OCR GATEWAY SCIENCE CHEMISTRY C3 all of module higher tier revision cards

Nucleus
-Contains protons and neutrons
-Positive charge

Electrons
-Negative charge
-They are in shells around the nucleus

                                      Mass                             Charge

Proton                           1                                     +1
Neutron                         1                                      0
Electron                         0.0005                            -1

• Number of protons=Number of electrons
• Number of neutrons= Atomic number-Mass number
• Mass number is the top number of the element
• Atomic number is the bottom number of the element

Definition of an isotope:
Different atomic forms of the same element which have the same number of protons but different number of neutrons
^Basically they have the same atomic number but different mass number

Elements are made of only 1 type of atom
-They can't be broken down easily

Compounds are chemically bonded
-after the chemical reaction it's hard to separate elements again
-Properties of compound are different to the properties of the elements it was made from.

There are 2 types of chemical bonding:
-Ionic bonding
-Covalent bonding

Vertical columns are called groups
-Number of electrons an element has in its outer shell determines its group
-Elements in the same group have the same number of electrons in their outer shells
-Elements in the same group have similar properties

Rows are called periods
-Each period represents another full shell of electrons
-Number of shells an element has determines its period

Electron configuration

The maximum number of electrons in each shell is:
1st shell : 2
2nd shell: 8
3rd shell: 8

In ionic bonding atoms lose or gain electrons to form ions which are strongly attracted to each other
Atoms in group 1 and 2:
-Have 1/2 electrons in their outer shell
-get rid of extra electron/s by giving them to an atom with the opposite charge
-Now they are both ions with full outer shells
Atoms in group 7 and 8:
-Have 7/8 electrons in their outer shell
-They gain electrons from other atoms of the opposite charge to fill their outer shell
-Now they are both ions with full outer shells

• Ions are charged particles
• Full outer shells are called stable octets
• When metals form ions they lose electrons to form positive ions
• When non-metals form ions they gain electrons to form negative ions
• OILRIG (oxidation is gain , reduction is loss) <of electrons
• When a metal and a non metal combine they form ionic bonds

NaCl and MgO form giant lattices
-Ionic bonds always produce giant ionic structures
-The ions aren't free to move so when solid they don't conduct electricity
-Very strong bonds between all ions

• They have high melting and boiling points due to strong chemical bonds
• They conduct electricity when molten because the ions are free to move when in molten form so they can carry a current
• NaCl dissolves to form a solution that conducts electricity

• Alkali metals are all the metals in group 1
• These are : Lithium,Sodium,Potassium,Rubidium,Caesium and Francium
• As you go down group 1 the alkali metals get more reactive because the electron in the outer shell is more easily lost because its further from the nucleus
• They all have 1 outer electron

They all have similar properties:
-Low melting and boiling points
-Low density
-Very soft
-All very reactive
-Always form ionic compounds in an oxidation reaction

They react with cold water to make hydrogen gas
-Li,Na,K react vigourously -they move around the surface and fizz
-Sodium and Potassium melt in the reaction
-They form a hydroxide

Example of reaction with water:
2Na+ 2H₂O ===> 2NaOH + H₂

Alkali metals burn with colours:
Lithium=Red Flame
Sodium=Yellow/orange flame
Potassium=Lilac flame

Definition: Electrolysis is the breaking down of a substance using electricity
-It needs a liquid -the electrolyte- to conduct the electricity
-Electrolytes are usually free ions dissolved in water which are the things that conduct electricity

• In electrolysis electrons are taken away from ions at the positive anode and given to other ions at the negative cathode

Electrolysis of sulfuric acid:
-Water contains Hydrogen and water
-Water isn't a good conductor so if you dissolve sulfuric acid in ,it conducts electricty better

• Oxygen is produced at the anode
• Hydrogen is produced at the cathode

Negative ions are called anions, positive ions are callled cations

• At the cathode , 2 Hydrogen ions accept 2 electrons to become 1 Hydrogen molecule
• At the anode , 4 Hydroxide ions lose their electrons and become 1 oxygen molecule and 2 water molecules

Learn these off by heart:

Cathode       2H⁺ + 2e⁻  ====> H₂
Anode                    4OH⁻  ====>2H₂O + O₂ + 4e⁻

