Interactive Periodic Table

A period is a horizontal row of the periodic table. There are 7 periods in all. As we move across a period from left to right, electrons are added one by one to the same outermost shell, while the nuclear charge increases. So atomic radius decreases, ionisation energy increases, electronegativity increases, and metallic character decreases across a period. Each period ends with a noble gas (He, Ne, Ar, Kr, Xe, Rn). Periods 1, 2, 3 are short; 4 and 5 are long; 6 and 7 contain the lanthanides and actinides.

Metals occupy the left and centre of the periodic table — about three-quarters of all elements are metals. Specifically: Group 1 (alkali metals), Group 2 (alkaline-earth metals), all the d-block (transition metals), the f-block (lanthanides and actinides), and the heavier members of Groups 13–16 (post-transition metals like Al, Ga, Sn, Pb, Bi). A zig-zag “staircase” line from boron (B) down to astatine (At) separates metals on its left from non-metals on its right.

The credit for the modern periodic table goes mainly to Dmitri Ivanovich Mendeleev, a Russian chemist, in 1869. He arranged elements in increasing order of atomic mass and grouped them by similar properties. He even left blank spaces for undiscovered elements (like gallium and germanium) and predicted their properties — predictions that were stunningly accurate. A German chemist, Lothar Meyer, independently produced a similar table at almost the same time. Henry Moseley later (1913) refined it by ordering elements by atomic number rather than mass.

The modern periodic table is organised in increasing order of atomic number (number of protons), arranged in 7 horizontal periods and 18 vertical groups. Elements with similar electron configurations of the outermost shell fall in the same group and therefore show similar chemical properties. The table is divided into blocks: s, p, d and f, based on which type of orbital is being filled. This arrangement reveals clear trends in atomic size, ionisation energy, electron affinity, electronegativity and metallic character — the heart of inorganic chemistry.

The modern periodic table has 18 groups, numbered 1 through 18 (IUPAC system). Older systems used Roman numerals with A and B subgroups. Groups 1 and 2 are the s-block (alkali and alkaline-earth metals), Groups 3–12 are the d-block (transition metals), and Groups 13–18 are the p-block (including main-group non-metals, halogens and noble gases). The 14 lanthanides and 14 actinides are placed separately at the bottom and form the f-block.

The element with atomic number 67 is Holmium (Ho) — a soft, silvery-white lanthanide metal. Its electron configuration is [Xe] 4f11 6s2, which gives it the highest magnetic moment of any naturally occurring element. Holmium is therefore used in the strongest permanent magnets and in MRI machines as a flux concentrator. It is named after Stockholm (Holmia), the city near where it was discovered in 1878.

This is a popular online comic asking which elements are safe to lick! The honest answer is: do not lick the periodic table in real life — many elements are toxic (mercury, lead, arsenic, cadmium), some are radioactive (uranium, thorium), and some react violently with saliva (sodium, potassium, fluorine). The very few that are comparatively safe in pure metallic form include gold, platinum and titanium — and even those should not be licked, because surface contamination and oxidation make any such test risky. Stick with diagrams!

That is Group 18, the noble gases — helium, neon, argon, krypton, xenon and radon. Their outermost shells are completely filled (1s2 for He; ns2 np6 for the others), giving them a stable octet of electrons that they do not need to share, gain or lose. As a result, they are virtually inert chemically. Only the heavier ones (Kr, Xe, Rn) form a few compounds with very electronegative partners like fluorine and oxygen. Helium and neon have not been made to react with anything stable so far.

Non-metals are found on the right side of the periodic table, above the zig-zag staircase line. They include hydrogen (top-left, an exception), the upper members of Groups 14–16 (C, N, P, O, S), Group 17 (the halogens — F, Cl, Br, I, At) and Group 18 (noble gases — He, Ne, Ar, Kr, Xe, Rn). Non-metals tend to gain or share electrons, are poor conductors of heat and electricity (graphite is an exception), and form acidic oxides.

A vertical column in the periodic table is called a group or family. There are 18 groups in total. Elements within the same group share similar valence-electron configurations and therefore have very similar chemical properties. Well-known groups include Group 1 (alkali metals), Group 2 (alkaline-earth metals), Group 17 (halogens) and Group 18 (noble gases). Members of a group differ only in the principal quantum number of their valence shell.

