Lesson 7 of 7 · The periodic table
Element families
An element family is a set of elements with similar chemical behavior, usually found in the same vertical group of the periodic table. Main-group elements in a family have similar outer-electron arrangements, which help explain their common charges and reactions.
Groups versus periods
Groups are the 18 vertical columns. Periods are the seven horizontal rows. The detached lanthanide and actinide rows belong to periods 6 and 7; their placement below the main table saves space.
Hydrogen appears above group 1 because of its 1s¹ configuration, but it is a nonmetal and is not an alkali metal. Helium has 1s² rather than an outer p⁶ configuration, yet its closed shell and chemical behavior place it with the noble gases.
| Family | Location | Examples | Common pattern |
|---|---|---|---|
| Alkali metals | Group 1, excluding H | Li, Na, K | +1 ions |
| Alkaline earth metals | Group 2 | Mg, Ca | +2 ions |
| Halogens | Group 17 | F, Cl, Br, I | Often −1 in binary salts |
| Noble gases | Group 18 | He, Ne, Ar | Closed valence shells |
| Lanthanides | La–Lu series | Ce, Nd | +3 is common |
| Actinides | Ac–Lr series | Th, U | All are radioactive |
Compare familiar families
Sodium and potassium commonly form +1 ions; magnesium and calcium commonly form +2 ions. Pairing those cations with chloride gives NaCl, KCl, MgCl₂ and CaCl₂. The subscripts make the positive and negative charges balance.
The familiar halogens, such as fluorine and chlorine, are reactive nonmetals with seven valence electrons. Noble gases have closed valence shells and are generally much less reactive. Some still form compounds: xenon difluoride, XeF₂, is one example.
Reference: OpenStax Chemistry 2e, §2.6: Ionic and molecular compounds
Know the limits
Elements within a family can have very different physical properties. At room temperature and atmospheric pressure, fluorine and chlorine are gases, bromine is a liquid, and iodine is a solid. Shared valence patterns do not imply the same boiling point or appearance.
What is a transition element?
The d block and the term transition element are related but not perfectly interchangeable. In the stricter definition, transition elements have an incomplete d subshell in the atom or can form cations with an incomplete d subshell. For example, zinc sits in the d block, but both Zn and its usual Zn²⁺ ion have a filled 3d subshell.
Reference: IUPAC Gold Book: Transition element
Work through the examples
Worked example 1
Predict a formula from a family.
- Calcium belongs to group 2 and commonly forms Ca²⁺.
- Chlorine is a halogen and commonly forms Cl⁻ in ionic salts.
- Balance two negative charges against one 2+ charge.
Answer: Calcium chloride has formula CaCl₂.
Worked example 2
Is hydrogen an alkali metal?
- Hydrogen and alkali metals have one electron in an outer s subshell.
- Hydrogen is a nonmetal with distinct bonding and physical behavior.
Answer: No. Its group position does not make it an alkali metal.
Avoid these mistakes
- A family name and a broad category such as “nonmetal” are not synonyms.
- The f-block rows do not create extra periods.
- Patterns for familiar members should not be asserted as measured properties of every superheavy element.
Check your understanding
Open printable worksheetTry each question before opening the answer key. When you check your answers, read the explanations too. Your choices stay in this browser.
Read the complete answer key
1. B — Br. Bromine is in group 17, the halogens.
2. B — They generally have low reactivity. Their closed shells are associated with low reactivity, but compounds of some noble gases are known.
3. A — 6. It is part of period 6. Moving it below the table is a layout convention.
4. B — 2. Group 2 includes beryllium, magnesium, calcium, strontium, barium and radium.
Common questions
Are all group 1 elements metals?
No. Hydrogen is a nonmetal. The alkali metals are the group 1 elements below hydrogen.
Do elements in a group have identical properties?
No. Related valence configurations produce similarities, but atomic size, mass, bonding and other effects change down a group.
References & model notes
Use these sources to check the definitions and data, or to read more about the topic. The lesson notes where a model or rounded value simplifies the chemistry.