Chemistry 2 Revision

• Use relative atomic mass to determine the mass of an electron
• Carbon contains 6 protons and 6 neutrons so its relative atomic mass is 12
• Helium is a noble atom: 2 neutrons and 2 protons so its RAM is 4

The Modern Periodic Table

• Order is based on inceasing atomic number, as Mendeleev did
• Horizontal Rows are called periods, veritcal columns are known as groups
• Each group contains elements with the same properties
• Main groups are 1 - 7, based on electron configuration

Isotopes

• Different atoms of the same element
• Proton number defines atom; chlorine contains 17 protons, yet some have 18/20 neutrons
• The relative abundance of chlorine of 35/17 Cl is 75% chlorine atom, while the proportion of 37/17 is 25%. This is why the relative atomic mass of chlorine is 35.5 rather than a whole number

Relative atomic mass = (75x35)+(25x37) / (75+25) = 2625+925 / 100 = 3550/100 = 35.5

Ion Flame Tests - Cations

• Calium Ca2+ - Brick Red
• Copper Cu2+ - Green/Blue
• Sodium Na+ - Yellow
• Potassium K+ - Lilac

Precipitation Tests

• To identify aqueaus chloride anaions - a few drops of nitric aicd and silver nitrate, a white precipitate is formed
• Sulphate anions - dilute hydrochloric acid and barium chloride = white precipitate of barium sulphate

Test for carbonate ions

• Any acid, CO2 produced, bubbled through limewater, goes milky

Inks, paints and food contain mixtures of coloured compounds. Chromatography can be used to detect what colouring is in those substance

Process -

• Substance are put on a start line on a piece of paper; which is drawn in pencil as it doesn't contain ink
• The substances have different solubility so some move at different speeds and distances
• A substance can identified by comparing the horizontal spots 

Chromatography can identify substances by using

Rf values = distance moved by soluable subtance

                  ________________________________

                           distance moved by solvent

Diamond -

• very hard because all atoms are joined with strong covalent bonds
• used to make cutting tools
• do not conduct electricty because there are no