Atoms and Radioactivity: Structure, Properties, and Applications

Atoms and Their Components

Subatomic Particles

Atoms are the fundamental building blocks of matter, composed of smaller particles known as subatomic particles. The three primary subatomic particles are the proton, neutron, and electron.

• Protons have a positive (+) charge.

• Electrons have a negative (−) charge.

• Neutrons are neutral (no charge).

• In a neutral atom, the number of protons equals the number of electrons, resulting in no overall charge.

Structure of an Atom

The internal structure of an atom consists of a dense central nucleus containing protons and neutrons, surrounded by a region called the electron cloud where electrons move rapidly.

• Nucleus: Contains protons and neutrons; accounts for most of the atom's mass.

• Electron cloud: The space around the nucleus where electrons are likely to be found; mostly empty space.

• Electrons are constantly moving, making their exact location difficult to determine.

Relative Mass and Location of Subatomic Particles

Although atoms and their subatomic particles are extremely small, they are still considered matter. The mass of an atom is concentrated in its nucleus.

Subatomic Particle	Symbol	Charge	Relative Mass	Location in Atom
Electron	e−	1−	0.0005 (1/2000)	Outside the nucleus
Proton	p	1+	1	Nucleus
Neutron	n	0	1	Nucleus

• The mass of an electron is about 2000 times less than that of a proton or neutron.

• For most calculations, the electron's mass is considered negligible.

Atomic Mass Unit (amu)

The atomic mass unit (amu) is a standard unit used to express atomic and molecular masses.

• 1 amu is defined as one-twelfth the mass of a carbon-12 atom (which has 6 protons and 6 neutrons).

• Protons and neutrons each have a mass of approximately 1 amu.

• Electrons are considered to have a mass of 0 amu for most practical purposes.

Visual Representation of Atomic Structure

Atoms can be visualized as a dense nucleus (containing protons and neutrons) surrounded by a diffuse electron cloud. For example, a lithium atom consists of a nucleus with protons and neutrons, and electrons distributed in the surrounding space.

• Example: Lithium metal is composed of many lithium atoms, each with a nucleus and an electron cloud.

Additional info: The above content is foundational for understanding atomic structure, which is essential for topics such as isotopes, radioactivity, and nuclear chemistry.