1.1 Atoms and molecules
Everything around us, and in us, is made up of atoms, which you can consider as minute spheres. They are very, very small. A page of a book is about one million (1 000 000) atoms thick. There are about 100 or so different types of atom, including oxygen atoms, carbon atoms, nitrogen atoms, gold atoms and iron atoms, and atoms provide the basic building blocks for everything. It is like having a ‘Lego’ set with about a hundred different types of brick. Each type of atom is a different size and has a different mass from all the other types. Because atoms are so very small, chemists do not deal with their actual mass, but instead they give the smallest and lightest atom, which is hydrogen, a mass of 1 and then express the mass of all the other atoms relative to that. So, for example, an oxygen atom is 16 times as heavy as a hydrogen atom and so it has a relative atomic mass of 16. The different types of atoms are called chemical elements or just elements, for short. By using different atoms, and joining them in different ways, you can produce water, sugar, salt, proteins, paper, rocks and, in fact, everything in the Universe! Different materials can exist as either a solid, a liquid or a gas, but one of these ‘states’ is most familiar. For example, water is generally thought of as a liquid, but it can freeze to a solid, ice, and it can occur as a gas, water vapour or steam.
Air is not a pure gas, but a mixture of various different gases. Spend a few moments thinking of as many gases as you can, either occurring in the air or elsewhere.
The following may be amongst the ones you have listed: oxygen, nitrogen, carbon dioxide, helium (familiar for its use to fill balloons, but also has many industrial uses), neon (in coloured signs), methane (the main component of natural gas), chlorine and hydrogen.
Helium and neon both exist as individual atoms in the atmosphere. But the smallest gaseous particle of hydrogen, oxygen, chlorine and nitrogen is composed of two identical atoms of the element attached together to form a molecule. The link between atoms, usually referred to as a chemical bond, can be represented by drawing a ‘stick’ holding the two ‘balls’, representing the atoms, together (Figure 1).
The relative atomic mass of nitrogen is 14, so are nitrogen atoms heavier or lighter than oxygen atoms?
As given above, an oxygen atom is 16 times heavier than a hydrogen atom. Oxygen has a relative atomic mass of 16. So oxygen atoms are slightly heavier than nitrogen atoms, whose relative atomic mass is 14 (each one is 14 times heavier than a hydrogen atom).