CfE Higher Chemistry Unit 1 Chemical Changes and Structure Bonding and Structure in the First 20 Elements – Hydrogen to Calcium

The types of bonding in these elements are metallic, covalent and London dispersion forces.

Metallic Bonding The outer electrons in a metal are “delocalised” They are free to move around the whole metal structure This is how and why metals conduct electricity in the solid state

Metallic Bonding + e-

Metallic Bonding + e-

Metallic Bonding e- e- e- e- e- e- e- e- e- e- + + + + + + + + + + Delocalised outer energy level electrons e- e- e-

Metallic Bonding e- e- e- e- e- e- e- e- e- e- + + + + + + + + + + Delocalised outer energy level electrons e- e- e- Nuclei and inner energy level electrons, i.e. positively charged ions

Metallic Bonding e- e- e- e- e- e- e- e- e- e- + + + + + e- e- e- + + e- + e- + + e- e- e- A metal can be considered to be a regular array of positively charged ions in a sea of delocalised electrons.

Metallic Bonding Each positively charged ion is attracted to the pool of electrons Each electron is attracted to the positively charged ion These electrostatic attractions hold the whole metal structure together The delocalised electrons are not attached to any particular ion – they are free to move throughout the metal lattice

How Strong are Metallic Bonds? Generally they are strong (80 – 600 kJ mol-1) The greater the number of delocalised electrons, the stronger the bonds e.g. Na versus Al

The Covalent Bond + - - + A covalent bond is the electrostatic attraction between the positively charged nuclei and the negatively charged shared pair of electrons

Hydrogen A hydrogen molecule with a shared pair of electrons X H A hydrogen molecule with a shared pair of electrons - A single covalent bond

This is a triple bond. Shown as N N Nitrogen o X X o X N N o o X X o This is a triple bond. Shown as N N

Covalent Bonds in Compounds X o H o H This molecule is H2O

Structure of Covalent Substances The examples given are all molecules – discrete groups of atoms covalently bonded Covalent networks also exist – these are very strong, 3 dimensional network structures

London Dispersion Forces For substances to form liquids and solids on cooling, there must be forces of attraction between the particles The diatomic elements (e.g. hydrogen, nitrogen, oxygen) and the noble gases can be liquefied on cooling There must be forces of attraction between these molecules and atoms These forces of attraction are due to the movement of electrons in the atom or molecule and are always present

London Dispersion Forces The electrons are constantly moving – the distribution of charge is not even within the atom or molecule e N e e

London Dispersion Forces The electrons are constantly moving – the distribution of charge is not even within the atom or molecule e N e e

London Dispersion Forces The electrons are constantly moving – the distribution of charge is not even within the atom or molecule e N e e

London Dispersion Forces The electrons are constantly moving – the distribution of charge is not even within the atom or molecule e N e e

London Dispersion Forces The electrons are constantly moving – the distribution of charge is not even within the atom or molecule e e N e e This side is more positive This side is more negative

London Dispersion Forces This side has a temporary negative charge - This side has a temporary positive charge +

London Dispersion Forces - + Temporary dipole

London Dispersion Forces The temporary uneven distribution of electrons causes temporary dipoles to be established within atoms and molecules The temporary dipole in one atom or molecule will cause a temporary dipole to establish in a neighbouring atom/molecule – an induced dipole The oppositely charged ends of the temporary dipoles result in attraction between particles

London Dispersion Forces + N e N e - - - + temporary force of attraction

London Dispersion Forces These forces need to be overcome before the discrete molecular elements melt or boil They are weak bonds (4 kJ mol-1) The discrete molecular elements are gases, liquids or low melting point solids at room temperature

London Dispersion Forces The strength of the London dispersion forces increases with increasing size of the atom or molecule.

Metallic lattice

Covalent network

Covalent molecular diatomic gases

Covalent molecular solids

Monatomic gases

Learn This! Metals only have metallic bonding Covalent networks only have covalent bonding Monatomic gases only have London dispersion forces Covalent molecular elements have covalent bonding inside the molecule and London dispersion forces between the molecules

Types of Bonding Stand and Deliver Work in groups of 4, number yourselves 1-4. You will each be given an information card about a type of bonding Metallic bonding Covalent Molecular bonding Covalent Network bonding London Dispersion Forces To begin, number 1’s should work with another number 1, 2’s with other 2’s and so on. Read over your type of bonding and make a summary in your notes. Compare your notes with the others and make any changes. Return to your original group and then take it in turns to explain your type of bonding to the group. Number 1’s will go first, then 2 then 3 then 4. Write a summary in your notes for the other 3 types of bonding. Complete the card sort to test your knowledge.

Summarising…… For each type of bonding you should make notes on the following; A description of the bond e.g covalent bonds are shared pairs of electrons……. A diagram of the bond. The strength of the bond (this could be within the structure or between atoms or molecules. The properties that arise from this type of bonding e.g metals can conduct electricity due to the freely moving electrons within the structure.

Covalent Network Solids Boron, carbon and silicon all form strong covalent networks Boron forms a network based on interlocking B12 molecular units

Covalent Network Solids Silicon has a network structure that is based on a tetrahedron

Covalent Networks of Carbon Diamond has a network structure that is based on a tetrahedron Each C is bonded to 4 other C – very hard structure Graphite has a network structure of 6 member rings of carbon layers. weak London dispersion forces between layers Each C is bonded to 3 other C – leaving a delocalised electron, allowing conduction of electricity

Covalent Molecular Solids In 1985, a third form of carbon was discovered. Carbon was also found to exist as molecules – called fullerenes. The smallest fullerene is a C60 molecule – called buckminsterfullerene

Covalent Molecular Solids Phosphorus forms tetrahedral P4 molecules. Sulphur forms 8 membered puckered ring shaped S8 molecules. There are London dispersion forces between these covalent molecules. Phosphorus, sulphur and fullerenes are solids at room temperature compared to the gases of the diatomic elements. This is because the London dispersion forces increase with increasing molecular mass