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 The
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The Natural world is Understandable
Science Demands Evidence
Science is a Blend of Logic & Imagination
Scientific Knowledge is Durable
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Nature of Science
Theory = used to explain complex natural processes.
Scientific Law = often use mathematical formulas to show
relationships and make predictions about the natural world. A
description of what happens.
Subject to Change
Scientists Attempt to Avoid Bias
Science is a complex social activity.
Scientific Method
 Question/Problem/Observation
 Hypothesis
– an EDUCATED Guess proposed reason
for what is observed
 Experiment
– To test hypothesis. Create a
controlled experiment with one
experimental variable, constants, and
controls.


Quantitative Data = numeric data.
Qualitative Data = nonnumeric data.
 Analyze
Data – Create Graphs, Perform calculations
Etc.
 Conclusion – Compare experimental results with
hypothesis. Create a new hypothesis.
Observation
Hypothesis
Experiment
Law
Non linear nature of science video
Theory
Observation Versus Inference
 An
observation is the gathering of
information by using our five senses: sight,
smell, hearing, taste, touch


Qualitative- Quality = descriptive Ex. The shirt is blue.
Quantitative- Quantity = numerical Ex. The flower has 7 petals.
 An
inference is something a scientist thinks is true,
based on observations or evidence. They are
based on your past experiences and prior
knowledge. Inferences often change when new
observations are made.
Examples:
 Observation: The grass on the playground is wet.
 Possible inferences: It rained. The sprinkler was on. There is morning
dew on the grass.
Observation vs Inference
Examples:
 Observation: The grass on the
playground is wet.
 Possible inferences: It rained.
The sprinkler was on. There is
morning dew on the grass.
 Observation: The line at the
water fountain is long.
 Possible inferences: It's hot
outside. The students just
came in from
 I. The Greek Philosophers
 A. Around 450 BC a Greek
philosopher, Democritus
proposed the all matter is
actually composed of tiny,
indivisible particles, which he
called atomos.
 B.
At the same time Aristotle and
other philosophers did not
agree. They thought that if matter
were made up of tiny particles it
would fall apart. Aristotle's view
made more sense at the time, so
it prevailed for 21 centuries.
II. Late 1700's
A. Law of Conservation of
Matter
(Antoine Lavoisier)
– Matter can neither be
created nor destroyed in a
chemical reaction
Example: 16 X + 8 Y  8YX2
Mass  Mass
Atoms  Atoms
B. Law of Constant Composition
A
given compound always contains
the same elements in the same
proportions by mass.
 Example:
H2O is always 11.1 %
hydrogen and 88.9 % oxygen;
no matter how much water
there is. Same proportions of
H&O
Same proportions
of H & O (by mass)
“Now that’s
High Quality
H2O”
C.Law of Multiple Proportions
 -Applies
to different compounds made
from the same elements.
 -The mass ratio for one of the elements
that combines with a fixed mass of the
other element can be expressed in small
whole #’s
 Examples:
H2O : 2 H + 1 O (2:1)
H2O2 : 2 H + 2 O (2:2)
 1)
Each element is composed of extremely small
particles called atoms, which are identical in their
chemical properties.
 2)
All atoms of a given element are identical, but
they differ from those of any other element.
 3)
Atoms of different elements combine in simple
whole number ratios to form chemical compounds.
 4)
Atoms are neither created nor destroyed when
they are combined, separated or rearranged in a
chemical reaction.
Solid Sphere Model. Nothing smaller = no
subatomic particles
 Experimented
with cathode rays
 He concluded that there were negatively
charged particles he called electrons.
 The "Plum Pudding" or "Raisin Bun" model.
 Like a ball of chocolate chip cookie
dough.Choc. Chips = electronsDough =
positive charge
 Raisins (electrons) dispersed throughout
positive dough.
Skip Picture
Back
raisins = eSoft pudding-like dough =
positive charge
The Charge on the electron
 Robert
Millikan
discovered the
numerical charge
on the electron
using the oil drop
experiment
 Gold
Foil experiment
 When Rutherford directed a beam of positive
α particles at a thin gold foil, most of the
particles passed through unaffected, but a
small fraction deflected in all directions. The
small number that were deflected indicated
that most of the atom was empty space.
 Rutherford concluded that the positive
charge of the atom was concentrated in a
small compact nucleus.
Back to Rutherford
Rutherford’s Experiment
Back to Rutherford
Rutherford’s experiment
Back to Rutherford
• Model called the "Nuclear atom"
Positive charge concentrated in the
nucleus, w/ e- moving around it.
•Atom is mostly empty space
• Positive Particles in nucleus later
called protons
•If this dot
were the nucleus of an atom,
the atom would have the diameter of a
football field. The nucleus is very tiny
compared with the rest of the atom.
 James
Chadwick (1932) discovered a
particle with no charge and a mass equal
to a proton-he called it a neutron.
 Planetary
MODEL
 Experimented on Hydrogen
 proposed that e- in an atom can reside
only in certain energy levels or orbitals
 The rungs on a ladder are similar to the
energy levels within an atom. A person
can move up or down the ladder only by
standing on its rungs; it is impossible to
stand between them
e-
e-
ee-
ee-
e-
e-
ee-
•Nucleus (p+ & n0)
•Concentric Circular orbits
Cloud Model
Particle
Symbol
Charge
Mass
(AMU)
Electron
e-
-1
0
Proton
p+
+1
1
Neutron
n0
0
1
•Element = made of one kind of Atom.
•Compounds = made of different atoms combined in
whole number ratios.
•Mixtures are physical combinations of elements or
compounds with variable composition.
What holds nucleus together?
Nuclear Tug-Of-War
 Electrostatic force – like charges repel and unlike
+
+
charges attract +
 Strong
Nuclear Force – holds nucleons (p+ & n0)
together, very strong nuclear force but over short
distances


