chap. 8 atoms, ions & isotopes

• An atom is the smallest particle of a chemical element that can exist
• The nucleus of an atom consists of protons and neutrons, collectively known as nucleons, which account for its mass
• Proton (p):

  • Symbol: p
  • Location: nucleus
  • Relative mass: 1
  • Relative charge: +1
• Neutron (n):

  • Symbol: n
  • Location: nucleus
  • Relative mass: 1
  • Relative charge: 0 (neutral)
• Electron (e):

  • Symbol: e
  • Location: in electron shells around nucleus
  • Relative mass: 1/1840 (negligible)
  • Relative charge: -1
• The proton (atomic) number of an element is the number of protons in its atoms, which is equal to the number of electrons
• The atomic mass/nucleon number of an element is the number of protons and neutrons in its atoms
• Isotopes are atoms of the same element with the same number of protons but different numbers of neutrons. Isotopes have the same chemical properties but slightly different physical properties
• Electronic configuration is the way electrons are arranged in an atom. Electrons are arranged around a nucleus in shells, with a maximum number of electrons each shell can accommodate:

  • Shell 1 (innermost): 2
  • Shell 2: 8
  • Shell 3: 8
• The outermost shell in an atom that is partially or completely filled is known as the valence shell. The electrons in the outermost shell are known as valence electrons. Elements with the same number of valence electrons have similar chemical properties
• Ions are charged particles formed by atoms gaining or losing electrons to obtain the electronic structure of a noble gas (inert gas).

  • Positive ions (cations) are formed when atoms lose electrons
  • Negative ions (anions) are formed when atoms gain electrons
• Metals with 1, 2, or 3 valence electrons will form cations with charges 1+, 2+, and 3+ respectively

  • Non-metals with 5, 6, or 7 valence electrons will form anions with charges -3, -2, and -1 respectively
• Elements in group 18 or the rightmost column have completely filled electron shells and will not form ions
• Atom of element = each element separate like perfectly fried rice

  Molecule of compound = e.g., water (H2O)

  Molecule of element = atoms of the same element chemically bonded together, e.g., N2 (nitrogen)