Chapter 7 – The Mole and Chemical Composition Sec 2 - Relative Atomic Mass and Chemical Formulas. Average Atomic Mass and the Periodic Table. You have learned that you can use atomic masses on the periodic table to find the molar mass of elements. Many of these values on the periodic - PowerPoint PPT Presentation
Citation preview
Chapter 7 The Mole and Chemical CompositionSec 2 - Relative
Atomic Mass and Chemical FormulasAverage Atomic Mass and the
Periodic TableYou have learned that you can use atomic masses on
the periodic table tofind the molar mass of elements. Many of these
values on the periodictable are close to whole numbers. However,
most atomic masses are writtento at least three places past the
decimal.Most Elements Are Mixtures of IsotopesYou remember that
isotopes are atoms that have different numbers ofneutrons than
other atoms of the same element do. So, isotopes have
differentatomic masses. The periodic table reports a average atomic
massweighted average of the atomic mass of an elements isotopes.
Aweighted average takes into account the relative importance of
eachnumber in the average. Thus, if there is more of one isotope in
a typicalsample, it affects the
Chapter 7 The Mole and Chemical CompositionSec 2 - Relative
Atomic Mass and Chemical Formulas (mass of atom1 x % quantity1) +
(mass of atom2 x % quantity2) +..Average Atomic Mass = 100Remember
from Chapter 3 the formula to calculate the average atomic
massCalculate the average atomic mass of Copper using the
information below. atomic mass of a Cu-63 atom = 62.94 amu
abundance of Cu-63 = 69.17% atomic mass of Cu-65 = 64.93 amu
abundance of Cu-65 = 30.83%
Chapter 7 The Mole and Chemical CompositionSec 2 - Relative
Atomic Mass and Chemical Formulas (62.94 x 69.17) + (64.93 x
30.83)Mass of Copper = 10063.55 amu
Chapter 7 The Mole and Chemical CompositionSec 2 - Relative
Atomic Mass and Chemical FormulasChemical Formulas and MolesUntil
now, when you needed to perform molar conversions, you weregiven
the molar mass of compounds in a sample. Where does this molarmass
of compounds come from? You can determine the molar mass
ofcompounds the same way that you find the molar mass of individual
elementsby using the periodic table.Formulas Express CompositionYou
have learned that covalent compounds, such as water and
hexachloroethane,consist of molecules as units. Formulas for
covalent compounds show both the elements and the number of atoms
of each element in a molecule. Hexachloroethane has the formula
C2Cl6. Each molecule has 8 atoms covalently bonded to each other.
Ionic compounds arent found as molecules, so their formulas do not
show numbers of atoms. Instead, the formula shows the simplest
ratio of cations and anions.
Chapter 7 The Mole and Chemical CompositionSec 2 - Relative
Atomic Mass and Chemical FormulasFormulas Are Used to Calculate
Molar MassesA formula tells you what atoms (or ions) are present in
an element orcompound. So, from a formula you can find the mass of
a mole of the substance,or its molar mass. To do this you use the
formula to tell you how many of whichAtoms an to look up there mass
from the periodic table.Find the molar mass for each of the
following compounds:a. CsI b. C12H22O11 c. HC2H3O2d. CaHPO4 e. I2
f. Mg3(PO4)2259.8 g/mol342.0 g/mol60.0 g/mol136.1 g/mol253.8
g/mol262.9 g/mol
Chapter 7 The Mole and Chemical CompositionSec 2 - Relative
Atomic Mass and Chemical Formulas
Chapter 7 The Mole and Chemical CompositionSec 2 - Relative
Atomic Mass and Chemical Formulas
Chapter 7 The Mole and Chemical CompositionSec 2 - Relative
Atomic Mass and Chemical Formulas
Chapter 7 The Mole and Chemical CompositionSec 2 - Relative
Atomic Mass and Chemical Formulas
Chapter 7 The Mole and Chemical CompositionSec 2 - Relative
Atomic Mass and Chemical Formulas
Chapter 7 The Mole and Chemical CompositionSec 2 - Relative
Atomic Mass and Chemical Formulas
