Chemistry 1: Atomic structure and the periodic table Electronic Structure 1st shell– Lowest energy level and can hold 2 electrons Atoms Atoms are tiny, too small to see. They have a radius of 0.1 nanometres ( 1 x 10 –10 m) 2nd shell– Energy level can hold up to 8 electrons Atoms have no charge because they have the same number of protons and electrons. 3rd shell onwards– Can hold up to 8 electrons.

Electron Proton Electron structure and the periodic table Elements in the same group have the same number of Nucleus Neutron electrons on their outer shell. Mass Number : protons + neutrons Electron - Orbit around nucleus in shells Atomic number: Proton - Found in the nucleus Protons Proton number = Electron Number Neutron - Found in the nucleus Number of neutrons= Mass number—Atomic number

Ions An ion is an atom that has lost or gained electrons. Isotopes An isotope is an atom that has the same number of protons but a different In an ion the number of protons is not equal to the number of electrons so the atom has number of neutrons. an overall charge. They have the same atomic number but different atomic mass numbers.

Relative atomic mass (Ar) Relative atomic = sum of (isotope abundance x isotope mass number) An average mass of an element that has a number of different isotopes. Mass (Ar) sum of abundance of all the isotopes

Balancing equations: Chemical Equations There must always be the same number of atoms on both sides of a symbol equation. Chemical reactions are shown using: Atoms can’t just disappear. Word equations Magnesium + Oxygen Magnesium Oxide You balance equations by putting numbers in front of the number. (reactants) (product) Symbol equations—Show the atoms on both sides 2Mg + O2 2MgO History of the atom Compounds Mixtures Ideas about atoms have change over time. - Have a fixed composition - No fixed composition Plum pudding model Rutherford’s nuclear model Bohr’s model - Can be separated by a - Can be separated by physical An atom was a ball of positive Electrons orbiting the nucleus Electrons orbit the chemical reaction means - No chemical bonds between charge with electrons which contains very dense nucleus at set distances - Chemical bonds between atoms scattered in the ball. positively charged protons. in fixed energy levels (shells). atoms

Separating Mixtures Filtration Separates insoluble solids from liquids. - Put filter paper in a funnel and pour the solution through it. The liquid passes through and the solid is caught in the filter paper. Evaporation The Periodic table Used to separate a soluble salt from a solution. The arrangement of the periodic table has changed. - Heat the solution until the solvent evaporates. Early 1800s Arranged my relative atomic mass. Crystallisation Scientists had not yet discovered proton, neutrons or electrons. Used to separate a soluble salt from a solution. There were gaps for missing elements that had not been found yet. - Heat the solution and then leave to cool until crystals form. Dimitri Mendeleev Distillation Used to separate liquid from a solution. Ordered mainly by atomic mass. You will need to Heat solution and the part with the lowest boiling point evaporates and is condensed back into a liquid. Elements with similar properties in the same group. know the first 20 Gaps left for elements that hadn’t been found yet. element names Fractional Distillation Modern Day and their symbols Used to separate a mixture of liquids from a solution. In order of increasing atomic mass. Paper chromatography Repeating patterns in the properties of the Can be used to separate different dyes in an ink. elements. - Compounds are dissolved by using filter paper and a solvent, in which the compounds are placed. Metals are on the left and non– metals are on the right. Properties of metals - Ductile - Malleable - High melting and boiling point Group 1– Alkali metals Li Group 7– Halogens Group 0– Noble gases - Conduct heat - Conduct electricity Na - Eight electrons on He - One electron on outer - Seven electrons on outer F shell K shell outer shell Ne Properties of non- metals - Brittle Rb - Less reactive down the Cl - Unreactive as they Ar - Insulators of heat and electricity - Very reactive Cs group Br have a full - Not always solids - lower Kr Reactivity increases Fr - Higher melting and boiling I outer shell and are density Xe down points down the group At stable the group. - Colourless gases Rn