If two or more atoms are connected in a covalent way, and neutral particles are mad, than those particles must be molecules.
Mostly we deal then with different atoms, but sometimes with the same atoms.
Something about the threedimensional shape of molecules.
Have a close look at the models below (of molecules):
left could be tetra chloro methane and right di cloro methane.
Molecules are built up of two or more connected atoms.
The occupy space and have a threedimensional shape.
You can have extremely simple molecules, like H-H (H2).
This Hydrogen molecule is very small, linear and symmetric.
But most molecules occupy much more space, are bigger, like glucose.
the cyclic form of glucose
If a particle has an unpaired electron, this particle will be very reactive and is called a radical.
The number of atoms of one kind that is present in a molecule, is indicated with a number right under. That's how you get a MOLECULAR FORMULA.
Very often two non metals can form a molecule in only one way, but sometimes there are different combinations.
If two non metals can form different molecules, than we should adjust the names.
In that case we apply extra rules for nomenclature, or: we use prefixes (see module 4):
mono
1
di
2
tri
3
tetra
4
penta
5
hexa
6
hepta
7
okta
8
nona
9
deka
10
The name of a substance can, according to these rules, become rather complicated, which not always is needed.
Some names are abbreviated.
Look at the table below with a couple of examples. Certainly you have heard of carbon monoxyde or carbon dioxyde.
CO
(mono)carbon mon(o)oxyde
CO2
(mono)carbon dioxyde
P2O5
(di)phosphor pent(a)oxyde
P2O3
(di)phosphor trioxyde
Gaining or loosing electrons completely is limited to the number of three; 4+ or 4- ions are very rare.
Such a limitation does not exist for sharing of electrons in covalent bondings.
An atom may have four or six shared electrons with another atom.
In the structural formula of a molecule you can indicate all valency electrons as dots.
Then you have god an ELECTRONIC FORMULA. An electronic formula does not need to limit itselve to one atom.
If you indicate all valency electrons with dots in the formula, you can exactly see where the electrons are shared.
In stead of dots, we mostly use dashes (two dots equals one dash).
Normally electrons perform in pairs. One dash between two atoms indicates such a shared electron pair.
If atoms share each others electrons, they form molecules. In the case of an atom group with a charge, we talk about a complex ion.
If you would investigate alle substances in the earth crust, you might draw the conclusion that molecules dominate; there are more molecules than ionic of metalic substances.
