Transcript Chapter 1

Chapter 2
The Chemical Basis of Life
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
– Elements: The simplest type of matter with
unique chemical properties
• 112 known elements (92 naturally occurring)
– Atoms: Smallest particle of an element that has
chemical characteristics of that element
Atomic Structure
• Atoms: composed of subatomic
particles
– Neutrons: no electrical charge
– Protons: positive charge
– Electrons: negative charge
• Nucleus
– Formed by protons and
neutrons
– Most of volume of atom
occupied by electrons
• Relative size:
– gumball vs. stadium.
Atomic Structure
• Atomic Symbol
• Atomic Number:
Equal to the number
of protons in an
atom.
• Mass Number:
Number of protons
and neutrons in an
atom.
Particle
Electric
Charge
Atomic
mass
Location
Proton
+1
1
Nucleus
Neutron
0
1
Nucleus
Electron
-1
0
Electron
shells
• Atomic number
– Equal to the number of protons in each atom
• Mass number
– Equal to the number of protons and neutrons in
each atom
• Electrons determine the chemical properties of the
atom.
• Electron shells - Electrons encircle the nucleus in
electron shells or energy levels.
– Orbital - an electron can occupy any position in a
certain volume of space called an orbital
• The innermost shell can hold up to two electrons.
• The outermost shell, holding the valence electrons, can
have eight electrons.
Atomic Configuration
•
Electron arrangement is determined by total number of
electrons and electron shell they occupy. (Bohr Model)
1. Electrons with least
amount of potential
energy are located in K
shell closest to nucleus;
electrons having more
potential energy are
located in shells farther
from the nucleus.
2. Inner shell contains up to
two electrons; additional
shells contain eight
electrons.
3. Periodic table is arranged
according to number of
electrons in outer shell.
Atomic Structure of Isotopes
•
Isotopes have the same
atomic number but a
different mass.
– same number of
protons but differ in the
number of neutrons
– e.g., a carbon atoms
has six protons but
may have more or less
than usual six
neutrons.
•Isotopes
–Two or more forms of the same element that have
the same number of protons and electrons but have a
different number of neutrons.
Atomic Mass
• Individual atoms have very little mass.
– Hydrogen = 1.67 X 10 -24g.
• Unified atomic mass units (u) or Dalton (D)
– Proton or neutron has an atomic mass of 1 .
• Atomic Mass = the average mass of its
naturally occurring isotopes taking into
account the relative abundance of each
isotope.
– Carbon has the isotopes 12C, 13C and 14C.
– The atomic mass of Carbon is 12.01 D
Electrons and Chemical Bonding
• The chemical behavior of an atom is
determined largely by its outermost
electrons (valence electrons).
• Chemical bonding occurs when the
outermost electrons are transferred or
shared between atoms.
• Chemical bonding can be grouped into
categories: Ionic, covalent, metallic and
hydrogen bonds
Ionic Bonding
• Ions are charged particles.
– cations - Positively charged ions ( have lost an electron)
– anions - Negatively charged ions (have gained an
electron)
• Oppositely charged molecules are attracted to each
other and tend to remain close to each other.
• Ionic bonding occurs when one or more valence
electrons from one atom are completely transferred
to a second atom.
• Common ions found in the body include:
– Ca++, Na+, K+, H+, OH-, Cl-
• Ionic compounds readily form crystals.
• Ionic bonds tend to dissociate in water.
Covalent Bonding
• Covalent bonding: atoms share one or more
pairs of valence electrons to form stable valence
shells.
– Single covalent bond: One electron pair is
shared between two atoms.
– Double covalent bond: Two atoms share 4
electrons
– Polar and non polar covalent bonds
– Nonpolar covalent bond: Electrons are shared
equally
– Polar covalent bonds: Electrons are not shared
equally
Intermolecular Forces
• Result from weak electrostatic attractions between
oppositely charged parts or molecules, or between
ions and molecules
• Weaker than forces producing chemical bonding
Hydrogen Bonding
•
Hydrogen bond: Weak attractive force between
slightly positive hydrogen atom of one molecule
and slightly negative atom in another molecule
Many hydrogen
bonds taken
together are
relatively strong.
Hydrogen bonds
between complex
molecules of cells
help maintain
structure and
function.
