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• elements that react to form positive ions are metals
• elements that don’t form positive ions are non metals
• metals: strong, malleable, good conductors of electricity/heat, high melting and boiling point
• non-metals: weak, brittle, poor conductors of heat or electricity, low melting and boiling points
• group 0 are called the noble gases
• group 1 are called alkali metals
• group 7 are called the halogens
• Noble gases are: unreactive, don’t form molecules because their atoms are in stable arrangements of electrons
• the boiling point increases as you go down the noble gases
• the reactivity increases going down group 1 metals
• group one have a single electron in their outer shell
• group one react with water, chloride and oxygen
• Halogens have 7 electrons on their outer shell. They consist of molecules made up of pairs of atoms
• Reactivity decreases down group 7. A more reactive halogen can replace a less reactive halogen
• An atom is the smallest part of an element to exist. All substances are made of atoms
• There are around 100 elements and they are found on the periodic table
• a compound is formed by a chemical reaction. they consist of two or more elements chemically combined in fixed proportions.
• chemical reactions involve the formation of one or more new substances and often involve a detectable change
• a mixture consists of two or more elements or compounds not chemically combined together. mixtures can be separated by physical processes such as filtration, crystallisation, simple distillation or fractional distillation.
• compounds can separated by chemical reactions into elements
• In an atom, the number of electrons is equal to the number of protons in the nucleus. Atoms have no overall electric charge
• The number of protons in an atom of an element is its atomic number. All atoms of a partial element have the same number of protons.
• The sum of protons and neutrons in an atom is its mass number.
• Isotopes are atoms with the same number of protons but different number of neutrons
• elements in the periodic table are arranged in the order of atomic mass, so that elements with similar properties are in columns.
• elements in the same group in the periodic table have the same number of electrons in their outer shell. this gives them similar properties
• John Dalton described atoms as solid spheres and said that different spheres are made up of different elements.
• JJ Thomson made the discovery of electrons and concluded it was called the plum pudding model. It suggested an atom was a ball of positive charge with negative electrons embedded in.
• Ernest Rutherford conducted the Alpha particle scattering experiments. This led to the conclusion that the mass of an atom was concentrated at the centre (the nucleus) are that the nucleus was charged. The nucleus model replaced the plum pudding model.
• Neil Bohr adapted the nuclear model by suggesting electrons orbit the nucleus at specific distances. His theoretical calculations agreed with experimental calculations.

  Later experiments led to the idea that the positive charge of any nucleus could be subdivided into a whole number of smaller particles, each particle having the same anlint of positive charge. The name proton was given to these particles.
• 20 years after the nucleus was an accepted scientific idea, James Chadwick provided the evidence to shoe the existence of neutrons in the nucleus.
• New experimental evidence may lead to a scientific model being replaced or changed.