Define electronic configuration .

An electronic configuration is the arrangement of electrons in the shells and subshells of an atom. In the ground state, electrons fill from the lowest energy shell upward.

Shell n = 3 can hold a maximum of .......... electrons, and shell n = 4 can hold a maximum of .......... electrons.

Shell n = 3 can hold a maximum of 18 electrons, and shell n = 4 can hold a maximum of 32 electrons.

True or False? The n = 3 principal quantum shell can hold a maximum of 8 electrons .

False. The n = 3 shell can hold a maximum of 18 electrons . The capacity increases with shell number: n = 1 holds 2, n = 2 holds 8, n = 3 holds 18 and n = 4 holds 32.

Why is the 4s orbital filled before the 3d orbital ?

The 4s orbital has slightly lower energy than the 3d orbital , despite being in a higher principal quantum shell. Electrons always fill the lowest energy orbital first, so 4s fills before 3d.

An orbital is a region of space around the nucleus where there is a high probability of finding an electron . Each orbital can hold a maximum of 2 electrons .

True or False? A higher principal quantum number corresponds to a higher energy shell .

True. As the principal quantum number ( n ) increases, the shell is further from the nucleus and has higher energy . Electrons in outer shells are held less tightly than those in inner shells.

What is the ground state of an atom?

The ground state is the most stable electronic configuration of an atom, in which electrons occupy the lowest available energy subshells first (starting with 1s).

In order of increasing energy, the subshells are: s, .......... , .......... and .......... .

In order of increasing energy, the subshells are: s, p , d and f .

How many electrons can the n = 2 shell hold, and why?

The n = 2 shell can hold 8 electrons . It contains one s subshell (2 electrons) and one p subshell (6 electrons), giving a total of 2 + 6 = 8 electrons .

Define degenerate orbitals.

Degenerate orbitals are orbitals within the same subshell that have identical energies . For example, the three p orbitals (p x , p y and p z ) within a given shell are all degenerate.

The p subshell holds a maximum of .......... electrons and the d subshell holds a maximum of .......... electrons.

The p subshell holds a maximum of 6 electrons and the d subshell holds a maximum of 10 electrons.

How many orbitals does the p subshell contain, and what are they called?

The p subshell contains 3 orbitals , labelled p x , p y and p z . Each orbital holds up to 2 electrons, so the p subshell holds a maximum of 6 electrons in total.

True or False? The p orbitals are spherical in shape.

False. The p orbitals are dumbbell-shaped , with two lobes on opposite sides of the nucleus. It is the s orbital that is spherical.

Describe the shape and size trend of s orbitals.

The s orbital is spherical in shape. Its size increases with the principal quantum number . The 3s orbital is larger than the 2s, which is larger than the 1s.

True or False? All orbitals within the same subshell have the same energy .

True. Orbitals within the same subshell are degenerate , meaning they have identical energies. For example, p x , p y and p z all have the same energy within a given p subshell.

How are the three p orbitals arranged relative to one another?

The three p orbitals (p x , p y and p z ) are oriented along the x , y and z axes. They point perpendicular to one another, so the lobes of each orbital are at right angles to the other two.

The s subshell contains .......... orbital, the p subshell contains .......... orbitals and the d subshell contains .......... orbitals.

The s subshell contains 1 orbital, the p subshell contains 3 orbitals and the d subshell contains 5 orbitals.

How many electrons can the f subshell hold, and why?

The f subshell can hold 14 electrons . It contains 7 orbitals , and each orbital holds a maximum of 2 electrons (7 × 2 = 14).

Define electron box notation .

An electron box notation is a diagram showing electrons as arrows within boxes, each box representing one orbital, used to display electron spin and filling order.

Electrons occupy the .......... -energy orbitals available first. Within a sub-shell, electrons fill .......... orbitals before pairing.

Electrons occupy the lowest -energy orbitals available first. Within a sub-shell, electrons fill separate orbitals before pairing.

Why do two electrons in the same orbital have opposite spins?

Opposite spins minimise electron repulsion (spin-pair repulsion), making this the lower-energy arrangement.

True or False? Three electrons can occupy the same orbital.

False. Each orbital holds a maximum of two electrons, which must have opposite spins.

Why do electrons in the same sub-shell occupy separate orbitals before pairing?

Occupying separate orbitals reduces electron-electron repulsion, giving a lower overall energy.

Define free radical .

A free radical is a species with one or more unpaired electrons.

True or False? Two electrons in the same orbital must have opposite spins.

True. Opposite spins reduce spin-pair repulsion and are required by the Pauli exclusion principle.

Hund's rule states that electrons in the same sub-shell occupy .......... orbitals with the .......... spin before pairing up.

