Atomic Volume & Angstrom Hydrogen Atom Volume | NEET Smart Notes

 - Dr.Sanjaykumar Pawar   

NEET Chemistry: Atomic Volume, Angstrom Unit & Hydrogen Atom Volume 

NEET Smart Notes: Calculation of Atomic Volume of One Mole of Hydrogen Atoms Using Angstrom Unit (Å).

NEET Smart Notes

Atomic Volume & Angstrom (Hydrogen Atom Volume)

Part 1: Question & Answer (Q.1.14)

Question 1.14:

The unit of length convenient on the atomic scale is known as an angstrom (Å):

1 Å = 10⁻¹⁰ m

The size of a hydrogen atom is about 0.5 Å. What is the total atomic volume in m³ of a mole of hydrogen atoms?

Solution:

Given:

• Radius of hydrogen atom = 0.5 Å
• 1 Å = 10⁻¹⁰ m
• Number of atoms in one mole = Avogadro number (N_A) = 6.022 × 10²³ atoms

Convert radius into metre:

r = 0.5 × 10⁻¹⁰ m

r = 5 × 10⁻¹¹ m

Volume of one hydrogen atom:

V = (4/3)πr³

V = (4/3) × 3.14 × (5 × 10⁻¹¹)³

V = 5.23 × 10⁻³¹ m³

Volume of one mole of hydrogen atoms:

Total Volume = Volume of one atom × Number of atoms

= (5.23 × 10⁻³¹) × (6.022 × 10²³)

= 3.15 × 10⁻⁷ m³

Answer: Total atomic volume of one mole of hydrogen atoms = 3.15 × 10⁻⁷ m³

Part 2: Short Notes

Angstrom (Å)

• Angstrom is a unit of length used for measuring atomic and molecular sizes.
• Symbol: Å
• 1 Å = 10⁻¹⁰ metre
• It is commonly used in atomic physics and chemistry.

Atomic Volume

• Atomic volume represents the space occupied by an atom.
• Atoms are considered approximately spherical for volume calculation.
• Volume of atom:

V = (4/3)πr³

Part 3: NEET Smart Notes

Topic	Important Point
Angstrom	1 Å = 10⁻¹⁰ m
Hydrogen Atom Radius	0.5 Å = 5 × 10⁻¹¹ m
Atomic Volume Formula	V = (4/3)πr³
Avogadro Number	6.022 × 10²³ atoms/mol
Molar Atomic Volume	Volume of one atom × Number of atoms

NEET Exam Tricks

• Always convert Å into metre before calculation.
• Remember: 1 Å = 10⁻¹⁰ m.
• Atomic volume depends on the cube of radius (r³).
• A small change in atomic radius causes a large change in volume.
• For one mole atoms multiply atomic volume by Avogadro number.

Final Result

Atomic volume of one mole of hydrogen atoms:

3.15 × 10⁻⁷ m³