Electron configuration and ions — Chemistry, 14–17
The electrons in an atom are arranged in energy levels. That arrangement helps you predict how atoms form ions and why some elements react more readily than others.
The electron arrangement matters
An atom is not just a tiny ball of positive and negative charge. Its electrons occupy energy levels, and the outer electrons are especially important in reactions. If an atom loses or gains electrons, it becomes an ion with a charge.
Why arrange electrons this way?
Chemists needed a way to explain why sodium forms Na⁺ while neon hardly reacts. The energy levels give a useful answer: atoms often become more stable when their outer level is filled. Losing or gaining electrons can do this, but it changes the atom’s charge.
From sodium atom to sodium ion
Sodium has atomic number 11, so a neutral atom has 11 electrons: 2 in the first level, 8 in the second and 1 in the third. It can lose that outer electron. The nucleus still has 11 protons, but there are now 10 electrons, so the ion is Na⁺ with configuration 2,8.
A shell is not an orbit
It is tempting to picture electrons circling the nucleus like planets, because shell diagrams look that way. They are energy levels, not fixed tracks that you could photograph. Also, an ion is not a different element: its proton number stays the same; only its electron number changes.
Electron arrangements in lamps
In a sodium street lamp, electrical energy excites sodium electrons to higher energy levels. When they fall back, they emit light of particular colours, producing the familiar yellow glow. The colour is evidence that electron energies come in specific amounts, not any value at all.
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