Every number in an element's detail panel tells part of its story. Here is what each one
means, with real examples from the table and the patterns to look out for.
Identity: What Makes an Element
Atomic Number
The number of protons in an atom's nucleus. It is the element's identity card: change it and you have a different element.
Example: Every atom with 6 protons is carbon, whether it sits in a diamond, a pencil or your DNA.
Trend: Goes up by exactly one with each step through the table, reading left to right and top to bottom, from hydrogen (1) to oganesson (118).
The average mass of an element's atoms, weighted by how common each isotope is in nature. 1 u is one twelfth of the mass of a carbon-12 atom.
Example: Chlorine is 35.45 u, not a whole number, because about three quarters of its atoms are chlorine-35 and a quarter are chlorine-37.
Trend: Usually rises with atomic number, with a few famous exceptions: tellurium (127.6 u) is heavier than iodine (126.9 u), even though it comes first.
Atoms of the same element with different numbers of neutrons. They behave almost the same chemically but have different masses, and some are radioactive.
Example: Carbon-12 and carbon-13 are stable; carbon-14 slowly decays, which is what makes radiocarbon dating possible.
The table splits into four blocks, named after the kind of orbital that the last electron fills. The blocks are what give the table its shape.
Example: The s-block is groups 1–2 (plus helium), the p-block is groups 13–18, the d-block is groups 3–12, and the f-block is the two rows at the bottom.
The colours in the table sort elements by how they behave: alkali metals, alkaline earth metals, transition metals, post-transition metals, metalloids, nonmetals, noble gases, lanthanides and actinides. "Unknown" marks superheavy elements whose chemistry has never been measured, because only a few atoms have ever existed.
Example: Metalloids, such as silicon, sit on the border between metals and nonmetals and share properties of both, which is exactly why silicon makes such good computer chips.
The two rows below the main table. They really belong inside periods 6 and 7, but putting them there would make the table 32 columns wide, so they are printed underneath.
Example: Glenn Seaborg proposed moving the actinides into their own row in 1944, and was told it would ruin his reputation. It won him a Nobel Prize instead.
A list of which orbitals an atom's electrons occupy. The app shows it twice: the full version, and a short version that starts from the previous noble gas in square brackets.
Example: Oxygen is 1s² 2s² 2p⁴, or [He] 2s² 2p⁴ for short. Copper breaks the simple filling rule: [Ar] 3d¹⁰ 4s¹, not 3d⁹ 4s², because a full d-subshell is extra stable.
Energy levels that hold electrons at increasing distances from the nucleus. The first holds up to 2, the second up to 8, and so on. The app's 3D Bohr model draws them as rings.
Example: The Bohr model is a simplification: real electrons don't orbit like planets, they spread out in fuzzy clouds called orbitals. The rings are still a great way to count electrons.
How strongly an atom pulls shared electrons towards itself in a bond, like a score in a tug-of-war.
Example: Fluorine is the strongest puller at 3.98; caesium and francium are the weakest at 0.79. When sodium (0.93) meets chlorine (3.16), chlorine wins outright and they form ionic table salt.
Trend: ↑ across a period, ↓ down a group. Noble gases rarely bond, so they often have no value.
The energy released when a neutral atom captures an extra electron. A high value means the atom is eager to gain an electron.
Example: Chlorine has the highest value, 349 kJ/mol, slightly ahead of fluorine (328 kJ/mol), whose tiny, crowded outer shell pushes back. Noble gases resist extra electrons, so their values are negative.
Trend: Generally ↑ across a period towards the halogens.
The charge an atom would carry if all of its bonds were fully ionic. Many elements can take several states, which is why they form so many different compounds.
Example: Iron is usually +2 or +3, and rust is iron in the +3 state. Manganese ranges all the way from −3 to +7; in purple potassium permanganate it is +7.
Half the distance between the nuclei of two identical atoms joined by a single bond. It describes the size of an atom when it is bonded, rather than on its own.
Example: Carbon's covalent radius is 77 pm, so a carbon–carbon single bond is about 154 pm long.
The temperature at which a solid turns into a liquid. To convert to degrees Celsius, subtract 273.15.
Example: Tungsten melts at 3,695 K (about 3,422 °C), the highest of any metal, which is why it was used in light-bulb filaments. Mercury melts at 234 K (−39 °C), so it is liquid at room temperature, and gallium (303 K) melts in your hand.
The temperature at which a liquid turns into a gas at normal atmospheric pressure.
Example: Helium boils at just 4.2 K, only a few degrees above absolute zero, which makes liquid helium ideal for cooling MRI magnets. Tungsten boils at 6,203 K.
The repeating pattern in which atoms stack when an element is solid. The smallest repeating box is called the unit cell, and the app shows it in 3D.
Example: Copper and gold are face-centred cubic, a stacking that lets layers of atoms slide, which is why they bend instead of snapping. Iron at room temperature is body-centred cubic. For superheavy elements the structure is only predicted.