Monday, March 29, 2010

Polarity

video

Metallic bonds and simple covalent molecules

video

Metallic structures

video

Simple covalent molecules

Podcasts


video

Giant covalent structures


video

Ionic lattices

Types of particles in given substances

Summary:
Metallic substances contain atoms
Ionic substances contain ions
Giant covalent substances contain atoms
Simple covalent molecules contain atoms

Solid /Type of particle / Attractive force between particles

sodium oxide / ions / intramolecular ionic bond

sulfur trioxide / molecules / intermolecule dipole-dipole interaction

silicon dioxide / atoms / intramolecular covalent bonds

aluminium oxide / ions / intramolecular ionic bonds

Bond polarity questions

To work out bond polarity you need to do the following:
1. Draw the lewis diagram.
2. Work out the shape.
3. check that the bond polarities cancel out. Is the a net dipole moment?

in your answer for explaining polarity... include the following words.

polar bonds, electronegativity, net dipole, symmetrical, asymmetrical

Remember:

symmetrical molecules = non-polar
asymmetrical molecules = polar

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)

Tuesday, March 23, 2010

Wiki questions

http://tll-chem-science.wikispaces.com


Metals structure and its properties
Copper can be beaten out into thin sheets without shattering into pieces.
(a) Name this property.
(b) Explain how this property is related to the metallic structure and bonding of Copper.

Simple covalent molecules and shapes of molecules
The molecules CH2O and NH3 both consist of a central atom with three other atoms bonded to it covalently. In spite of this similarity, the shapes and bond angles of the two molecules are quite different.
a) Discuss the reasons for this.
b) Explain why BH3 is trigonal planar while CH4 is tetrahedral.

Properties of Materials
Discuss with reference to structure and bonding:
a) Chlorine is a gas at room temperature but sodium chloride is solid

b) Ammonia has a bond angle of 107º whereas the bond angles in water are only 105º.

Bonding and Atomic structure summary

Saturday, March 20, 2010

covalent bonding



This is an animation of two hydrogen atoms forming a covalent bond by sharing it valence electrons in the formation of a covalent bond.

Tuesday, March 9, 2010