Chapter 7 - Midway ISD

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Transcript Chapter 7 - Midway ISD

Chapter 7
Chemical Formulas and Chemical Compounds
Sect. 7-1: Chemical Names and
Chemical formulas indicate what
elements/ions are in the compound and in
what ratio
Naming monatomic ions
Cations get the element name
Anions get the root of the element name with –ide
Polyatomic ions get ion name ( pg. 210)
Binary Ionic Compounds –
Steps for formula writing
1. Write down the symbols for the ions, cation
listed first
2. Identify charges and “criss-cross” as needed
3. Re-write formula without showing charges
Naming binary ionic compounds
Name cation
Name anion (remember –ide ending)
If cation is multi-valent (can have more than
one charge), add roman numeral in
parenthesis following cation name to
indicate charge
Stock system of nomenclature
Compounds containing polyatomic Ions
Oxyanions – polyatomic ions containing
Many are made of same 2 elements, so more
common ion gets –ate ending and the one with
less oxygen gets –ite ending
If more than 2 oxyanions, hypo- is added for less
then the –ite and per- is added for more than –ate
Naming of compounds is same as binary
When more than one polyatomic ion is
needed to balance the charges in a formula,
parenthesis are required around the
polyatomic ion
Naming Binary Molecular Compounds
“Old” system of naming
Prefixes are used to tell how many of each
element are present in the molecular formula
Less electronegative element is listed first and is
only given a prefix if there is more than one
2nd element is given a prefix, then the root of the
element name, and then –ide ending
“o” or “a” at end of prefix is dropped when
element name starts with a vowel
Numerical Prefixes
1 mono2 di3 tri4 tetra5 penta-
6 hexa7 hepta8 octa9 nona10 deca-
Rules for naming acids
Naming Acids
 Binary
Acids (contains hydrogen and
one other element)
– Use prefix hydro- to name the
hydrogen part of the compound
– The rest of the name consists of a
form of the root of the element
plus the suffix –ic and then the
word acid
Naming Oxyacids
 Oxyacid-
acid that contains hydrogen
and an oxyanion
– First determine anion present
– If anion ends with –ate, replace with
suffix –ic
HNO3; NO3-1 is nitrate
– Name
is Nitric Acid
anion ends with –ite, replace
with suffix –ous
– If
HNO2; NO2 is nitrite
– Name
is Nitrous Acid
Sect. 7-3: Using Chemical Formulas
Formula Mass – sum of the average atomic
mass of all atoms in a formula unit, molecule,
or ion
Units are amu (atomic mass units)
Molar mass for a compound is calculated by
summing the masses of all elements present
in one mole of the compound
Molar mass is numerically equal to formula
mass, but units are g/mol
Ex: Calculate the molar mass of water
Molar mass can be used as a conversion
factor to convert between moles and grams
(use t-chart method)
1mol = molar mass in grams
Percent by mass of a compound =
Mass of element in sample of compound x 100
Mass of sample of compound
Can also be calculated by
Mass of element in 1 mol of compound x 100
Molar mass of compound
Percent composition – the percent by mass
of each element in a compound
Sect. 7-4: Determining Chemical
Empirical formula – shows the smallest
whole number ratio of elements in a
compound (may or may not be same as
molecular formula)
Steps for determining Empirical
Determine percent composition (if not
already given)
Assume 100 g sample and change % to
units of grams
Convert grams of each element to moles
Divide all answers from step #3 by the
smallest answer to obtain a whole number
If step #4 does not give very close to whole
numbers, multiply all answers by the same
number to obtain whole numbers
Example 2.5 would be multiplied by 2 to get 5 or
2.3 would be multiplied by 3 to obtain 7
Calculation of a Molecular Formula
X (empirical formula) = molecular formula
X = molar mass of molecular formula
molar mass of empirical formula
X must be a whole number