3.1: Electron Configurations (Problems) (2024)

PROBLEM \(\PageIndex{1}\)

Using complete subshell notation (no abbreviations), predict the electron configuration of each of the following atoms:

1. C
2. P
3. V
4. Sb
5. Sm

Answer a

1s²2s²2p²

Answer b

1s²2s²2p⁶3s²3p³

Answer c

1s²2s²2p⁶3s²3p⁶3d³4s²

Answer d

1s²2s²2p⁶3s²3p⁶3d¹⁰4s²4p⁶4d¹⁰5s²5p³

Answer e

1s²2s²2p⁶3s²3p⁶3d¹⁰4s²4p⁶4d¹⁰4f⁶5s²5p⁶6s².

PROBLEM \(\PageIndex{2}\)

Using complete subshell notation, predict the electron configuration of each of the following atoms:

1. N
2. Si
3. Fe
4. Te
5. Tb

Answer a

1s²2s²2p³

Answer b

1s²2s²2p⁶3s²3p²

Answer c

1s²2s²2p⁶3s²3p⁶4s²3d⁶

Answer d

1s²2s²2p⁶3s²3p⁶4s²3d¹⁰4p⁶5s²4d¹⁰5p⁴

Answer e

1s²2s²2p⁶3s²3p⁶4s²3d¹⁰4p⁶5s²4d¹⁰5p⁶6s²4f⁹

PROBLEM \(\PageIndex{3}\)

Use an orbital diagram to describe the electron configuration of the valence shell of each of the following atoms:

1. N
2. Si
3. Fe
4. Te
5. Mo

Answer a

Answer b

Answer c

See Also

1.3: Atomic Structure - Electron Configurations7.3: Electron Configurations of AtomsElectron Configuration Calculator2.3: Electron Configurations

Answer d

Answer e

PROBLEM \(\PageIndex{4}\)

Using complete subshell notation (1s²2s²2p⁶, and so forth), predict the electron configurations of the following ions.

1. N^3–
2. Ca²⁺
3. S^–
4. Cs²⁺
5. Cr²⁺
6. Gd³⁺

Answer a

1s²2s²2p⁶

Answer b

1s²2s²2p⁶3s²3p⁶

Answer c

1s²2s²2p⁶3s²3p⁵

Answer d

1s²2s²2p⁶3s²3p⁶4s²3d¹⁰4p⁶5s²4d¹⁰5p⁵

Answer e

1s²2s²2p⁶3s²3p⁶4s²3d²

Answer f

1s²2s²2p⁶3s²3p⁶4s²3d¹⁰4p⁶5s²4d¹⁰5p⁶6s²4f⁵

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PROBLEM \(\PageIndex{5}\)

Which atom has the electron configuration: 1s²2s²2p⁶3s²3p⁶4s²3d¹⁰4p⁶5s²4d²?

Answer

Zr

PROBLEM \(\PageIndex{6}\)

Which atom has the electron configuration: 1s²2s²2p⁶3s²3p⁶3d⁷4s²?

Answer

Co

PROBLEM \(\PageIndex{7}\)

a. Which ion with a +1 charge has the electron configuration 1s²2s²2p⁶3s²3p⁶3d¹⁰4s²4p⁶?

b. Which ion with a –2 charge has this configuration?

Answer a

Rb⁺

Answer b

Se²⁻

PROBLEM \(\PageIndex{8}\)

Which of the following atoms contains only three valence electrons: Li, B, N, F, Ne?

Answer

B

PROBLEM \(\PageIndex{9}\)

Which of the following has two unpaired electrons?

1. Mg
2. Si
3. S
4. Both Mg and S
5. Both Si and S.

Answer

Although both (b) and (c) are correct, (e) encompasses both and is the best answer.

PROBLEM \(\PageIndex{10}\)

Which atom would be expected to have a half-filled 6p subshell?

Answer

Bi

PROBLEM \(\PageIndex{11}\)

Which atom would be expected to have a half-filled 4s subshell?

Answer

K

PROBLEM \(\PageIndex{12}\)

In one area of Australia, the cattle did not thrive despite the presence of suitable forage. An investigation showed the cause to be the absence of sufficient cobalt in the soil. Cobalt forms cations in two oxidation states, Co²⁺ and Co³⁺. Write the electron structure of the two cations.

Answer

Co²⁺: 1s²2s²2p⁶3s²3p⁶4s²3d⁵

Co³⁺: 1s²2s²2p⁶3s²3p⁶4s²3d⁴

Click here to see a video of the solution

See Also

3.4: Electronic Structure of Atoms (Electron Configurations)

PROBLEM \(\PageIndex{13}\)

Thallium was used as a poison in the Agatha Christie mystery story “The Pale Horse.” Thallium has two possible cationic forms, +1 and +3. The +1 compounds are the more stable. Write the electron structure of the +1 cation of thallium.

Answer

1s²2s²2p⁶3s²3p⁶3d¹⁰4s²4p⁶4d¹⁰5s²5p⁶6s²4f¹⁴5d¹⁰

PROBLEM \(\PageIndex{14}\)

Write the electron configurations for the following atoms or ions:

1. B³⁺
2. O^–
3. Cl³⁺
4. Ca²⁺
5. Ti

Answer a

1s²

Answer b

1s²2s²2p⁵

Answer c

1s²2s²2p⁶3s²3p²

Answer d

1s²2s²2p⁶3s²3p⁶

Answer e

1s²2s²2p⁶3s²3p⁶4s²3d²

PROBLEM \(\PageIndex{15}\)

Cobalt–60 and iodine–131 are radioactive isotopes commonly used in nuclear medicine. How many protons, neutrons, and electrons are in atoms of these isotopes? Write the complete electron configuration for each isotope.

