CAIE A-Level Chemistry AS 1.3 Electrons Energy Levels and Atomic Orbitals Questions

Practise building ground-state electron configurations from shells, sub-shell energies, orbitals and electron-repulsion rules.

Exam points

distinguish shells, sub-shells and orbitals and state the electron capacity of each relevant sub-shell
fill orbitals in increasing energy while applying opposite spin and single occupancy before pairing
determine atom and ion configurations, including transition-element loss of 4s electrons before 3d electrons

Covered syllabus points

1.3.0—Scope note 1.3.1—Terms 1.3.2—Number of orbitals making up s, p and d 1.3.3—Order of increasing energy of the sub-shells 1.3.4—Electronic configurations to include 1.3.5—Electronic configurations 1.3.6—Determine the electronic configuration 1.3.7—The electrons in boxes notation 1.3.8—And sketch the shapes of s and p orbitals 1.3.9—Free radical as a species with one or more

[Maximum number: 3]

Vanadium, niobium and tantalum are metals in the same group of the Periodic Table.

(a)

The shorthand electronic configuration of vanadium in the ground state is $[\mathrm{Ar}] 3 \mathrm{~d}^{3} 4 \mathrm{~s}^{2}$ .

[ 3 ]

(i)

State what is meant by the term ground state.

[ 1 ]

(ii)

Show the electronic configuration of vanadium using electrons in boxes notation.

Figure for Question (ii) — CAIE A-Level Chemistry AS

[ 1 ]

(iii)

Deduce the total number of electrons in the p sub-shells of a vanadium atom.

[ 1 ]

[Maximum number: 6]

Atoms contain the subatomic particles electrons, protons and neutrons. Protons and electrons were discovered by observations of their behaviours in electric fields.

(a)

Electrons in atoms up to ${ }_{36} \mathrm{Kr}$ are distributed in s, p and d orbitals.

[ 6 ]

(i)

State the number of occupied orbitals in an isolated atom of ${ }_{36} \mathrm{Kr}$ .

Table for Question (i) — CAIE A-Level Chemistry AS

[ 3 ]

type of orbital	s	p	d
number of orbitals	4	9	5

(ii)

Complete the diagram to show the number and relative energies of the electrons in an isolated atom of ${ }_{14} \mathrm{Si}$ .

[ 2 ]

(iii)

The diagram shows a type of orbital.

Figure for Question (iii) — CAIE A-Level Chemistry AS

State the total number of electrons that exist in all orbitals of this type in an atom of ${ }_{9} \mathrm{~F}$ .

[ 1 ]

[Maximum number: 5]

(a)

The electronic configuration of a sulfur atom is $1 s^{2} 2 s^{2} 2 p^{6} 3 s^{2} 3 p^{4}$ .

[ 4 ]

(i)

Identify which orbital in a sulfur atom has the lowest energy.

[ 1 ]

(ii)

Sketch the shape of a p orbital.

[ 1 ]

(iii)

During the process of ionisation a sulfur atom loses an electron.

\mathrm{S}(\mathrm{~g}) \rightarrow \mathrm{S}^{+}(\mathrm{g})+\mathrm{e}^{-} \quad \Delta H=1000 \mathrm{~kJ} \mathrm{~mol}^{-1}

Identify the orbital from which this electron is removed. Explain your answer.
orbital
explanation

[ 2 ]

(b)

Complete the diagram to show the arrangement of electrons within the third shell of a phosphorus atom.

Figure for Question (b) — CAIE A-Level Chemistry AS

[ 1 ]

[Maximum number: 1]

Vanadium, niobium and tantalum are metals in the same group of the Periodic Table.

The shorthand electronic configuration of vanadium in the ground state is $[\mathrm{Ar}] 3 \mathrm{~d}^{3} 4 \mathrm{~s}^{2}$ .

State what is meant by the term ground state.

[Maximum number: 1]

The electronic configuration of a sulfur atom is $1 s^{2} 2 s^{2} 2 p^{6} 3 s^{2} 3 p^{4}$ .

Identify which orbital in a sulfur atom has the lowest energy.

[Maximum number: 1]

HCN has been detected in interstellar gas. The molecules below have also been detected in interstellar gas.

Which molecule contains the same total number of valence shell (outer shell) electrons as HCN ?

HNO

$\mathrm{NH}_{3}$

[Maximum number: 2]

The electronic configuration of a sulfur atom is $1 s^{2} 2 s^{2} 2 p^{6} 3 s^{2} 3 p^{4}$ .

During the process of ionisation a sulfur atom loses an electron.

\mathrm{S}(\mathrm{~g}) \rightarrow \mathrm{S}^{+}(\mathrm{g})+\mathrm{e}^{-} \quad \Delta H=1000 \mathrm{~kJ} \mathrm{~mol}^{-1}

Identify the orbital from which this electron is removed. Explain your answer.
orbital
explanation

[Maximum number: 1]

What is the electronic configuration of $\mathrm{Mg}^{2+}$ ?

$1 s^{2} 2 s^{2} 2 p^{6}$

$1 s^{2} 2 s^{2} 2 p^{6} 3 s^{2}$

$1 s^{2} 2 s^{2} 2 p^{6} 3 s^{2} 3 p^{2}$

$1 s^{2} 2 s^{2} 2 p^{6} 3 s^{2} 3 p^{6} 3 d^{2} 4 s^{2}$

[Maximum number: 1]

Which atom has exactly three unpaired electrons in the ground state?

an isolated gaseous aluminium atom

an isolated gaseous carbon atom

an isolated gaseous chromium atom

an isolated gaseous phosphorus atom

[Maximum number: 1]

Which statement about the electrons in a ground state carbon atom is correct?

Electrons are present in four different energy levels.

There are more electrons in p orbitals than there are in s orbitals.

The occupied orbital of highest energy is spherical.

The occupied orbital of lowest energy is spherical.

[Maximum number: 1]

In which pairs are both species free radicals?
1 Cl and O
$2 \mathrm{Cl}^{-}$ and $\mathrm{O}^{2-}$
3 Cl and $\mathrm{O}^{-}$ $4 \mathrm{Cl}^{+}$ and $\mathrm{O}^{2+}$

1, 3 and 4

1 and 3 only

1 only

2 only

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Covered syllabus points

Question 1

Question (a)

Question (i)

Question (ii)

Question (iii)

Question 2

Question (a)

Question (i)

Question (ii)

Question (iii)

Question 3

Question (a)

Question (i)

Question (ii)

Question (iii)

Question (b)

Question 4

Question 5

Question 6

Question 7

Question 8

Question 9

Question 10

Question 11