Ion
An atom or group of atoms that has gained or lost electrons, so it carries an electrical charge. Losing electrons makes a positive ion. Gaining them makes a negative ion.
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Analogy
An ion is like a person who gave away or picked up a few coins. They are no longer balanced.
Example
Na: loses 1 -> Na+Mg: loses 2 -> Mg2+Cl: gains 1 -> Cl-O: gains 2 -> O2-
In practice
Sodium loses one electron to become Na+. Chlorine gains one to become Cl-.
Practice
Flashcards
- What is the charge on an ion that has lost two electrons?2+
- Why can ionic compounds conduct electricity when molten?The ions are free to move and carry charge.
Questions people ask
Why do atoms form ions?
Atoms are more stable with a full outer shell of electrons. Metals reach this by losing their few outer electrons. Non-metals reach it by gaining a few. This is why sodium, with one outer electron, forms Na+ and chlorine, with seven, forms Cl-.
How do you know the charge of an ion from its group?
Group 1 ions have a charge of 1+, group 2 ions 2+, group 6 ions 2- and group 7 ions 1-. Metals lose their outer electrons, so the group number gives the positive charge. Non-metals gain enough to reach eight, so subtract the group number from 8.