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Atomic Theory
Announcements
accounts for
Quizzes handed back on Thursday.
Conservation
of Mass
Law of Multiple
Proportions
Law of Definite
Composition
explained by
Atomic
Structure
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that
have
with the
same number
of protons
comprising
Continue Reading/Working Chapter 2
Chapter 2: 1, 13, 17, 19, 25, 33, 46, 61, 65, 67,
69, 71, 73, 75 89, 95, 99 (Principles of Chemistry)
Chapter 2: 2.17, 2.19, 2.25, 2.46, 2.85, 2.89,
2.95, 2.99, 2.101, 2.103, 2.105 (4th Chemistry
Molecular Nature of Matter)
HOUR EXAM 1
July 18 6-7:30PM
Chemists use a short-hand notation to communicate
information about isotopes or “nuclides” of atoms.
Atomic
Number
A
ZX
Electrons
containing
constitute
most of an atoms
protons
and
neutrons
possessed by
all
Compounds
which are either
with a
different number
of neutrons
Isotopes
Ionic
Compounds
Covalent
Compounds
made from
reactions between
made from
reactions between
volume
symbolized by
Metals
give rise to
A
nuclear
properties
chemical
properties
Z
X
Non-metals
that gain
electrons
that loose
electrons
cations
anions
Non-metals
that we call
Molecules
exploited in
that explains
radioactivity, fission
and atomic bombs
symbolized by
symbolized by
chemical
formula
molecular
formula
Isotopes are atoms that have the same number of
protons (i.e. same elements), but those elements
have a different number of neutrons in the nucleus.
All elements are mixtures of isotopes!
# protons + # neutrons
Mass
Number
Nucleus
chemical
process
Elements
Atoms
Atomic
Symbol
# protons
23
Na
11
Elements exist as a
mixture of isotopes.
24
11
Na
The Atomic mass (atomic weight) of an element in
the periodic table is a weighted average of the
isotopes that are found in each element.
Elemental carbon consists
of two isotopes, 12C with a
mass of 12 amu and
relative abundance of
98.89% and 13C nucleus
with a mass of 13.0034
amu and a relative
abundance of 1.11%.
n
�
Ai Mi = A1 M1 + A2 M2 + A3 M3 ... + ...An Mn
i=1
Cavg
Cavg
= (0.9889 x 12 amu) + (0.0111 x 13.0034) amu
= 12.011 amu
Isotope abundance Problem
SOLUTION:
Isotope
107Ag
109Ag
n
�
Mass(amu)
106.90509
108.90476
Abundance(%)
51.84
48.16
Ai Mi = A1 M1 + A2 M2 + A3 M3 ... + ...An Mn
i=1
atomic mass = .5184 106.90509 amu + .4816 108.90476 amu
atomic mass of Ag = 55.42amu + 52.45amu = 107.87amu
Example: Naturally occurring carbon consists of two
isotopes, 12C with a relative abundance of 98.89% and 13C
with a relative abundance of 1.11%. What is the average
atomic mass of carbon that we see printed in the peridic
table?
The average atomic weight of chlorine is 35.45 amu
and the element has two stable isotopes 17Cl35 and
37
17Cl . Estimate the relative abundances in percent of
these two isotopes.
Solution: Let x represent the fraction of Cl35,
then (1-x) gives the fraction of Cl37.
The weighted average atomic weight is then:
35x + 37(1-x) = 35.45
Solving for x:
2x = 1.55,
x = 0.775
so the abundances are 77.5% Cl35 and 22.5% Cl37.
Groups show similar chemistry and have a “group name”
Alkali Metals
Noble Gases
Alkaline Earths
Main Group
Transition
Metals
Use the data provided and obtain the weighted average of
carbon by multiplying each isotope by its relative abundance and
summing the two values. There are only two terms (isotopes) in
this example.
n
�
Halogens
Ai Mi = A1 M1 + A2 M2 + A3 M3 ... + ...An Mn
i=1
Cavg = (0.9889 x 12 amu) + (0.0111 x 13.0034) amu
Cavg = 12.011 amu
The mass of any object on our planet is measured
relative to a defined standard...the kilogram.
Platinum-iridium Kg
block stored in Paris
that defines a
kilogram.
Say you purchase 5.0 kg of potatoes. This can be expressed
in 2- ways:
1. The relative mass of the potatoes on the kilogram scale is
the number 5.
