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BIO 1010 Chapter 2 - Chemistry
Why study chemistry?
Corpse flower
Devil’s Gardens
Why are there 800 year old stands of only lemon trees in the middle of the
Amazon rain forest?
Some Basic Chemistry
Take any biological system apart, and you eventually end up at the chemical level.
Chemical reactions are always occurring in the human body and our environment.
Figure 1.2-3
Organisms5
12
3
4
7
6
8
109
BiosphereEcosystems
Populations
Communities
Organ Systemsand Organs
Tissues
Cells
OrganellesMolecules and Atoms
NucleusAtom
Are Chemicals Bad or Good for you?
Misconceptions and Concerns about chemicals
Appreciation for chemical nature of our bodies and our world
Potential harms and benefits
Several chemicals are added to food for a variety of reasons
–Help preserve it–Make it more
nutritious
–Make it look better
Matter: Elements and Compounds
Matter is anything that occupies space and has mass.
Matter is found on Earth in three physical states:
solid,
liquid, and
gas.
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Matter is composed of chemical elements.
An element is a substance that cannot be broken down into other substances by chemical reactions.
There are 92 naturally occurring elements on Earth.
All of the elements are listed in the periodic table.
Matter: Elements and Compounds
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Elements & AtomsElement: a substance that can neither be broken down nor converted to another substance by chemical reactions. Pure substance that contains only one type of atom
Figure 2.1a
Atomic number(number of protons)
Mass number(number of
protons plus neutrons)
Element symbol
12
6
C
He
Ne
Se Br
Cl
F
Ar
Kr
Xe
ONCB
SPSiAl
I
Ge AsGa
TeSbSnIn
MnCr
Po At RnPb BiTI
CoFeV CuNi Zn
Tm Yb LuHo ErDy
BeLi
MgNa
K ScCa Ti
MoNb RuTc PdRh AgYSrRb Zr
H
Cd
LaBa TaHf OsRe IrW AuPt HgCs
BhSg MtHs RgDs CnFr AcRa Rf Db
Md No LrEs FmCfAm Cm BkNp PuU
Eu Gd TbPm SmNd
Pa
Pr
Th
Ce
Figure 2.1b
Thermometers, dental fillings and batteriesMercury in the air settles into water. It can pass through the food chain and build up in fish, shellfish and animals that eat fish. Exposure to high levels can damage the brain and kidneys. Can damage the kidneys and the nervous system, and interfere with development of the brain in the very young children
Mercury
Figure 2.1c
Deficiencies of copper can cause premature hair graying, sterility and premature wrinkling of the skin.
Figure 2.1d
Affects nearly all system: Hearing loss, kidney problems, lower IQ, children are more vulnerable because they tend to place things in their mouths.Houses built before ‘78, present toys, pipes, faucets
Lead
Twenty-five elements are essential to people.
Four elements make up about 96% of the weight of most cells:
oxygen,
carbon,
hydrogen, and
nitrogen.
Matter: Elements and Compounds
© 2013 Pearson Education, Inc.
ELEMENTS, ATOMS, AND MOLECULES
What is matter?There are 92 chemical elements in nature
Life requires 25 essential elements; some are called trace elements.
Figure 2.2
Oxygen (O):65.0%
Carbon (C): 18.5%
Calcium (Ca): 1.5%
Magnesium (Mg): 0.1%
Chlorine (Cl): 0.2%
Sodium (Na): 0.2%
Sulfur (S): 0.3%
Potassium (K): 0.4%
Phosphorus (P): 1.0%
Hydrogen (H):9.5%
Nitrogen (N):3.3%
Trace elements: less than 0.01%
Iron (Fe)Iodine (I)Fluorine (F)Copper (Cu)Cobalt (Co)Chromium (Cr)Boron (B)
Zinc (Zn)Vanadium (V)Tin (Sn)Silicon (Si)Selenium (Se)Molybdenum (Mo)Manganese (Mn)
Trace elements are
required in only very small amounts and
essential for life.
