Period (periodic table)

In the periodic table of the elements, a period is a horizontal row of the table.

The elements are laid out in a series rows so that those with similar properties line up in vertical columns: this reflects the periodic recurrence of similar properties as the atomic weight increases.

Modern quantum mechanics explains these periodic trends in properties in terms of electron shells. As atomic number increases, electron shells are filled in roughly this order. The filling of each shell corresponds to a row in the table.

1s 2s         2p 3s         3p 4s      3d 4p 5s      4d 5p 6s   4f 5d 6p 7s   5f 6d 7p 6f 7d   7f ...

Hence the structure of the periodic table. Since the valence electrons determine chemical properties, those tend to be similar within periodic table groups.

Elements adjacent to one another within a group have similar physical properties, despite their significant differences in mass. In the d-block of the periodic table, periodic trends across periods become significant, and the f-block elements show a high degree of similarity across rows (particularly the lanthanides).

Periode (periodieke tabel) دورة جدول دوري Periodu de la tabla periódica পর্যায় সারণীর পর্যায় Perioda periodnog sistema elemenata Период на периодичната система Període de la taula periòdica Periode des Periodensystems Periodo de la tabla periódica Periodo de la perioda tabelo Taula periodikoaren periodo Période du tableau périodique 주기율표 주기 Periode tabel periodik Lota (lotukerfið) Periodo della tavola periodica Períut de la taula periòdica Periódusos rendszerbeli periódus Kala jadual berkala Periode (scheikunde) 元素の周期 Periodane i periodesystemet Periood (Chemie) Prawo okresowości Mendelejewa Período (química) Perioadele tabelului periodic Период периодической системы Periodic table period Perióda (periodická tabuľka) Периода периодног система елемената Perioda periodnog sistema elemenata Periode tabel periodik Jakso (jaksollinen järjestelmä) Periodiska systemets perioder คาบในตารางธาตุ دور (دوری جدول) Chu kỳ tuần hoàn 元素周期