topic 1 chemistry

• A compound is a substance containing two or more different elements at a fixed rate.
• An element is mad up of the same atoms that have the same number of protons.
• A compound formed by metals and non-metals consists of ions as the atoms loose and gain electrons forming ionic bonding.
• A compound formed by non metals consists of molecules, each atom shares electrons forming covalent bonding.
• Isotopes are forms of the same elements, but with a different number of neutrons and therefore mas numbers.
• Atomic number = number of protons
• Mass number = number of protons + number of neutrons
• protons have a charge and mass of 1
• neutrons have no charge and a mass of 1
• electrons have no mass and a negative charge
• Relative atomic mass = abundance x mass number (of isotopes)/abundance of all isotopes.
• the number of protons equals the number of eletrons
• Filtration separates insoluble solids from liquids.
• A solvent is able to dissolve other substances in it.
• Evaporation and crystallisation separates soluble solids from solutions.
• Rock salts can be separated by filtration and crystallisation.
• A solution in water is called an aqueous solution.
• A solution is a mixture of one or more solutes dissolved in a solvent.
• simple distillation is used to remove liquid from a solution.
• Fractional distillation is used to separate two or more (mixture) liquids.
• Fractional distillation is harder when the boiling points of the liquids are similar.
• Paper chromatography uses paper as the stationary phase.
• paper chromatography is used to separate different dyes in an ink.
• Distillation, fractional distillation, crystallization, filtration and evaporation are all used to separate mixtures.
• Filtration separates solids from liquids by passing them through a filter.
• Evaporation removes water from a mixture leaving behind solid particles.
• In the early 1800's John Dalton described the atom as a solid sphere, however in 1897 JJ Thomson proved they wasn't (found the electron) and came up with the plum pudding model.
• The plum pudding model showed the atom as a ball of positive charge with electrons stuck in it.
• In 1909 Ernest Rutherford carried out the alpha scattering experiment.
• During the alpha-scattering experiment most alpha particle passed through the foil, meaning most of the atom is empty space.
• During the alpha-scattering experiment some of the alpha particles where deflected, meaning there is a nucleus with a positive charges that repelled the also positive alpha particles.
• During the alpha-scattering experiment a few of the alpha particles reflected straight back, meaning the centre of an atom is small and contains a great deal of mass.
• After Observing the outcome of the Alpha-scattering experiment, Ernest Rutherford created the nuclear model of the atom.
• Rutherford's nuclear model comprised of a positively charged nucleus surrounded by a cloud of negatively charged electrons.
• After the discovery was made that the electrons couldn't be in a cloud around the nucleus, Niels Bohr proposed that the electrons were in shells each at different fixed distances from the nucleus.
• 20 years after the nuclei was accepted, James Chadwick discovered neutrons.
• Electrons have 3 shells, the first fits 2 electrons, the second fits 8 electrons, and the third fits 8 electrons.
• The number of electrons in the outer shell tell us which group an element is in.
• Elements with a full outer shell are found in group 0.
• In the early 1800s elements were arranged by their properties and atomic weight. However due to the presence of isotopes, putting elements in order of atomic weight was not viable.