The Periodic Table

The periodic table looks like a wall of cryptic squares, but it’s really one of the most powerful diagrams ever drawn. Arrange the elements by atomic number and their properties fall into repeating patterns — so neatly that Dmitri Mendeleev used the gaps to predict elements nobody had found yet.

Reading a single cell

Every cell packs in an element’s essentials. Take iron:

• Atomic number (26) — the number of protons; sits at the top.
• Symbol (Fe) — a one- or two-letter shorthand, sometimes from an older Latin name (ferrum).
• Name (Iron).
• Atomic mass (55.85) — the average mass of its atoms, in atomic mass units.

Rows are periods, columns are groups

• A period is a horizontal row. As you move left to right across a period, you’re adding one proton — and one electron — at a time, filling up the same outer shell.
• A group is a vertical column. Elements in a group share the same number of outer-shell electrons, which is why they behave alike. Group 1 metals are all soft and violently reactive; Group 18 (the noble gases) are all but inert.

That’s the “periodic” in periodic table: properties repeat each time a new row starts a fresh outer shell.

Metals, non-metals, metalloids

A rough diagonal staircase splits the table:

• Metals (most of the table, to the left) — shiny, conduct heat and electricity, bend rather than shatter.
• Non-metals (upper right) — dull, poor conductors, often gases or brittle solids.
• Metalloids (along the staircase, like silicon) — in-between, which is what makes them so useful in electronics.

Explore the whole table

Hover a cell for a quick summary, click it for details, and use the filter buttons to light up the metals, non-metals, or metalloids. Notice how the colours cluster — that’s the periodicity made visible.

Check yourself

Now that we can read the table, let’s see what happens when atoms actually join up — that’s bonding, and molecules.