The number of protons in an atom of an element is the atomic number, or proton number.
Elements are arranged in the periodic table in order of their atomic numbers.
There is always the same amount of protons as electrons.
Each electron in an atom is in an energy leverl, or shell.
Elements in the same group of the periodic table have the same number of electrons in their outer shell.
Noble gases (group 8 or 0) are unreactive because their atoms have stable arrangements of electrons.
Atoms of other elements can get a stable arrangement by gaining or losing electrons to make ions, or sharing electrons to make covalent bonds.
When an element in group 1 reacts with an element in group 7, an electron is transferred between them. The group 1 atom will lose an electron, the group 7 one will gain it. The group 1 atom will become positively charged. The group 7 atom will become negatively charged.
Positive and negative ions attract to make ionic bonds.
Ionic bonds hold together oppositely charged ions. Strongelectrostatic forces of attraction act in all directions.
These compounds have giant structures that are very regular.
Sodium Chloride (NaCl) is an ionic structure with a cubic lattice.
The ratio of ions in the formula and the structure of an ionic compound depend on the charges on the ions.
The formula of an ionic compound is the simplest ratio of ions in the compound, and does not represent a molecule.