chem (miss bahia)

• covalent bonding

  the electrostatic force of attraction between a shared pair of electrons and the nuclei of the bonded atoms
• dative covalent bond (coodinate bond)

  both the electrons in the shared pair come from one of the bonding atom
• ionic bonding

  the electrostatic force of attraction between oppositely charged ions in all directions
• metallic bonding

  the electrostatic force of attraction between metal cations and the sea of delocalised electrons
• periodicity

  repeating trend in properties of elements across each period
• first ionisation energy


  the energy required to remove 1 electron from each atom in 1 mole of gaseous atoms to form 1 mole of gaseous 1+ ions
• first ionisation formula


  O(g) --> O+(g) + e-
• second ionisation formula


  O+(g) --> O2+(g) + e-
• third ionisation formula


  O2+(g) --> O3+(g) + e-
• oxidising agent

  causes another species to lose electrons
• ionisation energy (down group)

  • atomic radius increases
  • shielding increases
  • which outweighs the increase in nuclear charge
  • weaker nuclear attraction

  I.E DECREASES
• ionisation energy (across period)

  • atomic radius decreases
  • nuclear charge increases
  • shielding stays the same
  • stronger nuclear attraction

  I.E INCREASES
• ionisation energy deviations

  • Mg and Al

  Mg e- = 3s subshell

  Al e- = 3p subshell

  3p is a higher energy subshell

  • P and S

  S= e- in 3p subshell are paired

  electrons repel

  easier to lose an electron
• electronegativity

  the ability of an atom to attract a shared pair of electrons in a covalent bond closer to itself
• electronegativity (down a group)

  • atomic radius increases
  • electron shielding increases
  • less nuclear attraction between the nuclear and shared pair of electrons

  ELECTRONEGATIVITY DECREASES
• electronegativity (across a period)

  • atomic radius decreases
  • electron shielding stays the same
  • nuclear charge increases
  • greater nuclear attraction between nucleus and shared pair of electrons

  ELECTRONEGATIVITY INCREASES
• water anomalies

  • ice is less dense than water

  H bonds keep the molecules at a fixed position further apart

  • higher bp

  stronger H bonds, more energy required
• disproportionation

  same species (element) is both oxidised and reduced
• disproportionation reaction example

  Cl2 (aq) + H2O (l) --> HClO (aq) + HCl

  chlorine is used as a disinfectant for drinking water
• disproportionation reaction example

  chlorine reacting with cold, dilute aqueous sodium hydroxide:

  Cl2 (aq) + 2NaOH (aq) --> NaClO (aq) + NaCl (aq) + H2O (l)

  
  

  NaClO= in household bleach
• risks of chlorine use

  • toxic gas
  • respiratory irratant in small concentrations
• test for carbonates

  • add an acid (HNO3)
  • fizz- releases CO2
• test for sulfate

  • add HNO3
  • add BaNO3
  • white precipitate (insoluble solid)
• test for halides

  • HNO3 followed by silver nitrate
  • if turns white (Cl-), cream (Br-), yellow (I-) precipitate
• ammonium test

  • add NaOH (aq)
  • place in a warm beaker
  • use PH indicator paper
  • turns blue
• carbonate test (formula)

  CO3^2- (aq) + 2H+ --> CO2 (g) + H2O (l)
• sulfate test (formula)

  Ba2+ (aq) + SO4^2 (aq) ---> BaSO4 (s)
• halide test (formula)

  white precipitate= Ag+ (aq) + Cl- (aq) --> AgCl (s)

  cream precipitate= Ag+ (aq) + Br- (aq) --> AgBr (s)

  yellow precipitate= Ag+ (aq) + I- (aq) --> AgI (s)
• orbital

  a region around the nucleus that can hold up to two electrons with opposite spins
• reducing agent

  causes another species to gain electrons
• group 2 mp

  • atomic radius increases
  • attraction between cations and delocalised electrons decreases
  • less energy needed to overcome

  MELTING POINT DECREASES
• group 2 (type of agent)

  reducing agents
• group 2 reactivity

  • increase atomic radius
  • increased shielding
  • weaker nuclear attraction
  • easier to remove electrons

  REACTIVITY INCREASES
• uses of group 2 compounds (in agriculture)

  lime Ca(OH)2 added to fields to neutralise the acid in the soil
• uses of group 2 compounds (in agriculture) FORMULA

  Ca(OH)2 (s) + 2H+ (aq) --> Ca2+ (aq) + 2H2O (l)
• uses of group 2 compounds (in medicine)

  magnesium hydroxide or calcium carbonate used in antacid medication to neutralise excess stomach acid
• uses of group 2 compounds (in medicine) FORMULA

  Mg(OH)2 (s) + 2HCl (aq) --> MgCl2 (aq) + 2H2O (l)

  (calcium carbonate just produces CO2 as well)
• group 7 mp

  • more electrons
  • greater london forces

  MELTING POINT INCREASES
• group 7 reactivity

  • increased atomic radius
  • increased shielding
  • harder to gain electrons

  REACTIVITY DECREASES
• fluorine

  pale yellow gas