Chemistry 1A
Chapter 2
What I’d be doing if I
were you…
• Support for this presentation
– Read pdf file for Chapter 2 of An Introduction to
Chemistry (link on the Chemistry 1A webpage)
http://www.preparatorychemistry.com/Bishop_Book_2_eBook.pdf
– Read pdf file for Chapter 8 of An Introduction to
Chemistry (link on the Chemistry 1A webpage)
http://www.preparatorychemistry.com/Bishop_Book_8_eBook.pdf
– Or read Chapters 1 and 2 in the text.
Group Numbers on the Periodic Table
Group Names
Alkali Metals
Alkaline Earth Metals
Halogens
Noble Gases
Characteristics of
Metallic Elements
• Metals have a shiny metallic luster.
• Metals conduct heat well and
conduct electric currents in the solid
form.
• Metals are malleable.
– For example, gold, Au, can be
hammered into very thin sheets without
breaking.
Metals, Nonmetals, and
Metalloids
Classification of
Elements
Solid, Liquid, and
Gaseous Elements
Atoms
• Tiny…about 10-10 m
– If the atoms in your body were 1 in. in
diameter, you’d bump your head on
the moon.
• Huge number of atoms in even
a small sample of an element
– 1/2 carat diamond has 5 × 1021
atoms…if lined up, would stretch to
the sun.
Particles in the Atom
• Neutron (n)
0 charge
1.00867 u
in nucleus
• Proton (p)
+1 charge
1.00728 u
in nucleus
• Electron (e−)
−1 charge
nucleus
0.000549 u
outside
Electron Cloud for
Hydrogen Atom
The Electron
“If I seem unusually clear to you, you must have
misunderstood what I said.”
Alan Greenspan,
Head of the Federal Reserve Board
“It is probably as meaningless to discuss how much
room an electron takes up as to discuss how much room
a fear, an anxiety, or an uncertainty takes up.”
Sir James Hopwood Jeans,
English mathematician, physicist and
astronomer (1877-1946)
Wave Diffraction Patterns
Effect on Chemical
Changes
• Electrons
– Can be gained, lost, or shared…actively
participate in chemical changes
– Affect other atoms through their -1 charge
• Protons
– Affect other atoms through their +1 charge
– Determine the number of electrons in
uncharged atoms
• Neutrons
– No charge…no effect outside the atom and
no direct effect on the number of electrons.
Carbon Atom
Example Ions
Ions
• Ions are charged particles due to a
loss or gain of electrons.
• When particles lose one or more
electrons, leaving them with a
positive overall charge, they become
cations.
• When particles gain one or more
electrons, leaving them with a
negative overall charge, they
become anions.
Isotopes of Hydrogen
Isotopes
• Isotopes are atoms with the same
atomic number but different mass
numbers.
• Isotopes are atoms with the same
number of protons and electrons in
the uncharged atom but different
numbers of neutrons.
• Isotopes are atoms of the same
element with different masses.
Tin has ten natural isotopes.
Possible Discovery of
Elements 113 and 115
• Dubna, Russia
• Dubna’s Joint Institute for Nuclear
Research and Lawrence
Livermore National Laboratory
• Bombarded a target enriched in
americium, 243Am, with calcium
atoms, 48Ca.
• From analysis of decay products,
they concluded that four atoms of
element 115 were created.
Elements 113 and 115
• Created 288115, which lasted
about 100 milliseconds…a
very long time for this large an
isotope.
• 288115 emitted an α-particle,
4He, to form 284113.
• The results need to be
confirmed.
Why try to make
elements that last
such a short time?
• To support theories of the nature of
matter.
– The standard model of the nature of
matter predicts that elements with
roughly 184 neutrons and 114 protons
would be fairly stable. (See next slide.)
– 288115, which lasted a relatively long
time, has 115 protons and 173 neutrons.
Band of
Stability
Why try to make
elements that last such a
short time? (cont.)
• The technology developed to make
new elements is also being used
for medical purposes.
– Heavy-ion therapy as a treatment for
inoperable cancers
• Beams of carbon atoms shot at tumor.
• Heavier particle beam is less likely to
scatter.
• Releases most of energy at end of path
so easier to focus.
To Describe Structure
of Elements
• What particles?
– Noble gases – atoms
– Other nonmetals - molecules
• Diatomic elements – H2, N2, O2, F2, Cl2,
Br2, I2
• S8, Se8, P4
• C(diamond) huge molecules
– Metallic elements – cations in a sea of
electrons
To Describe Structure
of Elements (2)
• Solid, liquid, or gas?