An iodine deficiency causes goiter.
Fluorine
is added to dental products and drinking water and
helps to maintain healthy bones and teeth.
Matter: Elements and Compounds
© 2013 Pearson Education, Inc.
Trace elements are common additives to food and water
–Without iron, your body cannot transport oxygen
–An iodine deficiency prevents production of thyroid hormones, resulting in goiter
-Deficiencies of copper can cause premature hair graying, sterility and premature wrinkling of the skin.
Figure 2.3
Elements can combine to form compounds.
Compounds are substances that contain two or more elements in a fixed ratio.
Common compounds include
NaCl (table salt) and
H2O (water).
Matter: Elements and Compounds
© 2013 Pearson Education, Inc.
Sodium Chloride(Kitchen salt)
Chlorine(poisonous gas)
Sodium(metal)
+
Compound—a substance consisting of two or more different elements combined in a fixed ratio
Atoms
Each element consists of one kind of atom.
An atom is the smallest unit of matter that still retains the properties of an element.
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Electroncloud
Protons
2e–Nucleus
Electrons
Massnumber = 4Neutrons
2
2
2
Atoms consist of protons, neutrons, and electrons
Electrons are kept in orbit by the attraction between the negatively charged electrons and positively charged protons
Atomic number: 2 (number of protons)
Mass number: 4 (sum of the number of protons and neutrons in its nucleus
The Structure of Atoms
Atoms are composed of subatomic particles.
A proton is positively charged.
An electron is negatively charged.
A neutron is electrically neutral.
Most atoms have protons and neutrons packed tightly into the nucleus.
The nucleus is the atom’s central core.
Electrons orbit the nucleus.
© 2013 Pearson Education, Inc.
Atomic Number
C12Mass number(atomic weight)
( # Protons + # Neutrons)
6Atomic Number(# of Protons in an atom)
Atomic Symbol(Carbon)
The atomic number determines which
element it is.
# protons = atomic number# electrons = atomic number
(in an uncharged atom)# neutrons = mass number – atomic number
Elements differ in the number of subatomic particles in their atoms.
The number of protons, the atomic number, determines which element it is.
Mass is a measure of the amount of material in an object.
An atom’s mass number is the sum of the number of protons and neutrons in its nucleus.
The Structure of Atoms
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Isotopes
Isotopes are alternate mass forms of an element.
Isotopes
have the same number of protons and electrons but
differ in their number of neutrons.
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Atomic Weight (Mass Number) May Vary
Isotope: a variant form of an atom with same number of protons but different numbers of neutrons
Naturally occurring carbon 99% ~1% Minute quantities
Stable isotopes Radioactive: the nucleus decays
Atomic number:
Mass number:
Table 2.1
The nucleus of a radioactive isotope decays spontaneously, giving off particles and energy.
Radioactive isotopes have many uses in research and medicine.
They can be used to determine the fate of atoms in living organisms.
They are used in PET scans to diagnose heart disorders and some cancers.
Isotopes
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Radioisotopes in Medicine & Research
when radioactive compounds are used in metabolic processes, they act as radioactive tracers
An imaging instrument that uses positron-emission tomography (PET) detects the location of injected radioactive materials
Normal Alzheimer’s
C isotope studies can be used to identify areas with histories of vegetation change
How the Maya were able to sustain such large populations is still a question today.
Use of Carbon Isotopes in Determining Ancient Maya Land Use
Jungle: C3 Plants
Discriminate more against CO2 containing 13C isotope
Maize: C4 Plants
Why is the energy emitted in radioactive decay hazardous?
.
Radioactive Isotopes Can Harm
Uncontrolled exposure to radioactive isotopes can harm living organisms by damaging DNA.
The 1986 Chernobyl nuclear accident released large amounts of radioactive isotopes.
Naturally occurring radon gas may cause lung cancer.
