Transcript chemical reactions

Chapter 2
The Chemical Basis of Life
-Part One-
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The Chemical Basis of Life
• Key to understanding normal structure and
function and understanding disease
processes
• The information in this chapter will help in
the understanding of how different organ
systems function
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Basic Chemistry
• Matter, Mass, and Weight
– Matter: anything that occupies space and has mass
– Mass: the amount of matter in an object
– Weight: the gravitational force acting on an object
of a given mass
• Elements and Atoms
– Element: the simplest type of matter with unique
chemical properties; composed of atoms of only
one kind
– Atom: smallest particle of an element that has
chemical characteristics of that element
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– Compounds: combination of two or more elements
Periodic table of the elements
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Atomic Structure
• Atoms: composed of
subatomic particles
– Neutrons: no electrical
charge
– Protons: one positive
charge
– Electrons: one negative
charge
• Nucleus: formed by
protons and neutrons
• Most of the volume of an
atom occupied by
electrons
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Atomic Number and
Atomic Mass
• Atomic Number: equal
to number of protons in
each atom. Has a
neutral charge. Thus,
has an equal number of
electrons
• Atomic Mass: number
of protons plus number
of neutrons
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Isotopes and Atomic Weight
• Isotopes: two or more forms of same element with
same number of protons and electrons but different
neutron number
– For example; there are three types of hydrogen
– Denoted by using symbol of element preceded by mass number
as 1H, 2H, 3H
• Atomic Weight: average masses of naturally occurring
isotopes
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Radioactive Isotopes
• Forms of atoms that emit radioactivity
such as gamma rays, which can then be
measured
• Unstable isotopes which undergo nuclear
decay
• Used clinically and in research
• Examples of uses
– Tracking hormone uptake
– Treating cancer
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– Sterilization of materials to be used in surgery
Electrons and Bonding
• Electrons occupy energy levels called
electron shells
• Electrons closest to the nucleus are most
strongly attracted
• Each shell has distinct properties
– The number of electrons has an upper limit
– Shells closest to the nucleus fill first
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Electrons and Bonding
• Bonding involves interactions between
electrons in the outer shell (valence shell)
These valence electrons of elements
interact with each other to form
chemical reactions
• Full valence shells do not form bonds
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Inert Elements
• Atoms are stable (inert) when the
outermost shell is complete
• These are the element of the periodic
table on the furthest right.
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Inert Elements
• Atoms will gain, lose, or share electrons to
complete their outermost orbitals and
reach a stable state
• Octet Rule
– Atoms are considered stable when their
outermost orbital has 8 electrons
– The exception to this rule is Shell 1, which
can only hold 2 electrons
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Which are stable?
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Types of BONDS
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Electrons and Chemical Bonding
• Intramolecular bonding occurs when
outermost electrons are either
shared with or transferred to another
atom
– Ionic Bonding: atoms exchange
electrons
– Covalent Bonding: two or more
atoms share electron pairs
• Ion: an atom loses or gains
electrons and becomes charged
– Cation: positively charged ion
– Anion: negatively charged ion
• In an ionic bond, cations and anions
are attracted to each other and
remain close to each other
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Covalent Bonding
Atoms share one or more
pairs of electrons
– Single covalent: two
atoms share one pair of
electrons
– Double covalent: Two
atoms share 4 electrons
– Nonpolar covalent:
Electrons shared
equally because nuclei
attract the electrons
equally
– Polar covalent:
Electrons not shared
equally because one
nucleus attracts the
electrons more than the
other does
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Molecules and Compounds
• Molecules: two or more atoms chemically combine to form
an independent unit
– Example: a hydrogen molecule (H2)
• Compounds: a substance composed of two or more
different types of atoms chemically combined
– Example: water (H2O)
• Molecular Mass: determined by adding up atomic weights
of its atoms or ions
– Example: NaCl (22.99 + 35.45)
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• What is the difference between a compound and a molecule?
• A molecule is formed when two or more atoms join together
chemically. A compound is a molecule that contains at least two
different elements. All compounds are molecules but not all
molecules are compounds.
• Molecular hydrogen (H2), molecular oxygen (O2) and molecular
nitrogen (N2) are not compounds because each is composed of a
single element. Water (H2O), carbon dioxide (CO2) and methane
(CH4) are compounds because each is made from more than one
element. The smallest bit of each of these substances would be
referred to as a molecule. For example, a single molecule of
molecular hydrogen is made from two atoms of hydrogen while a
single molecule of water is made from two atoms of hydrogen and
one atom of oxygen.
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Intermolecular Forces
• Forces between molecules
• Result from weak electrostatic
attractions between oppositely charged
parts or molecules, or between ions and
molecules
• Weaker than forces producing chemical
bonding
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Intermolecular Forces: Hydrogen Bonds
• Occur when the positively
charged H of one molecule
is attracted to the
negatively charged O, N or
F of another molecule
– For example, in water the
positively charged hydrogen
atoms of one water molecule
bond with the negatively
charged oxygen atoms of
other water molecules
– Hydrogen bonds play an
important role in determining
the shape of complex
molecules
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Polar vs Non polar
This is a very important concept that is used in biology every day!
• Polar molecules
– Have a charge
because the electrons
are NOT equally
shared
– Dissolve in water
– Ionic bond, polar
covalent bond and
hydrogen bonding
– Example is Water
– Hydrophilic
• Non-polar
– Do not have a charge
– Nonpolar covalent
bonding where the
charges are distributed
evenly
– Do NOT dissolve in
water
– Example is Oil
– Hydrophobic
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Intermolecular Forces: Solubility and Dissociation
• Solubility: ability of one
substance to dissolve in
another
– For example, sugar or salt
dissolves in water
• Dissociation or Separation:
in ionic compounds, cations
are attracted to negative end
and anions attracted to
positive end of water
molecules; the ions separate
and each becomes
surrounded by water
molecules
• Electrolyte: dissociation of an
ionic compound in water
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Electrolytes and Nonelectrolytes
• Electrolytes: solutions made by the dissociation of
cations (+) and anions (-) in water
– Have the capacity to conduct an electric current
– Currents can be detected by electrodes
• Nonelectrolytes: solutions made by molecules that
dissolve in water, but do not dissociate; do not
conduct electricity
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Chemical Reactions
• Atoms, ions, molecules or compounds interact to form or
break chemical bonds
– Reactants: substances that enter into a chemical
reaction.
– Products: substances that result from the reaction
• Chemical bonds are made (synthesis; anabolism) and
broken (decomposition; catabolism) during chemical
reactions
• Metabolism: collective term used for the sum of all of the
anabolic and catabolic reactions in the body
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Synthetic Reactions
• Two or more reactants chemically combine to form a
new and larger product. Anabolism.
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–
–
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Chemical bonds made; energy stored in the bonds.
Responsible for growth, maintenance and repair
Dehydration: synthetic reaction where water is a product
Produce chemicals characteristic of life: carbohydrates,
proteins, lipids, and nucleic acids
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Decomposition Reactions
• A large reactant is broken down to form smaller products.
Catabolism.
– Chemical bonds broken; energy released.
– Hydrolysis: water is split into two parts that contribute to the
formation of the products
– Example: the breakdown of ATP to form ADP and inorganic
phosphate with a concomitant release of free energy
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Reversible Reactions
• Chemical reactions in which the reaction
can proceed either from reactants to
products or from products to reactants.
• Equilibrium: rate of product formation is
equal to rate of reactant formation
• Example: CO2 and H+ formation in plasma
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