Rutherford's scattering experiment | A beam of alpha particles are directed at a very thin gold foil | Most of the alpha particles passed right through. A few (+) alpha particles were deflected by the positive nucleus. A tiny number of particles reflected back from the nucleus. |
B01) Atomic Structure
Atoms, elements and compounds
Atom | The smallest part of an element that can exist | Have a radius of around 0.1 nanometres and have no charge (0). |
Element | Contains only one type of atom | Around 100 different elements each one is represented by a symbol e.g. O, Na, Br. |
Compound | Two or more elements chemically combined | Compounds can only be separated into elements by chemical reactions. |
Method | Description | Example |
Filtration | Separating an insoluble solid from a liquid | To get sand from a mixture of sand, salt and water. |
Crystallisation | To separate a solid from a solution | To obtain pure crystals of sodium chloride from salt water. |
Simple distillation | To separate a solvent from a solution | To get pure water from salt water. |
Fractional distillation | Separating a mixture of liquids each with different boiling points | To separate the different compounds in crude oil. |
Chromatography | Separating substances that move at different rates through a medium | To separate out the dyes in food colouring. |
Mixtures | Two or more elements or compounds not chemically combined together | Can be separated by physical processes. |
The development of the model of the atom
Pre 1900 | | Tiny solid spheres that could not be divided | Before the discovery of the electron, John Dalton said the solid sphere made up the different elements. |
1897 ‘plum pudding’ | | A ball of positive charge with negative electrons embedded in it | JJ Thompson ‘s experiments showed that showed that an atom must contain small negative charges (discovery of electrons). |
1909 nuclear model | | Positively charge nucleus at the centre surrounded negative electrons | Ernest Rutherford's alpha particle scattering experiment showed that the mass was concentrated at the centre of the atom. |
1913 Bohr model | | Electrons orbit the nucleus at specific distances | Niels Bohr proposed that electrons orbited in fixed shells; this was supported by experimental observations. |
James Chadwick | Provided the evidence to show the existence of neutrons within the nucleus |
Chemical equations | Show chemical reactions - need reactant(s) and product(s) energy always involves and energy change | Law of conservation of mass states the total mass of products = the total mass of reactants. |
Word equations | Uses words to show reaction reactants 🡪 products magnesium + oxygen 🡪 magnesium oxide | Does not show what is happening to the atoms or the number of atoms. |
Symbol equations | Uses symbols to show reaction reactants 🡪 products 2Mg + O2 🡪 2MgO | Shows the number of atoms and molecules in the reaction, these need to be balanced. |
Relative electrical charges of subatomic particles
Name of Particle | Relative Charge | Relative Mass |
Proton | +1 | 1 |
Neutron | 0 | 1 |
Electron | -1 | Very small |
7
Li
3
Mass number | The sum of the protons and neutrons in the nucleus | |
Atomic number | The number of protons in the atom | Number of electrons = number of protons |
Relative atomic mass
Isotopes | Atoms of the same element with the same number of protons and different numbers of neutrons | 35Cl (75%) and 37Cl (25%) Relative abundance = (% isotope 1 x mass isotope 1) + (% isotope 2 x mass isotope 2) ÷ 100 e.g. (25 x 37) + (75x 35) ÷ 100 = 35.5 |
Central nucleus | Contains protons and neutrons |
Electron shells | Contains electrons |
Electronic structures
Electronic shell | Max number of electrons |
1 | 2 |
2 | 8 |
3 | 8 |
4 | 2 |