Salts, their names and formulas

• Scheikunde
• Middelbare school
• vwo
• Leerjaar 4

Salts: names and formulas

How are salts made? What is their structure?

 ionic species

How to name and formulate salts?

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"

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...

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)

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

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")

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!

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*)

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