A chemical element is a substance that cannot be made into a simpler form by ordinary chemical means.
The smallest unit of a chemical element is an atom, and all atoms of a particular element are identical.
Parts of an Atom
There are two parts to an atom
At the center of an atom is a nucleus made up of two types of particles called protons and neutrons.
Protons have a positive electrical charge. The number of protons in the nucleus determines what element the atom is.
Neutrons are about the size of protons but have no charge.
Electrons, much smaller than protons or neutrons, have a negative electrical charge, move at nearly the speed of light,
and orbit the nucleus at exact distances, depending on their energy.
Because electrons are minuscule compared with protons and neutrons, the number of protons plus neutrons gives the atom its atomic mass.
All atoms of a given element always have the same number of protons, but may differ in the number of neutrons found in the nucleus.
Atoms of an element with differing numbers of neutrons are called isotopes. For example, carbon always has 6 protons but may have 6, 7, or 8 neutrons.
This means there are three isotopes of carbon: carbon-12, carbon-13, and carbon-14, however, carbon-12 is by far the most abundant.
Atoms are stable when they have a full outermost electron energy level. To fill its outermost shell, an atom will give, take, or share electrons.
When an atom either gains or loses electrons, this creates an ion. Ions have either a positive or a negative electrical charge. What is the charge of an ion if the atom loses an electron? An atom with the same number of protons and electrons has no overall charge, so if an atom loses the negatively charged electron, it has a positive charge. What is the charge of an ion if the atom gains an electron? If the atom gains an electron, it has a negative charge.
When a cation gets close to an anion, they link up because of their different net charges — positive charges attract negative charges and vice versa.
When two or more atoms link up, they create a molecule.
The molecular mass is the sum of the masses of all the atoms in the molecule. A collection of molecules is called a compound.
An atom has negatively-charged electrons in orbit around its nucleus, which is composed of positively-charged protons and neutrons, which have no charge.
Isotopes of an element must have a given number of protons but may have variety of numbers of neutrons.
An atom that gains or loses electrons is an ion.