There are 3 types of chemical bonding – ionic, covalent and metallic. Chemistry Paper 1 Keywords;,, filtration, crystallisation, chromatography, simple distillation, fractional distillation, proton, neutron, James Chadwick, relative mass, relative charge, isotope, atomic number, mass number, electronic configuration, percentage abundance, periodic table, electron, nucleus, orbital/shell, plum pudding model, Niels Bohr, alpha particle, positive, negative, models groups, Mendeleev, metals, non-metals, ions, physical properties, reactivity, halogens, noble gases Modern periodic table; The arrangement of elements in a table based on proton number, properties and outer electron number Atoms; An atom has no overall charge, the number of protons = the number of electrons Crystallisation; Removing a liquid leaving a solid behind Fractional distillation; Separating 2 different liquids based on different boiling points Group 7; Halogens 7 outer electrons Non-metals Molecules made of pairs of atoms Group 1; Alkali metals 1 outer electron Reactivity increases going down the group Isotopes; Atoms that have the same number of protons (element), but different numbers of neutrons Development of the model of the atom; New experimental evidence may lead to the model being changed or replaced Electronic configurations; Electrons fill the lowest energy levels first This starts from the nucleus, following a set pattern up to the following maximum 1st shell – 2 electrons 2nd shell – 8 electrons 3rd shell – 8 electrons 4th shell – 2 electrons Nucleus development; Experiments now show nucleus is made of smaller particles of positive charge There are 3 types of chemical bonding – ionic, covalent and metallic. Plum pudding; After the electron was discovered the atom became a ball of positive charge with negative electrons scattered in it Niels Bohr; Adapted the nuclear model suggesting electrons in orbitals at set distance Atoms in metals are closely packed and arranged in layers. In the highest energy level the electrons are delocalised. This means they can move about freely between atoms. James Chadwick; Evidence to show the existence of neutrons in the nucleus Alpha particle scattering; Showed that the mas of an atom was concentrated in the centre, it was charged too

Using energy transfers from reactions Electrolysis Exothermic reactions can be used in hand warmers and self heating cans. Endothermic changes can be used in instant cold packs for sports injuries. In reversible reactions the reaction in one direction is exothermic and in the reverse direction it will be endothermic. Electrolysis breaks down ionic compounds into elements using electricity. The ionic compounds must be molten or in solution for electrolysis to work. Masses of atoms & moles Relative atomic masses (Aᵣ) are used to compare the masses of atoms. Relative formula mass (Mᵣ) can be found by adding up the relative atomic masses of the atoms in its formula. Don’t forget one mole of any substance is its relative formula mass in grams. Percentages and Formulae The relative atomic masses of the elements in a compound and its formula can be used to work out its percentage composition. To calculate the percentage by mass of oxygen (O) in sodium hydroxide (NaOH)? First, work out the relative formula mass of the compound, using the Ar values for each element. In the case of sodium hydroxide, these are Na = 23, O = 16, H = 1. (You will be given these numbers in the exam.)  Next, divide the Ar of oxygen by the Mr of NaOH, and multiply by 100 to get a percentage. Yield of a chemical reaction: Percentage yield = X 100%