must knows ions atoms compounds

chapter 2.1 - 2.3 OCR A

  • electrons only change in ions NOT protons

  • Ar = (mass x % abundance) + (mass x % abundance) etc / 100 (total abundance)

- total abundance must add up to 100%

- mass number is found on periodic table

  • (aq) → split into ions

  • (s), (l), (g) → dont split

  • moles = volume (g) / 24

  • moles = volume x concentration

  • moles = mass / Ar (triangle)

  • Relative Isotopic Mass (RIM)
    👉 The mass of one atom of a particular isotope compared with 1/12 of the mass of a carbon-12 atom.

  • Relative Atomic Mass (Ar / RAM)
    👉 The weighted mean mass of an atom of an element compared with 1/12 of the mass of a carbon-12 atom.
    (Takes into account all isotopes + their abundances.)

  • Relative Molecular Mass (Mr / MAM)
    👉 The weighted mean mass of a molecule compared with 1/12 of the mass of a carbon-12 atom.
    (For giant structures like NaCl, we often use “relative formula mass.”)

Always soluble (never form a precipitate):

  • All Group 1 (alkali metal) salts: Na*, K*, Lit, etc.

  • Ammonium salts (NHa*)

  • Nitrates (NO3*)

  • Ethanoates (CH.C00-)

Usually soluble:

  • Chlorides, bromides, iodides (Cl, Br, F)

  • X Except with Ag*, Pb2+

+, Hg22+ → insoluble

• Sulfates (SO,?-)

X Except with Ba?+

+, Pb2+,

, Ca? (sparingly), Sr2+

Usually insoluble:

  • Carbonates (CO?*), hydroxides (OH), sulfides (S2-), oxides (02-)
    Except when paired with Group 1 or NHa* (then
    soluble)

  • Some hydroxides of Group 2 (like Ca(OH)2) are slightly soluble