CHAPTER 1. ATOMICCOMBINATIONS 1.11
trigonal pyramidal.Activity: Building molecular models
In groups, you are going to build a number ofmolecules using jellytots to represent the
atoms in the molecule,and toothpicks to represent the bonds betweenthe atoms. In other
words, the toothpicks will hold the atoms (jellytots) in the molecule together. Try to use differ-
ent coloured jellytots torepresent different elements.
You will build models of the following molecules:
HCl, CH 4 , H 2 O, HBr and NH 3For each molecule, youneed to:- Determine the basic geometry of the molecule
- Build your model so that the atoms are as far apart from each other as possible (remember
that the electrons aroundthe central atom will tryto avoid the repulsions between them). - Decide whether this shape is accurate for that molecule or whetherthere are any lone
pairs that may influenceit. - Adjust the position of the atoms so that the bonding pairs are further away from the lone
pairs. - How has the shape ofthe molecule changed?
- Draw a simple diagramto show the shape of the molecule. It doesn’t matter if it is not
100% accurate. This exercise is only to help youto visualise the 3-dimensional shapes of
molecules.
Do the models help youto have a clearer pictureof what the molecules look like? Try to
build some more models for other molecules you can think of.1.11 Oxidation numbers ESBW
When reactions occur, an exchange of electronstakes place. Oxidation is the loss of electrons from an
atom, while reduction is the gain of electrons by an atom. By giving elements anoxidation number,TipYou can remember this
by using OiLRiG: Oxida-
tion is Loss Reduction is
Gain.it is possible to keep track of whether that element is losing or gainingelectrons during a chemical
reaction. The loss of electrons in one part of thereaction must be balanced by a gain of electrons in
another part of the reaction.DEFINITION: Oxidation number
Oxidation number is the charge an atom wouldhave if it was in a compound com-
posed of ions.