2. The mass of the potatoes is 5.0 kg
Main Group
Lanthanides and Actinides
Chemists have defined the atomic mass unit as
the measurement unit for the mass of atoms:
1 12C atom =
= 12 amu
divide each side by 12 and switch sides
1 12C atom = 12 amu = 1 amu
12
12
1 x Mass of 1 12C atom
1 amu = __
12
Atomic mass (atomic weights) in the periodic table
are all relative to the carbon-12 isotope. 12C
6
Suppose a large number of atomic oxygen atoms
(O) weighs 1.200 g. What will be the weight of an
equal number of lithium atoms?
A He atom is 4 times heavier than a H atom
A C atom is 3 times heavier than a He atom
A F atom is 19/12 times heavier than a C atom
Pure
Substances
Suppose a large number of atomic oxygen atoms
(O) weighs 1.200 g. What will be the weight of an
equal number of lithium atoms?
are either
Elements
Compounds
are either
consist of a
mixture
of
Solution: We look at the Periodic Table and find the ratio of
masses of Li/O = 6.94/16.00, so the weight of the same
number of Li atoms would be:
# Li atoms = (1.200 g O) x (6.94g/15.99g) = 0.521 g Li.
chemical
process
Covalent
Compounds
Ionic
Compounds
Isotopes
made from
reactions between
which have the same
number of protons but
different number of neutrons
and symbolized using
Metals
Z
X
Non-metals
Non-metals
that loose
electrons
A
made by sharing
electrons between reacting atom
that gain
electrons
that we call
anions
Molecules
cations
symbolized by
symbolized by
chemical
formula
molecular
formula
Rules of
Nomenclature
Atoms and molecules tend to form three types of
chemical bonds: ionic, covalent and metallic.
Ionic BondingElectrons from one atom
are transferred to another
element that has a
tendency to accept
electrons (IE and EA).
Covalent Bonding
sharing of one or more
electrons pairs between
non-metal elements.
Non-metal elements react chemically (i.e. share
electrons with each other) to form covalent
compounds.
Cadmium
Metalloids
Non-Metals
Metals
Bromine
Iodine
Non-metal elements in Groups 4,5,6 in the Periodic
Table tend to share electrons between atoms forming
covalently bonded compounds called molecules or
molecular compounds.
A molecule is an aggregate of two or more atoms held
together by covalent bonds.
H
O
Example of Covalent Bonding
O
O2
share electrons
forming chemical bond
H
+
H
H
H
O
O
H
2H2O
H2
A diatomic molecule contains only two covalently-bonded
atoms
H2, N2, O2, Br2, HCl, CO
H
H
H
2 H ATOMS
1A
2A
A polyatomic molecule contains more than two covalently-bonded
atoms
H
O3, H2O, NH3, CH4
1 H2 MOLECULE
3A
4A
5A
6A
7A
NN 2
O2
O
FF2
PP4
SS 8
Cl
Cl
2
Se
Se
8
Br
Br
2
8A
Some elements occur in nature as molecules and not
(1)
(2)
(14)
(15) the (16)
(17)
(18)
as discrete
elements(13)as written
in
Periodic
Table.
HH 2
2
2
GROUP
4
2
8
8
2
2
Chemical formulas summarize the identity and number of
atoms in a compound. The molecular formula of a
compound specifies the number of each kind of atom
present in a single molecular unit of a compound.
• The number of atoms of each element is written as a subscript; when
only a one atom of an element is present, the subscript is dropped.
• In the case of organic (carbon-containing) compounds, it is
customary to place the symbols of the elements C, H, and O in this
order at the left end of the formula.
2
I2I
Name
Pictorial
Description
Longhand
Shorthand
2
<=PERIOD =>
tetratomic
molecules
octatomic
molecules
diatomic
molecules
What atoms must be combined to make the following
molecules?
carbon
monoxide
carbon
dioxide
1-atom of C
+
1-atom of O
1-atom of C
+
2-atom of O
C1O1
CO
C1O2
CO2
A structural formula is a symbolic depiction of
how atoms that make up a molecule are bonded
together in space.
No structural info
structural info
structural info
structural info
Note that it does not specify geometry!
Chemists also use colored balls and sticks to
visualize atoms and compounds. Atoms have
standard color shown below.
An ionic compound (salt) results from the chemical
reaction between atoms or elements of a metal
(cation) and non-metal (anion).
Cadmium
Non-Metals
Metals
Bromine
Iodine
Molecular and ionic compounds use different
terminology and display different physical properties.
\
Molecular
Compounds
Ionic
Compounds
Smallest
entity
molecules
cations and anions
Made by
reaction of....
non-metals
metal + non-metal
Electrical
Conductivity
poor
excellent when
molten or dissolved
Room
Temperature
solid, liquid or gas
solid
Other Names
covalent compounds
salts
Molecular Formula
Formula Unit
Formula