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

all of module c3 additional science

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  • Created by: Lucy64
  • Created on: 30-12-11 13:27

Atoms

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
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Isotopes,elements and compounds

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

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The periodic table

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

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Ionic Bonding

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
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Ions and ionic compounds

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
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Alkali metals

  • 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

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Alkali metals continued

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

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

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Electrolysis

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

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Electrolysis continued

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

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Extracting Aluminium

  • 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 Thumbnail for version as of 20:04, 31 August 2008ions 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 CO
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Extracting Aluminium continued

  • 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        Thumbnail for version as of 20:04, 31 August 2008 + 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
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Covalent Bonding

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
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Halogens

  • 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
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Halogens continued

Halogens react with alkali metals to form salts

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

More reactive halogens displace less reactive ones

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

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Metals

  • 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

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Superconductors

  • 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
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Transition metals

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
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Thermal decomposition

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 + CO
These reactions usually result in a colour change

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

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Precipitation

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

CuSO₄ + 2NaOH ===> Cu(OH)₂ + Na₂SO

Or this can be written as an ionic equation

Cu2⁺ + 2OH⁻ ====> Cu(OH)

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

  

 

 

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Comments

Deslie Thomas

Thank you so much saved my Lifee

Lucy64

It's okay :) thanks for commenting

Helen

These are so helpful! Thank you

Zeeshan.C

isn't this c4- c3 about reactions -exothermic endothermic reactions and calorimetry 

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