Chemistry

• Elements are arranged in the periodic table in order of increasing atomic number.
• The periodic table allows chemists to make accurate predictions of physical properties and chemical behaviour for any element, based on its position.
• The periodic table is organised into groups and periods.
• Groups in the periodic table contain elements with similar chemical properties resulting from a common number of electrons in the outer shell.
• Periods in the periodic table are rows of elements arranged with increasing atomic number, demonstrating an increasing number of outer electrons and a move from metallic to non-metallic characteristics.
• The first 20 elements in the periodic table are categorised according to bonding and structure: metallic (Li, Be, Na, Mg, Al, K, Ca), covalent molecular (H2, N2, O2, F2, Cl2, P4, S8) and fullerenes (C60), covalent network (B, C (diamond, graphite), Si), and monatomic (noble gases).
• The covalent radius is a measure of the size of an atom.
• The trends in covalent radius across periods and down groups can be explained in terms of the number of occupied shells, and the nuclear charge.
• The first ionisation energy is the energy required to remove one mole of electrons from one mole of gaseous atoms.
• The second and subsequent ionisation energies refer to the energies required to remove further moles of electrons.
• The trends in ionisation energies across periods and down groups can be explained in terms of the atomic size, nuclear charge and the screening effect due to inner shell electrons.
• Electronegativity is a measure of the attraction an atom involved in a bond has for the electrons of the bond.
• The trends in electronegativity across periods and down groups can be rationalised in terms of covalent radius, nuclear charge and the screening effect due to inner shell electrons.
• In a covalent bond, atoms share pairs of electrons. The covalent bond is a result of two positive nuclei being held together by their common attraction for the shared pair of electrons.