Structure and Bonding

Allotrope — each of two or more different physical forms in which an element can exist. Graphite, charcoal, and diamond are all allotropes of carbon.

The strong electrostatic force of attraction between

  • Metallic

    • a lattice of positive metal cations and a ‘sea’ of de-localised free moving electrons

  • Ionics

    • oppositely charges ions

  • Covalent

    • positively charged nuclei and a negatively charged pair of shared electrons

Structure

  • Molecular

    • 2 or more atoms bonded together in a fixed ratio

    • Have weak inter molecular forces

  • Lattice

    • Regular repeating structure of atoms/ions that have no definitive ending

    • Strong chemical bonds

  • Atomic

    • Individual atoms that are only attracted to one another very weakly

    • Group 8;0

Bonding

Simple covalent molecule

  • 2 or more atoms in a fixed ratio

Properties

  • Boiling point—low, tend to be gases due to weak inter molecular forces

  • Hardness—hard but brittle as solids

  • Malleability—None

  • Electrical conductivity—No free moving charged particles

  • Covalent bonds are strong but they have relatively weak inter molecular forces

Examples

  • Water, Chlorine, Oxygen, Nitrogen, Ethene

When boiling a SCM the covalent bonds don’t break but the IMF are being overcome

Single covalent bonds are less strong then double bonds which are less strong then triple bonds

Buckminsterfullerene - C60 — allotrope of carbon

  • Sublimes at 600 C

    • Needs to overcome relatively weak forces between molecules

  • Does not conduct electricity

  • Not soluble in water

  • Insulator

    • Has de-localised electrons but they can’t move from one molecule to another

  • Soft and brittle

Giant covalent lattice

  • Many atoms bonded together in a regular repeating arrangement

  • strong covalent bonds

Properties

  • Very high melting and boiling points due to the strong covalent bonds between the atoms

  • (Not graphite) Do not conduct electricity because there are no free moving charged particles

Examples

  • Diamond, Graphite, Quartz SiO2, Silicon

Diamond vs Graphite

Both have a high Mp but diamond is higher

  • Covalent bonds between atoms are stronger than IMF — GCL don’t have inter molecular forces

Diamond does not conduct electricity, Graphite does

  • Graphite has de-localised electrons between layers

  • Graphite has 3 bonds per carbon, Diamond has 4 bonds per carbon

Graphite

  • Each carbon atoms from 3 bonds leaving 1 electron spare.

  • These electrons are de-localised, meaning they are not associated with any single carbon atom

  • As the electrons are free to move through the structure graphite is able to conduct electricity

  • The weak forces between each layer make it:

    • Flakey and soft

    • An effective industrial lubricant

    • Good for pencils

Giant Ionic Lattices

  • A regular repeating structure of oppositely charged ions

  • Strong ionic bonds

Cations and Anions have strong electrostatic forces of attraction

Properties

  • High melting point

  • Hard and brittle

    • The ions are held together by very strong interactions but small defects in the lattice will cause it to break by placing like charges together

  • Some are soluble

    • Water molecules are able to form weak interactions with the ions, which is sometimes enough to overcome the attractive force between the ions

    • NaF-soluble

    • MgO-insoluble

    • The solubility of an ionic compound depends on how strong the ionic bond is and how many interactions the ions can make with water

  • In a liquid state they can conduct electricity

    • Once the electrons contact the liquid the charge builds up on each electrode due to the Voltage. This will cause ions to navigate towards them.

    • Once molten/aqueous ions are free to move. These ions can move towards the relevant electrode which leads to movement of charge, which is current

    • The FMCP are the ions

Giant Metallic lattice

  • A regular repeating structure of positive metal cations with a shared ‘sea’ of electrons

  • Force between cations and electrons

Properties

  • Hard very strong metallic bonds

  • High melting point - many strong metallic bonds lots of energy is needed to overcome

  • Density is high except Li Na K

  • Conductors of electricity

    • When voltage is applied the de-localised electrons are free to move throughout the lattice leading to the movement of charge (current)

  • Malleable

    • The ions can easily move past each other without resulting in breaks in the crystal structure.

    • Layers of cations can move past each other relatively easily

  • Not soluble

    • Metals can’t dissolve in water, because there are no favourable forces of attraction between the slightly positive hydrogen atoms in H2O with anything else. The electrons can’t be completely free in water

  • Conduct heat

    • The de-localised electrons can quickly move heat around the whole lattice, moving energy with them.

    • The ions just vibrate in place

How are metals made harder?

  • Pure metals are softer than alloys because the particles can easily move past each other.

  • The differently sized particles in alloys interfere with lateral movement