atom structure

• Atom


  Mainly made up of protons and neutrons in the nucleus, with electrons orbiting in shells
• Protons


  • Positive charge
• Neutrons


  • Zero charge
• Electrons


  • Negative charge, very small relative mass
• Mass number


  Number of protons and neutrons in the nucleus
• Atomic number


  Number of protons in the nucleus
• Atoms are neutral because the number of protons equals the number of electrons
• Ion


  Has a different number of electrons and protons, forming a stable charge
• Isotopes


  Elements with the same number of protons but different numbers of neutrons
• Isotopes of carbon

  • Carbon- 12
  • Carbon- 13
  • Carbon- 14
• History of atomic models

  1. Dalton's atomic model

  2. Thomson's plum pudding model

  3. Rutherford's nuclear model

  4. Bohr's shell model
• Time-of-flight mass spectrometer


  Vaporizes and ionizes sample, accelerates ions, ions drift at constant speed, ions detected based on mass-to-charge ratio
• Relative molecular mass


  Average mass of an atom of an element over 1/12 of the mass of the atom C^12
• Relative isotopic mass


  Mass of an isotope of an element, measured relative to carbon-12
• Mass spectrum


  Shows the relative abundance of isotopes of an element based on their mass-to-charge ratio
• Isotope


  Atoms of the same element with the same number of protons but different numbers of neutrons
• Mass spectrometer analysis of isotopes

  • Provides information about the mass-to-charge ratio of the isotopes
  • Provides information about the abundance of the isotopes
• Calculating relative atomic mass from isotope data

  1. Multiply abundance of isotope A by mass-to-charge ratio of A

  2. Multiply abundance of isotope B by mass-to-charge ratio of B

  3. Add the results

  4. Divide by total abundance
• Molecular ion peak


  The peak on a mass spectrum that corresponds to the unfragmented molecular ion
• Electron subshells


  • s
  • p
  • d
  • f
• Electron configuration


  • Electrons are filled in order of increasing energy level
  • Electrons fill orbitals singly first before pairing up
• Determining electron configuration of an atom

  1. Write the configuration as 1s2 2s2 2p6 3s2 3p6 3d6 4s2

  2. Fill the orbitals in order of increasing energy

  3. Singly occupy orbitals before pairing up
• Determining electron configuration of an ion

  1. Remove electrons from the highest energy level first

  2. Transition metals may have electrons move from 4s to 3d to create a more stable configuration
• Ionization energy


  The minimum energy required to remove one mole of electrons from one mole of atoms in the gaseous state
• Removing electrons from an ion

  1. Remove electrons from 4s first

  2. Then remove from 3D

  3. Check the numbers to ensure it adds up correctly
• Ionization energy


  The minimum amount of energy required to remove one mole of electrons from one mole of atoms in the gaseous state
• Ionization energy is always endothermic and has a positive value
• Shielding


  • The more shells or electron shells between the positive nucleus and the outer electron, the less energy is required and the weaker the attraction is
• Atomic size


  • The bigger the atom, the further away the electrons are from the nucleus, the weaker the attractive force, and the less energy is required to remove the outer electron
• Nuclear charge


  • The more protons in the nucleus, the bigger the attraction between the nucleus and the outer electron, and the more energy is required to remove the electron
• Successive ionization energy


  The removal of more than one electron from the same atom
• There are distinctive jumps in successive ionization energies as electrons are removed from shells increasingly closer to the nucleus
• As you go down a group (group 2)


  The first ionization energy decreases
• Reasons for decrease in first ionization energy down a group


  • Atomic radius increases
  • Shielding increases
• As you go across a period


  The first ionization energy generally increases
• Reasons for increase in first ionization energy across a period


  • Nuclear charge increases
  • Shielding is similar
• Exception at sulfur


  Evidence for electron repulsion, the energy required to remove an electron from sulfur is less due to repulsion between the paired electrons in the 3p orbital