Stable nuclei are SMALL
Large nuclei tend to be unstable (radioactive)
Where do Atoms Come From?
Fusion
= smaller atoms
combine to form larger atoms
(stars & supernovas)
Fission
= large atoms split
(atomic bombs, nuclear
reactors)
Why don’t electron’s fly off?
 Electrostatic
 Holds
Force
electrons on atom
 Nuclear Pull: + nucleus pulls – electrons towards
itself. More charge = more attraction
Increases
Counting Particles in Atoms Notes
 Atomic
Number = (smaller #) = # of p+
= unique for each element
 Atomic
Mass Number = mass of an atom =
p+ & nº (e- have no mass)
 Complete
Shorthand Symbol “top heavy”
atomic Mass Sym
Atomic #
 Example:
Counting e Atoms
are neutral so, p+ = e(assume an atom is neutral unless a charge is
written)
 Ions = charged atoms (lost or gained e-)
(charge in upper right hand corner )


Cation = positive atom (lost e-)
Anion = negative atom (gained e-)
Neutrons
Isotopes
= atoms of the same element
with diff. numbers of nº and atomic
masses
Sym-mass
13C
U-235
H-3
C-14
6
The
number is the atomic mass
Formulas:



# of p+ = Atomic Number
# of nº = Atomic Mass – Atomic Number
# of e- = Atomic Number – charge
Examples:
 35 Cl –1
17

Mg+2

19 F –1
9
Average Atomic Mass
 All
masses are based on the mass of C =
12 amu (atomic mass unit)


Relative to Carbon
Relative Atomic Mass
 Use

mass spectrometer
Average Atomic Mass
 Weighted
average of the masses of the
isotopes of that element
 Reflects relative abundance of isotopes in
nature
Problem #1: Carbon
To calculate the average atomic weight, each exact atomic
weight is multiplied by its percent abundance (expressed as a
decimal). Then, add the results together and round off to an
appropriate number of significant figures.
mass number
exact weight
percent
abundance
12
12.000000
98.90
13
13.003355
1.10
This is the solution for carbon:
(12.000000) (0.9890) + (13.003355) (0.0110) = 12.011 amu
.
Average Atomic Mass =
Σ
[abundance * mass]
(sum of)
EX:
63 Cu
29
69.1 %
65 Cu
29
30.9 %
(63 * 0.691) = (65 * 0.309) = 63.618
Try These
Problem #3: Chlorine
Problem #4: Silicon
mass
number
exact
weight
percent
abundanc
e
mass
number
exact
weight
percent
abundanc
e
35
34.968852
75.77
28
27.976927
92.23
37
36.965903
24.23
29
28.976495
4.67
30
29.973770
3.10
The answer for chlorine: 35.453
The answer for silicon: 28.086
Warm up 9-15-14
1.
For Ca2+ find the:
 Electrons
 Protons
 Neutrons
 Atomic
Mass
 Atomic Number
2.
Find the Average mass for
Silver:
Isotope name
Isotope mass (a
mu)
percentage
Silver-107
106.90509
51.86
Silver-109
108.90470
remainder
Radioactive Isotopes
(radioactive…radioactive)
 Some
types of atoms spontaneously change
because they are unstable. They eject sub particles
or emit energy and are transformed into different
types of atoms.
 Atoms
that are changed in this way are called
radioactive, and the transformation process is
called radioactive decay.
Products of Decay
 Natural
Decay Products - there are three major
products emitted by the decay of naturally
occurring radioactive isotopes.



