Transcript Writing and Naming Binary Compounds
Writing and Naming Binary Compounds & Hydrates
You will need: A periodic table A list of common polyatomic ions Patience and understanding
Generic Chemical Formulas
MgCl
2
Chemical symbols Subscript
Binary Compounds
A chemical compound consisting of two parts, a CATION (+) and an ANION (-) Examples: 1. Two elements chemically bonded 2. An element and a polyatomic ion chemically bonded 3. Two polyatomic ions chemically bonded
Binary Compounds
Have two parts Left side is the cation Positively charged MgCl 2 Right side is the anion Negatively charged
Hydrates
A hydrate is a binary compound that has water attached to its ions and the water is a PART of the chemical formula.
Naming hydrates uses terms that indicate the number of water molecules.
1 2 3 4 5 6 7 8 9 10 mono di tri tetra penta hexa hepta octa nona deca
CaSO 4 • 2 H 2 O
Hydrates
Calcium sulfate dihydrate AlO 3 • 3 H 2 O Binary compound Aluminum oxide trihydrate CuSO 4 • 5 H 2 O Binary compound Copper (II) sulfate pentahydrate Binary compound
Writing Binary Formulas
6 Steps 1. Write chemical symbols for cation and anion 2. Add cation and anion oxidation numbers as superscripts 3. Check to see if oxidation numbers add to zero 4. If yes, leave as written 5. If no, make oxidation numbers subscripts 6. Check for lowest whole number ratio
1 Writing Binary Formulas
Write the formula for sodium chloride.
+
Na Cl
2 3
superscripts
4
Writing Binary Formulas
Write the formula for magnesium nitride
1 2 +2
Mg N
3 -3 2 3 4 5
Writing Binary Formulas
Write the formula for hydrogen carbonate
+
H CO
2 3 -2 1 2 3 4 5
Writing Binary Formulas
Write the formula for magnesium phosphate
1 2 +2
Mg PO
3 4 -3
)
2 3 4 5
Writing Binary Formulas
For transition metals the oxidation number is given in parentheses, In Roman numerals.
Write the formula for iron (III) oxide.
Fe
+3
O
-2
Fe
2
O
3
Writing Binary Formulas For hydrates, that is, binary compounds with water (hydrate) attached: nickel (II) sulfate hexahydrate a. Write the formula of the binary compound (first part) using rules 1-4:
NiSO 4
b. Insert a “raised dot” after the binary compound:
NiSO 4
●
c. Use name prefix to note the number of water molecules (hydrates): NiSO 4
● 6 H 2 O
Polyatomic Ions (learn these)
Table 4 Page 619
Name
Ammonium Acetate Chlorate Hydroxide Nitrate Carbonate Sulfate Phosphate
Formula
NH 4 + C 2 H 3 O 2 ClO 3 OH NO 3 CO 3 2 SO 4 2 PO 4 3-
More Polyatomic Ions (learn these, too)
Formula Name
Hydrogen carbonate (bicarbonate) Nitrite Permanganate Sulfite HCO 3 NO 2 MnO 4 SO 3 2-
A quick review of hydrates.
Naming Binary Formulas
Binary Compound = CATION + ANION First: Get a periodic table and table of common polyatomic ions Next: Determine the cation and anion in the compound Then: Note the cation and apply the 5 naming rules
IN ORDER
Naming Binary Formulas
5 Rules that begin with the location or kind of the CATION Rule 1. For elements in the first two columns of the periodic table Rule 2. For elements from group 3 up to the staircase Rule 3. For elements to the right (above) the staircase Rule 4. For CATIONS that are polyatomic ions Rule 5. For hydrates
Naming Binary Formulas – Rule 1 For cations (elements) in the first two columns of the periodic table: MgCl 2 LiOH a. Cation: Write the name of the element as the first part of the compound:
magnesium lithium
b. Anion: Write the name of the
element
with an
ide
ending: mag
nesium chloride
or
c. Anion: Write the name of the polyatomic ion:
lithium
hydroxide
Naming Binary Formulas – Rule 2 For cations (elements) from the third group of the periodic table up to the “staircase” FeCl 2 Cu 2 SO 4 a. Cation: Name of element with Roman Numeral to show oxidation number:
iron (II) copper (I)
b. Anion: Name the
element
with an
ide
ending: iron (II)
chloride c. Anion: Name the polyatomic ion:
or
Exceptions to rule: Ag +1 Zn +2 Cd +2 Al +3 (Use Rule 1)
copper (I)
sulfate
Naming Binary Formulas – Rule 3 For cations (elements) to the right (above) the “staircase” CO 2 CO N 4 S 3 a.
