Subatomic Particles and Atomic Mass Units in GOB Chemistry

Subatomic Particles

Overview of Subatomic Particles

Atoms are composed of three main subatomic particles: neutrons, protons, and electrons. These particles differ in mass and charge, and their properties are fundamental to understanding atomic structure in chemistry.

• Neutron: A neutral particle found in the nucleus of an atom.

• Proton: A positively charged particle also located in the nucleus.

• Electron: A negatively charged particle found outside the nucleus.

Comparison Table: Subatomic Particles

The following table summarizes the key properties of the three subatomic particles:

Subatomic Particle	Actual Mass (kg)	Relative Mass (amu)	Relative Charge
Neutron	1.67493 × 10-27	1.000 866	0
Proton	1.67262 × 10-27	1.000 727	+1
Electron	0.00091 × 10-27	0.000 555	-1

Atomic Mass Unit (AMU)

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

• Definition: 1 AMU = $1.66 \times 10^{-27}$ kg

• Application: Used to compare the masses of atoms and subatomic particles.

Example: The mass of a proton is approximately 1 AMU.

Calculations Using Atomic Mass Units

Example Problem: Converting Grams to Atomic Mass Units

To convert a mass in grams to atomic mass units (AMU), use the following formula:

• $\text{Number of AMU} = \frac{\text{mass in grams}}{1.66 \times 10^{-24} \text{ g/AMU}}$

Example: Osmium has a mass of 190.23 grams. What is its value in terms of atomic mass units?

• Calculation: $\frac{190.23}{1.66 \times 10^{-24}} = 1.15 \times 10^{26}$ AMU

Practice Problems

• Practice 1: How many electrons are needed to have a combined mass of $1.0465 \times 10^{-25}$ kg?

  • Solution: $\frac{1.0465 \times 10^{-25}}{9.11 \times 10^{-31}} = 1.15 \times 10^{5}$ electrons

  • Answer: $1.15 \times 10^{5}$ electrons

• Practice 2: How many atoms are contained in 0.239 g of sodium (Na)? The mass of one sodium atom is 23.99 amu.

  • Convert amu to grams: $23.99 \text{ amu} \times 1.66 \times 10^{-24} \text{ g/amu} = 3.98 \times 10^{-23}$ g/atom

  • Number of atoms: $\frac{0.239}{3.98 \times 10^{-23}} = 6.01 \times 10^{21}$ atoms

  • Answer: $7.197 \times 10^{21}$ atoms (as per provided answer)

Key Terms and Concepts

• Atomic Mass Unit (AMU): A unit of mass used to express atomic and molecular weights.

• Relative Mass: The mass of a particle compared to the mass of a carbon-12 atom.

• Relative Charge: The charge of a particle compared to the charge of a proton.

Summary Table: Subatomic Particle Properties

Particle	Location	Mass (kg)	Charge
Proton	Nucleus	$1.67262 \times 10^{-27}$	+1
Neutron	Nucleus	$1.67493 \times 10^{-27}$	0
Electron	Outside Nucleus	$9.11 \times 10^{-31}$	-1

Additional info: The notes and questions focus on the basic properties and calculations involving subatomic particles and atomic mass units, which are foundational topics in GOB Chemistry.