All practice pages/Interatomic theory/Elements
Element 11, an alkali metal
A metal soft enough to cut with a butter knife that fizzes and flares on water, and one of the two elements in table salt.
Period 3, group 1. The other alkali metals are tinted, and every cell opens its own article.
Sodium has 11 electrons, one for every proton, so the atom carries no charge. Below are the same 11 electrons written two ways.
1s² 2s² 2p⁶ 3s¹
Short form: [Ne] 3s¹, where [Ne] stands for the 10 electrons neon already has.
The simple form counts electrons shell by shell. The orbital form says which subshell each one sits in: s holds 2, p holds 6, d holds 10 and f holds 14. Shell 2 here is 2s² 2p⁶, and 2 + 6 is 8.
Sodium sits in period 3 and has 3 shells. The period number counts the shells.
The outer shell holds 1 electron. Those are the ones sodium can lose, gain or share, so they are the ones that decide what it bonds with. For a main-group element the group number gives that count: group 1 means 1.
One valence electron, which sodium gives up easily to form the Na⁺ ion. Like the other alkali metals, it reacts with water.
The sixth most abundant element in the crust, about 2.4% by mass, always combined: in beds of rock salt, in feldspar minerals, and dissolved in the ocean, where sodium chloride makes up most of the salt. Every cell in your body depends on Na⁺ ions to carry nerve signals.
Humphry Davy isolated it in 1807 by passing electricity through molten sodium hydroxide, days after doing the same for potassium. The name comes from soda. The symbol Na comes from its Latin name natrium, after natron, a natural soda the ancient Egyptians used in mummification.
Sodium chloride seasons and preserves food, melts ice on roads, and is the starting point for making chlorine and sodium hydroxide. Sodium bicarbonate is baking soda. The metal itself lights orange-yellow street lamps, cools some nuclear reactors as a liquid, and helps extract titanium from its ore.
The metal reacts violently with water, releasing hydrogen that can ignite, so it is stored under oil. Sodium hydroxide is strongly corrosive to skin and eyes.