Electrons, energy levels and atomic orbitals

What do you understand by the term atomic orbital?

An atomic orbital is a region of space around the nucleus of an atom that can be occupied by one or two electrons. 

Each subshell contains one or more atomic orbitals.

Draw diagrams to show the shape of:

i. an s orbital

ii. a p orbital

i. an s obital

• 1 orbital (ns)
• spherical in shape
• non-directional
• As n increases, size increases

ii. a p orbital

• set of 3 degenerate orbitals (`np_x, np_y, np_z`)
• dumb-bell shaped
• directional along x, y, or z axis
• perpendicular to each other
• as n increases, size increases

Element x has the electronic configuration `1s^2 2s^2 2p^6 3s^2 3p^6 3d^8 4s^2`.

i. Which block in the Periodic Table does element x belong to?

ii. State the maximum number of electrons in a d subshell.

iii. Element X forms an ion of type `X^(2+)`. 

Write the full electronic configuration for this ion using 1 `s^2` notation.

iv. Write the symbol for the subshell that begins to fill after the 3d and 4s are completely full.

i. Element X belongs to the d-block in the Periodic Table. 

ii. The maximum number of electrons in a d sub-shell is 10.

iii. Since `X^(2+)` indicates that the element has lost two electrons, we will start with the neutral atom's configuration and then remove two electrons. Thus, the full electronic configuration for the ion `X^(2+): 1s^2 2s^2 2p^6 3s^2 3p^6 3d^8`.

iv. That is 4p sub-shell

i. Give the electron arrangement of an `Fe^(2+)` ion

ii. State why iron is placed in the d block of the Periodic Table.

i. Full electronic configuration of Fe: `1s^2 2s^2 2p^6 3s^2 3p^6 4s^2`. The full electronic configuration of `Fe^(2+): 1s^2 2s^2 2p^6 3s^2 3p^6`

ii. Because of outermost electrons in the d sub-shell/orbital or highest energy level / last sub-shell to be filled / is 3d

In which pair does each species have the same number of unpaired electrons?

A. `Al and Cu^(2+`

B. `Ca and Cr^(3+`

C. `Ca and Ni^(2+`

D. `Fe^(3+) and O^(2−`

The answer is A.

A. `Cu²⁺` has the electron configuration `[Ar]3d⁹`, while Al has the electron configuration `1s²2s²2p⁶3s²3p¹`. One unpaired electron is present in `Al` and one in `Cu²⁺`. Consequently, the amount of unpaired electrons in these two species is equal. 

B. The electron configurations of `Ca`and `Cr³⁺`are `[Ar]4s²` and `[Ar]3d³`, respectively. In contrast to `Cr³⁺`, which contains three unpaired electrons, `Ca` has none. Consequently, the quantity of unpaired electrons in these two species differs. 

C. `Ni²⁺` has the electron configuration `[Ar]3d⁸`, while Ca has the same electron configuration as in (B). `Ni²⁺` has two unpaired electrons, whereas `Ca` has none. As a result, the amount of unpaired electrons in these two species differs. 

D. The electron configurations of `Fe³⁺` and `O²⁻` are `[Ar]3d⁵` and `[He]2s²2p⁶`, respectively. `O²⁻` has no unpaired electrons, but `Fe³⁺` has five. Consequently, the quantity of unpaired electrons in these two species differs. As a result, the response is A.

Which ion has the same electronic configuration as `Cl^-`?

A. `F^-`

B. `P^+`

C. `Sc^(3+`

D. `Si^(4+`

The answer is C.

Chlorine is a p-block element, belonging to group 17 and period 3. From this, we can say that it has 7 electrons in its outermost orbital and that it has 3 orbitals. Atomic number of Chlorine is 17 and its electronic configuration is `1s²2s²2p⁶3s²3p5`. Thus, the electronic configuration of `Cl^-` is `1s²2s²2p⁶3s²3p6` which has 18 electrons.

