周期表エクスプローラー

Reading the table the way chemists do

The periodic table is not just an alphabetical chart of elements — its shape encodes the rules of chemistry. This explorer lays out all 118 confirmed elements, from Hydrogen (1) to Oganesson (118), in their standard grid positions, then colour-codes each tile by category. Once you understand what the rows, columns, and colours mean, the layout becomes a map you can read at a glance, and that is where the real value lies beyond looking up a single fact.

A period is a horizontal row. As you move left to right along one, the atomic number climbs by one each step and electrons fill the same outer shell, so properties shift gradually from metallic to non-metallic. A group is a vertical column, and elements in the same group share the number of outer-shell electrons — which is why they behave alike. The soft, reactive alkali metals (Lithium, Sodium, Potassium) all sit in the first column; the inert noble gases (Helium, Neon, Argon) all sit in the last.

What each tile tells you

Click any element and the detail panel opens with values drawn from standard IUPAC and widely accepted reference data, hard-coded into the page rather than fetched from a server. For each element you get the atomic number, symbol, full name, atomic mass, electron configuration, state at room temperature, melting and boiling points in degrees Celsius, and the discovery year and discoverer where known. Ancient elements such as Carbon, Iron, Copper, and Gold carry no single discovery year because humans have used them since antiquity.

A worked example: Iron versus Helium

Click Fe (Iron, 26). The panel shows an atomic mass near 55.85, the electron configuration [Ar] 3d⁶ 4s², a solid at room temperature, melting at 1538 °C and boiling at 2861 °C, classified as a transition metal. Those high melting and boiling points are typical of transition metals and are exactly why iron is a structural workhorse. Now click He (Helium, 2): atomic mass about 4.003, configuration 1s², a gas, melting near −272 °C — the lowest of any element — and a noble gas. Reading the two side by side, the table's logic appears: a dense, high-melting metal in the middle of a period, and a featherweight, almost unfreezable gas at the far right where the outer shell is already full.

The electron configuration notation is worth decoding. [Ar] 3d⁶ 4s² means "everything argon has, plus six electrons in the 3d subshell and two in 4s." The bracketed noble gas is shorthand for the filled inner core, so you only read the chemically active outer electrons.

Searching and filtering efficiently

The search box accepts three kinds of input — element name, chemical symbol, or atomic number — so you can jump straight to Au, Gold, or 79 and reach the same tile. The highlight buttons dim everything except metals, non-metals, or metalloids, which turns the abstract "metalloid staircase" into something you can actually see. The metalloids (Boron, Silicon, Germanium, Arsenic, Antimony, Tellurium) form a diagonal step between the metals on the left and the non-metals on the upper right; filtering makes that boundary obvious.

Who this is genuinely useful for

• Students. Checking a configuration, confirming whether an element is a gas or solid at room temperature, or revising group trends before an exam.
• Teachers. Projecting the table and clicking through examples live, using the category filters to illustrate why columns behave as families.
• Hobbyists and makers. Looking up a melting point before working with a metal, or settling a trivia question about who discovered what and when.

Practical tips

• Compare by switching, not splitting. The panel shows one element at a time. To compare two, click the first, note its values, then click the second — trends jump out fastest when you look at neighbours in the same group or period.
• The two detached rows belong inside the table. The lanthanides (57–71) and actinides (89–103) are pulled out below to keep the main grid a sensible width; in a strict layout they would slot into period 6 and 7.
• Mind the temperature units. All melting and boiling points here are in Celsius. If you need Kelvin, add 273.15; for Fahrenheit, multiply by 9/5 and add 32.

A common misconception to avoid

Atomic mass is not the same as atomic number. The atomic number is the whole-number count of protons and defines the element; the atomic mass is a weighted average of an element's naturally occurring isotopes and is almost never a whole number. Hydrogen's mass of 1.008, not exactly 1, reflects the trace of heavier deuterium mixed into ordinary hydrogen. Reading the table well means keeping those two numbers separate in your mind.