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Chapter 7 and 8
7.3
So what do you call these compounds?
Binary ionic compounds are named according to the elements they are composed of: positive ion first, negative ion second.
The positive ions use the same name as the neutral atom; the negative ions have an –ide ending. Polyatomic ions just use their name.
NaCl (sodium, chlorine) sodium chloride
K2O (potassium, oxygen) potassium oxide
Ca3(PO4)2 (calcium, phosphate) calcium phosphate
LiH (lithium, hydrogen) Lithium hydride
Oxidation numbers are a way of tracking changes in the possession of electrons.
We’ll discuss them later in more detail. For now, just remember that for the Main Group ions, the oxidation number usually equals the ion charge.
Many atoms have more than one oxidation number.
Example: Iron can be Fe+2 or Fe+3.
Iron can form either FeCl2 or FeCl3 .
Fe Fe +2 +3
Cl Cl -1 -1
FeCl2 FeCl3
FeCl2 is called Iron (II) chloride
- the compound has the Fe2+ ion
FeCl3 is called Iron (III) chloride
- the compound has the Fe3+ ion
Caution!
Roman numerals are not used when the metal only has 1 oxidation number.
NaCl isn’t sodium (l) chloride because sodium only has one oxidation number.
Remind me to list the common ones for you; they can go on your new best friend.
If you don’t know the oxidation number for an element, you can usually figure it out.
Pb(SO4)2
Lead can be 2+ or 4+, which is it?
Pb(SO4)2
Look at any oxidation numbers/charges you do know.
SO4 -2 2-
2-
?
0
Pb ?
Since the two sulfates have a total charge of -4, and there is only 1 lead atom, it must be Pb4+.
Lead (lV) sulfate
SO4 -2
8.2
What do you think “hydrate” means?
Hydrates are compounds that have water molecules in their structure.
Hydrates are dry powders, not solutions.
The formula for a hydrate will indicate how many water molecules are included:
CaCl2 • 2H2O
This compound has 2 water molecules.
The • does not mean ‘multiply’. It just separates the compound from its water of hydration.
If the compound is in a form that does not contain the water molecules, the term anhydrous is used.
CaCl2 calcium chloride, anhydrous
CaCl2•2H20 calcium chloride dihydrate
Greek prefixes pg 248. These can go on your best friend.
8.2
Binary Acids are formed when hydrogen bonds with another nonmetal, usually a halogen.
For example:
HCl is hydrogen chloride gas.
When it is dissolved in water, it forms hydrochloric acid solution, HCl(aq)
Binary acids are named as follows:
The prefix ‘hydro’ is added (for the hydrogen) and nonmetal takes an -ic ending.
HCl hydrogen chloride
HCl(aq) hydrochloric acid
HF hydrogen fluoride
HF(aq) hydrofluoric acid
The little (aq) indicates an aqueous solution (dissolved in water)
Ternary or oxyacids contain a hydrogen, an oxygen and another nonmetal.
Often the oxygen and the other nonmetal are bonded as a polyatomic ion.
If the anion’s name ends in –ate, it changes to –ic + acid.
H2SO4 hydrogen sulfate
H2SO4(aq) sulfuric acid
There is no hydro prefix.
If the anion’s name ends in –ite, it changes to –ous + acid. H2SO3 hydrogen sulfite H2SO3(aq) sulfurous acid
There is no hydro prefix.
Pay attention to the relationship between the anion and the acid name for the ternary acids.
8.2
Most* covalently bonded compounds use Greek prefixes to indicate how many atoms are in the compound.
The least electronegative element is usually** stated first; the second element takes an –ide ending.
*If it’s H and a halogen, then the prefixes are usually omitted. **If it’s oxygen and a halogen, then the halogen comes first.
CO2 carbon dioxide
N2O5 dinitrogen pentoxide
S2I3 disulfur triiodide
Table 8-3 on page 248 in your book has the Greek prefixes. Figure 8.20 on page 265 has the electronegativity values. You may add both to your best friend.
CO carbon monoxide
Extra vowels are usually* omitted by dropping the “a” or “o” from
the prefix.
Mono is omitted unless needed for clarity. This is not monocarbon
*Don’t drop the “i” from di- and tri-.
The Greek prefixes are also used with the hydrates.
CaCl2•2H20 calcium chloride dihydrate
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