PRINCIPLES OF CHEMISTRY - CHEMISTRY

define element

A substance which only has one type of atom, which contains the same number of protons

Define compound

A substance which contains two or more types of particles in a fixed ratio, which have reacted chemically with eachother

Define mixture

A substance which contains two or more elements or compounds not chemically combined.

How do you calculate Rf value

Distance moved by substance/distance moved by solvent

How to conduct simple distillation

• the solution is heated and the part that has the lowest boiling point evaporates

• The vapour is then cooled, condensed and collects

• The rest of the solution is left in the flask

• This can only be used for a mixture with very different boiling points

How to conduct fractional distillation

1. Heat your flask of mixture into a fractionating column

2. The different liquid will have different boiling points, so liquid with lowest boiling point evaporates first

3. It is passed through the fractionating column until it condenses and runs into a test tube

4. Once all the first liquid has been collected, raise the temperature and repeat

5. This can be used for mixture of liquid with similar boiling point

Solvent definition

The liquid the solute is dissolved in

Solute definition

The substance which dissolves in a liquid to form a solution

Saturated solution definition

A solution with the maximum concentration of solute dissolved in solvent

How to calculate solubility

Solute mass/solvent volume x100

Isotope definition

Atoms of the same element which have the same number of protons but a different number of neutrons

Features of ionic compounds

• regularly arranged alternating positive/negative ions that are tightly packed

• There are strong electrostatic forces between +/-, which hold the compound together

• Giant ionic lattices have high boiling points as there are strong electrostatic forces of attraction between. Oppositely charged electrons which need energy to overcome

• Ionic compounds are poor conductor when solid as ions are in fixed position

• They are good conductors when molten or in solution as the ions are free to move and carry a charge

Features of covalent compounds

• covalent bonds between atoms are strong as the electrostatic attraction between nuclei and shared pair of electrons is strong as they are oppositely charged

• In simple molecular structures, covalent bonds are strong, but intermolecular forced are weak so boiling points are low

• In giant covalent structures, all atoms are bonded by strong covalent bonds, so boiling points are strong as there are many of these strong bonds. Giant covalent structures do not conduct electricity (except when molten) and are insoluble in water

Features of metallic compounds

• giant structures of regularly arranged atoms, which lose their outer electrons to become positively charged

• Most have high boiling points as there is strong electrostatic forces between metal cations and electrons

• Metals conduct electricity as the delocalised electrons are free to carry a charge

• Metals are malleable as the atoms are arranged in layer which can slide over eachother

Features of buckminsterfullerene

• hollow spheres

• Simple molecular structure

• Held by intermolecular forces, making it soft

• Each carbon has one delocalised electron but it cannot move through molecules

Features of graphite

• 3 covalent bonds, creating layers of atoms and high boiling point

• Layers are held together by weak intermolecular forces

• Only ¾ outer electrons are used, creating delocalised electrons

Features of diamond

• diamond is made from atoms joined by 4 covalent bonds

• Rigid lattice structure means its very hard

• Strong covalent bonds mean high melting point