Download The Atomic Theory

The Atomic Theory
Lavoisier's law of conservation of mass: in
a chemical reaction, the mass of the
products equals the mass of the reactants.
Proust's law of definite proportions: a
pure chemical compound always contains
exactly the same proportion of elements by
mass.
The Atomic Theory
Dalton's law of multiple proportions: If
two elements form more than one compound
between them, then the ratios of the masses
of the second element which combine with a
fixed mass of the first element will be
ratios of small whole numbers.
The Atomic Theory
Gay-Lussac's law of combining volumes:
When gases react together to form other
gases, and all volumes are measured at the
same temperature and pressure the ratio
between the volumes of the reactant gases
and the products can be expressed in simple
whole numbers.
The Structure of the Atom
The Rutherford model of the atom
proton
electron
neutron
The Structure of the Atom
Isotopes
12
6
C
Carbon-12
13
6
C
Carbon-13
14
6
C
Carbon-14
Average Atomic Mass
How much do atoms weigh?
Average Atomic mass calculations (more
often used):
Average atomic mass =
fraction1×atomic mass1 +fraction2 ×atomic mass2 …
or
Average atomic mass =
abundance 1×atomic mass1 +abundance 2 ×atomic mass2 …
The Structure of the Atom
How can atoms be counted?
We count particles by converting masses
into numbers of particles using the 'mole':
1 mole is the number of particles in
12
exactly 12.0000000... grams of 6C
This number is known as Avogadro's number
23
and is equal to 6.02214179×10
The Structure of the Atom
How can atoms be counted?
The molar mass of a substance is then the
mass of one mole of the substance.
Molar mass of
12
6
Molar mass of
1
1
1
C=12.000000…g
H=?g
Atomic mass 1H=1.00782503u
12
Atomicmass 6C =12.000000 u
The Structure of the Atom
Ions
Electrons can be removed or added to
neutral atoms to make anions or cations
respectively.
Neutral atom
Cation
The Structure of the Atom
Ions
Electrons can be removed or added to
neutral atoms to make anions or cations
respectively.
Neutral atom
Anion
The Periodic Table
NonMetals
Metals
Chemical Compounds
Molecular Compounds:
Discrete aggregates of atoms.
●Held together by covalent bonds consisting
of shared pairs of electrons
●
Water
Ammonia
Methane
Chemical Compounds
Ionic Compounds:
Groups of oppositely charged atoms or
polyatomic species held together by
electrostatic forces. No discrete,
identifiable molecules.
Sodium Chloride
Chemical Compounds
Molecular Compounds
Empirical Formula: shows the type of atoms
in the molecule and their relative numbers.
Molecular Formula: shows the type of atoms
in the molecule and their actual numbers.
Hydrogen peroxide:
Hydrazine:
empirical: HO
molecular: H2O2
empirical: NH2
molecular: N2H4
Chemical Compounds
Molecular Compounds
Structural Formula: shows the type of atoms
in the molecule, their actual numbers and
how they are connected.
Water:
Chemical Compounds
Mass Percent Composition
A relative measure of the masses of the
elements in a compound.
●
Lavoisier's original estimate of the
composition of water was 85% oxygen and 15%
hydrogen by mass.
Chemical Compounds
Determining Empirical Formulas
Recall that the empirical formula gives us
only the ratio of atoms to each other in a
compound.
The problem in finding empirical formulas
is then generally “how do we determine the
ratios of atom A to atom B (to atom C ...
etc.) in our compound”.
Chemical Compounds
Determining Empirical Formulas
1. Use the given % composition, or
determine what the %composition is and then
find the mass of each element in a 100 g
sample of the substance.
2. For each elemental mass, determine the
number of mols of the element in the 100 g
sample using the corresponding atomic mass
from the periodic table.
Chemical Compounds
Determining Empirical Formulas
3. If necessary, divide each mol quantity
by the smallest of the numbers of mols to
get whole numbers. If any fractions result,
multiply all results by the appropriate
number to obtain all whole numbers.