Electron arrangement determines the chemical properties of an atom
Only electrons are involved in chemical activity
Electrons occur in energy levels called electron shells The number of electrons in
the outermost shell determines the chemical
properties of an atom
Electron Arrangement and the Chemical Properties of Atoms
Electrons orbit the nucleus of an atom in specific electron shells.
The farther an electron is from the nucleus, the greater its energy.
The number of electrons in the outermost shell determines the chemical properties of an atom.
© 2013 Pearson Education, Inc.
The number of electrons in the valence shell (outermost shell) determines the chemical properties of the atom
Elements whose outer shells contain unfilled
orbitals are chemically reactive
When all the orbitals are filled, the element
is inactive (inert)
An uncharged atom of gold has an atomic number of 79 and a mass number of 197. This atom has _________ protons, _______ neutrons, and __________ electrons.
a. 79 …118 …79
b. 118 …79 …118
c. 276 …118 …79
d. 79 …276 …79
The most abundant element found in the human body by weight is _________.
a. oxygen
b. carbon
c. fluorine
d. hydrogen
Isotopes of atoms differ in their number of __________.
a. neutrons
b. electrons
c. protons
d. atomic nuclei
Intro to Atoms, Ions etc
http://www.youtube.com/watch?v=UhXS-iR2L3U
Chemical Bonding and Molecules
Chemical reactions enable atoms to give up or acquire electrons, completing their outer shells.
Chemical reactions usually result in atoms
staying close together and
being held together by attractions called chemical bonds.
© 2013 Pearson Education, Inc.
NaSodium atom
Transfer ofelectron
ClChlorine atom
Ionic bonds are attractions between ions of opposite charge
The octet rule:atoms are moststable when theirouter most energyshells are either fullor empty
Ions: atoms electrically charged as a result of gaining or losing electrons
Complete transfer of electrons. Attraction between ions of opposite charge
NaSodium atom
Transfer ofelectron
ClChlorine atom
Na+
Sodium ionCl–
Chloride ion
Sodium chloride (NaCl)
+ –
Na+
Cl–
Covalent bonds join atoms into molecules through electron sharing
A covalent bond results when atoms share outer-shell electrons
– A molecule is formed when atoms are held together by covalent bonds
Covalent BondsThe number of covalent bonds an atom can form is equal to the number of additional electrons it needs to fill its valence shell
– A single bond forms when two electrons are shared between two atoms
– A double bond forms when four electrons are shared between two atoms
– A triple bond forms when ______ electrons are shared between two atoms
Electrons are Unequally Shared in Polar Covalent Bonds
Fig 2.8
Oxygen draws sharedelectrons towards itselfOxygen becomes “a little” negativeHydrogens become “a little” positiveResults in Hydrogen Bonds betweenneighboring molecules
Water molecule
Polar molecule: opposite charges on opposite ends
Weak electrical attractions
Hydrogen bond
Water molecules are electrically attracted to oppositely charged regions on neighboring molecules
Because the positively charged region is always a hydrogen atom, the bond is called a hydrogen bond
Hydrogen bonds are weak bonds important in the chemistry of life
Type Chemical basis Strength Example
Covalent bonds Atoms share electron pairs
Strong Hydrocarbons, methane
Ionic bonds Atoms donate one or more electrons to other atom of opposite charge
Moderate Sodium chlorideSodium iodide
Hydrogen bonds Atoms with partial negative charge attract hydrogen atoms
Weak Water, DNA
Chemical bonds and attractive forces
WATER’S LIFE-SUPPORTING PROPERTIES
WATER AND LIFE
Life on Earth began in water and evolved there for 3 billion years.
Modern life remains tied to water.
Your cells are composed of 70–95% water.
The abundance of water is a major reason Earth is habitable.
© 2013 Pearson Education, Inc.
Water’s Life-Supporting Properties
The polarity of water molecules and the hydrogen bonding that results explain most of water’s life-supporting properties.
Water molecules stick together.
Water has a strong resistance to change in temperature.
