Chemistry Topic 2: Covalent Bonds

Covalent bonds occur between a non-metal compound. 

They occur between two orbitals and they share electrons.

Non metals have incomplete outershells, and only outershells ar involved in covalent bonding. 

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  • Created by: Livy
  • Created on: 07-10-13 18:26

How do they work?

Covalent bonds ar a result of electrostatic attraction between the positive nuclei and the negative (shared) electrons. 

The group of atoms bonded together in this way is called a molecule.

The types and numbers of atoms in a molecule are shown in its formula.

Examples of covalent molecules

NameStructureModel Hydrogen (H2) H - H (http://www.bbc.co.uk/schools/gcsebitesize/science/images/hydrogen_chem_struc.gif) two atoms joined with a straight horizontal line (http://www.bbc.co.uk/schools/gcsebitesize/science/images/hydrogen_model.gif) Water (H2O) H - O - H (http://www.bbc.co.uk/schools/gcsebitesize/science/images/water_chem_struc.gif) three atoms joined (http://www.bbc.co.uk/schools/gcsebitesize/science/images/water_model.gif) Ammonia (NH3) H - N - H (with a line down from the N to an H)  (http://www.bbc.co.uk/schools/gcsebitesize/science/images/ammonia_chem_struc.gif) four atoms joined (http://www.bbc.co.uk/schools/gcsebitesize/science/images/ammonia_model.gif) Methane (CH4) H - C - H in a row, line from above the C to an H, line from below the C to an H  (http://www.bbc.co.uk/schools/gcsebitesize/science/images/methane_chem_struc.gif) five atoms joined (http://www.bbc.co.uk/schools/gcsebitesize/science/images/methane_model.gif)

Covalent compounds are usually gases or liquids with low melting points or boiling points and they don't conduct electricity.

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Multiple Bonds

Double bond = 2 shared electrons

Triple bond = 3 shared pairs

These occur when more than one pair of shells/orbitals overlap, resulting in multiple electrons being shared.

Multiple bonds are stronger then single bonds

A non-bonding atom (e.g. the two on the other side of the O when combined to make CO2) is called a lone pair. 

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Simple Covalent Substances

A Molecule = a group of atoms bonded with covalent bonds

The number of atoms is <100 (simple covalent substances)

Covalent molecules do not conduct electricity, as their particles are NOT charged. 

Covalent compounds have no free electrons and no ions so they don't conduct electricity

Properties                                        Reason

Insulator/Non-conductor                        No charges on molecules, so no current can flow

Holding the shape together                    Covalent bonds holding them together&forces of                                                                          attraction between layers 

Low mpt/bpt                                         Intermolecular forces are weak



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Giant Covalent Structures

Van Der Waals = intermoleclar forces

They are weak, intermolecular BONDS are strong

Sand, diamond and graphite have millions of atoms joined by covalent bonds

The bonds in these substances don't form molecules but lattices (vast network/giant covalent structures)

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Allotrope's

An allotrope is a different structure of the same element

For example, carbon can form diamond or graphite, and they all have different properties because the structures aren't the same 

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Diamond Structures and Properties

Diamond:

Number of covalent bonds each atom forms: 4

Hardness: Very hard, because of structure

Electrical and thermal conductivity: Doesn't conduct electricity as no atoms can move

(http://www.chemguide.co.uk/atoms/structures/drawdiamond.GIF)

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Graphite Structure and Properties

Graphite:

Number of covalent bonds each carbon atom forms: 3

Melting Point: Very high, as lots of bonds have to be broken 

Hardness: Soft and slippery, layers of atoms can slide over eachother

Electrical and thermal conductivity: Conducts heat and electricity, as some atoms are free to move 

(http://www.chemguide.co.uk/atoms/structures/graphite.GIF)

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