound
Mr of MgCl2 = 24 + (35.5 x 2)
One mole of a substance is equal to it’s ……… in grams
One mole of a substance is equal to it’s Mr in grams
What is the formula for working out the number of moles in a certain amount of a compound/element?
Number of moles = Mass in g (of element/compound) ÷ Mr (of element/compound)
Work out how many moles there are in 42g of carbon
Number of moles = Mass in g (of element/compound) ÷ Mr (of element/compound)
= 42 ÷ 12
= 3.5 moles
What is the formula for working out the percentage mass of an element in a compound?
Percentage mass = ((Ar × number of atoms of the element) ÷ Mr of whole compound) × 100
Find the percentage mass of sodium in sodium carbonate, NaCO3
Ar of sodium = 23
Ar of carbon = 12
Ar of oxygen = 16
Mr of sodium carbonate = (2x23) + 12 + (3x16) = 106
Percentage mass = (23 x 2) ÷ 106 x 100 = 43.4%
Outline how you find the empirical formula of a compound in 5 steps
- List all the elements in the compound
- Write the experimental masses or percentages of each elemt
- Divide each mass/percentage by the Ar of the element
- Turn these numbers into a ratio
- Get the ratio in it’s simplest form
Find the empirical forumla of iron oxide when 44.8g of Iron reacts with 19.2g of Oxygen
- 8 19.2
- 8/56 =0.8 19.2/16=1.2
= 2 atoms of Fe to every 3 of O
List the three important steps used to calculate masses in reactions
- Write out the balanced symbol equation
- Work out the Mr for the two parts of the reaction you want
- Divide to get one, multiply to get all
What mass of magnesium oxide is produced when 60g of magnesium is burned in air?
2Mg + O2 ⇒2MgO
Ar of Mg = 24
Ar of O = 16
2 x 24 ⇒ 2 x (24+16)
48g of Mg ⇒ 80g MgO
1g of Mg ⇒ 1.66666666667g MgO
60g of Mg ⇒ 100g of MgO
What is the equation for the percentage yield of a reaction?
Percentage yield = (actual yield ÷ predicted yield) x 100
All units in grams
What are the three reasons why the percentage yield of a reaction might not be 100%?
- Reversible reactions - not all of the reactants will be completely converted to products because some of the products will react together to change back to the original reactants.
- Filtration - when you filter a liquid to remove solid particles you nearly always lose a bit of liquid/solid.
- Unexpected reactions - sometimes unexpected reactions occur, which use up the reactants so there’s not as much product created as you might expect.
How can artificial colours be separated and identified?
Describe the process of paper chromatography (4 steps)
- Extract the substance you wish to analyse and place it in a solvent (eg. water/ethanol/salt water)
- Put spots of the coloured solution on a pencil baseline on filter paper
- Roll up the sheet and put it in a beaker with some solvent, keeping the baseline above the level of solvent.
- As the solvent seeps up the paper, different substances are taken with it, forming different coloured spots in different places.
What are the three advantages of using inmachines to analyse unknown substances?
- Very sensitive
- Very fast
- Very accurate
Outline the process of gas chromatography
- A gas is used to carry substances through a column packed with a solid material
- The substances travel through at different speeds and separate
- The time they take to reach the detectos is called the retention time
- The recorder draws a gas chromatograph.
- The gas chromatography column can be linked to a mass spectrometer (GC-MS) and can identify the substances leaving the column accurately.
What do the number of peaks and the position of the peaks on a gas chromatograph indicate?
Number of peaks = Number of substances
Position of peaks = retention time of each substance
What can you work out about each of the substances analysed on the graph created by GC-MS?
The relative molecular mass of each of the substances (you read off of the molecular ion peak)