Frozen water floats.
Water is a common solvent for life.
© 2013 Pearson Education, Inc.
Biology and Society: More Precious than Gold
A drought is
a period of abnormally dry weather that changes the environment and
one of the most devastating disasters.
© 2013 Pearson Education, Inc.
Figs 2.12, 2.13
Surface Tension Capillary Action
Cohesion: attraction between molecules (water= hydrogen bonds)
Hydrogen bonds give water a high surface
tension
Droughts can cause
severe crop damage,
shortages of drinking water,
dust storms,
famine,
habitat loss, and
mass migration.
Biology and Society: More Precious than Gold
© 2013 Pearson Education, Inc.
Throughout human history, droughts have helped wipe out societies and even whole civilizations.
Droughts are catastrophic because life cannot exist without water.
Biology and Society: More Precious than Gold
© 2013 Pearson Education, Inc.
Water resistance to temperature change stabilizes ocean temperatures.
Evaporative cooling: when a substance evaporates, the surface of the liquid remaining behind cools down
Water’s hydrogen bonds moderate temperature
Because of hydrogen bonding, water has a greater ability to resist temperature change than other liquids.
The efficiency of evaporative cooling is affected by humidity.
Water Expands When Frozen
Fig 2.15
Fewer molecules than an equal volume of liquid
What is a solution? Example
What is a solvent? Example
What is an aqueous solution?
What is a solute? Example
Ionic bond between Na+ and Cl- holds
ions together in a solid crystal
Dissolve in water:The chloride anion (-) attracts the (+) pole of water
The sodium cation (+) attracts the (-) pole of water
Dissolved ions cannot
re-associate into a solid
Water is a polar solvent:A polar molecule has opposite charges on opposite ends
Ion insolution
Saltcrystal
Water is the solvent of life
Fig 2.17
Ionization of Water:Water dissociates
hydrogen ions H+
hydroxide ions OH-
Bases: release OH- (or accept H+): decrease [H+]
Sodium Hydroxide Na+ & OH -
Acids: release H+ (or accept OH-): increase [H+]
Hydrochloric acid: HCl H+ & Cl- (in your stomach)
The chemistry of life is sensitive to acidic and basic conditions
Figure 2.17a
OH−
OH−
OH−
OH−
OH−
OH−H
H
Basic solution
OH−
OH−
OH−OH−
H
H
H
H
OH−
OH−
H
H
HH
H
H
Neutral solution
Acidic solution
The pH Scale
A pH scale (pH = potential of hydrogen) is used to describe whether a solution is acidic or basic.
–pH ranges from 0 (most acidic) to 14 (most basic)
–A solution that is neither acidic or basic is neutral (pH = 7)
Acid rain Water reacting with pollutants (SO2, NO)pH 2-3
Normal rain:pH 5.6
Buffers minimize changes in pH
Buffers Act as H+ reservoirs
• Take up H+ ions when they are abundant, release them when they are scarce.
• Keep proton concentration steady.
• A buffer that maintains pH 7:
• accepts protons if pH is < 7,
• releases protons if pH is > 7
The Carbonic-Acid-Bicarbonate Buffer in Blood
When we exercise, we increase the H+ concentration in our blood stream:
[H+] increases
Blood pH decreases
Our blood contains a buffering system
Chemical reactions make and break bonds, changing the composition of matter
You learned that the structure of atoms and molecules determines the way they behave
– Remember that atoms combine to form molecules
– Hydrogen and oxygen can react to form water
2 H2 O2 2 H2O
Reactants
Product
You should now be able to
1. Describe the importance of chemical elements to living organisms
2. Explain the formation of compounds
3. Describe the structure of an atom
4. Distinguish between ionic, hydrogen, and covalent bonds
5. Define a chemical reaction and explain how it changes the composition of matter
6. List and define the life-supporting properties of water
7. Explain the pH scale and the formation of acid and base solutionsCopyright © 2009 Pearson Education, Inc.