COMPOUNDS & MOLES
Unit 5
Overview
Naming Ionic Covalent Acids Simple Organic
The Mole Molar Mass Mole Conversions
Calculations Percent
Composition Empirical Formula Molecular Formula
Why do we name compounds? Think of some common compounds that you
know of H2O = water NaCl = table salt CaCO3 = limestone
Imagine if we had to memorize common names for the millions of known compounds that we had today…IMPOSSIBLE!
Standard system was created to name compounds IUPAC (International Union of Pure and
Applied Chemistry)
Chemical Formulas
Indicate the relative numbers of atoms of each kind in a chemical compound
C8H18Indicates 8
carbon atoms
Indicates 18 hydrogen
atoms
Molecular vs. Structural Formulas Molecular Formula
Lists elements in a compound and how many of each element you have
Example: C2H6O
Structural Formula Shows how atoms are “connected” in the
structure Example CH3CH2OH or CH3OCH3
Monatomic Ions
Ions formed from a single atom
Naming cations Simply give the element’s name Example
Ca+2 = calcium ion Na+1 = sodium ion
Naming anions Drop the ending of the element’s name and add “-ide” Example
F-1 = fluoride ion O-2 = oxide ion
Binary Ionic Compounds
Ionic compound composed of 2 elements
Writing Names Name the cation 1st Name the anion 2nd
Example: NaCl = sodium chloride MgF2 = magnesium fluoride Sr3N2 = strontium nitride
Binary Ionic Compounds
Writing FormulasExample: aluminum oxide
Write the symbols for the ions side by side (cation first)
Al+3 O-2
Criss-cross the charges (use absolute value)Al2 O3
Simplify (divide both numbers by largest common factor)
Al2O3
Binary Ionic Compounds
More examples (name to formula)
Calcium nitride = Ca3N2
Potassium sulfide = K2S
Magnesium oxide = MgO
Polyatomic Ions
Electrically charged group of two or more atoms
Oxyanion – polyatomic anion that contains oxygen
General naming rules Most common oxyanion ends in “-ate”
Example ClO3
-1 = chlorate NO3
-1 = nitrate SO4
-2 = sulfate
Polyatomic Ions
The number of oxygen atoms may be altered giving new endings and prefixes to oxyanions
1 more oxygen = per_______ate Common form = _______ate1 less oxygen = _______ite2 less oxygens = hypo_______ite
Example ClO4
-1 = perchlorate ClO3
-1 = chlorate ClO2
-1 = chlorite ClO-1 = hypochlorite
Notice that the charge of the oxyanion does not change (only the number of oxygen atoms)
Polyatomic Ions
Ionic compounds (contain “ions”)
Writing Name If ion comes first, name the polyatomic ion then
name the anion If the ion comes second, name the cation then
name the polyatomic ion (do not change ending) Examples
NH4Cl = ammonium chloride CaSO4 = calcium sulfate Ba3(PO4)2 = barium phosphate
Polyatomic Ions
Writing Formula Follow same rules as binary ionic
compound, but when charges are criss-crossed, use parenthesis to indicate number belongs to entire polyatomic ion
Example: calcium nitrate
Ca+2 NO3-1 = Ca(NO3)2
Stock System (Ionic Compounds) For elements that form two or more cations
with different charges (example Pb+2 and Pb+4) Uses roman numeral to indicate ion’s charge Transition metals, Sn, and Pb use this system
Writing Formulas Roman numeral indicates charge of the cation
(use that to criss cross) Examples
Copper (II) bromide = CuBr2
Iron (III) sulfide = Fe2S3
Tin (IV) phosphate = Sn3(PO4)4
Stock System (Ionic Compounds) Writing Names Use the anion (known charge) that the cation is
bonded to and solve for the charge of the cation Total positive charge (from cation) must equal total
negative charge (from anion)
Example: VF6
Fluorine has a charge of -1 There are six fluorines bonded to the vanadium 6 × -1 = -6 so the charge of vanadium is 6 Name = vanadium (VI) fluoride
Stock System (Ionic Compounds) Example 2: Sn3N2
The charge of nitrogen is -3 There are 2 nitrogen atoms 2 × -3 = -6 There are 3 tin atoms that add up to a charge of +6 +6 ÷ 3 = -2 so each tin atom has a charge of +2 Name = tin (II) nitride
Exception: some transition metals only have one charge (nickel, silver, zinc, etc.) so the roman numeral is omitted
Prefixes
Used in naming covalent compounds
Indicate how many of each atom you have
Number Prefix
1 mono-
2 di-
3 tri-
4 tetra-
5 penta-
6 hexa-
7 hepta-
8 octa-
9 nona-
10 deca-
Binary Covalent Compounds
Writing Names Name the cation followed by the anion (-ide ending) Use prefixes to indicate how many of each atom you
have
Examples: P4Br10 = tetraphosphorous decabromide Si2O5 = disilicon pentoxide
Note If an o or a are doubled, drop the o or a of the prefix Never use mono- on cation (only on anion)
Binary Covalent Compounds
Writing Formulas Prefix indicates how many of each atom
you have Do not criss-cross numbers
Examples: Trinitrogen octachloride = N3Cl8 Arsenic tetrabromide = AsBr4
Summary
Is it ionic?
