Atomic Structure

- all substances are made up of atoms

- periodic table lists all chemical elements, with 8 main groups each containing elements with similar chemical properties

- elements contain only one type of atom

- compounds contain more than one type of atom

- an atom has a tiny nucleas as it's centre, surrounded by electrons

- no new atoms are ever created or destroyed in a chemical reaction;

    total mass of reactants = total mass of products

- same number of each type of atom on each side of a balanced symbol equation

- can include state symbols to give extra information in balanced symbol equations:

    (s) for solid

    (l) for liquid

    (g) for gas

    (aq) for solution

- mixture is made up of two or more substances that are not chemically combined together

- fractional distillation is an effective way of separating miscible liquids, using a fractioning column. 

    ...the separation is possible because of the different boiling points of the liquids in the mixture

- paper chromatography separates mixtures of substances dissolved in a solvent as they move up a piece of chromatography paper. 

    ...the different substances are separated beacuse of their different solubilities in the solvent used 

- ideas about atoms have changed over time

- new evidence has been gatherd from the experiments of scientists who have used their model of the atom to explain their observations and calculations

- key ideas proposed successively by Dalton, Thomson, Rutherford and Bohr, before arriving at the model of the atom you use at GCSE level today

- atoms are made of protons, neutrons and electrons

- protons have relative charge of +1

- electrons have a relative charge of -1

- neutrons dont have a charge, so they are neutral

- relative masses of a proton and a neutron are both 1

- atoms contain an equal number of protons and electrons, so carry no overall charge

    atomic number = number of protons = number of electrons

- mass number = number of protons + neutrons

- atoms of the same element have the same number of protons and electrons in their atoms

- atoms that gain electrons form negative ions, if atoms lose electrons they form positive ions

- can represent atomic number and mass number of an atom using notation:

- isotopes are atoms of the same element with different numbers of neutrons, they have identical chemical properties, but their physical properties such as density, can differ

- electrons in an atom are arranged in energy levels or shells

- the lowest energy level (1st shell) can hold up to 2 electrons and the next energy level (2nd shell) can hold up to 8 electrons

- the 4th shell starts to fill after 8 electrons occupy the 3rd

- the number of electrons in the outer most shell of an elements atom determines the way in which that element reacts