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Transcript
The Chemistry of Life
Chapter 2
Why should we study
chemistry in
Life depends on chemistry!
• When you eat food or inhale oxygen,
your body uses these materials in
chemical reactions that keep you alive.
• Just as buildings are made from bricks,
steel, glass, and wood, living things are
made from chemical compounds.
• Wouldn’t you want an architect to
understand building materials? Same
idea applies to geneticists, ecologists,
zoologists, botanists, biologists, and
etc.
• The study of chemistry begins with the basic
unit of matter…the
History
• Greeks were first to try to explain chemical
reactions
• 400 BC: thought all matter composed of:
–
–
–
–
Fire
Earth
Water
Air
• Democritus first used word “atomos”, meaning
indivisible
• Atoms are composed of 3 main
particles: (subatomic particles)
– Protons (+)
– Neutrons
– Electrons (-)
Protons and Neutrons
• Strong forces bind protons and
neutrons together to form the
nucleus, which is at the center of
the atom.
• Both particles have about the
same mass.
Electrons
• Electrons are negatively charged
with about 1/1840 the mass of a
proton.
• They are in constant motion in the
space surrounding the nucleus.
• Atoms have equal numbers of
electrons and protons.
• Because these subatomic particles
have equal but opposite charges,
atoms are neutral.
Elements
• Elements are the building blocks
of all matter.
• Elements cannot be decomposed
into simpler matter.
Group Number:
1
2
3 4 5 6 7 8
The Elements
• 110 known elements
• 88 occur naturally
The 110 elements form a plethora of
compounds, just as 26 letters of the
alphabet make a seemingly endless
number of words.
Atomic Number
Counts the number
of
protons
in an atom
Atomic Number on the
Periodic Table
Atomic Number
Symbol
11
Na
All atoms of an element have
the same number of protons
11 protons
Sodium
11
Na
Atomic Mass
• Mass of an atom.
• Approximately equal to the number
of protons and neutrons
• Find number of neutrons by
subtracting the number of protons
from the mass.
Review:
• An element's atomic number tells how
many protons are in its atoms.
• An element's mass number tells how
many protons and neutrons are in its
atoms.
Learning Check 1
State the number of protons for atoms of
each of the following:
A. Nitrogen
1) 5 protons
2) 7 protons 3) 14 protons
B. Sulfur
1) 32 protons
2) 16 protons
3) 6 protons
C. Barium
1) 137 protons 2) 81 protons
3) 56 protons
The Periodic Table
Isotopes
• Isotopes are atoms that have the
same atomic number but different
mass number.
• Most elements have two or more
isotopes.
• Same chemical properties because
the electron number does not
change.
Isotope symbols
Mass number
A
Z
Atomic number
X
Example
11
B
5
•How many protons does this have?
•How many neutrons does this have?
•Is the “5” necessary ?
More about isotopes:
• Some isotopes have unstable nuclei
which break down over time.
• They are called radioactive
isotopes
• Some radiation is harmful.
• Radiation can also be useful
Radioactive Dating
Cancer
Treatment
Tracers with X-rays
Kill bacteria
More About Atomic
Structure
• The center of the atom is called
the nucleus.
• Electrons live in something
called shells.
• Shells are areas that surround
the center of an atom.
• A shell is sometimes called an
orbital or energy level.
More About Electrons
• Every shell can hold only so many
electrons
• The further from the nucleus, the more
electrons a shell can hold
Valence Electrons
• The electrons on the outside edge of
the atom
• This is where the action is- where
bonding takes place
• Atoms have no more than 8 valence
electrons
The Octet Rule:
• Atoms will combine to form
compounds in order to reach eight
electrons in their outer energy level.
This is very stable!
•
Atoms with less than 4 electrons
tend to lose electrons.
•Atoms with more than 4
electrons tend to gain
electrons.
Compound
• Two or more elements chemically
combined in specific proportions
• Examples:
– Water
– Salt
– Sugar
H 2O
NaCl
C6H12O6
Chemical Formulas
are used to
represent
compounds
Two types of compounds:
Ionic
Covalent
Ionic Compounds
• Form when electrons are transferred
from one atom to another.
Ions - Atoms with a net charge due to
gaining or losing electrons
– Gaining electrons gives an ion a negative charge
– Losing electrons gives an ion a positive charge
**If they have to choose, atoms
would rather be stable (with a full
“octet”) than neutral.
How Does This Happen?
Some atoms have a few too
many electrons
Some atoms only need a few
electrons
What do you do if you are a sodium (Na)
atom with one extra electron?
Go look for an atom that
wants it!
Ionic Bonding
• Negative ions and positive ions are held
together by ionic bond.
• Ionic compounds form between
metals and nonmetals
What If No One Will Give Up
An Electron?
• Atoms with less than 8 valence electrons
can move close to each other and share
their electrons
• The electrons spend their time around
both atoms.
• And they lived happily ever after!
Covalent Bonds
• Formed when a pair of electrons is shared
between two atoms.
• Sometimes the atoms share two pairs of
electrons and form a double bond, or three
pairs of electrons to form a triple bond.
• Structures formed by
covalent bonds are
molecules.
• Covalent compounds form between
2 nonmetals
Van der Waals Forces
• There are small
attractive forces
between all atoms
• Help to hold molecules to
each other
– Ex: Gecko
Let’s summarize what we know!
Why do compounds form?
• Atoms are trying to get 8 valence electrons
How do compounds form?
• By ionic (e- transfer) or covalent (e- sharing)
bonding
How can you tell if a compound is ionic or
covalent?
