Page 239 - 9780077418427.pdf

/Users/user-f465/Desktop
tiL12214_ch08_203-228.indd Page 216 9/1/10 9:45 PM user-f465
tiL12214_ch08_203-228.indd Page 216 9/1/10 9:45 PM user-f465 /Users/user-f465/Desktop

the element, and the number below the symbol is the rounded
atomic weight of the element. Horizontal rows of elements run
1s
from left to right with increasing atomic numbers. Each row is
called a period. The periods are numbered from 1 to 7 on the left
2s 2p
side. A vertical column of elements is called a family (or group)
of elements. Elements in families have similar properties, but
3s 3p 3d
this is more true of some families than of others. The table is
subdivided into A and B groups. The members of the A-group
4s 4p 4d 4f families are called the main group, or representative elements.
The members of the B group are called the transition elements
5s 5p 5d 5f (or metals). Some science organizations use a 1-to-18 designa-
tion for the A and B groups, as shown in Figure 8.17. The A and
6s 6p 6d 6f B designations will be used throughout this text.
As shown in Table 8.4, all of the elements in the first column
7s 7p 7d have an outside electron configuration of one electron. With the
exception of hydrogen, the elements of the first column are shiny,
low-density metals that are so soft you can cut them easily with a
knife. These metals are called the alkali metals because they react
FIGURE 8.16 A matrix showing the order in which the orbitals violently with water to form an alkaline solution. The alkali met-
are filled. Start at the top left, then move from the head of each ar- als do not occur in nature as free elements because they are so
row to the tail of the one immediately below it. This sequence moves reactive. Hydrogen is a unique element in the periodic table. It is
from the lowest energy level to the next-higher level for each orbital. not an alkali metal and is placed in the group because it seems to
fit there because it has one electron in its outer s orbital.
CONCEPTS Applied The elements in the second column all have an outside
configuration of two electrons and are called the alkaline earth
metals. The alkaline earth metals are soft, reactive metals but
Firework Configuration
not as reactive or soft as the alkali metals. Calcium and mag-
Certain strontium (atomic number 38) chemicals are used nesium, in the form of numerous compounds, are familiar
to add the pure red color to flares and fireworks. Write the examples of this group.
electron configuration of strontium, and do this before you The elements in group VIIA all have an outside configura-
look at the solution that follows.
First, note that an atomic number of 38 means a total tion of seven electrons, needing only one more electron to com-
of 38 electrons. Second, refer to the order of filling matrix pletely fill the outer (p) orbitals. These elements are called the
in Figure 8.16. Remember that only two electrons can halogens. The halogens are very reactive nonmetals. The halogens
occupy an orbital, but there are three orientations of the fluorine and chlorine are greenish gases. Bromine is a reddish-
p orbital, for a total of six electrons. There are likewise brown liquid and iodine is a dark purple solid. Halogens are used
five possible orientations of the d orbital, for a total of ten as disinfectants and bleaches and are combined with a metal as
electrons. Starting at the lowest energy level, two electrons a source of light in halogen lights. Halogens react with metals to
2
2
go in 1s, making 1s ; then two go in 2s, making 2s . That form a group of chemicals called salts, such as sodium chloride.
6
2
is a total of four electrons so far. Next 2p and 3s use In fact, the word halogen is Greek, meaning “salt former.”
6
eight more electrons, for a total of twelve so far. The 3p ,
10
6
2
4s , 3d , and 4p use up twenty-four more electrons, for
a total of thirty-six. The remaining two go into the next
2
sublevel, 5s , and the complete answer is TABLE 8.4
6
2
6
2
2
10
6
2
Strontium: 1s 2s 2p 3s 3p 4s 3d 4p 5s 2
Electron structures of the alkali metal family
Number of Electrons in
Electron Main Energy Level
Element Configuration 1st 2nd 3rd 4th 5th 6th 7th
8.5 THE PERIODIC TABLE
1
Lithium (Li) [He]* 2s 2 1 — — — — —
1
The periodic table is made up of rows and columns of cells, with Sodium (Na) [Ne] 3s 2 8 1 — — — —
each element having its own cell in a specific location. The cells Potassium (K) [Ar] 4s 1 2 8 8 1 — — —
are not arranged symmetrically. The arrangement has a mean- Rubidium (Rb) [Kr] 5s 2 8 18 8 1 — —
1
ing, both about atomic structure and about chemical behaviors. 1
Cesium (Cs) [Xe] 6s 2 8 18 18 8 1 —
It will facilitate your understanding if you refer frequently to 1
Francium (Fr) [Rn] 7s 2 8 18 32 18 8 1
a periodic table during the following discussion (Figure 8.17).
An element is identified in each cell with its chemical sym-
2
2
1
*[He] is shorthand for the structure of He, which is 2s . Lithium, therefore, is 2s 1s . [Ne]
bol. The number above the symbol is the atomic number of means the structure of neon, and so on.
216 CHAPTER 8 Atoms and Periodic Properties 8-14