Atoms and Radioactivity: Structure, Properties, and Applications

Atoms and Their Components

Subatomic Particles

Atoms are the fundamental units of matter, composed of three basic subatomic particles: protons, neutrons, and electrons. These particles organize to form all atoms and determine their chemical properties.

• Protons: Positively charged particles located in the nucleus.

• Neutrons: Neutral particles (no charge) also found in the nucleus.

• Electrons: Negatively charged particles found outside the nucleus in the electron cloud.

• Atoms are electrically neutral because the number of protons equals the number of electrons.

Structure of an Atom

The structure of an atom consists of a dense nucleus containing protons and neutrons, surrounded by a region called the electron cloud where electrons are found. Most of the atom's volume is empty space.

• Nucleus: Central part of the atom containing protons and neutrons.

• Electron Cloud: Region around the nucleus where electrons move rapidly and are difficult to pinpoint.

• Most of the atom's mass is concentrated in the nucleus.

Relative Mass and Charge of Subatomic Particles

Although atoms and subatomic particles are extremely small, they are classified as matter. The mass of an electron is about 2000 times less than that of a proton or neutron, so its contribution to atomic mass is negligible.

Subatomic Particle	Symbol	Electrical Charge	Relative Mass	Location in Atom
Electron	e-	1-	0.0005 (1/2000)	Outside nucleus
Proton	p or p+	1+	1	Nucleus
Neutron	n or n0	0	1	Nucleus

Atomic Mass Unit (amu)

The atomic mass unit (amu) is a standard unit used to express atomic and molecular weights. One amu is defined as one-twelfth the mass of a carbon-12 atom (which contains 6 protons and 6 neutrons).

• Proton and neutron each have a mass of approximately 1 amu.

• Electron's mass is so small it is considered 0 amu for most calculations.

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, lithium atoms in lithium metal are composed of a nucleus with protons and neutrons, and electrons occupying the surrounding space.

• Proton: Red sphere in diagrams

• Neutron: Blue sphere in diagrams

• Electron: Small gray sphere in diagrams

Additional info: The electron cloud model reflects the quantum mechanical nature of electrons, which do not follow fixed orbits but exist in regions of probability.