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Chapter 2
The Chemistry of Life
Atoms
• Atoms
– The study of chemistry begins with the basic
unit of matter, the atom.
– Placed side by side, 100 million atoms would
make a row only about 1 centimeter long.
– Atoms contain subatomic particles that are
even smaller.
Atoms
– The subatomic particles that make up atoms
are
• Protons –Positively Charged
• Neutrons - No Charge
• Electrons – Negatively Charged
Atoms
• The subatomic
particles in a
helium atom.
Atoms
• Protons and neutrons have about the
same mass, 1 amu
• Strong forces bind protons and neutrons
together to form the nucleus, which is at
the center of the atom.
Atoms
• The electron with 1/1840 the mass of a
proton.
• Electrons are in constant motion in the
space surrounding the nucleus because of
the energy of their motion.
Atoms
• Because atoms have equal numbers of
electrons and protons, and because
these subatomic particles have equal but
opposite charges, atoms are neutral.
Elements and Isotopes
• Elements and Isotopes
• A chemical element is a pure substance that
consists entirely of one type of atom.
• Elements are represented by a one- or two-letter
symbol.
– C stands for carbon.
– Na stands for sodium.
Elements and Isotopes
• The number of protons in an atom of an
element is the element's atomic number.
• Carbon has 6 protons, so its atomic number is
6.
Elements and Isotopes
– Isotopes
• Atoms of the same element that differ in the
number of neutrons they contain are known as
isotopes.
• The sum of the protons and neutrons in the
nucleus of an atom is called its mass number.
Elements and Isotopes
Isotopes of Carbon
6 electrons
6 protons
6
7
8 neutrons
Chemical Compounds
• Chemical Compounds
• In nature, most elements are found combined with
other elements in compounds.
• A chemical compound is a substance formed by
the chemical combination of two or more elements
in definite proportions.
Chemical Bonds
• Chemical Bonds
• The atoms in compounds are held together by
chemical bonds.
• Bond formation involves the electrons that
surround each atomic nucleus.
• The electrons that are available to form bonds are
called valence electrons.
Chemical Bonds
– The main types of chemical bonds are:
• ionic bonds – transfer electrons
• covalent bonds – share electrons
Chemical
Bonds
Chlorine ion (Cl-)
Sodium atom (Na)
Sodium ion (Na+)
Chlorine atom (Cl)
Protons
Electrons
+11
- 11
10
Protons
Electrons
+17
18
- 17
Charge
+10
Charge
-10
Chemical Bonds
• In a water
molecule, each
hydrogen atom
forms a single
covalent bond with
the oxygen atom.
Chemical Bonds
– Ionic Bonds
• An ionic bond is formed when one or more
electrons are transferred from one atom to another.
• An atom that loses electrons has a positive
charge.
• An atom that gains electrons has a negative
charge.
• These positively and negatively charged atoms are
known as ions.
Chemical Bonds
– Covalent Bonds
• Sometimes electrons are shared by atoms instead
of being transferred.
• Sharing electrons means that the moving electrons
actually travel in the orbitals of both atoms.
Chemical Bonds
• A covalent bond forms when electrons
are shared between atoms.
• When the atoms share two electrons, the bond is
called a single covalent bond.
• When atoms share four electrons it is called a
double bond.
• When atoms share six electrons it is called a triple
bond.
Chemical Bonds
• The structure that results when atoms are
joined together by covalent bonds is called
a molecule.
• A molecule is the smallest unit of most
compounds.
Chemical Bonds
– Van der Waals Forces
• When molecules are close together, a slight
attraction can develop between the oppositely
charged regions of nearby molecules.
• Chemists call such intermolecular forces of
attraction van der Waals forces, after the scientist
who discovered them.
Chemical Bonds
• Although van der Waals forces are not as
strong
• as ionic bonds or covalent bonds, they can
hold
• molecules together, especially when the
molecules
• are large.
Chemical Bonds
• For example, van der
Waals forces form
between the
molecules on the
surface of a gecko’s
foot and the
molecules on the
surface of the wall.
• The combined
strength of all the van
2-2 Properties of Water
• Water stores heat efficiently
– Water retains heat longer than many other
substances
– Water is essential in maintaining homeostasis
2-2 Properties of Water
• Polarity
– Water is considered to be a polar molecule
due to an uneven distribution of charge.