Halogens are in Group 17, the second column from the right. The members are fluorine (F), chlorine (Cl), bromine (Br), iodine (I) and astatine (At). They have 7 valence electrons (ns2 np5) and need just one more electron to complete the octet — so they readily gain an electron to form X- ions or share one to form covalent bonds. They are the most reactive non-metals, with reactivity decreasing F > Cl > Br > I > At down the group. Their salts are called halides.

The largest atoms are found in the bottom-left corner of the periodic table. Atomic radius increases down a group (because new shells are added) and decreases across a period (because of increasing nuclear charge pulling electrons in). So caesium (Cs) and francium (Fr) — both in Group 1, Periods 6 and 7 — are the largest of all naturally occurring atoms. Francium is radioactive, so caesium (radius ≈ 265 pm) is usually given as the largest stable atom.

Horizontal rows are called periods. The periodic table has 7 periods. As we move from left to right within a period, the atomic number increases by one each step, and a new electron is added to the same outermost shell. Each period ends with a noble gas, after which the next electron starts a new shell — and a new period. Note: Periods 1, 2 and 3 are short (containing 2, 8 and 8 elements respectively), while later periods are long.

Fe is the symbol for Iron, atomic number 26 — a transition metal in Period 4, Group 8. Its electron configuration is [Ar] 3d6 4s2. Iron is the most abundant element in the Earth's core (along with nickel) and the fourth most abundant in the crust. It forms two important oxidation states: Fe2+ (ferrous, more reducing) and Fe3+ (ferric, more stable). Iron is essential for haemoglobin in our blood. Its name in Latin is ferrum, hence the symbol Fe.

K stands for Potassium, atomic number 19 — an alkali metal in Group 1, Period 4. Its electron configuration is [Ar] 4s1, with one valence electron that it loses easily to form K+. Potassium is highly reactive, must be stored under kerosene, and reacts violently with water producing hydrogen gas and a lilac flame. The symbol K comes from its Latin name kalium, derived from Arabic al-qali (meaning plant ash). It is essential for nerve and muscle function in the body.

P is the symbol for Phosphorus, atomic number 15 — a Group 15 non-metal in Period 3. Its electron configuration is [Ne] 3s2 3p3 — exactly half-filled p subshell, giving it extra stability. Phosphorus exists in several allotropes: white (P4, reactive, glows in air, very toxic), red (polymeric, used in match boxes), and black (layered, semiconducting). It is essential to life — the backbone of DNA, RNA and ATP all contain phosphate (PO43-) groups.

S is the symbol for Sulfur (Sulphur in British English), atomic number 16 — a yellow non-metal in Group 16, Period 3. Its electron configuration is [Ne] 3s2 3p4, giving it 6 valence electrons and a usual valency of 2 (it can also show 4 and 6 in compounds like SO2 and SO3). Sulfur burns in air to form SO2, which is the basis of sulphuric acid manufacture (Contact Process). It exists as S8 rings and is found near volcanoes.

Use mnemonics group by group! Examples that students enjoy: Group 1 (H Li Na K Rb Cs Fr): “Happy Little Naughty Kids Rub Cats Furiously”. Group 2 (Be Mg Ca Sr Ba Ra): “Beggars May Call Some Bachelor Rams”. First-row p-block (B C N O F Ne): “Boys Catch Naughty Owls For Nest”. Plus, study by patterns — group properties, period trends, and by writing electron configurations regularly. Most importantly, practise problems; that builds memory faster than any list.

Gold (Au, atomic number 79) is a transition metal in Period 6, Group 11. Its electron configuration is [Xe] 4f14 5d10 6s1. Gold is famously unreactive — it does not tarnish, resists most acids, and is found in nature in its free metallic state. It dissolves only in aqua regia (3:1 conc. HCl : conc. HNO3). Gold is the most malleable metal known: 1 g can be beaten into a 1 m2 leaf. Its symbol Au comes from the Latin aurum, meaning “shining dawn”.