Semi- Metals: Elements near the diagonal divide are semi- metals or metalloids with in- between
properties.
• Metallic Bonding: The electrostatic attraction between positive metal ions and delocalised
electrons.
• Giant Metallic Lattice: Each atom has donated its negative outer- shell electrons to a shared pool
of delocalised electrons. The positive ions are fixed in position, maintaining structure.
• Electrical Conductivity: Metals are good conductors as delocalised electrons can move through
structure/ are mobile.
• Melting and Boiling Points:
– High temperatures needed to provide large amount of energy.
– Needed to overcome the strong electrostatic attraction between cations and electrons.
– So having high melting and boiling points.
Strength of Metallic Bond: Increase across period from Na+
to Al3+. Group 3 are the strongest.
– Ionic charge increases
– So number of delocalised electrons increases.
– The attraction between ions and electrons increases.
– So making the metallic bonding stronger which requires more energy to break.
• Solubility: Metals do not dissolve/ insoluble, unlike ionic compounds.
Would most likely be a reaction instead.
• Make sure to label the diagram and definition if lines provided under.
• Giant Covalent Structures: A 3D structure of atoms, bonded together by strong covalent bonds.
Examples are boron, carbon and silicon.
• Be careful don’t assume that a compound is ionic, SiO2 is giant covalent.
• Carbon and Silicon: Carbon in diamond form and silicon use the four electrons in outer shell to
form four covalent bonds to other carbon or silicon atoms in a tetrahedral structure. Bond angles
are 109.5o
.
• Melting and Boiling Point:
– High temperatures needed to provide large quantity of energy.
– Needed to break the strong covalent bond.
– So have high melting and boiling points.
• Solubility: Covalent insoluble. Covalent bonds too strong to be broken by interaction with
solvents.
• Electrical Conductivity: Do not conduct electricity.
• Graphene and Graphite: Only exceptions. Graphene and graphite form planar hexagonal layers
with 120o bond angles. Three of the four outer- shell electrons used in covalent bonding. The
remaining electron is delocalised electron between layers so conducts electricity.
• Graphite: Layers bonded by weak London Forces- therefore graphite soft.
• Diamond and graphite form gaseous atoms of carbon when ionised, so unnecessary to refer to
carbon as diamond/ carbon for ionisation energies.
• Periodic Trend in Melting Points: This pattern repeated across Period 2, Period 3 and the s- blocks
and p- blocks from Period 4 downwards.
• Melting point across period- need to compare- metallic bonds and covalent bonds are stronger
than London Forces in simple molecular. So more energy is needed to overcome bonds.