Chemistry Reference
In-Depth Information
represent some elements. Some elements, such as carbon (C), have the
first letter in their name as the symbol. Other elements, such as aluminum
(Al), use the first two letters in their name as the symbol. Gold (Au) de-
rives its symbol from that Latin word aurum, which means gold. Some ele-
ments, such as ununbium (Uub), have temporary systematic names and
symbols given to them, until a common name can be agreed upon.
In Figure 3-7b the bottom number in each box represents the atomic
mass of the element. The atomic mass, which is still misleadingly called
“atomic weight” by some people, actually represents a weighted average of
the atomic masses of the various isotopes of an element.
All of the elements on the periodic table break up into three major
categories: metals, nonmetals, and semimetals. Metals are elements with
relatively few valence electrons, which tend to form positive ions by losing
one or more electrons. Metals tend to be good conductors of heat and
electricity. Nonmetals are elements that have more valence electrons and
tend to form negative ions by gaining one or more electrons. Nonmetals
tend to be poor conductors of heat and electricity. Semimetals, which are
also called metalloids or semiconductors, tend to have some characteristics
of metals and some of nonmetals. Figure 3-7b shows a periodic table that
shows the locations of the three basic types of elements.
1
18
1
2
3 4 5 6 7
2
3
3456789012
4
5
6
7
Figure 3-7b
