Download Chemistry Comes Alive: Part A

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Chemistry Comes Alive: Part A
Matter
• Anything that has mass and occupies space
• States of matter:
1. Solid—definite shape and volume
2. Liquid—definite volume, changeable shape
3. Gas—changeable shape and volume
Energy
• Capacity to do work or put matter into motion
• Types of energy:
• Kinetic—energy in action
• Potential—stored (inactive) energy
Forms of Energy
• Chemical energy—stored in bonds of chemical substances
• Electrical energy—results from movement of charged particles
• Mechanical energy—directly involved in moving matter
• Radiant or electromagnetic energy—exhibits wavelike
properties (i.e., visible light, ultraviolet light, and X-rays)
Energy Form Conversions
• Energy may be converted from one form to another
• Conversion is inefficient because some energy is ―lost‖ as heat
Composition of Matter
• Elements
• Cannot be broken down by ordinary chemical means
• Each has unique properties:
• Physical properties
• Are detectable with our senses, or are measurable
• Chemical properties
• How atoms interact (bond) with one another
Composition of Matter
• Atoms
Unique building blocks for each element
• Atomic symbol: one- or two-letter chemical shorthand for each
element
Major Elements of the Human Body
• Oxygen (O)
• Carbon (C)
• Hydrogen (H)
• Nitrogen (N)
Lesser Elements of the Human Body
• About 3.9% of body mass:
• Calcium (Ca), phosphorus (P), potassium (K), sulfur (S), sodium
(Na), chlorine (Cl), magnesium (Mg), iodine (I), and iron (Fe)
Trace Elements of the Human Body
• < 0.01% of body mass:
• Part of enzymes, e.g., chromium (Cr), manganese (Mn), and zinc
(Zn)
Atomic Structure
• Determined by numbers of subatomic particles
• Nucleus consists of neutrons and protons
Atomic Structure
• Neutrons
• No charge
• Mass = 1 atomic mass unit (amu)
• Protons
• Positive charge
• Mass = 1 amu
Atomic Structure
• Electrons
•
•
•
•
Orbit nucleus
Equal in number to protons in atom
Negative charge
1/2000 the mass of a proton (0 amu)
Models of the Atom
• Orbital model: current model used by chemists
• Depicts probable regions of greatest electron density (an electron
cloud)
• Useful for predicting chemical behavior of atoms
Models of the Atom
• Planetary model—oversimplified, outdated model
• Incorrectly depicts fixed circular electron paths
• Useful for illustrations (as in the text)
Identifying Elements
• Atoms of different elements contain different numbers of
subatomic particles
• Compare hydrogen, helium and lithium (next slide)
Identifying Elements
• Atomic number = number of protons in nucleus
Identifying Elements
• Mass number = mass of the protons and neutrons
• Mass numbers of atoms of an element are not all identical
• Isotopes are structural variations of elements that differ in the
number of neutrons they contain
Identifying Elements
• Atomic weight = average of mass numbers of all isotopes
Radioisotopes
• Spontaneous decay (radioactivity)
• Similar chemistry to stable isotopes
• Can be detected with scanners
Radioisotopes
• Valuable tools for biological research and medicine
• Cause damage to living tissue:
• Useful against localized cancers
• Radon from uranium decay causes lung cancer
Molecules and Compounds
• Most atoms combine chemically with other atoms to form
molecules and compounds
• Molecule—two or more atoms bonded together (e.g., H2 or
C6H12O6)
• Compound—two or more different kinds of atoms bonded
together (e.g., C6H12O6)
Mixtures
• Most matter exists as mixtures
• Two or more components physically intermixed
• Three types of mixtures
• Solutions
• Colloids
• Suspensions
Solutions
• Homogeneous mixtures
• Usually transparent, e.g., atmospheric air or seawater
• Solvent
• Present in greatest amount, usually a liquid
• Solute(s)
• Present in smaller amounts
Concentration of Solutions
• Expressed as
• Percent, or parts per 100 parts
• Milligrams per deciliter (mg/dl)
• Molarity, or moles per liter (M)
• 1 mole = the atomic weight of an element or molecular weight
(sum of atomic weights) of a compound in grams
• 1 mole of any substance contains 6.02 1023 molecules
