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46 Chemistry: Matter and Change
Solving Problems: A Chemistry Handbook
SOLVING PROBLEMS:
A CHEMISTRY HANDBOOK
CHAPTER
5
The element boron has five electrons, four of which fall into the
same configuration as beryllium. Recall that the second principal
energy level has two energy sublevels available (s and p) and that
the p sublevel is of higher energy than the s sublevel. One rule governing electron configurations is the aufbau principle, which states
that each successive electron occupies the lowest energy orbital
available. In the case of boron, the lower-energy s orbitals are full,
so the fifth electron is found in one of the three available orbitals in
the higher-energy 2p sublevel. Therefore, boron’s electron configuration is 1s 2 2s 2 2p 1 .
Recall that the three orbitals available in a p sublevel can each
hold a maximum of two electrons. Continuing from boron through
carbon (1s 2 2s 2 2p 2 ), nitrogen (1s 2 2s 2 2p 3 ), oxygen (1s 2 2s 2 2p 4 ),
fluorine (1s 2 2s 2 2p 5 ), and neon (1s 2 2s 2 2p 6 ), the 2p sublevel becomes
filled with six electrons.
With the element sodium, the eleventh electron begins the 3s
sublevel to give the configuration 1s 2 2s 2 2p 6 3s 1 . The same pattern
that occurred with lithium through neon repeats here, with successive electrons filling the 3s orbital and 3p orbitals. The element
argon has a filled 3p sublevel. Argon has 18 total electrons, and the
configuration 1s 2 2s 2 2p 6 3s 2 3p 6 .
You may recall that three sublevels—s, p, and d—are available
in the third energy level, so you might expect the next electron to
begin the 3d sublevel. However, a complication occurs here because
the 4s sublevel is of lower energy than the 3d sublevel. Thus, following the aufbau principle, the next (nineteenth) electron begins the
4s sublevel in the element potassium, producing the configuration
1s 2 2s 2 2p 6 3s 2 3p 6 4s 1 . Scandium is the first element that has electrons
in the 3d sublevel. As an example of an element that has electrons in
the 4p sublevel, the electron configuration of arsenic is
1s 2 2s 2 2p 6 3s 2 3p 6 4s 2 3d 10 4p 3 . Notice that the configuration is written
by placing the sublevels in order of increasing energy, not in
numerical order.
46 Chemistry: Matter and Change
Solving Problems: A Chemistry Handbook
SOLVING PROBLEMS:
A CHEMISTRY HANDBOOK
CHAPTER
5
The element boron has five electrons, four of which fall into the
same configuration as beryllium. Recall that the second principal
energy level has two energy sublevels available (s and p) and that
the p sublevel is of higher energy than the s sublevel. One rule governing electron configurations is the aufbau principle, which states
that each successive electron occupies the lowest energy orbital
available. In the case of boron, the lower-energy s orbitals are full,
so the fifth electron is found in one of the three available orbitals in
the higher-energy 2p sublevel. Therefore, boron’s electron configuration is 1s 2 2s 2 2p 1 .
Recall that the three orbitals available in a p sublevel can each
hold a maximum of two electrons. Continuing from boron through
carbon (1s 2 2s 2 2p 2 ), nitrogen (1s 2 2s 2 2p 3 ), oxygen (1s 2 2s 2 2p 4 ),
fluorine (1s 2 2s 2 2p 5 ), and neon (1s 2 2s 2 2p 6 ), the 2p sublevel becomes
filled with six electrons.
With the element sodium, the eleventh electron begins the 3s
sublevel to give the configuration 1s 2 2s 2 2p 6 3s 1 . The same pattern
that occurred with lithium through neon repeats here, with successive electrons filling the 3s orbital and 3p orbitals. The element
argon has a filled 3p sublevel. Argon has 18 total electrons, and the
configuration 1s 2 2s 2 2p 6 3s 2 3p 6 .
You may recall that three sublevels—s, p, and d—are available
in the third energy level, so you might expect the next electron to
begin the 3d sublevel. However, a complication occurs here because
the 4s sublevel is of lower energy than the 3d sublevel. Thus, following the aufbau principle, the next (nineteenth) electron begins the
4s sublevel in the element potassium, producing the configuration
1s 2 2s 2 2p 6 3s 2 3p 6 4s 1 . Scandium is the first element that has electrons
in the 3d sublevel. As an example of an element that has electrons in
the 4p sublevel, the electron configuration of arsenic is
1s 2 2s 2 2p 6 3s 2 3p 6 4s 2 3d 10 4p 3 . Notice that the configuration is written
by placing the sublevels in order of increasing energy, not in
numerical order.