Today: Chemical Principles (Ch. 2)
Chemistry of Atoms
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Atom:smallest possible unit of matter that retains properties of its element
o Neutrons: no charge (neutral)
o Protons: +1 electrostatic charge
o Electrons: -1 electrostatic charge
 Electrically neutral atoms have an equal number of protons and
electrons
Atomic number: number of protons in an atom (written 11Na)
Atomic weight: equal to number of protons and neutrons
Elements of Life
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Element: a substance that cannot be broken down into other substances by
chemical reactions
About 25 elements are essential to life:
o C, O, H, N: make up 96% of living matter
o Ca, P, K, S, Na, Cl, Mg, Fe, I: make up most of remainder
o Trace elements: required by an organism in extremely minute quantities,
ex. B, Mn, Zn and others
Electron Configuration
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Electrons are in orbit around the nucleus, are involved in chemical reactions.
o Orbital: three-dimensional space where an electron will most likely be
found 90% of the time
o First energy level: one s orbital, holds 2 electrons
o Second energy level: one s and three p orbitals, holds 8 electrons
Chemical properties of an atom depend on the number of valence electrons
Valence electrons: electrons in outermost energy shell (valence shell)
o Unfilled spaces determine number of bonds which can form
Chemical Bonds
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Chemical bonds: attractive forces that hold atoms together in a molecule
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1. Covalent bond: bond between atoms formed by sharing one or more pairs of
valence electrons
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2. Ionic bond: bond formed by the electrostatic attraction after the complete
transfer of an electron from a donor atom to an acceptor
o Ion: charged atom or molecule
o Anion: a negatively charged ion
o Cation: a positively charged ion
o ionic compounds are called salts (e.g. NaCl or table salt)
Example: Ionic Bond
Bonds (continued)
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3. Hydrogen bond: bond formed by the charge attraction when a hydrogen atom
covalently bonded to one electronegative atom is attracted to another
electronegative atom
o weak attraction, 20X weaker than covalent
o is a charge attraction between oppositely charged portions of polar
molecules
o generally between H that has slight positive charge and another highly
electronegative atom (usually O and N)
Example: Polar Covalent Bond
Chemical Reactions
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Chemical Reactions: the making and breaking of chemical bonds
o energy requiring - endergonic
o energy releasing - exergonic
Synthesis - anabolic, new bonds formed
Decomposition - catabolic, bonds broken
Reversibility - all reactions (in theory) are reversible
Activation energy - initial energy needed for reaction to proceed
Enzyme catalysis - lowers activation energy
Important Molecules in Life
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Water
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most abundant constituent of cells
important solvent
hydrogen bonding keeps temperature constant
Acids/Bases and Buffers
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acid: substance which dissociates into hydrogen ions (H+) and negative
anions
base: dissociates into hydroxide ions (OH-) and positive cations
balance of acids and bases determines pH of the solution
 pH = -log10[H+]
buffer: compound which keeps pH constant
Organic Compounds
o carbon containing compounds
o functional groups:
 hydroxyl - alcohol
 carbonyl - aldehyde/ketone
 amino - amine
 ester - ester
 ether - ether
 sulfhydryl - sulfhydryl
 carboxyl - organic acid
Macromolecules/Energy
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macromolecules: large molecules which are polymers composed of repeating
small molecules called monomers
o carbohydrates
o lipids
o proteins
o nucleic acids
Energy: adenosine triphosphate (ATP)
o ATP is the principle energy carrying molecule of the cell