Alpha particles (α)
Beta particles (β- & β+)
Gamma ray (γ)
Radiation
Radiation Interaction and
Penetration Through Matter
alpha
High charge, dense ionization, short path
beta
Less mass/charge than alpha, longer path
alpha
gamma
No charge or mass, much less interaction
neutron
No charge, interacts through nuclear events
Not to scale
Alpha Particle a
Characteristics
Range
Shielding
Hazards
Sources
• +2 charge
• 2 protons
• 2 neutrons
• Large mass
• Very short
range
• 1" -2" in air
• Paper
• Outer layer
of skin
• Internal
• Plutonium
• Uranium
• Radium
• Thorium
• Americium
a
a
a
a
a
Beta Particle b
Characteristics
Range
• -1 charge
• Short range • Plastic
safety
glasses
• About 10'
in air
• Thin
metal
• Small mass
Shielding
Hazards
Sources
• Skin and
eyes
•Radioisotopes
• Can be
internal
• Activation
Products
• Sealed
sources
Gamma Ray g
Characteristics Range
Shielding
• No charge
• No mass
• Similar
to x-rays
• Lead
• External
• Steel
(whole body)
• Concrete • Can be
internal
• Long range
• About 1100'
in air
Paper Plastic Lead
Hazards
Sources
• X-ray
machines
• Electron
microscopes
• Sealed
sources
• Accelerators
• Nuclear
reactors
• Radioisotopes
Neutron Particle h
Characteristics Range
Shielding
Hazards
Sources
• No charge
• Found in
nucleus
• Water
• Plastic
• External
(whole body)
• Fission
• Reactor
operation
• Sealed
sources
• Accelerators
• Extended
range
Paper Lead
Water
Half Life
 Half
Life = (t1/2) The amount of time it takes
for ½ of the radioactive isotope to decay
(no longer there- changed into something
else.
 Multiply the mass by ½ for each ½ life that
passes (or divide by 2)
Estimating the AGE of Materials
 Radioactive
carbon-14 atoms are used to estimate
the age of materials that were once living.

Living things all have the same ratio of radioactive carbon to
ordinary carbon. Once something dies, the amount of C-14 begins
to decrease. The ratio of C-14 to C-12 can be used to determine
its age.
 Radioactive
uranium is used to date non-organic
material such as rocks.
Examples of half Life
1. How much of a 10.0 g sample of I-131 is left
after 48 days? (1/2 life = 8 days)
2. After how many days will a 24 g sample
decay to 3.0 g?
3.
After 95 days, a 24 g sample of radioactive material
decays, leaving 0.75g. What is the half-life of this
material?
Periodic Law (Periodicity)
 Properties
repeat at regular intervals
when elements are arranged
according to increasing atomic
number
 Group/family = column; Period =
row
*
Halogens
Alkali Metals
Alkaline Earth Metals
Transition Metals
Inner Transition Metals
Noble Gases
Metal/Metalloid/Nonmetal
Nonmetals
Metals
Metalloids
Representative Elements (1,2,13 – 18)
1A
8A
2A
3A
5A
4A
B’s
7A
6A
.
 Atomic
Number = # of protons
INC
 Atomic
Mass = # of protons & neutrons
INC
 Nuclear
pull = electrostatic attraction of +
nucleus for the negative outer eINC
 Shielding
= e- in between nucleus & outer
e- shield pull
Constant
INC
Atomic Radius
 Atomic
Radius = the distance between the
nucleus and the outermost electrons.
INC
 e-
are added to successively higher
energy levels.
 We remain in the same principle energy
level. Each element has one p+ and one
e- more than the preceding element. The
nuclear pull increases pulling each new ecloser to the nucleus.
The atomic radii of these representative
elements are given in nanometers (nm).
H
0.030
Increasing
atomic radii
Li
0.123
Be
0.089
Na
0.157
Mg
0.136
B
0.080
C
0.077
N
0.070
Al
0.125
Si
0.117
P
0.110
S
0.104
Cl
0.099
Ge
0.122
As
0.121
Se
0.117
Br
0.114
Sb
0.140
Te
0.137
I
0.133
K
0.203
Ca
0.174
Ga
0.125
Rb
0.216
Sr
0.191
In
0.150
Increasing atomic radii
Sn
0.140
O
0.066
F
0.064
Ionic Radius (Size)
Size or radius of an ion
INC
Cations
Anions
The overall trend is the same as Atomic size –
for the same reasons, however:
• Cations have lost e- so they are smaller
• Anions have gained e- so they are larger
The ionic radii shown here are given in nanometers.
Li+
0.060
Be2+
0.031
Na+
0.095
Mg2+
0.065
K+
0.133
Ca2+
0.099
Rb+
0.148
Cs+
0.169
Sr2+
0.113
Ba2+
0.135
B3+
0.020
Al3+
0.050
Ga3+
0.062
In3+
0.081
Tl3+
0.095
C4+
0.015
Si4+
0.041
Ge4+
0.053
Sn4+
0.071
Pb4+
0.084
N30.171
O20.140
P30.212
S20.184
Cl0.181
As30.222
Se20.198
Br0.195
Sb30.245
Te20.221
I0.216
F0.136