Valence electrons and ions: understanding charge
An ion forms when electron count no longer exactly balances proton count. Losing electrons makes net charge more positive; gaining electrons makes it more negative.
The essential idea
An ion forms when electron count no longer exactly balances proton count. Losing electrons makes net charge more positive; gaining electrons makes it more negative.
A concrete example
Neutral sodium has 11 protons and 11 electrons. After losing one electron it still has 11 protons but 10 electrons, giving a net charge of +1.
Why does sodium readily form Na⁺?
The outermost electrons are especially important because they participate in chemical change. They are commonly called valence electrons.
Neutral sodium has one electron in its outer shell in the simplified model.
If it loses that electron, 11 protons remain but only 10 electrons: net charge +1.
Na⁺ is still sodium because its nucleus still contains 11 protons.
Neutral chlorine is represented as 2 · 8 · 7. In many reactions it can gain an electron and become Cl⁻, represented as 2 · 8 · 8. This opposite tendency leads directly into chemical bonding.
Na and Na⁺: same element, different charge
Na is the symbol for sodium. The + in Na⁺ means the atom has lost one electron and therefore has a positive charge. Its nucleus still contains 11 protons, so it is still sodium.
Understanding check
Can you restate the idea in your own words and explain the example without rereading the paragraph?
Show the answer
If yes, continue. If not, return to the essential idea and identify what really changes: proton count, electron arrangement or type of interaction.
Guided exercise
Neutral chlorine has 17 protons and 17 electrons. If it gains one electron it becomes Cl⁻ with 18 electrons but still 17 protons.
Mini problem
A chlorine atom gains one electron. How many protons and electrons does it then have?
Show the solution
The nucleus does not change: 17 protons. The gained electron brings the total to 18 electrons. Net charge becomes −1: Cl⁻.
Mini lab · build an ion
Choose proton and electron counts. The lab calculates net charge without changing the element's identity.
Common mistake
Do not infer charge from proton count alone. Net charge depends on the difference between proton and electron counts.