chemistry

• elements are arranged in order of their increasing atomic number
• ionic bond = metals and non metals react by transferring electrons
• covalent bonding= non metal atoms share electrons between eachother
• metallic bonding= between 2 metals
• atomic number is the number of protons in the element( bottom number)
• isotopes= same element with same number of protons but different number of neutrons
• mass number= protons + neutrons ( at the top)
• %mass of element=number of atoms of element x Ar of element/ Mr of compound x100
• there are over 100 elements
• compounds are formed by chemical reactions
• mixtures can be separated by filtration, crystallisation, distillation or chromatography
• before electron was discovered, atoms were apparently tiny, undividable spheres
• 1-plum pudding model=atom is a ball of positive charge with electrons in it

  2-nuclear model=alpha scattering, nucleus was discovered

  3-niels bohr=electrons orbit the nucleus at specific distances

  4-later experiments showed that the nucleus had protons in it

  5-chadwick=found nuetrons in the nucleus
• relative charge of:

  proton= +1

  neutron=0

  electron=-1
• number if electrons is equal to number of protons
• hydrocarbons are compounds that ONLY contain hydrogen and carbon
• alkanes have double bonds between carbons
• alkenes have single bonds between carbons
• the general formula for alkenes is CnH2n
• the general formula for alkanes is CnH2n+2
• cracking is a chemical process whereas fractional distillation is a physical process
• fractional distillation separates crude oil into different fractions based on boiling point
• crude oil is separated by fractional distillation to produce petrol, diesel fuel, paraffin wax, LPG (liquefied petroleum gas) and bitumen
• petrol has the lowest boiling point so it comes out first from the bottom of the column
• bitumen has the highest boiling point so it comes out last from the top of the column
• elements that react to form positive ions are metals
• elements that do not form positive ions are non metals
• noble gases are unreactive and have full outer shells apart from helium
• boiling point increase as you go down group 0 and their atomic mass also increases
• in group 1, reactivity increases as you go down
• in group 7, they are all non metal elements
• an ionic compound is a giant structure if ions are held together by strong electrostatic forces.
• diamond and sillicon dioxide are giant covalent structures
• a polymer is a long chain of monomers joined together by covalent bonds