`F^-` has 10 electrons (atomic number of F is 9)

`P^+` has 14 electrons (atomic number of P is 15)

`Sc^(3+` has 18 electrons (atomic number of Sc is 21)

`Si^(4+` has 10 electrons (atomic number of Si is 14)

Which atom has its outermost electron in an orbital of the shape shown, with principal quantum number 3?

A. sodium 

B. chlorine 

C. calcium 

D. bromine

The answer is B

The graphic depicts a dumbbell shape, which is equivalent to a p-orbital. The electron is in the third energy level, as indicated by its primary quantum number of 3. Thus, the element whose outermost electron is in a 3p orbital is what we are searching for.

A. The electron configuration of sodium is `[Ne] 3s¹`

B. The electron configuration of chlorine is `[Ne] 3s² 3p⁵`

C. The electron configuration of calcium is `[Ar] 4s²`

D. The electron configuration of bromine is `[Ar] 4s² 3d¹⁰ 4p⁵`

The ion `X^(2+` has the same electronic configuration as the atom Kr. What is the electronic configuration of an atom of X?

A. `[Ar]4s²3d^10 4p^6`

B. `[Ar]4s²3d^10 4p^6 5s²`

C. `[Ar]4s²4d^10 4p^6`

D. `[Ar]4s²4d^10 4p^6 5s²`

The answer is B.

The electronic configuration of an atom of X, which has the same configuration as the ion `X^(2+)` and the atom Kr, is `[Ar] 4s²3d^10 4p^6`. To find the electronic configuration of the neutral atom X, we need to add two electrons to this configuration thus the correct electronic configuration of the neutral atom X is [Ar] `4s²3d^10 4p^6 5s²`.

Which statement about a 3p orbital is correct? 

A. It can hold a maximum of 6 electrons. 

B. It has the highest energy of the orbitals with principal quantum number 3. 

C. It is at a higher energy level than a 3s orbital but has the same shape. 

D. It is occupied by one electron in an isolated phosphorus atom.

The answer is D.

A. It has a maximum capacity of six electrons: Incorrect. Reason: 3p subshell contains 6 electrons not 3p orbital.

B. Of the orbitals with principal quantum number 3, it has the highest energy: Incorrect Reason: We have 3s, 3p, and 3d orbitals with principal quantum number 3, and the energy of 3d is at its maximum.

C. It has the same shape as a 3s orbital but is at a higher energy level: wrong. The reason is that the p orbital is dumbell shaped, while the s orbital is spherical.

D. A solitary phosphorus atom has one electron occupying it: correct. Because `1s^2 2s^2 2p^6 3s^2 3p""_x^1 3p""_y^1 3p""_z^1`.

This question refers to isolated gaseous atoms. 

In which atom are all electrons paired? 

A. Ba

B. Br 

C. S

D. Si

The answer is A.

The distribution of electrons among an atom's orbital shells and subshells is known as its electron configuration, and it is used to characterize the orbitals of an atom in its ground state.

A. Ba (Barium): Barium has an atomic number of 56. Its electron configuration is `1s² 2s² 2p⁶ 3s² 3p⁶ 4s² 3d¹⁰ 4p⁶ 5s² 4d¹⁰ 5p⁶ 6s²`. The last two electrons are in the 6s orbital, and they are paired. 

B. Br (Bromine): Bromine has an atomic number of 35. Its electron configuration is `1s² 2s² 2p⁶ 3s² 3p⁶ 4s² 3d¹⁰ 4p⁵`. The last electron is in the 4p orbital, and it is unpaired. 

C. S (Sulfur): Sulfur has an atomic number of 16. Its electron configuration is `1s² 2s² 2p⁶ 3s² 3p⁴`. The last two electrons are in the 3p orbital, and they are paired. 

D. Si (Silicon): Silicon has an atomic number of 14. Its electron configuration is `1s² 2s² 2p⁶ 3s² 3p²`. The last two electrons are in the 3p orbital, and they are unpaired.