Is the cation a transition metal, Sn, or Pb?
Use Roman numerals
Name cation then anion
(write it like it is)
Use prefixes (covalent)
NOYES
YES NO
When writing names of formulas…
Acids
Binary acid – contains two elements (one usually hydrogen and the other usually a halogen)
Oxyacid – acids that contain hydrogen, oxygen, and a third element (usually a nonmetal) Usually hydrogen and a polyatomic ion
Acids
Naming binary acids Use form of
hydro_____ic acid
Examples: HF = hydrofluoric acid HCl = hydrochloric acid
Acids
As the number of oxygen atoms changes in oxyacids, so does the name (just like the oxyanions)
1 more oxygen = per_______ic acidCommon form = _______ic acid1 less oxygen = _______ous acid2 less oxygens = hypo_______ous acid
Example HClO4 = perchloric acid HClO3 = chloric acid HClO2 = chlorous acid HClO = hypochlorous acid
Carbon
• Basis for all life.
• Study of carbon compounds is called organic chemistry.
• Can form single, double and triple bonds.
• Long carbon chains can be produced.
• Will bond with many other elements.
• A HUGE number of compounds is possible (organic compounds)
Naming Simple Organic Compounds
Organic compounds containing only carbon and hydrogen are called hydrocarbons
Alkane – all carbons form single bonds Alkene – carbons form double bonds Alkyne – carbons form triple bonds
Whether a compound is an alkane, alkene, or alkyne determines the suffix (ending) in the name of the hydrocarbon
Naming Simple Organic Compounds
Prefix CarbonsMeth- 1Eth- 2Prop- 3But- 4 Pent- 5Hex- 6Hept- 7Oct- 8Non- 9Dec- 10
Number of carbons determines prefix
used in name
Naming Simple Organic Compounds
Examples CH4 = methane C2H6 = ethane
propane
propene
propyne
The Mole
The amount of a substance that contains as many particles as there are atoms in exactly 12 g of 12C SI unit of amount of a substance Abbreviated “mol”
Counting unit just like a “dozen” 1 dozen donuts is the same
amount as 1 dozen books 1 mole of hydrogen atoms is
the same amount as 1 mole of sodium atoms
Avogadro’s Number
6.022×1023 of anything is a mole Named after Italian scientist Amadeo Avogadro Experimentally determined number of atoms in 12 grams of
12C
How big is 602,200,000,000,000,000,000,000? One mole of donut holes would cover the Earth 5 miles deep
in the donut holes One mole of pennies stacked on top of each other would
reach from the Earth to the moon 7 times If you started counting when you were born and never
stopped until the day you died, you would never come close to reaching 6.022×1023
Avogadro’s Number
1 Liter of water contains 55.5 moles of H2O
A 5 lb bag of sugar contains 6.6 moles of sugar
How can that be?!
