Unit 4: Chemistry

• Elements are arranged as -

  Vertical rows are groups

  Horizontal rows are periods
• Metelloids

  Boron [B], Silicon [Si], Antimony [Sb], Tellurium [Te], Germanium [Ge], Arsenic [As], Astatine [At]
• Valence Electrons - the number of valence electrons corresponds with the group number
• Reactivity -

  ● Metals: Increase from top to bottom [group]. Decrease from left to right [period]

  ● Non-metals: Increase from bottom to top [group]. Decrease from left to right [period]
• Metals boiling point depends on -

  ○ Number of demoralized electrons

  ○ size of atoms or positive metal residues.
• Delocalised electrons

  Not bound by an orbital
• Halides - contain seven valence electrons [Group 17]
• Atomic radius - The distance from the nucleus to the outermost energy level
• Atomic radius -

  ° decreases from left to right [periods]

  ° decreases from top to bottom [groups]
• Ionization energy 


  Energy needed per Mol to remove an electron from an atom in the gaseous state
• First ionization energy 


  Energy needed per Mol to remove the first electron from an atomic in the gaseous state
• What influences ionization energy-

  ● Position: the greater the atomic no. the greater the no. of protons [stronger attraction between the nucleus and electrons]

  ● Valence electrons: first ionization is low if there are a few valence electrons or they are unpaired

  ● Atomic radius: the further the valence electrons from the nucleus the less energy needed to remove them.
• Electron affinity 


  The amount of energy released when a neutral atom accepts an electron to form a negative electron
• Electronegativity

  The tendency of an atom in a molecule to attract bonding electrons
• Non polar covalent - < 0,4

  Polar covalent - between 0,4 and 2,1

  Ionic - >2,1