Periods and Groups
Elements in the periodic table are arranged in periods (rows) and groups (columns). Atomic number increases as you move across a row or period.
Periods
Rows of elements are called periods. The period number of an element signifies the highest unexcited energy level for an electron in that element. The number of elements in a period increases as you move down the periodic table because there are more sublevels per level as the energy level of the atom increases
Groups
Columns of elements help define element groups. Elements within a group share several common properties. Groups are elements have the same outer electron arrangement. The outer electrons are called valence electrons. Because they have the same number of valence electrons, elements in a group share similar chemical properties. The Roman numerals listed above each group are the usual number of valence electrons. For example, a group VA element will have 5 valence electrons.
Representative vs. Transition Elements
There are two sets of groups. The group A elements are called the representative elements. The group B elements are the nonrepresentative elements.
What is on the Element Key?
Each square on the periodic table gives information about an element. On many printed periodic tables you can find an element's symbol, atomic number, and atomic weight.
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