Review of Atoms in Chemistry

Structure of the Atom

• Nucleus: Center of the atom containing protons and neutrons.
  • Protons:
    • Positively charged (+1)
    • Relative mass of 1
  • Neutrons:
    • Neutral charge
    • Relative mass of 1
• Electrons:
  • Orbit the nucleus in shells.
  • Negatively charged (-1)
  • Approximately 2000 times smaller than protons/neutrons.

Periodic Table and Element Information

• Nucleus Symbol: Represents an element.
  • Example: Li for Lithium
• Atomic Number (Bottom Left):
  • Number of protons in the atom.
  • Determines the element.
• Mass Number (Top Left):
  • Total number of protons and neutrons.
  • Example for Lithium: Mass number is 7 (3 protons + 4 neutrons).
• Electrons:
  • Number of electrons equals the number of protons.
  • Example: Lithium has 3 electrons.

Isotopes

• Atoms with the same number of protons but different numbers of neutrons.
• Different mass numbers.
• Examples of Lithium Isotopes:
  • Lithium-7: 3 protons, 4 neutrons
  • Lithium-6: 3 protons, 3 neutrons
  • Lithium-8: 3 protons, 5 neutrons
• Stability:
  • Typically, only 1 or 2 isotopes are stable.
  • Unstable isotopes decay into other elements, emitting alpha, beta, or gamma radiation (radioactive decay).

Electron Energy Levels

• Electrons are arranged in energy levels or shells.
• Shells are progressively further from the nucleus and higher in energy.
• Electrons can jump to a higher shell if they gain energy (excitation).
• Energy gained usually from electromagnetic radiation.
• Excited electrons fall back to their original shell, re-emitting energy as radiation.

Ionization

• Occurs when an electron absorbs enough energy to leave the atom.
• Leaves the atom positively charged (more protons than electrons), forming a positive ion.
• Ionizing Radiation: Radiation capable of knocking electrons off atoms, thus ionizing them.