Salts, their names and formulas

Salts: names and formulas
How are salts made? What is their structure?
 ionic species
How to name and formulate salts?
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Slide 1: Tekstslide
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Salts: names and formulas
How are salts made? What is their structure?
 ionic species
How to name and formulate salts?

Slide 1 - Tekstslide

The making of a salt
  • Remember Bohr's atomic model?
  • Protons (+) and neutrons (0) in the core
  • Electrons(-) in shells (K, L, M...) around it
  • Outer shell is called "valence shell", electrons there are called "valence electrons" (sic!)
  • "Noble gas configuration": when an atom has a filled valence shell, like the noble gas atoms (PTE Group 18) have.
  • The fact that atoms in period 2 of the PTE need 8 electrons for this is often referred as the "octet rule"

Slide 2 - Tekstslide

How to make a salt
  • Na has 1 valence electron (M shell)
  • If it can rid itself of that electron, its L shell will become its valence shell, which will be full.
  • This means it prefers to be Na+ if it can find someone to take an electron from it.
  • Cl has 7 valence electrons.
  • If it can get an electron somewhere, its M shell will be filled.
  • This means it prefers to be Cl- if it can find someone to give it an electron.
Please, for goodness sake, do not try this at home...

Slide 3 - Tekstslide

How to make a salt
  • Positive and negative ions attract strongly at short distances,
    this is called the ionic bond
    (so, not a real "bond", just strong attraction at atomic distances)
  • Any compound consisting exclusively of both negative and positive ions, is called a salt 
  • In the solid state, ions are organized in an ionic grid, with like charges shielded by the unlike charges. This structure is called a crystal
  • Therefore: any pure salt in the solid state will make a crystal, whose structure is unique to its ionic composition (e.g. NaCl will differ from LiCl)

Slide 4 - Tekstslide

Ingredients (simple ions)
  • Monoatomic or "simple" ions consist of a single atomic species
  • Most can only have a single charge (+, 2+, 3+). Some ions have several options.
  • e.g.: K can only be K+ (the "potassium ion")
  • e.g.: Fe can be Fe2+ (the "iron(II) ion") or Fe3+ (the "iron(III) ion")
  • If an atom has options, indicate the charge with Roman numerals!
  • Binas 40

Slide 5 - Tekstslide

Ingredients (simple ions)
  • Negative simple ions do not have charge options (yay!)
  • Their names end in -ide
  • e.g. Cl (chlorine), Cl- (the "chloride ion")

Slide 6 - Tekstslide

Ingredients (complex ions)
  • Polyatomic or "complex" ions consist of multiple atomic species
  • These have special prefixes and suffixes like hypo-, per-,  -ite and -ate. There's a method to this, but it's... complicated. Just learn the names of the ions. Or find them in Binas tabel 66B.
  • One special thing to note: NH4+ 
    This means NH4NO3 is... a salt, despite not containing any metals! You need to be able recognize this in the formula!

Slide 7 - Tekstslide

Naming a salt
  • The systematic name of a salt  is
    "name of the + ion" + "name of the - ion" 
  • Be mindful of ionic charges!!
  • E.g.: FeCl3 is iron(III)chloride  (Fe can choose between 2+ and 3+)
  •           AlCl3 is aluminiumoxide (Al only has the 3+ option)
  • If a salt has a trivial name: Binas tabel 66A
  • e.g: fluorite ( = calciumfluoride)
    (which uses an -ite suffix, despite not being a polyatomic ion, *sigh*)

Slide 8 - Tekstslide

Chemical formulas of salts
  • A bulk salt must always be neutral (equal + and -)
  • Salt crystals are not made of "molecules", they are continuous successions of + and - ions. Therefore, they do not have "molecular" formulas, their chemical formulas are called "condensed" formulas, these only indicate the ratios of ions in the salts.
  • FeCl3 has 3 Cl- for every Fe3+ to make it neutrally charged
  • For polyatomic ions, if you need more than one to offset the other ion, they go inside of brackets: e.g. Al(NO3)3

Slide 9 - Tekstslide

Slide 10 - Tekstslide