Periodic Table · PeriodicLab

A 3D periodic table: the 118 elements rise into columns to show the periodic trends in atomic radius, electronegativity and ionization energy. Drag the temperature to watch states of matter change, play the history of discovery, morph between the long form, a spiral and concentric rings, and open any element to see its atom and what it looks like.

Subject: Chemistry · Level: Middle school, High school · Topics: Periodic law, Electron shells, States and temperature, Discovering the elements

Chapters

Meet the periodic table

The 118 elements are arranged by atomic number (nuclear charge) into 7 rows and 18 columns. A row is a period: atoms in the same period have the same number of electron shells. A column is a group: atoms in the same group have the same number of outer electrons and similar chemistry.

Colour shows the category of each element. Click a category in the legend on the right to see where the metals, nonmetals and noble gases sit; click any block to open its close-up.

Shells and periods

Switch to the concentric rings: ring n is period n, and every atom in that period has n electron shells. The rings hold 2, 8, 8, 18, 18, 32 and 32 cells — exactly the number of elements in each period.

Open the close-up of sodium: its 3 shells hold 2, 8 and 1 electrons. With just 1 outer electron, which it loses easily, sodium is very reactive. Then look at potassium in the same group.

Atomic radius and electronegativity

The blocks rise into columns whose height shows the atomic radius. Across a period the nuclear charge grows while the number of shells stays the same, so the nucleus pulls the outer electrons harder and the radius shrinks; down a group the number of shells grows and the radius increases. That is why caesium and francium at the bottom left are the largest.

Now switch to electronegativity, a measure of how strongly an atom attracts electrons in a compound. The trend runs the other way: it grows towards the top right, and fluorine is the highest (3.98). Noble gases are usually not given a value.

The sawtooth of ionization energy

The first ionization energy is the least energy needed to remove one electron from a gaseous atom. Look at the line chart on the right: every period climbs from a valley at the alkali metal to a peak at the noble gas, like a row of saw teeth — the clearest picture of the periodic law.

Look closely at period 2 and you will see two small kinks: Be is higher than B, and N is higher than O. Be has a full 2s orbital and N a half-full 2p, both fairly stable arrangements, so removing an electron is harder.

States and temperature

Drag the temperature and see whether each element is solid, liquid or gas at normal pressure. At room temperature (298 K) only bromine and mercury are liquids, and 11 elements are gases — all of them nonmetals.

Cool to 10 K and everything except helium freezes; warm to 303 K and gallium and caesium melt too — gallium melts in your hand. Above 3000 K the metals glow white-hot; tungsten melts at 3695 K, the highest of any metal.

Discovering the elements

In ancient times only about a dozen elements were known. Press play and watch the elements light up in the year they were discovered: chemical analysis in the 18th century, electrolysis in the early 19th, spectroscopy in the 1860s — each new method brought a wave of new elements.

When Mendeleev drew up his table in 1869 he knew only 63 elements. He boldly left gaps for unknown ones and predicted their properties; gallium, scandium and germanium, found later, proved him right.

Spiral and rings

The periodic table can be drawn in more than one way. The spiral table lays the elements along one continuous spiral, one turn per period, so each group falls on its own “spoke” — stressing that properties repeat periodically with atomic number.

Choose a group and string its elements together with a line of light, then switch between the long form, the spiral and the rings to see how the line changes.

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