Blog

Chemical bonds, ionic, covalent and metallic

2.1.1  Chemical bonds

(See 2.1.2-2.1.5 below)

2.1.2  Ionic bonding

Ionic bonding
  • Transfer of electrons between metal & non-metal
  • Electrostatic force of attraction in all directions between oppositely charged ions
  • Occurs in ionic compound
  • Produce giant ionic lattice
  • Properties of ionic compounds
  • Properties Reasons
    High melting & boiling points Requires lots of energy to break large no of strong electrostatic force of attraction between oppositely charged ions
    Have regular structure

    (Giant ionic lattice)

    		 Strong electrostatic force of attraction in all directions between oppositely charged ions
    When melted/dissolved in water
    – conduct electricity    		 Ions are free to move & so charge can flow
    When solid
    – doesn’t conduct electricity    		 Ions in fixed positions
  • Ways of showing ionic bonding & limitationsDot & cross diagram

High melting & boiling pointsRequires lots of energy to break large no of strong electrostatic force of attraction between oppositely charged ions

Advantages Disadvantages
  • Useful for illustrating transfer of electron
  • Indicates from which atom the bonding electrons come from
  • X illustrate 3D arrangements of  atoms & electron shells
  • X indicate relative sizes of atoms

Ball and stick model

Advantages Disadvantages
  • Useful for illustrating 3D arrangement of atoms in space
  • Useful for visulising shape of molecule
  • Atoms aren’t solid sphere
  • Sticks represent bonds but there’s no  physical bond but electrostatic force of attraction
  • Atoms are placed far apart from each other but in reality the gaps between atoms are much smaller
  • X indicate movement of electrons

2D diagrams

Advantages Disadvantages
Displayed formulae are 2D representations and are basically simpler versions of the ball and stick model

  • Adequately indicate what atoms are in a molecule and how they are connected
    X illustrate the relative sizes of the atoms and bonds

  • X give you an idea of the shape of a molecule and what it looks like in 3D space Atoms are placed far apart from each other but in reality the gaps between atoms are much smaller

3D diagrams

Advantages Disadvantages
3D drawings and models depict the arrangement in space of the ions

Show the repeating pattern in giant lattice structures
 Only illustrate the outermost layer of the compound

Difficult and time consuming to draw
2.1.3  Ionic compounds

(See 2.1.2 Ionic bonding)

2.1.4  Covalent bonding

Covalent bonding

  • Sharing of pair of electrons between non-metal atoms
  • Electrostatic force of attraction between +ve nucleus & pair of -ve electrons
  • Occurs in covalent compound
  • Produce simple molecular compounds or giant covalent structure

Simple molecular compounds

Fullerenes       
  • Molecules of carbon atoms with hollow shapes
  • Hexagonal rings of carbon atoms but may also contain rings with 5 or 7 carbon atoms
  • 1st fullerene – Buckminsterfullerene (C60) – has spherical shape
 Properties

  • Low melting point
  • X conduct electricity
  • Soft, brittle & lubricant – shape like ball – roll

Uses

  • Drug delivery
  • Lubricants
Carbon nanotubes

 Long cylindrical fullerenes Properties

  • Strong – high length to diameter ratios
  • Conduct electricity

Uses

Reinforce composite materials eg tennis rackets – high tensile strength

Properties

Properties Reasons
Low melting & boiling point Weak intermolecular forces between molecules – easy to break
X conduct electricity X free electrons

Giant covalent structure

 

Diamond

 Each carbon bond to 4 other carbons covalently – hard Properties

  • High melting point
  • X conduct electricity
  • Hard & stron
  • Insoluble in water

Uses

  •  Cuttting Tools
Graphite
  • Each carbon bond to 3 other carbons covalently
  • Form layers of hexagonal rings which have no covalent bonds      between layers
  • Properties
    High melting point
    Conduct electricity – 1 electron from each carbon atom is delocalised
    Soft, brittle & slippery – weak (intermolecular) forces between layers – easy to break – layers can slide over each other
  • Uses
  • Electrodes, pencils, lubricant
Graphene

 Single layer of graphite
  • Properties
  • High melting point
  • Conduct electricity
  • Strong – atoms within layers are tightly bonded covalently – lots of energy to break
  • Use
  • In electronics, composites
Silicon dioxide (silica) SiO2
  • Each silicon bond to 4 O2 covalently
  • Each O2 bond to 2 silicon covalently
 Properties

  • High melting & boiling point
  • X conduct electricity
  • Hard
2.1.5  Metallic bonding
Metallic bonding
  • Bonding of metal atoms to form solid
  • Strong electrostatic attraction between closely packed +ve metal ions & sea of delocalised electrons
  • Produce giant metallic structure
  • Arranged in regular pattern
  • Properties
  • Properties Reasons
    High melting & boiling pt (See above for reasons)
    Conduct electricity & thermal energy
    Bend (ductile) & change shape (malleable)

Alloys

  • Mixture of 2 or more different types of metals
  • Not malleable/ductile, hard – different size of atoms disrupt structure – harder to slide – harder than pure metal
  • Smart alloys – return to original shape