Quick Reference

ATOMS

Everything you can touch, see, smell or taste is made of atoms. And they all look a bit like this:

Every atom is made of only three different particles: protons, neutrons and electrons. The protons and neutrons are lumped together in the middle forming a nucleus and the electrons whizz around the outside.

Note: The figure is not to scale - if a proton was the size of a football and in the centre of a football pitch, the electron would be the size of a pea somewhere in the stands.

There are only 111 different atoms in the whole Universe. About 92 occur in nature, the rest only exist in laboratories and the heart of exploding stars.

In their natural state, that is not mixed up with everything else, atoms are called elements. Each element has a name: hydrogen, oxygen, gold, neon, silicon and so on. To see the whole list click here.

And since it would be laborious writing out the full name each time, each element also has a symbol: T for tungsten, C for carbon, Hg for mercury and so on.

Now let us look at the components of the atom a little more closely.

PROTONS

Protons are massive particles (when compared to all the other bits that make up the universe). They have a positive electrical charge and make up about half of the nucleus. It is the numbers of protons in an atom that identify each element. Change the number of protons and you change the element.

The number of protons is called the atomic number (symbol A). Hydrogen has 1 proton and has the atomic number 1. Helium has 2 protons and has the atomic number 2, and so on all the way up to …. Which has 111 protons and not surprisingly has the atomic number 111.

NEUTRONS

Neutrons are a touch bigger than protons, do not have an electric charge and make up the rest of the nucleus. The number of neutrons in an element is not always the same. Hydrogen can for example have between 0, and 3 neutrons. Elements with differing numbers of neutrons are called isotopes. The total number of protons and neutrons in an atom is given the symbol Z.

ELECTRONS

The third bit in an atom, the electron, is really small and has a negative electrical charge. There are the same number of electrons orbiting the nucleus as there are protons in the nucleus. Why? Because the negative electrons are attracted to the positive protons. Atoms like to be electrically neutral so the numbers of protons and electron balance out.

And why doesn't the electron clamp itself to a proton? Well, electrons have thermal energy and want to escape. It is the balance between electrostatic attraction and thermal energy that keeps the electrons orbiting around the nucleus.

RELATIVE ATOMIC MASS

Giving atoms names and atomic numbers is not enough, we need to know how much they weigh. The problem is, atoms are so really tiny: a hydrogen atom weighs just ..... So the tefal heads have come up with a system that compares the mass of each atom with that of Carbon. This is called the Relative Atomic Mass (RAM) and is the total number of protons and neutrons in the nucleus. Carbon has a RAM of 16 (8 protons and 8 neutrons). Hydrogen has a RAM of 1 (1 proton), Helium a RAM of 4 (2 protons and 2 neutrons) and so on.

A glance at the table of elements will show that the RAM is not a whole number, this is because it takes into account the abundance of isotopes in a sample.

THERMAL ENERGY

All electromagnetic radiation is made up of billions of tiny particles called photons. Every photon has a thermal energy proportional to its frequency. When a photon collides with an electron its energy is absorbed by the electron which makes it bit hotter. This extra energy causes the electron to move to a higher (larger) orbit about the nucleus. If an electron absorbs enough energy it can escape from the atom: this pocess is called ionization.

This is hovering on the fringe of quantum mechanics. To find out more click here.

ATOMIC COLLISIONS

In gasses, all the atoms whizz about and occasionally crash into one each other. If there is enough force in the collision an electron can get knocked off one atom and onto another. The atom with the missing electron now has a positive charge (because there are more protons than electrons) and is called a positive ion. The atom with the extra electron now has a negative charge (because there are more electrons than protons) and is called a negative ion. And since opposites attract, the ions get it together to form molecules.

Everything you can touch, see, smell or taste is the result of atoms crashing into each other and swopping electrons.

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