Chemistry AS level wjec

• Positive ions are formed when an atom loses electrons.
• Positive ions are usually metals.
• Negative ions are formed when an atom gains electrons.
• Negative ions are usually non-metals.
• As a general rule the Group number will tell you the number of ions that will be lost or gained.
• Elements in Groups 4, 5 and 0 rarely form ions.
• The sum of the oxidation states must add up to the charge on the species (charge on an atom or molecule is zero).
• An element's oxidation number is zero.
• The more electronegative element is given a negative oxidation number.
• Fluorine’s oxidation state is always -1.
• Oxygen’s oxidation state is usually -2 except for F2O and peroxides (H2O2).
• Chlorine’s oxidation state is usually -1 except in compounds with O or F (NaClO).
• Hydrogen’s oxidation state is usually +1 except in metal hydrides here is it -1 (NaH).
• Group 1 metals oxidation states are always +1.
• Group 2 metals oxidation states are always +2.
• Ionic equations only show the ions that make the observed product (usually a precipitate from aqueous ions).
• Ions that make up a product that is not observed are called spectator ions and are not included in ionic equations.
• Atoms are made up of three subatomic particles: Protons, Neutrons and Electrons.
• Protons and neutrons are found in the nucleus.
• Electrons orbit the nucleus in discrete orbitals or shells.
• Proton has a relative mass of 1 and a relative charge of +1.
• Neutron has a relative mass of 1 and a relative charge of 0.
• Electron has a relative mass of 1/1836 and a relative charge of -1.
• Atomic Number is the number of protons in an atom.
• Mass Number is the total number of protons and neutrons in an atom.
• Isotopes of the same element have the same atomic number but different mass numbers; that is they have the same number of protons but different numbers of neutrons.
• When large, heavy radioactive isotopes decay the nuclei release radiation.
• There are three types of radiation: Alpha (α) particles (helium nuclei), Beta (β) particles (electrons) and Gamma (γ) rays (high energy EM radiation).
• α-particles are positively charged so are attracted towards the negative terminal of an electric field.
• Electrons as β-particles are negatively charged so are attracted to the positive terminal of an electric field.
• Positrons as β-particles are positively charged so are attracted to the negative terminal of an electric field.
• Gamma-rays are electromagnetic radiation and have no charge so an electric field has no effect.
• A helium nucleus is produced in α-emission so the mass atomic number decreases by 2 and the mass number decreases by 4.
• In β—-decay a neutron turns into a proton and a negatively charged electron is emitted, resulting in an increase in the atomic number but no change in the mass number.
• The higher energy and shielding of the 2p orbital make it easier to remove an electron from Boron, despite its higher nuclear charge.
• Radiocarbon dating can be used on objects such as wooden archaeological artefacts or ancient human remains.
• The ionisation energy increases as you move across a period until you get to Group 0.
• Electrons fill orbitals singly before pairing up.
• When two electrons occupy the same subshell the electrons pair up with the opposite spin.
• Boron has a lower ionisation energy than beryllium because the most easily removed electron in Boron is in the 2p orbital, which is higher in energy and more shielded than the 2s orbital in Beryllium.