differences between a group and a period in the periodic table
The periodic table is a chart that arranges all chemical elements according to their atomic structures, chemical properties, and reactivity. There are two major ways in which the elements in the periodic table are categorized: groups and periods.
Groups: The vertical columns in the periodic table are called groups (also called families). Elements in the same group share the same number of valence electrons, which are the electrons in the outermost shell of an atom. This means that elements in the same group have similar chemical properties and behave in a similar way. There are 18 groups in the periodic table.
Periods: The horizontal rows in the periodic table are called periods. Elements in the same period have different numbers of electron shells. As you move from left to right across a periodic table, the number of electrons in the outermost shell (valence electrons) increases by one for each element. Elements in the same period do not necessarily have similar chemical properties or valence electron configurations. There are seven periods in the periodic table.