Answer

Co has 27 protons, 27 electrons, and 33 neutrons: 1s²2s²2p⁶3s²3p⁶4s²3d⁷.

I has 53 protons, 53 electrons, and 78 neutrons: 1s²2s²2p⁶3s²3p⁶3d¹⁰4s²4p⁶4d¹⁰5s²5p⁵.

PROBLEM \(\PageIndex{16}\)

Atoms of which group in the periodic table have a valence shell electron configuration of ns²np³?

Answer

15 (5A)

PROBLEM \(\PageIndex{17}\)

Atoms of which group in the periodic table have a valence shell electron configuration of ns²?

Answer

2 (2A)

PROBLEM \(\PageIndex{18}\)

Does a cation gain protons to form a positive charge or does it lose electrons?

Answer

The protons in the nucleus do not change during normal chemical reactions. Only the outer electrons move. Positive charges form when electrons are lost.

PROBLEM \(\PageIndex{19}\)

Iron(III) sulfate [Fe₂(SO₄)₃] is composed of Fe³⁺ and \(\ce{SO4^2-}\) ions. Explain why a sample of iron(III) sulfate is uncharged.

Answer

Two cations with a +3 charge give a total of +6 charge, while three anions of -2 charge give a total of -6 charge. +6-6=0, so when these ions bond, the charges will cancel, leaving the resulting compound uncharged.

PROBLEM \(\PageIndex{20}\)

Which of the following atoms would be expected to form negative ions in binary ionic compounds and which would be expected to form positive ions: P, I, Mg, Cl, In, Cs, O, Pb, Co?

Answer

P, I, Cl, and O would form anions because they are nonmetals. Mg, In, Cs, Pb, and Co would form cations because they are metals.

PROBLEM \(\PageIndex{21}\)

Which of the following atoms would be expected to form negative ions in binary ionic compounds and which would be expected to form positive ions: Br, Ca, Na, N, F, Al, Sn, S, Cd?

Answer

Anions: Br, N, F, S,

Cations: Ca, Na, Al, Sn (because it's a metal), Cd (because it is a metal)

PROBLEM \(\PageIndex{22}\)

Predict the charge on the monatomic ions formed from the following atoms in binary ionic compounds:

1. P
2. Mg
3. Al
4. O
5. Cl
6. Cs

Answer a

P^3–

Answer b

Mg²⁺

Answer c

Al³⁺

Answer d

O^2–

Answer e

Cl^–

Answer f

Cs⁺

PROBLEM \(\PageIndex{23}\)

Predict the charge on the monatomic ions formed from the following atoms in binary ionic compounds:

a. I
b. Sr
c. K
d. N
e. S
f. In

Answer a

I^-

Answer b

Sr²⁺

Answer c

K⁺

Answer d

N^3-

Answer e

S^2-

Answer f

In³⁺

PROBLEM \(\PageIndex{24}\)

Write the noble gas electron configuration for each of the following ions:

a. As^3–
b. I^–
c. Be²⁺
d. Cd²⁺
e. O^2–
f. Ga³⁺
g. Li⁺
h. N^3–
i. Sn²⁺
j. Co²⁺
k. Fe²⁺
l. As³⁺

Answer a

[Ar]4s²3d¹⁰4p⁶

Answer b

[Kr]4d¹⁰5s²5p⁶

Answer c

1s²

Answer d

[Kr]4d¹⁰

Answer e

[He]2s²2p⁶

Answer f

[Ar]3d¹⁰

Answer g

1s²

Answer h

[He]2s²2p⁶

Answer i

[Kr]4d¹⁰5s²

Answer j

[Ar]3d⁷

Answer k

[Ar]3d⁶

Answer l

[Ar]3d¹⁰4s²

PROBLEM \(\PageIndex{25}\)

Write out the full electron configuration for each of the following atoms and for the monatomic ion found in binary ionic compounds containing the element:

1. Al
2. Br
3. Sr
4. Li
5. As
6. S

Answer a

Al: 1s²2s²2p⁶3s²3p¹

Al³⁺: 1s²2s²2p⁶

Answer b

Br: 1s²2s²2p⁶3s²3p⁶3d¹⁰4s²4p⁵

Br^-: 1s²2s²2p⁶3s²3p⁶3d¹⁰4s²4p⁶

Answer c

Sr: 1s²2s²2p⁶3s²3p⁶3d¹⁰4s²4p⁶5s²

Sr²⁺: 1s²2s²2p⁶3s²3p⁶3d¹⁰4s²4p⁶

Answer d

Li: 1s²2s¹

Li⁺: 1s²

Answer e

As: 1s²2s²2p⁶3s²3p⁶3d¹⁰4s²4p³

As^3-: 1s²2s²2p⁶3s²3p⁶3d¹⁰4s²4p⁶

Answer f

S: 1s²2s²2p⁶3s²3p⁴

S^2-: 1s²2s²2p⁶3s²3p⁶

Contributors

• Paul Flowers (University of North Carolina - Pembroke),Klaus Theopold (University of Delaware) andRichard Langley (Stephen F. Austin State University) with contributing authors.Textbook content produced by OpenStax College is licensed under a Creative Commons Attribution License 4.0 license. Download for free at http://cnx.org/contents/85abf193-2bd...a7ac8df6@9.110).

• Adelaide Clark, Oregon Institute of Technology

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