Atoms, Elements and Compounds

• What is a nuclear symbol used for?

  To describe atoms
• What does the mass number represent in an atom?

  Total number of protons and neutrons
• What is the atomic number of an atom?

  Number of protons in an atom
• What defines an element?

  Atoms with the same atomic number
• What are isotopes?

  Atoms with the same protons, different neutrons
• How is relative atomic mass (A_r) calculated?

  A_r = sum of (isotope abundance × isotope mass number) / total abundance
• What is a compound?

  Substance formed from two or more elements
• What happens in a chemical reaction involving compounds?

  At least one new substance is made
• What can usually be measured in a chemical reaction?

  An energy change
• What is a molecule?

  Particle containing two or more non-metal atoms
• What is a diatomic molecule?

  Molecule with only one type of atom
• What are the key characteristics of compounds?

  • Formed from two or more elements
  • Chemically bonded together
  • Fixed proportions
• What are the key characteristics of isotopes?

  • Same number of protons
  • Different numbers of neutrons
  • Different mass numbers
• What is the significance of relative atomic mass (A_r)?

  • Represents average mass of an element
  • Takes into account isotope abundance
• What is the relationship between atoms, elements, and compounds?

  • Atoms make up elements
  • Elements combine to form compounds