Indicate the number of unpaired electrons in : (a) P, (b) Si, (c) Cr, (d) Fe and (e) Kr.
Solution and Explanation
(a) Phosphorus (P): Atomic number = 15
The electronic configuration of P is: 1s2 2s2 2p6 3s2 3p3
The orbital picture of P can be represented as:
From the orbital picture, phosphorus has three unpaired electrons.
(b) Silicon (Si): Atomic number = 14
The electronic configuration of Si is: 1s2 2s2 2p6 3s2 3p2
The orbital picture of Si can be represented as:
From the orbital picture, silicon has two unpaired electrons.
(c) Chromium (Cr): Atomic number = 24
The electronic configuration of Cr is: 1s2 2s2 2p6 3s2 3p6 4s1 3d5
The orbital picture of chromium is:
From the orbital picture, chromium has six unpaired electrons.
(d) Iron (Fe): Atomic number = 26
The electronic configuration is: 1s2 2s2 2p6 3s2 3p6 4s2 3d6
The orbital picture of chromium is:
From the orbital picture, iron has four unpaired electrons.
(e) Krypton (Kr): Atomic number = 36
The electronic configuration is: 1s2 2s2 2p6 3s2 3p6 4s2 3d10 4p6
The orbital picture of krypton is:
Since all orbitals are fully occupied, there are no unpaired electrons in krypton.
Top Questions on Atomic Models
- The energy of an electron in the second orbit of a hydrogen atom is \( -3.4 \, \text{eV} \). What is the energy of the electron in the third orbit? (Given: Energy of an electron in the \( n \)-th orbit of hydrogen is \( E_n = -\frac{13.6}{n^2} \, \text{eV} \)).
- MHT CET - 2025
- Chemistry
- Atomic Models
- The energy of the nth orbit of the hydrogen atom is given by: \[ E_n = - \frac{13.6}{n^2} \, \text{eV} \] What is the energy of the second orbit (n = 2) of the hydrogen atom?
- MHT CET - 2025
- Chemistry
- Atomic Models
- Incorrect order of atomic radius is?
- JEE Main - 2025
- Chemistry
- Atomic Models
- One mole of an ideal gas expands from 10 dm\(^3\) to 20 dm\(^3\) through an isothermal reversible process. Find \( \Delta U \), \( q \), and \( w \).
- JEE Main - 2025
- Chemistry
- Atomic Models
- What did Dalton propose?
- JKCET - 2024
- Chemistry
- Atomic Models
Questions Asked in CBSE Class XI exam
- Describe the structure of the following with the help of labelled diagrams.
(i) Nucleus
(ii) Centrosome- CBSE Class XI
- An Overview Of Cell
- Convert the following into basic units:
- 28.7 pm
- 15.15 pm
- 25365 mg
- CBSE Class XI
- Percentage Composition
- Using s, p, d notations, describe the orbital with the following quantum numbers.
- n=1, l=0
- n = 3, l=1
- n = 4, l =2
- n=4, l=3
- CBSE Class XI
- Developments Leading to the Bohr’s Model of Atom
- Three reasons why the author’s grandmother was disturbed when he started going to the city school.
- CBSE Class XI
- The Portrait of a lady
- The author’s grandmother was a religious person. What are the different ways in which we come to know this?
- CBSE Class XI
- The Portrait of a lady
Concepts Used:
Structure of Atom
Atomic Structure:
The atomic structure of an element refers to the constitution of its nucleus and the arrangement of the electrons around it. Primarily, the atomic structure of matter is made up of protons, electrons and neutrons.
Dalton’s Atomic Theory
Dalton proposed that every matter is composed of atoms that are indivisible and indestructible.
The following are the postulates of his theory:
- Every matter is made up of atoms.
- Atoms are indivisible.
- Specific elements have only one type of atoms in them.
- Each atom has its own constant mass that varies from element to element.
- Atoms undergo rearrangement during a chemical reaction.
- Atoms can neither be created nor be destroyed but can be transformed from one form to another.
Cons of Dalton’s Atomic Theory
- The theory was unable to explain the existence of isotopes.
- Nothing about the structure of atom was appropriately explained.
- Later, the scientists discovered particles inside the atom that proved, the atoms are divisible.
Subatomic Particles
- Protons - are positively charged subatomic particles.
- Electron - are negatively charged subatomic particles.
- Neutrons - are electrically neutral particles and carry no charge
Atomic Structure of Isotopes
Several atomic structures of an element can exist, which differ in the total number of nucleons.These variants of elements having a different nucleon number (also known as the mass number) are called isotopes of the element. Therefore, the isotopes of an element have the same number of protons but differ in the number of neutrons. For example, there exist three known naturally occurring isotopes of hydrogen, namely, protium, deuterium, and tritium.