– The electrons in a water molecule are shared
unevenly between hydrogen and oxygen.
– The polarity of water makes it effective at
dissolving other polar substances such as
sugars, ionic compounds, and some proteins.
Polar Water Molecule
+
-
2-2 Properties of Water
• A hydrogen bond is
the force of attraction
between a positive
charge of one
molecule and
negative charge of
another.
2-2 Properties of Water
• Cohesion and Adhesion
– Cohesion is an attractive force that holds
molecules of a single substance together,
such as water molecules
– Adhesion is the attractive force between two
particles of different substances, such as
water molecules and glass molecules.
2-2 Properties of Water
• Solutions
– A solution consists of a solute dissolved in a
solvent
• i.e. Chocolate milk
– Milk is the solvent
– Chocolate powder is the solute
2-2 Properties of Water
• Acids and Bases
– Ionization of Water
• Water ionizes into hydronium ions (H3O+) and
hydroxide ions (OH–)
2-2 Properties of Water
• Acids
– Acidic solutions contain more hydronium
ions (H3O+) than hydroxide ions (OH–)
2-2 Properties of Water
• Bases
– Basic solutions contain more hydroxide ions
(OH–) than hydronium ions (H3O+).
2-2 Properties of Water
• pH
– Scientists have developed a scale for
comparing the relative concentrations of
hydronium ions (H3O+) and hydroxide ions
(OH–) in a solution.
– This scale is called the pH scale, and it
ranges from 0 to 14.
2-2 Properties of Water
• Buffers
– Buffers are chemicals that neutralize the
effects of an acid or a base by adding small
amounts of the opposite (either an acid or a
base) to a solution.
2-3 Carbon Compounds
•
•
•
•
Carbon is the element of life
Organic compounds – carbon containing
Inorganic compounds- carbon lacking
Carbon has 4 valence e– Will make 4 strong covalent bonds
Carbon found in many forms
– Straight chain
– Branched chain
2-3 Carbon Compounds
• Carbon found in many forms
– Carbon ring
– Double bonded
– Triple bonded
2-3 Carbon Compounds
• Macromolecules – “giant molecules”
– Small units called monomers, come together
in a process called polymerization
• They form polymers
2-3 Carbon Compounds
• Carbohydrates (CHO)
– C1H2O1
– Main energy source
– Only source of brain food (glucose)
– 4cal/1gram
– 1 cal = amount of energy needed to raise
1g of water, 1 °C
2-3 Carbon Compounds
• Carbohydrates
– Sugars
• Monosaccharides – simple sugars, I ring of carbon
– glucose
• Disaccharides- 2 sugars, 2 rings
– sucrose
• Polysaccharides- many sugars
– starches
2-3 Carbon Compounds
• Lipids – Fats
– Insulate, protect, shock absorber, energy
storage, cell membranes
– 9cal/1gram
2-3 Carbon Compounds
• Lipids
– Fatty Acid Chains
• Unsaturated -CH=CH- (double bonds) -liquids
• Saturated –CH2-CH2- (single bonds) -solids
2-3 Carbon Compounds
• Nucleic Acids
– DNA, RNA
• Nucleotide
– 5 Carbon sugar
– Nitrogen base
– Phosphate group
2-3 Carbon Compounds
• Proteins
– Building blocks of the body
– 4cal/1 gram
– Made of Amino Acids- 20 A.A.
• We produce 12 A.A.
• 8 essential A.A. we must consume
– Enzymes
• Varying functions in the body
2-4 Chemical Reactions and Enzymes
• Energy and Chemical Reactions
– Chemical rxns always involve changes in
chemical bonds
• Reactants are substances that enter
chemical reactions.
• Products are substances produced by
chemical reactions.
2-4 Chemical Reactions and Enzymes
• Energy and Chemical Reactions
– Energy is released or absorbed whenever
chemical bonds form or are broken
• Some rxns release energy (exothermic)
• Some rxns absorb energy (endothermic)
2-4 Chemical Reactions and Enzymes
• Energy and Chemical Reactions
2-4 Chemical Reactions and Enzymes
• Energy and Chemical Reactions
• Activation Energy
– Amount of energy necessary for a reaction
to begin
– Enzymes can lower activation energy level
– A Catalyst is a substance that speeds up a
chemical reaction
– Enzymes are Catalysts