1. Atoms and Ions: Protons, Neutrons, and Electrons

1. Atomic Structure

  • The Atom: Everything is made of tiny particles called atoms. They are so small that a single cell contains over 100 trillion of them.

  • The Nucleus: Located at the very center of the atom. It is a tight ball made of protons and neutrons. Even though it contains almost all the mass, it is 10,000 times smaller than the atom itself.

  • Electrons: These tiny particles orbit the nucleus in rings called shells.

  • Empty Space: Most of an atom is actually empty space between the nucleus and the orbiting electrons, similar to a solar system.

2. Subatomic Particles

  • Protons: Found in the nucleus. They have a relative mass of 1 and a positive charge of +1. (Memory tip: Proton = Positive).

  • Neutrons: Found in the nucleus. They have a relative mass of 1 and no charge (they are neutral). (Memory tip: Neutron = Neutral).

  • Electrons: Found in the shells. They are much smaller, with a relative mass of 1/2000 (often written as "very small" or 0). They have a negative charge of -1.

3. Atoms vs. Ions

  • Neutral Atoms: In a standard atom, the number of protons always equals the number of electrons. Because the positive and negative charges balance out, the atom has no overall charge.

  • Ions: An ion is an atom that has gained or lost electrons, causing the charges to become unbalanced.

    • Negative Ions: Formed when an atom gains electrons. If it gains one extra electron, it becomes a 1- ion.

    • Positive Ions: Formed when an atom loses electrons. If it loses one electron, leaving more positive protons behind, it becomes a 1+ ion.

4. Nuclear Symbols and Calculations

The periodic table uses "nuclear symbols" to provide information about each element:

  • Atomic Number (Bottom Left): This tells you the number of protons. This number defines the element; if the number of protons changes, it becomes a different element.

  • Mass Number (Top Left): This is the total number of protons and neutrons added together.

  • Calculating Neutrons: To find the number of neutrons, subtract the Atomic Number from the Mass Number.

    • Example (Lithium): Mass Number 7, Atomic Number 3. (7 - 3 = 4 neutrons).

    • Example (Oxygen): Mass Number 16, Atomic Number 8. (16 - 8 = 8 neutrons).