1.6 Science in Action: A Case Study
In 1985, a scientist discovered low levels of
ozone in the upper Antarctic atmosphere
The culprit was later revealed to be
chlorofluorocarbons (CFCs)
Coolants in air conditions; propellants in aerosols
CFCs condense into tiny ice crystals
Warmed by the sun, they attack and
destroy ozone
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Fig. 1.6 How CFCs attack and destroy ozone
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1.6 Science in Action: A Case Study
The ozone layer protects us from the sun’s
ultraviolet (UV) rays
1% drop in ozone Æ 6% increase in skin cancers
Its depletion is a serious world problem
So governments have rushed to correct the
situation
There is now a worldwide reduction in CFC
production
The ozone layer will recover by mid-21st century
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1.7 Stages of a Scientific Investigation
The scientific process can be divided into six
stages
1. Observation
Careful observation of a process or phenomenon
Question asked
2. Hypothesis
A probable answer regarding the observation
If more than one answer, alternative hypotheses are
formed
3. Prediction
Expected consequences based on the correct
hypothesis
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1.7 Stages of a Scientific Investigation
The scientific process can be divided into six
stages
4. Testing
The hypothesis is tested through an experiment
5. Controls
A factor that influences a process is called a variable
In a control experiment, all variables are held constant
6. Conclusion
Based on the results of the experiment, a hypothesis
is either accepted or rejected
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Observation
Question
Hypothesis
Conclusion
Prediction
Experiment
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Fig. 1.7
Observation
The scientific “method”
Question
Hypothesis 1
Hypothesis 2
Hypothesis 3
Hypothesis 4
Hypothesis 5
Potential
hypotheses
Reject
hypotheses
1 and 4
Experiment
Hypothesis 5
Hypothesis 3
Hypothesis 2
Remaining
possible
hypotheses
Experiment
Hypothesis 5
Reject
hypotheses
2 and 3
Last remaining
possible hypothesis
Predictions
Experiment 1
Experiment 2
Experiment 3
Experiment 4
Predictions
confirmed
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1.8 Theory and Certainty
A theory is a set of hypotheses that have been
tested many times and not rejected
It indicates a higher degree of certainty
However, there is no absolute truth in science
So the acceptance of a theory is provisional
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1.8 Theory and Certainty
Note:
To scientists, a theory represents that of
which they are most certain
To the general public, a theory represents
lack of knowledge or a guess
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1.8 Theory and Certainty
The limitations of science
It is limited to organisms and processes that
can be observed and measured
Supernatural and religious phenomena are
beyond the scope of science
There are also practical limits
Science cannot be relied upon to solve all
problems
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The Chemistry of Life
Chapter 3
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3.1 Atoms
Matter is any substance in the universe that
has mass and occupies space
All matter is composed of extremely small
particles called atoms
Every atom has the same basic structure
Core nucleus of protons and neutrons
Orbiting cloud of electrons
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Fig. 3.1
e- determine the
chemical behavior
of atoms
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3.1 Atoms
Atomic number
Number of protons
Atomic mass
Number of protons and neutrons
Element
A substance that cannot be broken down by
ordinary chemical means
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Electrons - chemical behavior
Energy is the ability to do work
Electrons have energy due to their relative
orbital position (potential energy)
Fig. 3.2
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Electrons
Each electron shell has a specific # of orbitals
Each orbital holds up to two electrons
Fig. 3.3
Atoms with incomplete
electron orbitals are
more reactive
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3.2 Ions and Isotopes
Ions are atoms in which the number of
electrons does not equal that of protons
Fig. 3.4
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3.2 Ions and Isotopes
Isotopes are atoms with the same number of
protons but different numbers of neutrons
Fig. 3.5
99% of all
carbon
Different
atomic mass
Same atomic
number
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Radioactive Decay
The nucleus of an unstable isotope breaks
down into particles with lower atomic numbers
Radioactive isotopes are used in:
1. Medicine
Tracers are taken up and used by the body
Emissions are detected using special lab equipment
2. Dating fossils
The rate of decay of a radioactive element is constant
The amount of decay can be used to date fossils
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3.3 Molecules
A molecule is a group of atoms held together
by energy
The holding force is called a chemical bond
There are three kinds of chemical bonds
1. Ionic bonds
2. Covalent bonds
3. Hydrogen bonds
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Ionic Bonds
Formed by the attraction of oppositely
charged ions
Two key properties
1. Strong
But not as strong as covalent bonds
2. Not directional
They are not formed between particular ions in the
compound
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Ionic Bonds
Everyday
tablesalt
NaCl
Crystal
Fig. 3.8 The formation of the ionic bond in table salt
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Covalent Bonds
Formed when two atoms share electrons
Two key properties
1. Strong
The strength increases with the number of shared
electrons
2. Very directional
They are formed between two specific atoms
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Covalent Bonds
Fig. 3.9 Water molecules contain two covalent bonds
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Hydrogen Bonds
Formed by the attraction of opposite partial
electric charges between two polar molecules
Two key properties
1. Weak
They are not effective over long distances
2. Highly directional
Polar molecules must be very close for the weak
attraction to be effective
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Hydrogen Bonds
Fig. 3.10 Hydrogen bonding in water molecules
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3.4 Hydrogen Bonds Give Water
Unique Properties
Water molecules are polar molecules
They can thus form hydrogen bonds with each
other and with other polar molecules
Each hydrogen bond is very weak
However, the cumulative effect of enormous
numbers can make them quite strong
Hydrogen bonding is responsible for many of
the physical properties of water
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3.4 Hydrogen Bonds Give Water
Unique Properties
Heat Storage
A large input of thermal energy is required to
disrupt the organization of liquid water
This minimizes temperature changes
Ice Formation
At low temperatures, hydrogen bonds don’t break
Water forms a regular crystal structure that floats
High Heat of Vaporization
At high temperatures, hydrogen bonds do break
Water is changed into vapor
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3.4 Hydrogen Bonds Give Water
Unique Properties
Cohesion
Fig. 3.12
Attraction of water molecules
to other water molecules
Example: Surface tension
Adhesion
Water strider
Attraction of water molecules
to other polar molecules
Example: Capillary action
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3.4 Hydrogen Bonds Give Water
Unique Properties
High Polarity
Polar molecules are termed hydrophilic
Water-loving
All polar molecules that dissolve in water are
termed soluble
Nonpolar molecules are termed hydrophobic
Water-fearing
These do not form hydrogen bonds and are
therefore not water soluble
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Salt dissolves
when all ions
have separated
from the crystal
Fig. 3.13 How salt dissolves in water
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