– Gases - H2, N2, O2, F2, Cl2, He, Ne,
Ar, Kr, and Xe
– Liquids – Br2 and Hg
– Solids – the rest
• Standard description of (1) solid,
(2) liquid, (3) gas, or (4) metal.
Description of Gas
• Particles constantly moving in straightline paths
• About 0.1% of volume occupied by
particles…99.9% empty.
• Average distance between particles is
about 10 times their diameter.
• No significant attractions or repulsions.
• Constant collisions that lead to
changes in direction and velocity.
• Variable volume and shape, due to
lack of attractions and a great freedom
of motion.
Description of Liquid
• Particles constantly moving.
• About 70% of volume occupied by
particles…30% empty
• Attractions are strong but not strong
enough to keep particles from moving
throughout the liquid.
• Constant collisions that lead to
changes in direction and velocity.
• Constant volume, due to significant
attractions between the particles that
keeps the particles at a constant
average distance, but not constant
shape, due to the freedom of motion.
Description of Solid
• Particles constantly moving.
• About 70% of volume occupied by
particles…30% empty.
• Strong attractions keep particles
trapped in cage.
• Constant collisions that lead to
changes in direction and velocity.
• Constant volume and shape due
to strong attractions and little
freedom of motion.
Helium Gas, He
Covalent Bond Formation
Hydrogen, H2,
Molecule
Hydrogen Gas, H2
Bromine Liquid
Iodine Solid
Typical Metallic
Solid and Its
“Sea of Electrons”
Elements and Compounds
Values from
Measurements
• A value is a quantitative description that
includes both a unit and a number
• For 100 meters, the meter is a unit by
which distance is measured, and the 100
is the number of units contained in the
measured distance.
• Units are quantities defined by standards
that people agree to use to compare one
event or object to another.
Base Units for the
International System of
Measurement
• length
meter, m, the distance that light
travels in a vacuum in 1/299,792,458 of a
second
• mass kilogram, kg, the mass of a platinumiridium alloy cylinder in a vault in France
• time second, s, the duration of 9,192,631,770
periods of the radiation emitted in a specified
transition between energy levels of cesium-133
• temperature kelvin, K, 1/273.16 of the
temperature difference between absolute zero
and the triple point temperature of water
Derived Unit
1 L = 10−3 m3
103 L = 1 m3
Some Base Units and Their
Abbreviations for the
International System of
Measurement
Type
Length
Mass
Volume
Energy
Base Unit
meter
gram
liter
joule
Abbreviation
m
g
L or l
J
Metric Prefixes
Prefix Abbreviation
giga
mega
kilo
centi
milli
micro
nano
pico
G
M
k
c
m
μ
n
p
Number
109 or 1,000,000,000
106 or 1,000,000
103 or 1000
10−2 or 0.01
10−3 or 0.001
10−6 or 0.000001
10−9 or 0.000000001
10−12 or 0.000000000001
Length
Range of Lengths
Volume
Range of Volumes
Mass and Weight
• Mass is usually defined as a measure of
the amount of matter in an object. Mass
can be defined as the property of matter
that leads to gravitational attractions
between objects and therefore gives rise
to weight.
• The weight of an object, on the Earth, is a
measure of the force of gravitational
attraction between the object and the
Earth.
• Matter is anything that occupies a volume
and has a mass.
Comparison of the Mass
and Weight of a 65 kg
Person
On Earth
Mass
Weight
65 kg
637 N
Between
Earth
and Moon
65 kg
≈0 N
On Moon
65 kg
1/6(637 N)
= 106 N
Mass
Range of Masses
Celsius and
Fahrenheit
Temperature
Comparing Temperature Scales
Precision and
Accuracy
• Precision describes how closely a series
of measurements of the same object
resemble each other. The closer the
measurements are to each other, the
more precise the measurement. The
precision of a measurement is not
necessarily equal to its accuracy.
• Accuracy is a measurement’s
relationship to the property’s true value.
Precision and Accuracy
(cont.)
Reporting Values
from Measurements
• One of the conventions that
scientists use for reporting
numbers from measurements
is to report all of the certain
digits and one estimated (and
thus uncertain) digit.
Graduated Cylinder
Graduated Cylinder Accurate
to ±0.1
Trailing Zeros
Trailing Zeros (2)
Digital Readout
Report all digits unless
otherwise instructed.
