4.6 CHAPTER 4. THE ATOM
reactions, when atoms come into contact with one another, it is theelectronsof these
atoms that will interact first. More specifically, it is thevalence electronsof the atoms that
will determine how they react with one another.
To take this a step further, an atom is at its most stable (and thereforeunreactive) when all
its orbitals are full. On the other hand, an atom is least stable (and therefore mostreactive)
when its valence electron orbitals are not full. This will make more sense when we go on
to look at chemical bonding in a later chapter. To put it simply, the valence electrons are
largely responsible for an element’s chemical behaviour and elements that have the same
number of valence electrons often have similar chemical properties.
The most stable configurations are the ones that have full energy levels. These configura-
tions occur in the noble gases. The noble gases are very stable elements that do not react
easily (if at all) with any other elements. This is due to the full energy levels. All elements
would like to reach the most stable electron configurations, i.e. all elements want to be
noble gases. This principle of stability is sometimes referred to as the octet rule. An octet
is a set of 8, and the number of electrons in a full energy level is 8.
See video: VPamk at http://www.everythingscience.co.zaInformal experiment: Flame tests
Aim: To determine what colour a metal cation will cause a flame to be.
Apparatus:- Watch glass
- Bunsen burner
- methanol
- tooth picks (or skewer sticks)
- metal salts (e.g. NaCl, CuCl 2 ,
CaCl 2 , KCl, etc. ) - metal powders (e.g. copper, magne-
sium, zinc, iron, etc.) Picture by offbeatcin on Flickr.com
Warning:Be careful when working with Bunsen burners as you can easily burn
yourself. Make sure all scarves/loose clothing are securely tucked in and
long hair is tied back. Ensure that you work in a well-ventilated space and
that there is nothing flammable near the open flame.88 Chemistry: Matter and Materials