Subatomic Particles and Atomic Mass Calculations

Atoms and Elements

Subatomic Particles

Atoms are composed of three fundamental subatomic particles: protons, neutrons, and electrons. These particles differ in mass and charge, and their arrangement determines the properties of each element.

• Proton: Positively charged particle found in the nucleus of an atom.

• Neutron: Neutral particle also located in the nucleus.

• Electron: Negatively charged particle found outside the nucleus in electron clouds.

The atomic mass unit (amu) is a standard unit used to express the masses of subatomic particles. It is defined as one-twelfth the mass of a carbon-12 atom.

• 1 amu = 1.66 × 10-24 g

Table: Properties of Subatomic Particles

Particle	Actual Mass (kg)	Relative Mass (amu)	Relative Charge	Charge (Coulombs)
Proton	1.67262 × 10-27	1.0073	+1	+1.602 × 10-19
Neutron	1.67493 × 10-27	1.0087	0	0
Electron	0.00091 × 10-27	0.00055	-1	-1.602 × 10-19

Atomic Mass Calculations

The atomic mass of an element is the weighted average mass of its atoms, measured in amu. It is used to calculate the number of atoms in a given sample.

• Formula to calculate number of atoms:

$\text{Number of atoms} = \frac{\text{Sample mass (g)}}{\text{Atomic mass (g/atom)}}$

Example Calculation

Example: Osmium, one of the densest elements, has an atomic mass of 190.23 grams. To find the number of atoms in 1.00 g of osmium:

• Atomic mass of osmium = 190.23 g/mol

• Number of atoms in 1.00 g = $\frac{1.00\ \text{g}}{1.67262 \times 10^{-24}\ \text{g/atom}} = 5.98 \times 10^{21}$ atoms

Practice Problems

• Practice 1: How many atoms are required to have a combined mass of 1.9405 × 10-19 kg?

• Solution: $\frac{1.9405 \times 10^{-19}\ \text{kg}}{1.67262 \times 10^{-27}\ \text{kg/atom}} = 1.16 \times 10^{8}$ atoms$

• Practice 2: How many atoms are contained in 0.250 g of sodium (Na)? The mass of one sodium atom is 3.82 × 10-23 g.

• Solution: $\frac{0.250\ \text{g}}{3.82 \times 10^{-23}\ \text{g/atom}} = 6.54 \times 10^{21}$ atoms$

Additional info: The atomic mass unit (amu) is a fundamental concept in chemistry, allowing for the comparison of masses of atoms and subatomic particles. Understanding the properties and calculations involving subatomic particles is essential for mastering atomic structure and chemical reactions.