Brief GCSE Chemistry Revision Notes

Bullet Pointed revision notes for Unit 2 and 3 GCSE Chemistry

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Classifying Materials
Mass Number (top)
Atomic No./Proton No. (bottom)
Periodic Table has approx. 100 elements
Groups of elements share similar properties
Similar properties
Same no. of electrons in the outer shell
chemical properties are determined entirely by atomic no. (electrons)
Electron shells
o Electrons always occupy shells
o Lowest energy level filled first
2 8 8
o Atoms lose/gain electrons to become charged atoms (ions) which are then strongly
o Giant Ionic Structures
Closely packed regular lattice arrangement
Very strong bonds between all ions
1. Very high melting/boiling points
2. Dissolve to form conductive solutions
3. Conductive when molten
CATIONS (+ve) ANIONS (-ve)
Li+ Be2+ O2- F-
Na+ Mg2+ CO32- Cl-
K+ Ca2+ Br-
Ba2+ OH-
o Sharing of electrons
o Giant Covalent Structures
Very strong atomic bonds
1. Very high melting/boiling points
2. NEVER conduct electricity
3. Usually insoluble

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o Very rigid
Each C atom forms 4 bonds
o High melting point
o Conductive
o Sheets can slide/be rubbed off
Each C atom forms only 3 bonds
Leaves free delocalised electrons
o Simple Covalent Structures
Very strong covalent bonds
Intermolecular forces are very weak
1. Low melting/boiling points
2. NEVER conduct electricity (no ions)
3. Usually `mushy' solids
E.g.…read more

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Cl2 + 2KI I2 + 2KCl
Group 0 Noble Gases
1. Inert
2. Colourless Gases (at room temperature)
3.…read more

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Relative Atomic Mass Ar
"How heavy atoms are compared with the mass of one atom of Carbon 12"
Same as the mass number (top no.)
Relative Formula Mass Mr
All the Ar's added together
"different atomic forms of the same element which have the same number of protons but different
number of neutrons"
o I.e same proton number/atomic number but different mass number
Percentage Mass
Ar x no. of atoms (of that element) x 100
Mr (of whole compound)
Empirical Formula (from masses/percentages)
i.…read more

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Transferring liquids
Between containers
Container surfaces are left wet
o Unexpected reactions
Caused by impurities or changes in reaction conditions
Reactants are used as they react to form unwanted products
o Reversible Reaction
Not all reactants become products
Changes in conditions move the equilibrium position
"one mole of atoms/molecules of any substance will have a mass in grams equal to the Mr of that
E.g.…read more

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e.g.…read more

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Usually molten ionic substances or dissolved salts
E.g. salt solution of NaCl
POSITIVE ANODE takes electrons away (from ions)
2Cl- Cl2 + 2e-
NEGATIVE CATHODE gives electrons (to ions)
2H+ + 2e- H2
o NaOH is left in the solution
o Chlorine gas is produced at the Anode
o Hydrogen gas is produced at the Cathode
Electrolysis of Brine (NaCl solution)
o Produces
Killing bacteria (e.g.…read more

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Volume of gas released
o Uses a gas syringe
GOOD quite accurate
Collision Theory
"rate of reaction depends on how often & how hard the reacting particles collide"
To increase rate of reaction
o HIGHER TEMPERATURE* move quicker
o HIGHER CONCENTRATION more particles of reactant amongst the same number of solvent
o LARGER SURFACE AREA the particles around the reactants have more area to work on
o CATALYSTS lower the activation energy
*also increases energy (speed) of collisions, i.e.…read more

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Reversible Reactions
"a reaction where the products can themselves react to produce the original reactants"
Will reach a dynamic equilibrium
o Position of equilibrium depends on
Raised = endothermic reaction increases (to lose extra heat)
Reduced = exothermic reaction increases (to give out extra heat)
Raised = encourages reaction that produces less volume
Reduced = encourages reaction that produces more volume
Haber Process
N2 + 3H2 2NH3 (forward is EXO, backward is ENDO)
Nitrogen from the air
Hydrogen from natural gas/crude oil
200…read more

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Al3+ WHITE (then dissolves) Al(OH) 3
NH4 none (heating ammonia then gas test)
Tests for Anions (NEGATIVE)
o Add Hydrochloric Acid
Carbonates (CO3)
Produces Carbon Dioxide + Water
o Test for CO2 with limewater
Sulfites (SO3)
Produces Sulfur Dioxide
o Test with Potassium Dichromate (VI) paper (orange to green)
o (Add HCl then) add Barium Chloride
Sulfates (SO42-)
HCl removes Carbonates and Sulfites
BaCl2 produces a white precipitate
o Add Nitric Acid & Silver Nitrate
Halide Ions (Fluorine, Chlorine, Bromine, Iodine…read more


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