Periodic Table - Across and down
Across and down
Each row of elements across the table is called a periodA horizontal row in the periodic table.. Rows in the periodic table are read left to right. All of the elements in a period have the same number of shellsA region of space around the center of the atom in which electrons are located.. A shell is the number of areas an atom needs to hold its electrons. The first shell holds two electrons, the second shell holds up to eight, and the third shell can hold up to
eighteen electrons. In 2003, the maximum number of shells found around any atom is seven. Thus, there are seven periods.
For example, carbon (C) atoms have six electrons: two electrons in the first shell and the remaining four are in the second shell. Hydrogen (H), which has one electron, needs only one shell. Helium...
[The entire page is 429 words long]
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