Periods are horizontal rows indicating the outer shell; groups are vertical columns of similar valence configuration.
Practise Atomic Structure & Periodicity All Atomic Structure & Periodicity topics
A period is a horizontal row of the periodic table, and its number gives the highest occupied principal quantum number of the element's outermost shell. A group is a vertical column whose elements share the same number of valence electrons in the main groups, and therefore show similar chemistry. Going down a group, properties change gradually, while across a period they change sharply, typically from metal to nonmetal. Period 2 runs from lithium to neon, and period 3 from sodium to argon. These patterns help predict chemical trends.
Key ideas: Periods (rows) share the highest shell, and properties change progressively from metal to nonmetal. Groups (columns) share valence configuration and similar chemistry. Families: alkali (1), alkaline earth (2), pnictogens (15), chalcogens (16), halogens (17), noble gases (18). Across a period radius falls and ionization energy generally rises; down a group radius and metallic character rise.
Common mistakes and connections: Students apply trends in the wrong direction, such as saying electronegativity increases down a group. Another error is thinking elements in a group are identical; the first member often differs (anomalous behavior of Li, Be, B, C, N, O, F). Periodicity underlies all the trend topics that follow.
Sulfur has three occupied shells so it is in period 3, and six valence electrons so it is in group 16 with oxygen. The interactive lesson shows this as a live animation or chart.
Period 3 runs from sodium, a reactive metal, to argon, an unreactive noble gas.
Periods are horizontal rows indicating the outer shell; groups are vertical columns of similar valence configuration.
Periods and Groups is a beginner topic in Atomic Structure & Periodicity. It needs no earlier chemistry lessons and is a good starting point.
Study these earlier topics in Atomic Structure & Periodicity first: Periodic Law, Mendeleev's Periodic Table, Modern Periodic Table.
The next topics in Atomic Structure & Periodicity are s-Block Elements and p-Block Elements.
Yes. The interactive lesson includes a self-check question on Periods and Groups, and the Atomic Structure & Periodicity quiz draws on every topic in this area.
Periods and Groups is topic 77 of 115 in Atomic Structure & Periodicity.