Title: The Chemistry of Life Chapter 2
1The Chemistry of LifeChapter 2
2Why should we study chemistry in
Biology?
Life depends on chemistry!
3Life 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. - Wouldnt you want an architect to understand
building materials? Same idea applies to
geneticists, ecologists, zoologists, botanists,
biologists, and etc.
4Atoms
- The study of chemistry begins with the basic unit
of matterthe - 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
Atom
5Atoms
- Atoms are composed of 3 main particles
(subatomic particles) - Protons ()
- Neutrons
- Electrons (-)
6Protons 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.
7Electrons
- Electrons are negatively charged with about
1/1840 the mass of a proton. - They are in constant motion in the space
surrounding the nucleus.
8Atoms
- Atoms have equal numbers of electrons and
protons. - Because these subatomic particles have equal but
opposite charges, atoms are neutral.
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10Elements
- 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
11The 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.
12Atomic Number
-
- Counts the number
- of
- protons
- in an atom
13Atomic Number on the Periodic Table
14All atoms of an element have the same number of
protons
15Atomic 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.
16Review
- 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.
17Learning 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
2) 7 protons
2) 16 protons
3) 56 protons
18The Periodic Table
19Isotopes
- 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.
What does that mean?
20Isotope symbols
21Example
22More about isotopes
- Some isotopes have unstable nuclei which break
down over time. - They are called radioactive isotopes
- Some radiation is harmful.
23- Radiation can also be useful
Radioactive Dating
Tracers with X-rays
Cancer Treatment
Kill bacteria
24More 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.
25More About Electrons
- Every shell can hold only so many electrons
- The further from the nucleus, the more electrons
a shell can hold
26Valence 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
27Energy Level (Shell) Maximum Number of Electrons Max number of Valence Electrons
1 2 2
2 8 8
3 18 8
4 32 8
5 50 8
6 72 8
7 98 8
28The 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.
29Compound
- Two or more elements chemically combined in
specific proportions - Examples
- Water H2O
- Salt NaCl
- Sugar C6H12O6
- Two types of compounds
- Ionic
- Covalent
30Ionic 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.
31How Does This Happen?
Some atoms have a few too many electrons
Some atoms only need a few electrons
32 What do you do if you are a sodium (Na) atom
with one extra electron?
- Go look for an atom that wants it!
33Ionic Bonding
- Negative ions and positive ions are held together
by ionic bond.
34- Ionic compounds form between metals and nonmetals
35What 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!
36Covalent 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.
37- Covalent compounds form between 2 nonmetals
38Van der Waals Forces
- There are small attractive forces between all
atoms - Help to hold molecules to each other
- Ex Gecko
39Why do compounds form?
Lets summarize what we know!
- 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)
40Learning 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
412-2 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
42- 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
43Hydrogen 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
44Types of Chemical Substances
- Compounds and Elements are called pure
substances. - Most matter is neither of these.
45Mixtures
- Mixtures are combinations of substances held
together by physical forces, not chemical bonds. - Each substance keeps its own properties
46Mixtures may be either
47Solutions
- 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
48Colloids
- Have medium size particles
- Do not separate
- Examples fog, whipped cream, milk, cheese,
mayonnaise
49Suspensions
- Have very large particles
- Settle out (separates into layers)
- Examples blood platelets, muddy water, calamine
lotion, oil water, Italian salad dressing
50pH 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
51Acids, Bases, and pH
- Water molecules form ions
- H2O H OH-
- Water hydrogen ion hydroxide ion
- Very few ions are formed in pure water, but there
are equal numbers of hydrogen and hydroxide ions - Water is neutral!
52pH of common substances
53pH 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
54Chemical Reactions
- When one set of chemicals changes into another
set of chemicals, a chemical reaction occurs - Bonds are either broken or formed (or both!)
55Chemical Equations
- Represent a reaction
- Give the types and amounts of substances that
react and form - Reactants Products
- 2H2 O2
yields
yields
2H2O
56Evidence 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
57Organic Compounds
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59Organic 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
60Organic 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
61Organic Compounds
- Four main types of organic macromolecules
- Carbohydrates
- Lipids
- Proteins
- Nucleic Acids
62Carbohydrates
- 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
63Carbohydrates
- 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
64Carbohydrates
- 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
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66Lipids
- Store more energy than CHOs because the chains
are longer - Ex Fats, oils, waxes
- Wont dissolve in water
67Lipids
- Important parts of biological membranes and
waterproof coverings - Steroids are lipids that act as chemical
messengers
68Lipids
- 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 (usually
liquid at room temperature)
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70Proteins
- 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!)
71Proteins
- Chains are folded and twisted giving each protein
a unique shape - Van der Waals forces and hydrogen bonds help
maintain proteins shape - Shape of protein is important to its function!
72Proteins
- 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
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74Nucleic Acids
- Contain C, H, O, N plus phosphorus
- Formed by bonding of individual units called
nucleotides
Nucleic Acid
nucleotide
75Nucleic Acids
- Store and transmit hereditary information
- Ex DNA (deoxyribonucleic acid)
- RNA (ribonucleic acid)
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