(Avogadro’s number)
Colloids and Suspensions
• Colloids (emulsions)
• Heterogeneous translucent mixtures, e.g., cytosol
• Large solute particles that do not settle out
• Undergo sol-gel transformations
• Suspensions:
• Heterogeneous mixtures, e.g., blood
• Large visible solutes tend to settle out
Mixtures vs. Compounds
• Mixtures
• No chemical bonding between components
• Can be separated physically, such as by straining or filtering
• Heterogeneous or homogeneous
• Compounds
• Can be separated only by breaking bonds
• All are homogeneous
Chemical Bonds
• Electrons occupy up to seven electron shells (energy levels)
around nucleus
• Octet rule: Except for the first shell which is full with two
electrons, atoms interact in a manner to have eight electrons in
their outermost energy level (valence shell)
Chemically Inert Elements
• Stable and unreactive
• Outermost energy level fully occupied or contains eight
electrons
Chemically Reactive Elements
• Outermost energy level not fully occupied by electrons
• Tend to gain, lose, or share electrons (form bonds) with other
atoms to achieve stability
Types of Chemical Bonds
• Ionic
• Covalent
• Hydrogen
Ionic Bonds
• Ions are formed by transfer of valence shell electrons between
atoms
• Anions (– charge) have gained one or more electrons
• Cations (+ charge) have lost one or more electrons
• Attraction of opposite charges results in an ionic bond
Formation of an Ionic Bond
• Ionic compounds form crystals instead of individual molecules
• NaCl (sodium chloride)
Covalent Bonds
• Formed by sharing of two or more valence shell electrons
• Allows each atom to fill its valence shell at least part of the time
Covalent Bonds
• Sharing of electrons may be equal or unequal
• Equal sharing produces electrically balanced nonpolar molecules
• CO2
Covalent Bonds
• Unequal sharing by atoms with different electron-attracting
abilities produces polar molecules
• H2O
• Atoms with six or seven valence shell electrons are
electronegative, e.g., oxygen
• Atoms with one or two valence shell electrons are
electropositive, e.g., sodium
Hydrogen Bonds
• Attractive force between electropositive hydrogen of one
molecule and an electronegative atom of another molecule
• Common between dipoles such as water
• Also act as intramolecular bonds, holding a large molecule in a
three-dimensional shape
Chemical Reactions
• Occur when chemical bonds are formed, rearranged, or broken
• Represented as chemical equations
• Chemical equations contain:
• Molecular formula for each reactant and product
• Relative amounts of reactants and products, which should
balance
Examples of Chemical Equations
H+H
H2 (hydrogen gas)
4H + C
CH4 (methane)
Patterns of Chemical Reactions
• Synthesis (combination) reactions
• Decomposition reactions
• Exchange reactions
Synthesis Reactions
•A+B
AB
• Always involve bond formation
• Anabolic
Decomposition Reactions
• AB
A+B
• Reverse synthesis reactions
• Involve breaking of bonds
• Catabolic
Exchange Reactions
• AB + C
AC + B
• Also called displacement reactions
• Bonds are both made and broken
Oxidation-Reduction (Redox) Reactions
• Decomposition reactions: Reactions in which fuel is broken
down for energy
• Also called exchange reactions because electrons are
exchanged or shared differently
• Electron donors lose electrons and are oxidized
• Electron acceptors receive electrons and become reduced
Chemical Reactions
• All chemical reactions are either exergonic or endergonic
• Exergonic reactions—release energy
• Catabolic reactions
• Endergonic reactions—products contain more potential energy
than did reactants
• Anabolic reactions
Chemical Reactions
• All chemical reactions are theoretically reversible
• A+B
AB
• AB
A+B
• Chemical equilibrium occurs if neither a forward nor reverse reaction is
dominant
• Many biological reactions are essentially irreversible due to
• Energy requirements
• Removal of products
Rate of Chemical Reactions
• Rate of reaction is influenced by:
•
•
•
temperature
rate
particle size
rate
concentration of reactant
• Catalysts:
rate
rate without being chemically changed
• Enzymes are biological catalysts