Atoms of some elements readily give up or lose an electron. What happens to the charge of such an atom? Its number of protons will be one greater than its number of electrons; therefore it will have a positive charge, (plus one , +) and become what is called a positive ion. By the same token, some elements will loose two or three electrons to become++, and +++ ions. Atoms of other elements may gain one, two, or three electrons thus become negative ions with a charge of negative 1,2, or 3 (- , –– , or – – -) .
Opposite charges attract; like charges repel. Therefore, positive and negative ions may stick together like opposite poles of tiny magnets. This is called ionic bonding. The bonding does not result in a random cluster of positive and negative ions. The particular size and charge of the ions results in their packing together in a very specific arrangements. As many millions pack together this results in the formation of a crystalof a givenmineral. Any rock is two or more minerals mixed together.
For example, table salt is a mineral, sodium chloride (Na+Cl-). These atoms/ions pack together to make whitish crystals that are perfect cubes.
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Also, examine some gains of salt under a microscope (low power). Kids will see that almost every grain is a perfect cube.