Digital Readout (2)
In many cases, it is best to round the
number in the value to fewer decimal
positions than displayed. For the mass
displayed above, 100.432 g would indicate
±0.001 g.
Unit Conversions
All science requires mathematics. The
knowledge of mathematical things is
almost innate in us. . . [Mathematics] is the
easiest of sciences, a fact which is obvious
in that no one's brain rejects it…
Roger Bacon (c. 1214-c. 1294)
Stand firm in your refusal to remain
conscious during algebra. In real life, I
assure you, there is no such thing as
algebra.
Fran Lebowitz (b. 1951)
Unit Analysis Step 1
• Step 1: State your question in an expression
that sets the unknown unit equal to the value
given.
• Start with the same number of units as
you want.
– If you want a single unit, start with a value
that has a single unit.
– If you want a ratio of two units, start with a
value that has a ratio of two units, or start
with a ratio of two values, each of which
have one unit.
• Put the correct type of unit in the correct
position.
Unit Analysis Step 2
• Step 2: Multiply the expression to
the right of the equals sign by one or
more conversion factors that cancel
the unwanted units and generate the
desired unit.
– If you are not certain which conversion
factor to use, ask yourself, "What is the
fundamental conversion and what
conversion factor do I use for that type
of conversion?"
Unit Analysis Steps
3&4
• Step 3: Check to be sure you used
correct conversion factors and that
your units cancel to yield the desired
unit.
• Step 4: Do the calculation, rounding
your answer to the correct number of
significant figures and combining it
with the correct unit.
English-Metric Conversion
Factors
Type of
Measurement
Probably
Most Useful
to Know
Others Useful to Know
Length
2.54 cm
1 in.
Mass
453.6 g
1 lb
2.205 lb
1 kg
Volume
3.785 L
1 gal
1.057 qt
1L
1.609 km
1 mi
39.37 in.
1m
1.094 yd
1m
Rounding Answers from
Multiplication and
Division Step 1
• Step 1: Determine whether each value is exact,
and ignore exact values.
– Exact values
• Numbers that come from definitions are exact.
• Numbers derived from counting are exact.
– Do Step 2 for values that are not exact.
• Values that come from measurements are never
exact.
• We will assume that values derived from
calculations are not exact unless otherwise
indicated.
Rounding Answers from
Multiplication and
Division Step 2
• Step 2: Determine the number of
significant figures in each value that is
not exact.
• All non-zero digits are significant.
• Zeros between nonzero digits are significant.
• Zeros to the left of nonzero digits are not
significant.
• Zeros to the right of nonzero digits in numbers that
include decimal points are significant.
• Zeros to the right of nonzero digits in numbers
without decimal points are ambiguous for
significant figures.
Rounding Answers from
Multiplication and Division
Step 3
• Step 3: When multiplying and
dividing, round your answer off to the
same number of significant figures as
the value used with the fewest
significant figures.
• If the digit to the right of the final digit you
want to retain is less than 5, round down (the
last digit remains the same).
• If the digit to the right of the final digit you
want to retain is 5 or greater, round up (the
last significant digit increases by 1).
Density
• Mass density is mass divided by
volume. It is usually just called
density.
Density = mass
volume
• It can be used as a unit analysis
conversion factor that converts
mass to volume or volume to mass.
Percentage and
Percentage Calculations
• Mass percentages and volume percentage
can be used as unit analysis conversion
factors to convert between units of the part
and units of the whole.
For X% by mass
X (any mass unit) part
100 (same mass unit) whole
For X% by volume
X (any volume unit) part
100 (same volume unit) whole
Conversion
Types
Temperature
Conversions
⎞
1.8
°F
⎟ + 32 °F
? °F = --- °C
1 °C ⎟⎠
⎛
⎜
⎜
⎝
? °C = --- °F - 32 °F 1 °C
1.8 °F
⎛
⎜
⎜
⎜
⎝
⎞
⎟
⎟
⎟
⎠
⎛
⎜
⎜
⎜
⎜
⎝
? K = --- °C + 273.15
? °C = --- K - 273.15
⎞
⎟
⎟
⎟
⎟
⎠
Comparing Temperature Scales
Rounding Answers from
Addition and Subtraction
• Step 1: Determine whether each value is
exact, and ignore exact values.
– Skip exact values.
– Do Step 2 for values that are not exact.
• Step 2: Determine the number of decimal
positions for each value that is not exact.
• Step 3: Round your answer to the same
number of decimal positions as the
inexact value with the fewest decimal
places.