A tabular arrangement of elements in rows and columns, highlighting the regular repetition of properties of the elements, is called a periodic table.
Periods and Groups
The basic structure of the periodic table is its division into rows and columns, or periods and groups.
- A period consists of the elements in any one horizontal row of the periodic table.
- A group consists of the elements in any one column of the periodic table.
The first period of elements consists of only hydrogen (H) and helium (He). The second period has 8 elements, beginning with lithium (Li) and ending with neon (Ne). There is then another period of 8 elements, and this is followed by a period having 18 elements, beginning with potassium (K) and ending with krypton (Kr). The fifth period also has 18 elements. The sixth period consists of 32 elements, but for the row to fit on a page, part of it appears at the bottom of the table. Otherwise, the table would have to be expanded, with the additional elements placed after barium (Ba, atomic number 56). The seventh period, though not complete, also has some of its elements placed as a row at the bottom of the table.
Metals, Nonmetals, and Metalloids
The elements of the periodic table are divided by a heavy “staircase” line into metals on the left and nonmetals on the right.
- A metal is a substance or mixture that has a characteristic luster, or shine, and is generally a good conductor of heat and electricity. Except for mercury, the metallic elements are solids at room temperature (about 20°C). They are malleable (can be hammered into sheets) and ductile (can be drawn into wire).
- A nonmetal is an element that does not exhibit the characteristics of a metal. Most of the nonmetals are gases (for example, chlorine and oxygen) or solids (for example, phosphorus and sulfur). The solid nonmetals are usually hard, brittle substances. Bromine is the only liquid nonmetal. Most of the elements bordering the staircase line in the periodic table (Figure 2.15) are metalloids, or semimetals.
- A metalloid, or semimetal, is an element having both metallic and nonmetallic properties.
Written by Fillios Memtsoudis