Atoms and molecules are so tiny that when we use units of moles (6.022×1023) it puts the particles into measurable quantities
Molar Mass
1 mole of hydrogen atoms = 1 mole of sodium atoms
BUT… 1 mole of hydrogen atoms DOES NOT
have the same mass as 1 mole of sodium atoms Individual atoms have different masses
They are the same amount but not the same mass
Molar Mass
The periodic table tells us the mass of 1 mole of any atom
It’s the same as the average atomic mass/relative atomic mass (decimal number on the table)
Molar Mass – mass of 1 mole of an atom or compound Units are “grams/mole” or “g/mol”
Molar Mass
To find the molar mass of a compound, add the molar masses of all atoms in a compound Also called formula mass or molecular mass
(compounds only)
Example: CO2 (1 atom of C and 2 atoms of O)
1 atom C x 12.011 = 12.011 2 atoms O x 15.9994 = 31.9988
Molar mass = 44.010 g/mol
AtomsMolecule
sMole Grams
Mole Relationships
6.02 x 1023Molar Mass
To go between units of grams, moles and atoms (or molecules) use conversions! 6.022×1023 is how many atoms or molecules
are in 1 mole of any substance The molar mass is how many grams are in
one mole of any substance
Mole Conversions
How many grams are in 5.0 moles of calcium?
5.0 mole × = 200.39 g
How many atoms are in 2.1 moles of xenon?
2.1 moles × = 1.26×1024 atoms
40.078 g1 mole
6.022×1023 atoms1 mole
Mole Conversions
There is no way to go straight from grams to atoms or molecules in one step Must use moles as the intermediate step
How many atoms are in 9.8 g of Pb?
9.8g × × = 2.8×1022 atoms
1 mol207.2 g
6.022×1023 atoms1 mole
Mole Conversions
When a conversion includes a compound, it will use the word molecules when a conversion includes an element, it will use the word atoms There are still as many molecules in a mole as there are
atoms
How many grams are in 3.4×1022 molecules of H2O? First solve for molar mass of H2O
(H2O molar mass = 18.02g/mol)
3.4×1022 molecules × × = 1.0 g
1 mole6.022×1023 molecules
18.02 g1 mole
Percent Composition
Percentage by mass of each element in a compound
Example: What is the percent composition of BaSO4?
Ba = 1 × 137.3 = 137.3(137.3/233.4) ×100= 58.8% Ba
S = 1 × 32.1 = 32.1 (32.1/233.4) ×100= 13.8% S
O = 4 × 16.0 = 64.0 (64.0/233.4) ×100= 27.4% O
233.4
Molar Mass part ÷ totalMultipl
y by 100
Total molar mass
Empirical Formula
Smallest whole-number ratio formula of a compound Simplest formula
What is the empirical formula of a compound that is 27.0% sodium, 16.5% nitrogen, and 56.5% oxygen by mass? Assume that you have a 100 gram sample
Na 27.0/22.99 = 1.17 /1.17 = 1
N 16.5/14.01 = 1.18 /1.17 = 1
O 56.5/16.00 = 3.53 /1.17 = 3
EmpiricalFormula = NaNO3
Molar MassDivide by
smallest
number
Empirical Formula
When numbers are too far to round, you may need to multiply all values by the same factor to make all numbers whole
What is the empirical formula of a compound that contains 40.6g of calcium and 9.5g of nitrogen?
Ca 40.6/40.1 = 1.01 /0.69 = 1.5 × 2 = 3
N 9.5/14.01 = 0.69 /0.69 = 1 × 2 = 2EmpiricalFormula = Ca3N2
too far to round
double both numbers to get whole numbers
Molecular Formula
Indicates actual number of atoms of each element in a compound Multiple of empirical formula
An empirical formula can be the molecular formula, but the molecular formula is not always the empirical formula
CH4
Empirical Formula
C3H12
Molecular Formula
Molecular Formula
If the molecular mass is known, you can solve for the molecular formula
The molar mass of a compound with empirical formula of CH2O is 180.12 g/mol. What is the molecular formula of this compound?
Molar mass CH2O = 30.02g/mol = 6
Molecular Formula = CH2O × 6 = C6H12O6
180.1230.02