Chemistry A level WJEC

• Positive ions are formed when an atom loses electrons.
• Negative ions are formed when an atom gains electrons.
• Elements in Groups 4, 5 and 0 rarely form ions.
• Sulfate SO 4 2-
• Nitrate NO 3 -
• Phosphate PO 4 3-
• Carbonate CO 3 2-
• Hydroxide OH -
• Hydrogencarbonate HCO 3 -
• Ethanoate CH 3 COO -
• Ammonium NH 4 +
• Alpha (α) particles, also known as helium nuclei, have a mass of 4 units and are stopped by a piece of paper.
• Beta (β) particles, which are electrons, have negligible mass and are stopped by 0.5cm of aluminium.
• Gamma (γ) rays, which are high energy electromagnetic radiation, are also negligible in mass and require more than 2cm of lead to stop them.
• Alpha particles are positively charged and are attracted towards the negative terminal.
• Alpha particles are relatively heavy and slow moving, so they are only deflected slightly in an electric field.
• Electrons as β-particles are negatively charged and are attracted to the positive terminal.
• Electrons are light and fast moving, so there is a large amount of deflection in an electric field.
• Positrons as β-particles are positively charged and are attracted to the negative terminal.
• Positrons are light and fast moving, so there is a large amount of deflection in an electric field.
• Gamma rays are electromagnetic radiation and have no charge, so an electric field has no effect.
• When a radioactive element decays, radiation is released from the nucleus.
• α-emission results in a helium nucleus being produced, causing the mass atomic number to decrease by 2 and the mass number to decrease by 4.
• β-emission involves the transformation of a neutron into a proton and the emission of a negatively charged electron, resulting in an increase in the atomic number but no change in the mass number.
• β+-emission involves the transformation of a proton into a neutron and the emission of a positively charged positron, resulting in a decrease in the atomic number but no change in the mass number.
• Electron capture involves an electron from the closest energy level falling into the nucleus, causing a proton to become a neutron and emitting a neutrino, resulting in a decrease in the atomic number but no change in the mass number.
• γ-emission involves the release of high energy which causes the energy of the nucleus to decrease.
• The half-life of an element is the time taken for the mass of an element to decrease by half.
• Man-made, naturally occurring sources and radiation from space all contribute to the background radiation.
• A large part of the background radiation comes from radon gas that is released by certain types of rock.
• When two electrons occupy the same subshell, the electrons pair up with the opposite spin.
• When an organism dies the carbon-14 decays with a half-life of 5730 years, so measuring the amount of carbon-14 in a sample gives a good idea of when the organism died.
• There are different orbitals or subshells that have different shapes and are known by different letters; s, p, d and f.
• s-orbitals are spherical in shape and contain two electrons.
• An electron can be found at any point within an orbital at any time, as explained by quantum mechanics.
• Radiocarbon dating uses a rare radioactive isotope of carbon.
• Electrons move around the nucleus of an atom in orbitals.
• p-orbitals are represented as p x, y, z.
• Alpha particles pose little danger to humans as they cannot penetrate the skin, but if a source of α-radiation is ingested it can cause serious illness and death.