Rows in the Periodic Table

 As you look at the periodic table once again, observe that each horizontal row of elements is called a period. Unlike the elements in a family, the elements in a period are not alike in properties. In fact, the properties of the elements change greatly across any given row.
But there is a pattern to the properties of the elements as one moves across a period from left to right. The first element in a period is always an ex~ tremely active solid. The last element in a period is always a particularly inactive gas. You can see this pattern by looking at the elements in Period 4 of the periodic table. The first element, potassium (K), is an active solid. The last element, krypton (Kr), is an inactive gas (and bears no relationship to the fictional element Kryptonite, which is the only thing feared by Supermanl). The symbols for the elements potassium and krypton should remind you of a rule for writing chemical symbols that you learned about in Chapter 4. The chemical symbol for an element consists of one or two letters. If it consists of one letter, the letter is always capitalized. If it consists of two letters, the iirst letter is always capitalized, but the second never is.

As you can see, there are seven periods of elements. You will also notice that one row has been separated out of Period 6 and one out of Period 7. Even though these two rows are displayed below the main part of the table, they are still part of the periodic table. They have been separated out to make the table shorter and easier to read. Elements in these two rOWS are rare-earth elements. You will read about these elements in just a little while.