4. Use the whole numbers from step 3 to
generate an empirical formula.
Chemical Compounds
Combustion Analysis
Chemical Compounds
Oxidation States
The idea of the oxidation state or
oxidation number comes about from
considering “what if all compounds were
ionic and electrons were completely
transferred from one atom to another”. Thus
there would be an identifiable charge on
each atom in the molecule ... it is this
'what if' charge that is referred to as the
oxidation state or oxidation number.
Chemical Compounds
Chemical Equations
The chemical equation is a shorthand
description of a reaction that gives the
molecular formulas of all of the reactants
and products:
2H2(g) +O2(g) → 2H2 O(g)
reactants
products
Chemical Compounds
How many neutrons are in the nucleus of a
sulfur-33 atom?
Mass number = number of protons +
number of neutrons
for sulfur-33:
number of protons =16
mass number =33
number of neutrons =33−16=17
Chemical Compounds
The U.S. Food and Drug Administration (FDA)
recommends that a person consume less then
2.4 g of sodium per day. What mass of
sodium chloride ( in grams) can you consume
and still be within the FDA guidelines?
Sodium chloride is 39% sodium by mass.
39g Na
2.4g Na
=
100g NaCl x gNaCl
x=
2.4g Na x 100gNaCl
=6.2g NaCl
39 gNa
Chemical Compounds
How many atoms of hydrogen are in 3.6 mols
of C9H8O4?
moles of hydrogen =3.6×8
=29
23
atoms of hydrogen =29 x 6.023 x 10
= 1.747 x 1025
Chemical Compounds
It was found that 56g of iron combined with
32g of sulfur. Calculate the empirical
formula of the compound formed.
1
moles Fe=56g×
55.85g/ mol
= 1.0 mol
1
moles S=32g×
32.07g/ mol
= 1.0 mol
Chemical Compounds
1.0
1.0
empirical formula is FeS
mole ratio Fe to S=
Chemical Compounds
A pure compound was found on analysis to
contain 31.9% potassium, 28.9% chlorine and
39.2% oxygen. Calculate its empirical
formula.
In a 100g sample there will be 31.9g K,
28.9g chlorine and 39.2g oxygen.
Chemical Compounds
Example Calculations
1
moles K=31.9 g×
39.10g / mol
= 0.815mol
1
moles Cl=28.9 g×
35.45g / mol
= 0.815mol
1
moles O=39.2 g×
16.00g/ mol
=2.45 mol
Chemical Compounds
Dividing by the smallest number, 0.815,
gives a K:Cl:O ratio of 1:1:3
empirical formula: KClO3
Chemical Compounds
Name the compounds:
Cr2O3:
MoS2:
K2SO3:
Fe2(SO4)3:
SiCl4:
P4O10:
KHCO3:
chromium(III) oxide
molybdenum(IV) sulfide
potassium sulfite
iron(III) sulfate
silicon tetrachloride
tetraphosphorus decaoxide
potassium hydrogen carbonate
Chemical Compounds
A metal sulfide, MS2, is 40.06% by mass
sulfur. What is the identity of the metal?
One mole of MS2 will have two mols of sulfur
atoms in it and one mol of the metal, M.
Two mols of sulfur has a mass of 32.07 x 2
= 64.14 g, which represents 40.06% of the
mass of one mole of MS2.
Chemical Compounds
We can now determine what the mass of one
mol of MS2 will be:
64.14g 40.06
=
mol
x g/mol
100
100×64.14
x=
g/mol
40.06
= 160.1 g/mol
Chemical Compounds
mass of M in one mole of MS2 =160.1g−64.14 g
= 95.96g
Referring to the periodic table we find
that the element with this molar mass is
molybdenum.
References
1.N.J. Tro, Chemistry: A Molecular
Approach, Pearson-Prentice Hall, 2008.
(your text!)
2.Extra problems at
http://chem4823.usask.ca/chem112