# 2.1.1: Electron Configurations (Problems)


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

1s22s22p2

1s22s22p63s23p3

1s22s22p63s23p63d34s2

1s22s22p63s23p63d104s24p64d105s25p3

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

1s22s22p3

1s22s22p63s23p2

1s22s22p63s23p64s23d6

1s22s22p63s23p64s23d104p65s24d105p4

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

PROBLEM $$\PageIndex{4}$$

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

1. N3–
2. Ca2+
3. S
4. Cs2+
5. Cr2+
6. Gd3+

1s22s22p6

1s22s22p63s23p6

1s22s22p63s23p5

1s22s22p63s23p64s23d104p65s24d105p5

1s22s22p63s23p64s23d2

1s22s22p63s23p64s23d104p65s24d105p66s24f5

Click here to see a video of the solution

PROBLEM $$\PageIndex{5}$$

Which atom has the electron configuration: 1s22s22p63s23p64s23d104p65s24d2?

Zr

PROBLEM $$\PageIndex{6}$$

Which atom has the electron configuration: 1s22s22p63s23p63d74s2?

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?

Rb+

Se2−

PROBLEM $$\PageIndex{8}$$

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

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.

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?

Bi

PROBLEM $$\PageIndex{11}$$

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

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.

Co2+: 1s22s22p63s23p64s23d5

Co3+: 1s22s22p63s23p64s23d4

Click here to see a video of the solution

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.

1s22s22p63s23p63d104s24p64d105s25p66s24f145d10

PROBLEM $$\PageIndex{14}$$

Write the electron configurations for the following atoms or ions:

1. B3+
2. O
3. Cl3+
4. Ca2+
5. Ti

1s2

1s22s22p5

1s22s22p63s23p2

1s22s22p63s23p6

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.

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?

15 (5A)

PROBLEM $$\PageIndex{17}$$

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

2 (2A)

PROBLEM $$\PageIndex{18}$$

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

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.

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?

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?

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

P3–

Mg2+

Al3+

O2–

Cl

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

I-

Sr2+

K+

N3-

S2-

In3+

PROBLEM $$\PageIndex{24}$$

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

a. As3–
b. I
c. Be2+
d. Cd2+
e. O2–
f. Ga3+
g. Li+
h. N3–
i. Sn2+
j. Co2+
k. Fe2+
l. As3+

[Ar]4s23d104p6

[Kr]4d105s25p6

1s2

[Kr]4d10

[He]2s22p6

[Ar]3d10

1s2

[He]2s22p6

[Kr]4d105s2

[Ar]3d7

[Ar]3d6

[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

Al: 1s22s22p63s23p1

Al3+: 1s22s22p6

Br: 1s22s22p63s23p63d104s24p5

Br-: 1s22s22p63s23p63d104s24p6

Sr: 1s22s22p63s23p63d104s24p65s2

Sr2+: 1s22s22p63s23p63d104s24p6

Li: 1s22s1

Li+: 1s2

As: 1s22s22p63s23p63d104s24p3

As3-: 1s22s22p63s23p63d104s24p6

S: 1s22s22p63s23p4

S2-: 1s22s22p63s23p6

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2.1.1: Electron Configurations (Problems) is shared under a not declared license and was authored, remixed, and/or curated by LibreTexts.