Hund's rule states that electrons in the same sub-shell occupy separate orbitals with the same spin before pairing up.

Define shorthand electron configuration .

A shorthand electron configuration is a way of writing electron arrangement using the symbol of the previous noble gas in square brackets to represent inner electrons, followed by the remaining sub-shells. For example, potassium: [Ar] 4s 1 .

Transition metals fill the .......... sub-shell before .......... , but lose electrons from .......... first when forming ions.

Transition metals fill the 4s sub-shell before 3d , but lose electrons from 4s first when forming ions.

What is the shorthand electron configuration of chromium (Cr, Z = 24)?

[Ar] 3d 5 4s 1 . The expected [Ar] 3d 4 4s 2 is not observed because a half-filled 3d sub-shell is energetically favourable, so one electron is promoted from 4s.

True or False? Copper has the electron configuration [Ar] 3d 9 4s 2 .

False. Copper's configuration is [Ar] 3d 10 4s 1 . A fully filled 3d sub-shell is energetically favourable, so one electron is promoted from 4s.

Write the shorthand electron configuration of Fe 2+ (Z = 26).

Iron has the configuration [Ar] 4s 2 3d 6 . Fe 2+ loses two electrons from 4s first, giving [Ar] 3d 6 .

In the periodic table, elements with valence electrons in an s orbital belong to the .......... block, in a p orbital to the .......... block, and in a d orbital to the .......... block.

In the periodic table, elements with valence electrons in an s orbital belong to the s block, in a p orbital to the p block, and in a d orbital to the d block.

True or False? When filling electron configurations, the 3d sub-shell is filled before the 4s sub-shell.

False. The 4s sub-shell has lower energy than 3d and fills first. However, when forming ions, electrons are lost from 4s before 3d.

Write the shorthand electron configuration of Ca 2+ (Z = 20).

Calcium is [Ar] 4s 2 . Ca 2+ loses both 4s electrons, giving the same configuration as argon: [Ar].

A LevelChemistryCambridge (CIE)Flashcards1. Atomic StructureElectrons, Energy Levels & Atomic Orbitals

Electrons, Energy Levels & Atomic Orbitals (Cambridge (CIE) A Level Chemistry): Flashcards

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FrontElectronic Structure
Define electronic configuration.

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Cards in this collection (36)

