What Changes Between an Atom & an Ion?
An atom is the smallest particle of a given element that retains the element's proprieties. It comprises a nucleus, which has protons and neutrons, as well as a cloud of electrons that orbit the nucleus in different energy levels, or orbitals. A neutral atom has the same number of protons and electrons. However, atoms tend to be most stable with eight electrons in their outermost orbital. Atoms can gain or lose electrons to fill their outermost orbitals with eight. The atom becomes an ion with a positive or negative charge, depending on whether electrons were lost or gained.
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Positive Ion
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When an atom loses one or more electrons, it loses negative charges. This can happen when the atom comes in close proximity to another atom that either has six or seven electrons in its outermost orbital. Because the nucleus is found in the center of the atom, and the protons are stuck there, it retains all positive charges. The loss of an electron results in an ion with a 1+ positive charge, the loss of two electrons results in an ion with a 2+ positive charge, and so on. For example, when a sodium atom with eleven protons loses an electron, resulting in only ten electrons, there is a net positive charge. Positive ions are called cations, and they can easily bond with negative ions and dissolve into an aqueous solution.
Negative Ion
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When an atom gains one or more electrons, it gains negative charges. This can happen when the atom comes in close proximity to another atom that either has one or two electrons in its outermost orbital. The nucleus is in the center of the atom retains all of its protons. The extra electrons yield an ion with a negative charge, with the amount of charge equal to the amount of electrons gained. The gaining of an electron results in an ion with a 1- negative charge, the gaining of two electrons results in an ion with a 2- negative charge, and so on. For example, when a chlorine atom with 17 protons gains an electron, it ends up with 18 electrons. The extra electron gives the ion a net negative charge. Negative ions are called anions, and they can easily bond with positive ions and dissolve into an aqueous solution.
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Energy
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When an atom becomes an ion, the number of electrons is not the only thing that changes. The energy in the atom also changes. Energy is also required to remove an electron from its orbital. This energy is known as ionization energy. In general, the fewer electrons there are in the outer orbital, the less ionization energy is required to pull an electron from the atom. For example, sodium has only one electron in its outermost orbital, so it does not take much energy to remove it. However, neon has eight electrons in its outermost orbital, which is the ideal configuration for any atom. Consequently, it takes an extreme amount of energy to make an ion from this atom.
Solids and Solutions
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When ions come together to form a solid compound, they are held in place by electromagnetic forces between the ions. Unlike covalent bonds, in which two atoms share two or more electrons to achieve eight in their outermost orbital, these ionic bonds give up their electrons to another atom. Ions are often found in water solutions. This happens because the ions can move freely around the molecules of water. An example of this is when table salt (sodium chloride) quickly dissolves in water.
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References
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