The periodic table has 18 groups: the vertical columns, numbered 1 to 18 from left to right. In the main groups, elements in the same column have the same number of electrons in their outer shell, which is why they behave in similar ways. Many groups also have a family name, such as alkali metals or halogens. This page lists the elements in each group and what they have in common. To see them in the table, open the interactive periodic table.
The 18 groups at a glance
| Group | Family name | Elements | Outer electrons |
|---|---|---|---|
| 1 | Alkali metals | Li, Na, K, Rb, Cs, Fr (and hydrogen, placed here) | 1 |
| 2 | Alkaline earth metals | Be, Mg, Ca, Sr, Ba, Ra | 2 |
| 3 to 12 | Transition metals | Sc to Zn, Y to Cd, and the heavy elements below them | varies |
| 13 | Boron group | B, Al, Ga, In, Tl, Nh | 3 |
| 14 | Carbon group | C, Si, Ge, Sn, Pb, Fl | 4 |
| 15 | Pnictogens (nitrogen group) | N, P, As, Sb, Bi, Mc | 5 |
| 16 | Chalcogens (oxygen group) | O, S, Se, Te, Po, Lv | 6 |
| 17 | Halogens | F, Cl, Br, I, At, Ts | 7 |
| 18 | Noble gases | He, Ne, Ar, Kr, Xe, Rn, Og | 8 (helium has 2) |
Groups 1 and 2: alkali metals and alkaline earth metals
Group 1 holds lithium, sodium, potassium, rubidium, cesium and francium. These soft, shiny metals have one outer electron and react strongly with water, which is why lithium, sodium and potassium are kept away from moisture. Hydrogen is placed above them in most tables, but it is a gas and not an alkali metal. Group 2 has two outer electrons: beryllium, magnesium, calcium, strontium, barium and radium. They are harder and less reactive than group 1, and magnesium and calcium are everyday elements in bones, plants and building materials.
Groups 3 to 12: transition metals
The ten columns in the middle are the transition metals, and they do not follow the simple outer-electron pattern of the main groups. Iron, cobalt and nickel are in groups 8, 9 and 10. Copper, silver and gold are in group 11, the metals long used for coins and jewelry. Group 12 (zinc, cadmium and mercury) is usually listed with them, and mercury is the only one of these that is liquid at room temperature. Group 3 is drawn in two ways in books: scandium and yttrium are always there, while the other two places go to lanthanum and actinium in some tables and to lutetium and lawrencium in others. In our table, group 3 shows scandium and yttrium, followed by the markers 57–71 and 89–103 that point to the two rows below.
Groups 13 to 16: boron, carbon, nitrogen and oxygen groups
Moving right, the outer electrons go from three to six.
- Group 13 (boron group): boron, aluminum, gallium, indium, thallium and nihonium. Aluminum is the most abundant metal in the Earth’s crust.
- Group 14 (carbon group): carbon, silicon, germanium, tin, lead and flerovium. Carbon is the base of living matter and silicon the base of most electronics.
- Group 15 (pnictogens): nitrogen, phosphorus, arsenic, antimony, bismuth and moscovium. Nitrogen makes up about four fifths of the air we breathe.
- Group 16 (chalcogens): oxygen, sulfur, selenium, tellurium, polonium and livermorium. Oxygen is about one fifth of the air.
These groups mix metals, metalloids and nonmetals, so in the color modes of the periodic table you will see them split across several categories, such as post-transition metals, metalloids and nonmetals.
Group 17: the halogens
Fluorine, chlorine, bromine, iodine, astatine and tennessine have seven outer electrons and are one electron short of a full shell. That makes them very reactive nonmetals, and the name halogen means “salt-forming”: chlorine combines with sodium to make table salt. At room temperature fluorine and chlorine are gases, bromine is a liquid and iodine is a solid. Fluorine is the most electronegative element of all.
Group 18: the noble gases
Helium, neon, argon, krypton, xenon, radon and oganesson have a full outer shell, so they rarely form compounds. Helium has two outer electrons and the others have eight. Neon and argon are common in lighting, and helium is used to fill balloons. Oganesson is made in laboratories and exists only for fractions of a second.
Lanthanides and actinides: the rows below the table
The two rows under the main table are the lanthanides (atomic numbers 57 to 71) and the actinides (89 to 103). They are shown separately only to keep the table narrow, and they do not have group numbers of their own. Uranium and plutonium belong to the actinides.
Old group labels: IA, IIA and Roman numerals
Older books, especially in the United States, number the main groups with Roman numerals and the letters A and B: group 1 is IA, group 2 is IIA, group 13 is IIIA, and so on up to group 18, which is VIIIA. The transition metals are the B groups. Both systems describe the same columns, so if a textbook says “group VIIA”, it means group 17, the halogens.
Frequently asked questions
What is a family of elements?
A family is a group that has its own name, like the halogens in group 17. The words are often used as synonyms, though some books apply “family” to larger sets of elements too.
Which group is hydrogen in?
Most tables place hydrogen in group 1 because it has one outer electron. It is a nonmetal gas, so some tables show it on its own or above group 17.
Do all elements in a group behave the same way?
They share a pattern, not identical behavior. Reactivity grows down group 1 and falls down group 17, so cesium reacts far more violently than lithium.
Why are noble gases unreactive?
Their outer shell is already full, so they have little reason to gain, lose or share electrons. A few heavier ones, such as xenon, can form compounds under special conditions.
Keep exploring
See every group in the interactive periodic table, find the symbols and origins of all 118 elements in the element symbols list, or put your elements to work in the molar mass calculator. More chemistry and math tools are in School.