Molecules2018-06-17T11:43:42+10:00

Hydrogen atoms make one bond with other atoms
Atoms are constantly moving. If you imagine a box containing only hydrogen atoms, then they will be moving in straight lines inside the box until they hit something, like the wall of the box, or another hydrogen atom. If they hit the wall, they will just bounce off, but if a hydrogen atom hits another hydrogen atom, they will stick together. This pair of hydrogen atoms is then called a hydrogen molecule. Eventually, all the hydrogen atoms will have collided with other hydrogen atoms to form hydrogen molecules. The join that sticks them together is called a chemical bond.

A molecule is a group of atoms bonded together.

Strangely, if another hydrogen atom collides with the hydrogen molecule, it will not stick to make a “threesome”. In other words, hydrogen atoms will only bond once to form a hydrogen pair, and that’s it. Molecules that contain only 2 atoms are called diatomic. Hydrogen is a diatomic molecule.

Formulas (or formulae if you’re British)
Scientists have different methods of writing molecules, called their formula. In the first method, the molecule can be shown as a simple drawing, called a ball and stick model. This is a picture version which shows the atoms as circles joined together by a “stick” to show the bond. As this is a bit cumbersome, scientists abbreviate to show just the symbols and the bond in a structural formula. The third way called the molecular formula is even simpler, with the number of atoms written as a small number to the right and a bit lower to the symbol, as H2. It depends on the situation as to which type of formula is used.


H-H H2
Ball and Stick model Structural Formula Molecular Formula
“picture version” Shows where the chemical Only counts the number
bonds are in the molecule of atoms

Note that the plural of formula can be either formulas or formulae, depending on which region you belong to. In this program we will use “formulas” because it is a simpler version. Radios have antennas and insects have antennae.
Oxygen atoms make two bonds with other atoms
Imagine that you have an oxygen atom as well as hydrogen atoms inside the box. When a hydrogen atom collides with the oxygen atom, it will stick. But the process does not stop at this point. If another hydrogen atom collides with the oxygen atom, it will also stick to it. At this point we have molecule consisting of 3 atoms joined together, one oxygen atom and two hydrogen atoms. But if a third hydrogen atom collides with this cluster, it will not stick. It seems that oxygen atoms can make two bonds with other atoms, but no more. Here are the formulas for this molecule.

H2O1
Ball and Stick model Structural Formula Molecular Formula

Notice how the molecular formula counts the number of each kind of atom in the molecule- one oxygen atom and two hydrogen atoms. However, scientists have agreed to take a shortcut whenever there is only one atom of a kind in a molecule, and drop the “1”. In fact, it is considered wrong to show the number “1” in molecular formulas, as it is understood that, when a number is not shown, it means that there is only one of that kind of atom in the molecule. It is a kind of “silent 1”. So the molecular formula is correctly written as H2O.
H2O1 is written as H2O

Recognise it? It’s the formula for water. When you drink a glass of water, trillions of trillions of these molecules go down your throat. Water is made of these molecules.

Nitrogen atoms make three bonds with other atoms
Imagine now that you have a nitrogen atoms as well as hydrogen atoms inside the box. When a hydrogen atom collides with a nitrogen atom, it sticks. When a second hydrogen atom collides with the same nitrogen atom, it also sticks. When a third hydrogen atom collides with the nitrogen atom, it also sticks. But when a fourth hydrogen atom collides with the nitrogen atom, it doesn’t stick and instead bounces off. Nitrogen can make three bonds with other atoms, but no more.

NH3

Ball and Stick model Structural Formula Molecular Formula

The substance that this molecule makes is called ammonia. Unlike water, it is not a liquid, but a colourless gas. It has a sharp odour, and it dissolves well in water.
Carbon makes four bonds with other atoms
Finally, let’s imagine a carbon atom as well as hydrogen atoms inside the box. It turns out that four hydrogen atoms will stick to a carbon atom, but not a fifth. Carbon can make four bonds with other atoms.

CH4

Ball and Stick model Structural Formula Molecular Formula

The substance that this molecule makes is called methane. Like ammonia, it is also a colourless gas, but it is odourless. It also burns very well. If you have a gas stove, these are the molecules that come out when you turn it on. It also famously comes out of both ends of cows!

Fluorine makes one bond with other atoms
If we put a fluorine atom in the box with hydrogen atoms, a hydrogen atom will stick to it when they collide. But that’s it. No more hydrogen atoms will bond to fluorine. Fluorine makes only one bond with other atoms, and that’s it.

H-F HF
Ball and Stick model Structural Formula Molecular Formula
The substance that this molecule makes is called hydrogen fluoride, and it’s also a colourless gas. But it’s not one that you want to mess with. Upon contact with your skin, it will corrode it away. If you breathe it, it can kill you.

Neon makes no bonds with other atoms
If we put a neon atom inside our box, then hydrogen atoms would collide with but not stick to it at all. Neon does not bond with any atoms, even itself. Atoms that don’t make any bonds remain single atoms. They are called monatomic.

Neon is a loner
Valency
The number of bonds that an atom makes with other atoms is called its valency. It is another word for an atom’s “bonding power”. Hydrogen’s valency is 1, oxygen’s valency is 2, nitrogen’s valency is 3, carbon’s valency is 4, fluorine’s valency is 1 and neon’s valency is zero.
In our examples above, we have bonded different kinds of atoms to hydrogen only. However, we can mix and match the atoms that bond to each other, as long as the valency rules are obeyed. The following diagrams show the valency of each kind of atom, and show how they would bond to any other kind of atom.

New Courses

Contact Info

1600 Amphitheatre Parkway New York WC1 1BA

Phone: 1.800.458.556 / 1.800.532.2112

Fax: 458 761-9562

Web: ThemeFusion