• Electrolysis removes aluminium form its ore
• Pure aluminium oxide (Al₂O₃) is found in Bauxite
• Aluminium is more reactive than Carbon so it is extracted from its ore using electrolysis
• -Al₂O₃ has a very high melting point of 2000⁰C
• This temperature is hard and expensive to maintain
• The solution is to dissolve it in Cryolite
• This brings the melting point down to about 900⁰C which is easier and cheaper
• The electrodes are made from graphite  -a good conductor of electricity
• Molten aluminium oxide contains free ions so it conducts electricity
• Positive ions are attracted to the Cathode where they pick up electrons and turn into aluminium atoms and sink
• Negative O2⁻ ions are attracted to the anode where they lose electrons
  -The oxygen atoms react together to form O₂ or with carbon dioxide to form CO₂

• As the Carbon anode is constantly being worn down it often needs replacing
• It's a redox reaction because reduction and oxidation are happening at the same time

At the cathode         + 3e⁻ =====> Al       (Reduction)

At the anode:      2O2⁻ ======>O₂ + 4e⁻           (Oxidation)

-Decomposition of aluminium oxide=  
Aluminium oxide =====> Aluminium+Oxygen

• Electrolysis uses a lot of electricity,lots of energy is needed and the cathode needs to be replaced frequently so it is an expensive process

Covalent bonding is when atoms share electrons with each other
-After covalent bonding they both have a full outer shell
-Each covalent bond provides one extra shared electron for each atom

• Usually have simple molecular structures
• Very strong covalent bonds in atoms
• Forces of attraction between molecules are weak
• Low melting and boiling points because of a weak intermolecular force
• Most molecular substances are gases or liquids at room temperature
• Molecular substances don't conduct electricity because there are no free electrons or ions

• Group 7 elements are the Halogens
• Fluorine,Chlorine,Bromine,Iodine and Astatine
• All have 7 electrons in their outer shell
• As you go down group 7 the halogens become less reactive because there's less inclination to gain the extra electron to fill the outer shell because it's further away from the nucleus

-Chlorine is a poisonous dense green gas
-Bromine is a poisonous dense orange liquid
-Iodine is a dark grey crystalline solid

• Halogens form covalent bonds with themselves
• They form ionic bonds with other elements like the alkali metals to form ions with a negative one charge
• RIG reduction is gain

Halogens react with alkali metals to form salts

2Na + 2Cl₂ ====> 2NaCl
2K + 2Br₂ ======> 3KBr₂

More reactive halogens displace less reactive ones

Cl₂ + 2KI ====> I₂ +  2KCl
Cl₂  + 2KBr ====> Br₂ + 2KCl

• Metals consist of a giant structure of atoms held together with metallic bonds
• These bonds allow the outer electrons of each atom to move freely
  Properties of metals:
• High melting and boiling points
• High density
• Shiny
• Strong attractions between the free electrons
• Strong metallic bonding
• High tensile strength
• Malleable
• Good conductors of heat and electricity

Stainless steel-saucepans-Good conductor of heat
Copper-Electrical wiring-Good conductor of electricty,easily bent
Aluminium-Aeroplanes-Low density,Strong,Doesn't corrode
Steel/Iron-Bridges-Strong

• If you make metals cold enough their resistance disappears, the metal is now called a superconductor
  -Without any resistance none of the electrical energy is turned to heat so none is wasted
• With superconductors you can make:
  >Power cables that transmit electricity without loss of power
  >Really strong electromagnets that don't need a constant power source
  >Really fast electronic circuits because there's no resistance to slow it down
• However metals only start superconducting at -265®c (expensive to do)
• Scientists are trying to develop room temperature superconductors but so far only got to -135®c

They are found in the middle section of the periodic table

• They make good catalysts:
  1) Iron is the catalyst used in Haber process for making ammonia
  2)Nickel is used for the hydrogenation of alkenes

They have colourful compounds:

• Iron II compounds are light green
• Iron III compounds are orange
• Copper compounds are blue

Definition: When a substance breaks down into at least 2 other substances by heat

Transition metal carbonates break down when heated then they break down into a metal oxide and carbon dioxide:

CuCO₃ ====> CuO + CO₂
These reactions usually result in a colour change

(If limewater goes milky then there's Carbon dioxide present)

Definition:A percipitation reaction is where 2 solutions react and an insoluble solid forms in the solid

CuSO₄ + 2NaOH ===> Cu(OH)₂ + Na₂SO₄

Or this can be written as an ionic equation

Cu2⁺ + 2OH⁻ ====> Cu(OH)₂

• Copper Hydroxide is a blue solid
• Iron II Hydroxide is a dark grey solid
• Iron III Hyrdoxide is an orange solid