Charged Up

Some atoms and molecules have a tendency to give up some of their electrons. Others have a habit of taking extra electrons. When an atom or molecule gains or loses an electron, the result is called an ion. Electrons have a negative charge, so an ion that has extra electrons is negatively charged, while an ion that has lost electrons is positively charged.

How likely an atom is to gain or lose electrons is affected by its electronegativity. Elements like chlorine and oxygen are more electronegative, and have a strong affinity for taking electrons away from other elements. Elements like sodium and calcium are more electropositive, and easily give up some of their electrons. The element's valence determines how many electrons it will gain or lose; sodium has a valence of 1 so it gives up one electron (its valence electron) and chlorine also has a valence of 1 so it gains one electron (often from sodium!). Oxygen has a valence of 2, so oxygen by itself prefers to gain two electrons.

Element	Symbol	Electronegativity
Fluorine	F	3.98
Oxygen	O	3.44
Chlorine	Cl	3.16
Nitrogen	N	3.04
Sulfur	S	2.58
Carbon	C	2.55
Hydrogen	H	2.20
Copper	Cu	1.90
Iron	Fe	1.83
Magnesium	Mg	1.31
Calcium	Ca	1.00
Sodium	Na	0.93

We'll come back to electronegativity later.

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