Year 9 Chemistry Revision 2013 *Bonding*
Ionic Bonding: occurs when a metal donates electrons to form a positive ion, and a non-metal
accepts electrons to form a negative ion.
The most vigorous reactions are between the most reactive metals and the most reactive non-metals.
Covalent Bonding: occurs when one or more pairs of electrons are shared between two atoms.
A single covalent bond contains one pair of shared electrons: e.g. Cl2 Cl – Cl
A double covalent bond contains two pairs of shared electrons e.g. CO2 O=C=O
A triple covalent bond contains three pairs of shared electrons e.g. N2 NΞN
Metallic Bonding: occurs within a metal when ‘a lattice of positive ions lies in a sea of old mized electrons.’
Intermolecular Forces (IMF): these control melting and boiling points.
Van der Waals: these are the weakest IMF, occur in non-polar molecules with relatively low boiling points e.g. butane
Dipole-dipole: these are medium strength IMF, occur in polar molecules with medium boiling points e.g. chloropropane, ethanoic acid
H-Bonding: these are the strongest IMF, occur in molecules which have N, O or F bonded to H. e.g. pentanol, water
*Periodicity*
The Periodic Table
The vertical columns are called Groups - The horizontal rows are called Periods
Properties
Atomic radius: the distance from the centre of the nucleus to the outmost (valence) energy level, in an atom.
Ionic radius: the distance from the centre of the nucleus to the outmost (valence) energy level, in an ion.
Electronegativity: the ability of an atom to attract a pair of electrons, across a covalent bond.
First Ionization Energy: the amount of energy required to remove one mole of electrons from one mole of gaseous atoms.
Trends Down Groups:
Group 1:
atomic radius and ionic radius increase, due to an increasing number of energy levels
electronegativity and first ionization energy decrease, due to a decrease in electrostatic attraction, as the valence electrons are further from the nucleus
reactivity (ability to lose electrons) increases, due to increased shielding from inner electrons and a decrease in electrostatic attraction, as the valence electrons are further from the nucleus
Group 7:
atomic radius and ionic radius increase, due to an increasing number of energy levels
electronegativity and first ionization energy decrease, due to a decrease in electrostatic attraction, as the valence electrons are further from the nucleus
reactivity (ability to gain electrons) decreases, due to increased shielding from inner electrons and a decrease in electrostatic attraction, as the valence electrons are further from the nucleus
Trends Across Periods
Period Three:
atomic radius and ionic radius decrease, due to valence electrons filling the same energy level, but an increase in electrostatic attraction due to an increase in the number of protons.
electronegativity and first ionization energy increase, as proton number increases, due to an increase in electrostatic attraction between the nucleus and the valence electrons.
Metallic oxides are basici, aluminium oxide is amphoteric (able to act as an acid or a base), and non-metallic oxides are acidic.