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Chemical Calculators | Atomic Collider Simulation 2
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World here explicitely means the universe, our Earth consists of the same substances as space. The elements are ordered in periods (from left to right) and in groups (top-down).
All matter around us, which we observe, is made from these elements. An element is a substance made of atoms, which all have the same amount of protons. Atom derives from the greek word for indivisible. If you take a certain amount of an element, e.g. a lump of gold, and divide it in two parts, you have two lumps which are still gold. You can divide them further and they will stay gold, but only up to a certain point. If you have a single gold atom, this also can be divided (in theory, but it is very difficult to do), but it won't be gold after that. So atoms are not indivisible by principle, they just become other atoms when divided.
Atoms for the very largest part consist of nothing (spatial that is). The rest is nucleus and shell. The nucleus consists of protons and neutrons, the shell of electrons. Neutrons are electrically neutral (hence their name), protons are positively charged. They are responsible for the negativelly charged electrons circling around the nucleus, because plus and minus attract each other, like with a magnet. The number and arrangement of the electrons determines the chemical properties of an element. Most important here are the electrons in the outermost shell, the valence electrons. Therefore different elements have different chemical properties, but elements of the same group have similar properties, because they have the same amount of valence electrons. The number of shells of an atom depends on the number of electrons, whereas the notion shell shouldn't be taken literally. Electrons doesn't make it easy for the imagination, they are not located at an exactly determinable place, but only are there with a certain probability.
Atoms aspire to fill their outermost shell with electrons. Amongst others, this causes chemical reactions and, as a consequence, compounds. This are molecules, where certain atoms 'lend' electrons from other, fitting atoms. Atoms that have a number of electrons that differs from their number of protons and that therefore are charged are called ions. With less electrons they are cations, with more anions. Compounds of cations and anions are called salts. Noble gases have their outermost hull already filled up and therefore don't react chemically at all or only very reluctantly.
The most simple element is hydrogen: one proton and therefore one electron. After that comes helium with two of each. For the further elements see above. Additionally there are also neutrons in the nucleus. These make it stable. For larger atoms, this stability is harder to achieve and more neutrons are needed. A certain element has a certain amount of protons, but the amount of neutrons can vary. Atoms with the same number of protons, but a different number of neutrons are called isotopes of an element. The number of neutrons is not...