Monday, March 29, 2010

Test and Exam hints for Bonding

When you are answering questions about the properties of materials you need to do the following:
1. work out the type of substance.
2. write an intro paragraph that describes the structure and bonding in the structure. (below)
3. Link the structure to the property in the question.

Starter paragraphs for each type of substances are as follows.
Learn these

Metallic substances.
Metals are made up of metal atoms stacked into a 3 dimensional lattice held together by strong electrostatic attraction betweent the atom and its valence electrons This attraction is nondirectional. These valence electrons form a sea of electrons.

Ionic structures
Ionic crystals are made up of a 3 dimensional lattice of alternating positive cations and negative ions held together by strong diredtional electrostatic attraction between the ions.

Giant covalent structures
(Diamond, Graphite, Buck balls and silicon dioxide only)
These structures are made up of atoms covalently bonded together in a 3 dimensional structure.
Diamond is made up of carbon atoms bonded to 4 other C atoms.
Graphite is made up of carbon atoms bonded in layers to 3 other C atoms, leaving a free electron wh ich is found between the graphite layers.

Simple covalent molecules
These are made up of strong intramolecular covelant bonds and weak intermolecular Van der Waals forces. These Van Der Waal forces are weak and very easy to break so not much energy is needed to overcome these forces.
Van Der Waals forces:
Dipole-dipole interactions
Instantaneous dipole interactions
H bonding (molecules that have H with O, N, F atoms)

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