Subatomic Particles, Charge, and Mass

Composition of Matter

• Everything in the world is made up of atoms.

• Examples: air, water, cell phones.

  • Atoms combine to form molecules and compounds, which create the variety of materials around us.

What are Atoms?

• Atoms are tiny particles.

  • The size of an atom is on the order of angstroms (1 Å = 10^{-10} m).

• Atoms are basic units of matter.

  • They are the smallest units that retain the chemical properties of an element.

• Atoms can be considered building blocks.

  • They join together to form more complex structures.

• Atoms themselves are made of smaller subatomic particles.

  • Protons

  • Neutrons

  • Electrons

  • These particles determine the atom's charge and mass.

Structure of an Atom

• Nucleus:

  • Located at the center of the atom.

  • The nucleus is dense and positively charged due to the presence of protons.

  • Composed of protons and neutrons.

  • Protons contribute to the positive charge, while neutrons are neutral.

• Electron Cloud:

  • Located outside the nucleus.

  • Region where electrons are most likely to be found.

  • Electrons exist in specific energy levels or shells within the electron cloud.

  • The electron cloud is much larger than the nucleus (100,000 times larger).

  • The electron cloud makes up most of the atom's volume.

Properties of Subatomic Particles

• Charge:

  • Protons: Positive charge (+1).

  • Electrons: Negative charge (-1).

  • Charges are equal and opposite; they cancel each other when paired.

    • This balance of charges results in a neutral atom.

  • Neutrons: No charge (neutral).

• Mass:

  • Unit of mass: unified atomic mass unit (u).

  • Protons: Mass of approximately 1 u.

  • Neutrons: Mass of approximately 1 u.

  • Electrons: Mass of approximately 0.0005 u.

  • Electrons are roughly 2,000 times smaller than protons or neutrons.

  • Mass{electron} ≈ \frac{1}{2000} \times Mass{proton/neutron}

• Mass Distribution:

  • Nearly all the mass of an atom resides in the nucleus.

  • The electron cloud contributes very little to the atom's mass.

Atoms and the World

• Atoms make up everything.

  • All matter, whether solid, liquid, or gas, is composed of atoms.

• Different materials (air, water, cell phones) are made of the same subatomic particles (protons, neutrons, and electrons).

  • The arrangement and number of these particles determine the properties of the material.