Unit 1 keywords

• Atom


  The smallest part of an element that can exist. All substances are made up of atoms.
• Compound


  A substance that combines two or more different elements through the formation of chemical bonds.
• Ion


  An atom/molecule that has lost or gained electrons, giving it an overall charge - positive if it has lost electrons, negative if it has gained electrons.
• Ionic equation


  A chemical equation that involves dissociated ions.
• Molecular formula

  The actual number of atoms of each element in a molecule.
• Oxidation number


  The charge of an ion or a theoretical charge of an atom in a covalently bonded compound assuming the bond becomes ionic.
• State Symbol


  Show the physical state of the substance during the reaction, usually in brackets: gas (g), liquid(l), solid(s) and aqueous(aq). Aqueous means the substance is dissolved in water.
• Absorption spectra


  A spectrum of frequencies of electromagnetic radiation that has been transmitted through an atom or molecule, that shows dark bands due to the absorption of the radiation at those specific wavelengths.
• Alpha-decay


  A type of radioactive decay, during which an atomic nucleus loses two protons and two neutrons. An alpha particle is equivalent to a helium nucleus. It reduces the atomic number by two and the mass number by four, making the element more stable.
• Beta-decay


  A type of radioactive decay, during which a beta particle is lost, which is equivalent to an electron and a neutron turns into a proton or a proton turns into a neutron. This changes the atomic number by one, but the mass number remains the same.
• Electromagnetic spectrum

  The range of frequencies of electromagnetic radiation and the respective wavelengths.
• Electron transition

  When an electron absorbs energy and moves from a low energy orbital to a vacant higher energy orbital.
• Electronic configuration


  The arrangement of electrons into orbitals and energy levels around the nucleus of an atom/ion. E.g. Ca: 1s^2 2s^2 2p^6 3s^2 3p^6 4s^2.
• Emission spectra


  A spectrum of frequencies of electromagnetic radiation that has been emitted by an atom or molecule undergoing a transition from a state with higher energy to a state with lower energy.
• Energy level


  The shell that an electron is in.
• First ionisation energy


  The energy required to remove 1 mole of electrons from 1 mole of gaseous atoms to form 1 mole of gaseous 1+ ions. For example, O(g)→ O+(g) +e-
• Frequency


  The number of wave oscillations per second. E = hf, f = c / λ (E = energy, h = Planck's constant, f = frequency, c = speed of light, λ = wavelength)
• Gamma radiation


  A type of electromagnetic wave that can be emitted when a nucleus undergoes radioactive decay.
• Half-life (t1/2)


  The time taken for the number of radioactive nuclei in a sample to decrease by half.
• Isotope


  Atoms of the same element with the same number of protons but different numbers of neutrons in the nucleus, e.g. 35Cl and 37Cl.
• Infrared


  The part of the electromagnetic spectrum that has wavelengths between 780 nm and 1 mm.
• Lyman series


  A group of lines present in the ultra-violet spectrum. The lines converge as frequency increases.
• Orbital


  A cloud of negative charge that can hold up to two electrons. Different orbitals have different shapes.
• p orbital


  A dumbbell shaped region in which up to two electrons can be found. There are three p orbitals at right angles to each other, so in total, the p subshell can hold up to 6 electrons.
• Radioactive decay


  A random process in which a radioactive nuclei loses energy by emitting radiation.
• s orbital


  s orbitals are spherical and symmetrical regions around the nucleus, they can each hold up to two electrons.
• Second ionisation energy


  The energy required to remove 1 mole of electrons from each ion in 1 mole of gaseous 1+ ions to form 1 mole of gaseous 2+ ions (could be asked for any successive ionisation energy).
• Shell


  The energy level that an orbital is in around the nucleus of an atom. The shell closest to the nucleus is the first shell. The outermost shell that is occupied by electrons is the valence shell.
• Shielding


  A decrease in the nuclear attraction experienced by an outer shell electron caused by electron-electron repulsion between the outer shell electron and electrons from adjacent quantum shells.
• Third ionisation energy

  The energy required to remove 1 mole of electrons from each ion in 1 mole of gaseous 2+ ions to form 1 mole of gaseous 3+ ions (could be asked for any successive ionisation energy).
• Ultra-Violet


  The part of the electromagnetic spectrum that has wavelengths between 10 nm and 400 nm.
• Visible light


  The part of the electromagnetic spectrum that has wavelengths between 380 and 700 nm.
• Wavelength


  The distance between two successive points on a wave, such as two troughs or two crests. Inversely proportional to frequency.
• Amount of substance

  The quantity of a chemical species, measured in moles. Used as a way of counting atoms. The amount of substance can be calculated using: Number of moles = Mass ÷ Mr, Number of moles = (Pressure x Volume) ÷ (Gas constant, R x Temperature), Number of moles = Concentration x Volume
• Atom economy

  Measure of the proportion of reacting atoms that become part of the desired product in the balanced chemical equation. Atom Economy = (Molar mass of desired product / Total molar mass of all products) x 100%
• Avogadro constant (L)

  The number of atoms, molecules or ions in one mole of a given substance. It is the number of atoms in exactly 12 g of C (6.02 x 10^23 mol).
• Empirical formula

  Smallest whole number ratio of atoms of each element in a compound. For example, the empirical formula of benzene (C6H6), cyclobutadiene (C4H4) and acetylene (C2H2) are all simply "CH".
• Ideal gas equation

  An equation that relates the number of moles of a gas to its volume, temperature and pressure. PV = nRT (P = pressure, V = volume, n = number of moles, R = gas constant, T = temperature)
• Mass spectrometry


  A technique used to identify compounds and determine their relative molecular mass.
• Molar Mass

  Mass of one mole of the substance expressed in gmol−1.