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Atoms are arrangements of protons, neutrons, and electrons. Protons and neutrons are comparatively large particles that have mass, and that form the dense center of the atom called the nucleus. Surrounding the nucleus are clouds of electrons, organised into orbits of different ‘energy potentials’, which we can think of as orbiting at different distances from the nucleus.
The number of protons determines which element it is. Atoms with an ‘atomic number’ of 1 are hydrogen. 2 is helium. 26 is iron. 79 is gold. 92 is uranium, etc. Each number is a different element with unique properties. Most elements can bond together to form compounds that have another range of totally different properties, but we’ll focus on compounds later.
While each element has a specific number of protons in its atom, there can be variation in the number of neutrons. There is usually one arrangement for each element that is the most stable (i.e. it doesn’t break down into radiation and nuclear waste) but we call the others isotopes, which can have slightly different properties than the usual arrangement.
Most elements do vary in the number of electrons they have. As electrons are much smaller than protons and neutrons and orbit the nucleus at a distance, the swapping and exchange of electrons between elements happens all the time. It’s the basis of their interactions and the formation of compounds, and leads to an extraordinary diversity of materials.