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Unit 4 updated

Unit 4 - How Atoms are Held Together

This section introduces the idea of covalent bonding, leading to
molecules and chemical formulae.

Covalent Bonds and Molecules

Compounds are made up of atoms of more than one element. In
Chemistry, compounds can be identified as either covalent

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a molecule.
Carbon Monoxide is made up of diatomic molecule.
Non-metal atoms bond together to form molecules.


Models are always used initially to determine the full structural
When using the Molymods the spheres are held together by
connections. Each connection represents a single covalent bond
which is represented…

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different chemical properties.
Physical Properties: a) Very hard. b) High Melting Point. c) Does not
conduct electricity.
Structure: It exists as one giant network, where each carbon is
found tetrahedrally joined to 4 others by covalent bonds. These
bonds exist throughout the whole 3D structure.

- (Carbon) this consists of…

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If a covalent compound has a name which gives a clue to its formula,
then use the meaningful name. If not use a bonding picture

Some chemical names give an indication in the formula;
e.g. carbon dioxide - this tells us that the molecule contains two
oxygen atoms.

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5. Leave out any 1's in the formula.
e.g. PCl3.


The valencies go below the symbols of the elements.
The final formula should contain small numbers to the bottom
right of the symbols.
Leave out the number 1 from any formula.
Cancel ell even numbers (except where you have…

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Energy is required to overcome forces of attraction. A lot of energy
is required to break covalent bonds.


Bonding - the join between different atoms.
Covalent Bonding - a bond formed between non-metals by the
sharing of a pair of electrons.
Molecule - a group of atoms held together…

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of the periodic table point to the corners of a tetrahedron. This is
because the electron clouds repel each other and try to get as far
away from each other as possible.
This explains why methane molecules are tetrahedral in shape and
water molecules are bent. Similarly, the compound of…

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A covalent bond is formed by the sharing of electrons in the
electron clouds of an element e.g. Hydrogen and Oxygen combine
to form water.

The chemical formula gives the numbers and type of atoms of each
element in a molecule. The numbers of atoms of each element in


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