module 2

• isotopes = atoms of the same element with different numbers of neutrons
• isotopes have the same chemical properties because the have the same number of electrons in the outer shell and the same electron configuration
• relative isotopic mass = mass of the isotope compared to 1/12th of the mass of an atom of carbon 12
• graphite is in a giant covalent lattice in layers and it is a good conductor because it has delocalized electrons that are free to move and It has a high boiling point because strong covalent bonds have to be broken, also it is soft because there are weak londons forces between the layers which slide over each other
• covalent bond = shared pair of electrons
• ammonia has a pyramidal shape and a bond angle of 107 because there are 3 bonded pairs and 1 lone pair and lone pairs repel more than bonded pairs
• dot and cross diagram of NH4+

  
• NH4+ has a tetrahedral shape and an angle of 109.5
• compounds can conduct electricity when dissolved in water or in liquid state because ions and electrons cannot move in a solid but are mobile in solution and can therefore carry electrical charge
• salt = when the H+ in an acid is replaced by a metal ion
• adding aqueous silver nitrate to halogens:

  1. chlorine = white ppt
  2. bromine = cream ppt
  3. iodine = yellow ppt
• equation for halogen + aqueous silver nitrate:

  Ag+ (aq) + X- (aq) -> AgX (s)
• benefits of adding chlorine to water:

  1. removes or kills bacteria
  2. kills germs / microorganisms
  3. makes it safe to drink
  4. sterilises water
• disadvantages of adding chlorine to water:

  1. it is a naturally toxic element
  2. poisonous
  3. could form chlorinated hydrocarbons
  4. forms carcinogens or toxins
• disproportionation reaction = when an element has been both oxidised and reduced in the same reaction and its oxidation state has increased and decreased
• the number in brackets in roman numerals e.g chloric (V) acid stands for the oxidation number/state of chlorine
• across a period, e.g from Na to Mg in period 3, the charge increases so the more to the right the element is, the more outer electrons it has and it has a greater attraction between ions and electrons with stronger metallic bonds
• reactivity of group 2 elements with water down the group increases because reactivity decreases down the group and atomic radii and shell number increases, so there is more shielding and nuclear attraction decreases, which outweighs nuclear charge so it is easier to remove outer electrons to form a positive ion and ionisation energy decreases
• relative atomic mass = weighted mean mass of an atom compared to 1/12th of the mass of an atom of carbon 12
• when magnesium reacts with sulfuric acid the mg dissolves and it fizzes/effervesces and gas is produced
• metallic bonding is the electrostatic attraction between the electrons and the positive ions

  
• ionic bond = electrostatic attraction between oppositely charged ions
• calcium oxide reacting with water = Ca(OH)2
• calcium oxdie reacts with nitric acid = Ca(NO3)2
• first ionisation energy = energy requires to remove one electron from each atom in one mole of gaseous atoms
• first ionisation energy increases across a period because outer electrons are closer to the nucleus and the radii decreases, so nuclear charge and proton number increase, and shielding stays the same
• first ionisation energy equation:

  X -> X+ + e-
• second ionisation energy equation:

  X+ -> X2+ + e-
• second ionisation energy = energy requires to remove one electron from each ion in one mole of gaseous 1+ ions of an element to form one mole of gaseous 2+ ions
• atomic number = number of protons in the nucleus
• hydrogen bonding diagram:

  
• boiling point increases down the halogens (group 7) because the number of electrons increase and van der Waals forces become stronger so more energy is needed to break them
• hydroxide ion in an alkali acts as a base and neutralises an acid because the H+ ion in the acid has been replaced by a metal ion
• .xH2O part of a formula shows the number of waters of crystallisation
• hydrogen bonding diagram of ammonia: NH3

  
• electronegativity = the attraction of an atom for the shared pair of electrons in a covalent bond
• ionic compounds are formed when metals react with non-metals, they have high melting points and boiling points due to strong electrostatic attractions between oppositely charged ions.
• covalent bonds form between non-metal atoms, they can be polar or nonpolar depending on whether there is unequal sharing of electrons
• the larger the difference in electronegativities, the greater the polarity of the bond
• molecules that contain polar bonds but cancel out their effects so that there is no overall charge separation are called nonpolar