Intermolecular Forces
• Solubility: Ability of one substance to dissolve in another
– Example: Sugar dissolves in water
• Dissociation or Separation
– Ionic compounds
– Cations are attracted to negative end and anions attracted to
positive end of water molecules
Intermolecular Forces
• Electrolytes: Cations (+) and anions (-) that
dissociate in water
– Capacity to conduct an electric current
– Currents can be detected by electrodes
• Nonelectrolytes: Molecules that do not dissociate
form solutions that do not conduct electricity
Chemical Reactions
• Chemical Reactions: Atoms, ions, molecules or
compounds interact to form or break chemical
bonds
– Metabolism: All anabolic and catabolic
reactions in the body
• Catabolism: Decomposition reactions
– Hydrolysis: Reactions that use water
• Anabolism: Growth, maintenance, and repair of the
body in synthesis reactions
– Produce molecules characteristic of life: ATP, proteins,
carbohydrates, lipids, and nucleic acids
Synthesis and Decomposition Reactions
• Synthesis Reactions
– Two or more reactants
chemically combine to
form a larger product
– Anabolism: All body’s
synthesis reactions
• Decomposition Reactions
– Reverse of synthesis
reactions
– Catabolism: Reactions
of decomposition in
body
Oxidation-Reduction Reactions
• Oxidation
– Loss of an electron by an atom
• Reduction
– Gain of an electron by an atom
• Oxidation-Reduction Reactions
– The complete or partial loss of an electron by
one atom is accompanied by the gain of that
electron by another atom
Rate of Chemical Reactions
• Reactant type - differ in their ability to undergo
chemical reactions.
• Concentration - greater concentrations of
reactants generally cause reactions to proceed
faster.
• Temperature - reaction speed increases with
higher temps.
• Catalysts - substance that increases the rate at
which a chemical reaction proceeds.
– Enzymes - are protein molecules that act as
catalysts in the body.
Energy
• Energy: The capacity to do work
– Potential Energy: Stored energy
– Kinetic Energy: Does work and moves matter
– Mechanical Energy: Energy resulting from the
position or movement of objects
– Chemical Energy: Form of potential energy in
the chemical bonds of a substance
– Heat Energy: Energy that flows between objects
of different temperatures
Energy and Chemical Reactions
Speed of Chemical Reactions
• Activation Energy: Minimum energy reactants must have to
start a chemical reaction
– Catalysts: Substances that increase the rate of chemical
reactions without being permanently changed or depleted
– Enzymes: Increase the rate of chemical reactions by
lowering the activation energy necessary for reaction to
begin
Activation Energy and Enzymes
Properties of Water - functions in
living organisms
• Stabilizing body temperature
– Water has a high specific heat and tends
to resist large temperature fluctuations.
• Evaporation (540 calories / gram of water).
• Protection
– Lubricant and Cushion
• Chemical reactions
– Water is an excellent solvent.
• Mixing medium
– solutions: any liquid that contains dissolved
substances
– suspensions: a liquid that contains nondissolved materials that settle out of of the
liquid unless it is continually shaken.
– colloid: a liquid that contains non-dissolved
materials that do not settle out of liquid. (Water
and proteins inside the cell).
Solution Concentrations
• Solutions = solvent (the liquid portion) + solutes (substances
dissolved in the solvent).
• Concentration - expressed in a number of different ways:
– percent solution (10% solution = 10 g solute / 100 ml of
solvent)
– Osmolarity (1 osmole = 1 mole (Avegadro’s # of
particles) in 1 kilogram of water).
• Osmolarity is a reflection of the number of particles in a
solution and not the type of particle in a solution.
– The osmolarity of body fluids = 300 mOsm
• important because it influences the movement of water in
and out of cells.
• Note: difference between molality and osmolality is that
osmolality takes into acount the number of particles a
molecule breaks into when it goes into solution.
Acids and Bases
When water ionizes or
dissociates, it releases a
small (107 moles/liter) but
equal number of H+ and
OH ions; Thus its ph is
neutral.
Acid: a proton donor.
Base: a proton acceptor.
•
Take up hydrogen ions
or release hyroxide
ions.
Stong vs Weak acids. -The more freely the acid or base
dissociates the stronger it is.
•Strong acid : HCl H+ Cl- dissociates almost completely
•Weak Acid : Acetic acid CH3COOH  CH3COO- + H +
•Some dissociates and some does not.
pH Scale
•The pH scale indicates acidity and basicity (alkilinity) of
a solution.
•Measure of free hydrogen ions as a negative logarithm
of the H+ concentration (-log [H+]).
–logarithmic scale - a change of pH by one unit
represents a 10 fold change in the concentration of
H+.
pH Scale continued
•
•
•
pH values range from 0 (100 moles/liter; most
acidic) to 14 (1014 moles/liter; most basic).
One mole of water has 107 moles/liter of
hydrogen ions; therefore, has neutral pH of 7.
– Acid has a pH less than 7
– Base has a pH greater than 7.
Normal Range in body = 7.35 - 7.45
– Acidosis - Nervous system depression,
disorientation and coma.
– Alkalosis - N. S. overexcited, convulsion possibly fatal.
Buffers
•
•
Buffers keep pH steady and within normal limits in
living organisms.
– Buffers stabilize pH of a solution by taking up
excess hydrogen or hydroxide ions.
– Carbonic acid helps keep blood pH within normal
limits:
– H2CO3
H+ + HCO3-.
The chemical nature of many molecules changes as
the pH of a solution in which they are dissolved
changes.
– Most enzymes work within a narrow pH range.
– Survival of an organism depends on its ability to
maintain it pH level within a narrow range.
The End.