IGCSE Chemistry Section A (Principles of Chemistry)

Solid- particles close together and touching one another in a regular and repeating pattern. They vibrate about fixed positions yet they do not move apart. The intermolecular forces are stronger than a liquid hence why they are fixed. (Ice)

Liquid- particles spacing is close together and are touching one another yet they are in an irregular arrangement. Liquid particles move around and slide past one another. The forces are not as strong as a solid. (Water)

Gas- spacing between particles are far apart and are at random for both spacing and arrangement. Gas particles move freely and constantly collide with each other. There are no existing forces between them. (Water vapour)

1. Filtration- separation of an undissolved solid from a mixture/solution

2. Evaporation- separate a dissolved solid from solution when solid has similar solubilities in both hot and cold solvent.

3. Crustallisation- dissolved solid from solution when solid is more soluble.

4. Distillation- separating a liquid from a solution

5. Fractional distillation- separating two or more liquids.

6. Paper chromotography- separate substances that have different solubilities in a given solvent.

Atomic number = protons in nucleus of an element  Mass number = protons + neutrons

Neutrons- relative charge = 0 relative mass = 1

Protons- relative charge = 1 relative mass = 1

Electrons- relative charge = -1 relative mass = 1/1836

First shell- 2 electrons

Second shell- 8 electrons

Third shell- 18 electrons

Fourth shell- 32 electrons

RAM: Chlroine has two isotopes (35 + 37)

75% = 35    25% = 37

(75 X 35) + (25 X 37) divided by 100 = 35.5

RFM: Potassium carbonate K2CO3

(2 X K) + C + ( O X 3 ) = ( 2 X 39 ) + 12 + ( 3 X 16 ) = 138       

Avogadro number = 6 X 10 (23) ( 1 mol of everything )

Mass = RAM

Mass = moles X formula mass

Moles = mass / formula mass

Gas

volume of a mole = 24dm(3)

volume = moles X 24

moles = volume / 24

Find the ratio:

10g of hydrogen, 80g of oxygen

10 / 1 = 10 moles

80 / 16 = 5 moles

10 : 5 = 2 : 1

Empircal formula = H20

An ion is an electrically charged atom or group of atoms. Ions are formed by the loss of gain of electrons.

Bonding

High melting and boiling points - Ionic bonds are very strong - a lot of energy is needed to break them. So ionic compounds have high melting and boiling points.

Conductive when liquid - Ions are charged particles, but ionic compounds can only conduct electricity if their ions are free to move. Ionic compounds do not conduct electricity when they are solid - only when dissolved in water or melted.

LATTICE ARRANGEMENT

Covalent bonds form between non-metal atoms. Each bond consists of a shared pair of electrons, and is very strong. Covalently bonded substances fall into two main types:

1. simple molecules and
2. giant covalent structures.

Simple molecules

These contain only a few atoms held together by strong covalent bonds. An example is carbon dioxide (CO₂), the molecules of which contain one atom of carbon bonded with two atoms of oxygen.

Low melting and boiling points - This is because the weak intermolecular forces break down easily.

Non-conductive - Substances with a simple molecular structure do not conduct electricity. This is because they do not have any free electrons or an overall electric charge.

Very high melting points - Substances with giant covalent structures have very high melting points, because a lot of strong covalent bonds must be broken. Graphite, for example, has a melting point of more than 3,600ºC.

Variable conductivity - Diamond does not conduct electricity. Graphite contains free electrons, so it does conduct electricity. Silicon is semi-conductive - that is, midway between non-conductive and conductive.

Metal is formed at cathode (negative)

Non metal is formed at anode (positive)

Cathode

Pb 2+ + 2 E- = Pb

Anode

Br- = Br + e-

Quantity = Current X Time

96500 = 1 faraday

Example:

0.01 A X 4 hours X RFM of Gold nitrate ( 60 ) X 60 degrees celcius = 144 C

Au ( 3+ ) + 3 E- = Au

3 X 96500 deposits 1 mol of gold 197g

144 C deposits ( 197 / 3 X 96500 ) X 144 = 0.098g of gold