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
Formulas

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
ending
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
1.
2.
3.
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
oxygen
–
–

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
Ex:
HNO3; NO3-1 is nitrate
– Name
is Nitric Acid
anion ends with –ite, replace
with suffix –ous
– If
Ex:
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
Formulas

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
Formula
1.
2.
3.
4.
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
ratio

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