Count the “number” of each element. (C-1, O-2 C-1, O-1 N-4, S-3) b. Use prefixes (mono, di, tri, tetra, penta, hexa, hepta, octa, nona, deca) to indicate the
number
of each atom present.
b.
Do not use “mono” if there is only one of the first element in the compound.
c.
CO 2 N 4 S 3 CARBON DI CO TETRA NITROGEN TRI SULFIDE CARBON MON OXIDE
Naming Binary Formulas – Rule 4 For cations that are polyatomic ions: NH 4 Cl NH 4 OH a. Cation: Name the polyatomic ion:
ammonium ammonium
b. Anion: Name the
element
with an
ide
ending: ammonium
chloride
or
c. Anion: Name the polyatomic ion:
ammonium
hydroxide
Naming Binary Formulas – Rule 5 For hydrates, that is, binary compounds with water (hydrate) attached: NiSO 4 ● 6 H 2 O a. Name of the binary compound (first part) using rules 1-4:
nickel (II) sulfate b. Note the number of water molecules (hydrates) by using prefixes: nickel (II) sulfate
hexahydrate
Rest stop!
Inhale and breathe easy!
The next group of slides goes into some detail about oxidation numbers in covalent compounds and in polyatomic ions. For this presentation, a periodic table that shows electronegativities is most helpful.
Covalent Compounds
Example: phosphate ion Electronegativity: 2.1
-2
P O
4 3 3.5
Polyatomic ion with a charge = -3 Since oxygen is the more electronegative element, it will have its normal oxidation number.
Covalent Compounds
Example: +5 -2
P O
4 3 + 5 - 8 - 3 The phosphate ion has a charge of negative three, so the oxidation numbers must add up to the total charge of the ion.
Ionic Compounds with Polyatomics Example: +2
Ca SO
4 This is an ionic compound, so the charge of the metal cation is its oxidation number
Ionic Compounds with Polyatomics Example: +2
Ca SO
4 The anion is a polyatomic ion, sulfate, and the charge of sulfate is negative two. So the oxidation numbers of sulfur and oxygen must add to -2
Ionic Compounds with Polyatomics Example: 2.5
3.5
+2 -2
Ca SO
4 Oxygen is the more electronegative of the two, so it keeps its normal oxidation number.
Ionic Compounds with Polyatomics Example: +6 +2
Ca SO
4 -2 Sulfur and the four oxygen atoms must add to negative two (the charge of the sulfate anion).
Ionic Compounds with Polyatomics Example:
Pb(OH)
4 This is an ionic compound, so the charge of the metal cation is its oxidation number. But this is a transition metal, so we cannot know it from its position on the periodic table.
Ionic Compounds with Polyatomics Example: +4 -1
Pb(OH)
4 But the anion, the hydroxide ion, carries a charge of negative one. All four hydroxides are negative one, but since the compound is neutral, the oxidation number of lead must balance it out.
Ionic Compounds with Polyatomics Example: 3.5
2.1
+4 -2
Pb(OH)
4 Within the anion, oxygen is the more electronegative of the two elements, and keeps its normal oxidation number.
Ionic Compounds with Polyatomics Example: +4 -2 +1
Pb(OH)
4 Within the hydroxide ion, the oxygen and hydrogen must add to the charge of the ion, -1