Define electronic configuration.
An electronic configuration is the arrangement of electrons in the shells and subshells of an atom. In the ground state, electrons fill from the lowest energy shell upward.
Shell n = 3 can hold a maximum of .......... electrons, and shell n = 4 can hold a maximum of .......... electrons.
Shell n = 3 can hold a maximum of 18 electrons, and shell n = 4 can hold a maximum of 32 electrons.
True or False?
The n = 3 principal quantum shell can hold a maximum of 8 electrons.
False.
The n = 3 shell can hold a maximum of 18 electrons. The capacity increases with shell number: n = 1 holds 2, n = 2 holds 8, n = 3 holds 18 and n = 4 holds 32.
Why is the 4s orbital filled before the 3d orbital?
The 4s orbital has slightly lower energy than the 3d orbital, despite being in a higher principal quantum shell. Electrons always fill the lowest energy orbital first, so 4s fills before 3d.
Define orbital.
An orbital is a region of space around the nucleus where there is a high probability of finding an electron. Each orbital can hold a maximum of 2 electrons.
True or False?
A higher principal quantum number corresponds to a higher energy shell.
True.
As the principal quantum number (n) increases, the shell is further from the nucleus and has higher energy. Electrons in outer shells are held less tightly than those in inner shells.
What is the ground state of an atom?
The ground state is the most stable electronic configuration of an atom, in which electrons occupy the lowest available energy subshells first (starting with 1s).
In order of increasing energy, the subshells are: s, .........., .......... and ...........
In order of increasing energy, the subshells are: s, p, d and f.
How many electrons can the n = 2 shell hold, and why?
The n = 2 shell can hold 8 electrons. It contains one s subshell (2 electrons) and one p subshell (6 electrons), giving a total of 2 + 6 = 8 electrons.
Define degenerate orbitals.
Degenerate orbitals are orbitals within the same subshell that have identical energies. For example, the three p orbitals (p_x, p_y and p_z) within a given shell are all degenerate.
The p subshell holds a maximum of .......... electrons and the d subshell holds a maximum of .......... electrons.
The p subshell holds a maximum of 6 electrons and the d subshell holds a maximum of 10 electrons.
How many orbitals does the p subshell contain, and what are they called?
The p subshell contains 3 orbitals, labelled p_x, p_y and p_z. Each orbital holds up to 2 electrons, so the p subshell holds a maximum of 6 electrons in total.
True or False?
The p orbitals are spherical in shape.
False.
The p orbitals are dumbbell-shaped, with two lobes on opposite sides of the nucleus. It is the s orbital that is spherical.
Describe the shape and size trend of s orbitals.
The s orbital is spherical in shape. Its size increases with the principal quantum number. The 3s orbital is larger than the 2s, which is larger than the 1s.
True or False?
All orbitals within the same subshell have the same energy.
True.
Orbitals within the same subshell are degenerate, meaning they have identical energies. For example, p_x, p_y and p_z all have the same energy within a given p subshell.
How are the three p orbitals arranged relative to one another?
The three p orbitals (p_x, p_y and p_z) are oriented along the x, y and z axes. They point perpendicular to one another, so the lobes of each orbital are at right angles to the other two.
The s subshell contains .......... orbital, the p subshell contains .......... orbitals and the d subshell contains .......... orbitals.
The s subshell contains 1 orbital, the p subshell contains 3 orbitals and the d subshell contains 5 orbitals.
How many electrons can the f subshell hold, and why?
The f subshell can hold 14 electrons. It contains 7 orbitals, and each orbital holds a maximum of 2 electrons (7 × 2 = 14).
Define electron box notation.
An electron box notation is a diagram showing electrons as arrows within boxes, each box representing one orbital, used to display electron spin and filling order.
Electrons occupy the ..........-energy orbitals available first. Within a sub-shell, electrons fill .......... orbitals before pairing.
Electrons occupy the lowest-energy orbitals available first. Within a sub-shell, electrons fill separate orbitals before pairing.
Why do two electrons in the same orbital have opposite spins?
Opposite spins minimise electron repulsion (spin-pair repulsion), making this the lower-energy arrangement.
True or False?
Three electrons can occupy the same orbital.
False.
Each orbital holds a maximum of two electrons, which must have opposite spins.
Why do electrons in the same sub-shell occupy separate orbitals before pairing?
Occupying separate orbitals reduces electron-electron repulsion, giving a lower overall energy.
Define free radical.
A free radical is a species with one or more unpaired electrons.
True or False?
Two electrons in the same orbital must have opposite spins.
True.
Opposite spins reduce spin-pair repulsion and are required by the Pauli exclusion principle.
Write the full electron configuration of carbon (Z = 6).
1s² 2s² 2p²
Hund's rule states that electrons in the same sub-shell occupy .......... orbitals with the .......... spin before pairing up.
Hund's rule states that electrons in the same sub-shell occupy separate orbitals with the same spin before pairing up.
Define shorthand electron configuration.
A shorthand electron configuration is a way of writing electron arrangement using the symbol of the previous noble gas in square brackets to represent inner electrons, followed by the remaining sub-shells. For example, potassium: [Ar] 4s¹.
Transition metals fill the .......... sub-shell before .........., but lose electrons from .......... first when forming ions.
Transition metals fill the 4s sub-shell before 3d, but lose electrons from 4s first when forming ions.
What is the shorthand electron configuration of chromium (Cr, Z = 24)?
[Ar] 3d⁵ 4s¹. The expected [Ar] 3d⁴ 4s² is not observed because a half-filled 3d sub-shell is energetically favourable, so one electron is promoted from 4s.
True or False?
Copper has the electron configuration [Ar] 3d⁹ 4s².
False.
Copper's configuration is [Ar] 3d¹⁰ 4s¹. A fully filled 3d sub-shell is energetically favourable, so one electron is promoted from 4s.
Write the shorthand electron configuration of Fe²⁺ (Z = 26).
Iron has the configuration [Ar] 4s² 3d⁶. Fe²⁺ loses two electrons from 4s first, giving [Ar] 3d⁶.
In the periodic table, elements with valence electrons in an s orbital belong to the .......... block, in a p orbital to the .......... block, and in a d orbital to the .......... block.
In the periodic table, elements with valence electrons in an s orbital belong to the s block, in a p orbital to the p block, and in a d orbital to the d block.
Write the shorthand electron configuration of gallium (Ga, Z = 31).
[Ar] 3d¹⁰ 4s² 4p¹
True or False?
When filling electron configurations, the 3d sub-shell is filled before the 4s sub-shell.
False.
The 4s sub-shell has lower energy than 3d and fills first. However, when forming ions, electrons are lost from 4s before 3d.
Write the shorthand electron configuration of Ca²⁺ (Z = 20).
Calcium is [Ar] 4s². Ca²⁺ loses both 4s electrons, giving the same configuration as argon: [Ar].

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