• By the types of elements in the compound
(ionic = M + M
covalent = M + NM)
Learning Check 2:
Indicate whether a bond between the following
would be 1) Ionic
2) covalent
___
A.
sodium and oxygen
___
B.
nitrogen and oxygen
___
C.
phosphorus and chlorine
___
D.
calcium and sulfur
___
E.
chlorine and bromine
2-2 Water is a Polar Molecule
• Polar: Molecule in which electrons are
shared unevenly between atoms,
causing each end of the molecule to
have a slight charge
Negative end
Positive end
• This causes water to be attracted to other
polar or charged particles
– Water is attracted to ions
– Water is attracted to itself, forming
hydrogen bonds
Hydrogen Bonds In Water Are
Responsible For:
• Adhesion
– Attraction between molecules of
different substances
– Graduated cylinder
• Cohesion
– Attraction between molecules of
the same substance
– Drops of water on a penny
• Ex: Surface Tension
• Jesus Lizard
Types of Chemical Substances
• Compounds and Elements are
called pure substances.
• Most matter is neither of these.
Mixtures
• Mixtures are combinations of
substances held together by
physical forces, not chemical bonds.
• Each substance keeps its own
properties
Mixtures may be either:
Solutions
Colloids
Suspensions
Solutions
• Have small particles
• Are transparent (not the same as colorless)
• Do not separate
• Water solutions are very common in
biological systems
– Examples: salt water, kool-aid, air, brass,
vinegar
Colloids
• Have medium size particles
• Do not separate
– Examples: fog, whipped cream, milk,
cheese, mayonnaise
Suspensions
• Have very large particles
• Settle out (separates into layers)
– Examples: blood platelets, muddy
water, calamine lotion, oil & water,
Italian salad dressing
pH Scale
• Measures concentration of hydrogen
ions in a solution
• Ranges from 0 to 14
• 7 is neutral
• 0-7 have more hydrogen ions (H+)
and are acidic
• 7-14 have more hydroxide ions (OH-)
and are basic
Acids, Bases, and pH
• Water molecules form ions
– H2O
H+
– Water
hydrogen ion
+
+
OHhydroxide ion
• Very few ions are formed in pure
water, but there are equal numbers
of hydrogen and hydroxide ions
• Water is neutral!
pH of common substances
pH and Homeostasis
• Maintaining a pH between 6.5 and
7.5 is important in cells
• Dissolved compounds called
buffers control pH
– Proteins
– Phosphates
– Hydrogen carbonate
Chemical Reactions
• When one set of chemicals changes
into another set of chemicals, a
chemical reaction occurs
• Bonds are either broken or formed
(or both!)
Chemical Equations
• Represent a reaction
• Give the types and amounts of
substances that react and form
Reactants
2H2 + O2
“yields”
“yields”
Products
2H2O
Evidence of a Chemical Reaction
• Formation of a precipitate (a solid
substance separated from a liquid)
• Gas is evolved (seen by bubbles
forming in a liquid)
• Change in heat or light energy
Organic
Compounds
Organic Compounds
• Make up most of living organisms
• Contain bonds between two or more
carbon atoms
• C can easily bond with up to 4 other
elements
4 valence
electrons =
4 covalent
bonds
Organic Compounds
• Carbon atom is versatile, can be
“backbone” of long chains or rings
• Organic molecules can be extremely
large and complex; these are called
macromolecules
Organic Compounds
• Four main types of organic
macromolecules:
Carbohydrates
Lipids
Proteins
Nucleic Acids
Carbohydrates
• Made of C, H, & O
• Main energy source for
living things
• Breakdown of sugars
supplies immediate energy
for cell activities
• Extra sugar is stored as
complex carbs called
starches
Carbohydrates
• Single sugar
molecules are called
monosaccharides
• Examples:
• glucose – in many plant
and animal tissues, most
common monosaccharide
• fructose – in many fruits
• galactose – component of
milk
Carbohydrates
• Large molecules of many
monosaccharide are
polysaccharides
• Examples:
• glycogen – animals use to store
excess sugar
• plant starch – plants use to store
excess sugar
• cellulose – fibers that give plants
their rigidity & strength
Lipids
• Store more energy than CHOs
because the chains are longer
• Ex: Fats, oils, waxes
• Won’t dissolve in water
Lipids
• Important parts of biological
membranes and waterproof
coverings
• Steroids are lipids that act as
chemical messengers
Lipids
• Many lipids are made from a
glycerol combined with fatty acids
– If all carbons have single bonds, lipid is
saturated
– Ex: butter, lard, animal fat (usually solid at room
temperature)
– If any carbons have double or triple
bonds, lipid is unsaturated
– Ex: vegetable oil, fish oil, peanut oil
room temperature)
(usually liquid at
Proteins
• Contain C, H, O, plus nitrogen
• Formed from amino acids joined
together
• More than 20 amino acids can be
joined in any order or number to
make countless proteins (think of how
many words can be made from 26 letters!)
Proteins
• Chains are folded and twisted giving
each protein a unique shape
• Van der Waals forces and hydrogen
bonds help maintain protein’s shape
• Shape of protein is important to its
function!
Proteins
• Provide structure
– Ex: Collagen- makes up your skin,
muscles & bones
• Aid chemical activities in your body
– Ex: Enzymes- work to speed up
rxns in your body
• Transport substances into or out of
cells
• Help fight diseases
Nucleic Acids
• Contain C, H, O, N plus
phosphorus
• Formed by bonding of
individual units called
nucleotides
nucleotide
Nucleic Acid
Nucleic Acids
• Store and transmit hereditary
information
–Ex: DNA (deoxyribonucleic acid)
RNA (ribonucleic acid)