Chemistry notes

Notes for gcse aqa chemistry includes; reversible reactions, rates of reactions, bonding and much more!

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  • Created on: 17-05-11 20:39
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NUCLEUS
Contains PROTONS and NEUTRONS
Positive overall charge
Most of mass concentrated in nucleus
ATOMS
NO OVERALL CHARGE
EQUAL NUMBERS OF PROTONS AND ELECTRONS
ELECTRONS
NEGATIVE
Small mass
Occupy shells
Explain whole of chemistry
If electrons are added/removed atom becomes CHARGED and is than an ION
PROTONS
MASS- 1
POSITIVE CHARGE
NUMBER OF PROTONS = NUMBER OF ELECTRONS
Atoms of same element have same number of protons
NEUTRONS
NO CHARGE
MASS- 1
Number of neutrons does not affect chemical behaviour of atom
ELEMENTS
One kind of atom only
COMPOUNDS
Chemically bonded
Hard to separate
Properties different from original elements
ISOTOPES
Same number of protons, different number of electrons
PERIODIC TABLE
Similar properties- in columns
Vertical columns- groups
GROUPS
The group an element belongs to depends on the number of electrons in their outer shell
That's why they have SIMILAR PROPERTIES
Group 1- alkali metals
Group 7- Halogens- react with alkali metals
Chemically bonding involves either transferring or sharing electrons in the highest
occupied shells of atoms.

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ELECTRON SHELLS
Lowest energy levels always filled first
1st shell- 2.
2nd shell-8
3rd shell- 8
Atoms are happy when all shells are full
Noble gases- group 0- all full outer shells- unreactive
If an outer shell is not full the atom wants to REACT.…read more

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INSOLUBLE
EXAMPLES OF GIANT COVALENT STRUCTURES:
DIAMOND
Each CARBON atom has 4 covalent bonds.
Very hard
GRAPHITE
Each CARBON atom has 3 Covalent bonds
Has layers- slide over each other easily
One electron is delocalized ­ allows graphite to conduct electricity and heat
SILICON DIOXIDE (SILICA)
What sand is made of
Each grain is a giant covalent structure
Can be melted to make limestone and glass.…read more

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How heavy an atom is compared to mass of an atom of carbon-12
Just the mass number of atom
When an element has more than one stable isotope, the Ar is the average value of all the
different isotopes e.g. chlorine.
RELATIVE FORMULA MASS- Mr
All the mass numbers in a compound added together
.
EMPIRICAL FORMULA
The formula of a compound
1. Find masses (given in question)
2. Look up Ar values
3. Divide masses by Ar
4.…read more

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ATOM ECONOMY
% OF REACTANTS CHANGED USEFULLY
Total Mr of useful products / total Mr of reactants X 100
High atom economy is better for profits and the environment
Reactions with low atom economy
1. Use up resources quickly
2. Make lots of waste materials to be disposed of
3. Unsustainable
4. Raw materials will run out
5.…read more

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Makes reaction reach EQUILIBRIUM QUICKER but you have the same amount of product.
THE HABER PROCESS
Important industrial process
Produces AMMONIA (NH3)- makes fertilizers
Uses NITROGEN and HYDROGEN
NITROGEN- Found easily from air (78% nitrogen, 21% oxygen)
HYDROGEN- From Natural gas/ other resources e.g.…read more

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Lowers activation energy- less energy needed to start reaction
Lower temperatures needed
Solid catalysts work best with a big surface area
Usually powder, pellets or a fine gauze- very large surface area
Transition metals-common catalyst in industrial processes
Reduce costs
1. Increases rate of reaction- saves money
2. Lower temperatures- less energy needed- better 4 sustainable development
DISADVANTAGES;
a. EXPENSIVE
b. NEED 2 BE CLEANED
c. DIFFERENT REACTIONS NEED DIFFERENT CATALYSTS
d.…read more

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Explains reaction rates
Rate of reaction depends on HOW OFTEN and HOW HARD the reacting particles COLLIDE
Chemical reactions can only occur when reacting particles collide with each other and with
sufficient energy
HIGHER TEMPERATURE INCREASES COLLISIONS
Particles move quicker when the temperature is increased
Increases ENERGY ­ Particles mover faster
Moving quickly and more energetically= more collisions
HIGHER CONCENTRATION/ PRESSURE INCREASES COLLISIONS
More concentrated means there are more particles of REACTANT knocking about between
the water particles- COLLISIONS MORE LIKELY
GAS- Particles more squashed…read more

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Whenever CHEMICAL REACTIONS occur ENERGY is usually TRANSFERRED to or from
surroundings
EXOTHERMIC REACTIONS
Heat is given out
Usually shown by a raise in temperature
a. BURNING FUELS (COMBUSTION)- Gives out a lot of heat
b. NEUTRALISATION REACTIONS- (Acid and alkalis)
c. OXIDATION REACTIONS- (Adding water to COPPER SULPHATE to turn it blue)
ENDOTHERMIC REACTIONS
Takes in ENERGY from SURROUNDINGS
Shown by FALL IN TEMPERATURE
LESS COMMON
THERMAL DECOMPISITIONS- e.g.…read more

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