1 definitions

• Atomic Number

  (atOm -> OM -> O -> PRO -> prOtOn) Number of protons in the nucleus of an atom
• Mass Number

  (mass -> weight -> whole body -> total#sum -> both the subatomic particles duh) Total number of protons and neutrons in the nucleus of an atom
• Nuclear charge

  Total charge of all the protons in the nucleus. It has the same value as the atomic number (coz protons duh). Increases as you go across the periodic table
• Isotopes

  Atoms of the same element with the same number of protons but different number of neutrons in the nucleus
• Relative Atomic Mass

  Average mass of an atom of an element, relative to 1/12 of the mass of an atom of carbon-12
• Relative Isotopic Mass

  Average mass of an atom of an isotope relative to 1/12 of the mass of an atom of carbon-12
• Relative Molecular Mass

  Average mass of a molecule relative to 1/12 of the mass of an atom of carbon-12
• Quantum shells


  Same as electron shells. They specify the energy level of an electron
• First Ionisation Energy


  The energy required to remove 1 mole of electrons from each atom in 1 moles of gaseous atoms to from 1 mole of gaseous 1+ ions. = X(g) → X+(g) + e-
• Second Ionisation Energy

  The energy required to remove 1 mole of electrons from each ion in 1 moles of gaseous 1+ ions to form 1 moles of gaseous 2+ ions. = X+(g) → X2+(g) + e-
• Periodicity

  Trends in element properties with increasing atomic number
• Hund's rule

  When electrons fill the orbitals, they occupy them singly before they pair up
• Orbital


  A region in an atom that can hold up to two electrons with opposite spins
• Pauli Exclusion Principle

  Electrons within the same orbital must have opposite spins
• Aufbau Principle

  As the atomic number increases, the electrons are added to the orbitals in order of increasing orbital energy until all electrons are accommodated. Exceptions: Cr, Cu
• Shielding

  A decrease in the nuclear charge experienced by an outer shell electron caused by electron-electron repulsion between the outer shell electron and electrons from adjacent quantum shells