CK-12-Chemistry Intermediate

http://www.ck12.org Chapter 5. Electrons in Atoms

TABLE5.2: Electron Arrangement Within Energy Levels

Principal Quan-

tum Number (n)

Allowable Sub-

levels

Number of Or-

bitals per Sub-

level

Number of

Orbitals per

Principal

Energy Level

Number of

Electrons per

Sublevel

Number of

Electrons

per Principal

Energy Level

1 s 1 1 2 2

2 s

p

1

3

4 2

6

8

3 s

p

d

1

3

5

9 2

6

10

18

4 s

p

d

f

1

3

5

7

16 2

6

10

14

32

Notice that the total number of allowable orbitals in each principal energy level (n) is equal ton^2. That is, whenn=
1, there is 12 = 1 orbital possible. Whenn= 2, there are 2^2 = 4 orbitals possible, and so on. Since each orbital holds
two electrons, the number of electrons that can exist in a given principal energy level is equal to 2n^2.

Lesson Summary

• de Broglie showed that electrons exhibit characteristics of both waves and particles.


• The behavior of atomic and subatomic sized particles is explained by quantum mechanics, where energy is
  gained and lost in small, discrete amounts.


• The Heisenberg uncertainty principle states that it is not possible to simultaneously know the location of an
  electron and its velocity at any precise moment.


• The Schrödinger wave equation proved mathematically that the energy of an electron must be quantized.


• The quantum mechanical model of the atom describes the probability that an atom’s electrons will be located
  within certain regions called orbitals.


• The arrangement of electrons in an atom is governed by four quantum numbers, which designate a principal
  energy level, an energy sublevel, an orbital orientation, and a spin for each electron in the atom.

Lesson Review Questions

Reviewing Concepts

1. How is the wavelength of a moving object related to its mass?


2. Why is the de Broglie wave equation meaningful only for submicroscopic particles, such as atoms and
   electrons but not for larger everyday objects?


3. How does the Heisenberg uncertainty principle affect the way in which electron locations are viewed in the
   quantum mechanical model as compared to the Bohr model?


4. What is an atomic orbital?


5. How many quantum numbers are used to describe each electron in an atom?