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The Chemical Basis of Life Energy levels of electrons

*chemical behavior due to electrons Electron configuration and chemical properties:

Covalent Bonds – A covalent bond forms when two atoms share one or more pairs of outer-shell electrons. – Atoms held together by covalent bonds form a molecule. Name Electron configuration (molecular formula) Hydrogen gas (H2)

Structural formula

Space-filling model

Ball-and-stick model

Single bond (a pair of shared electrons)

Oxygen gas (O2) Double bond (two pairs of shared electrons) Methane (CH4)

Ionic Bonds – When an atom loses or gains electrons, it becomes electrically charged. • Charged atoms are called ions. • Ionic bonds are formed between oppositely charged ions. Outer shell has 1 electron

Na Sodium atom

The outer electron is stripped from sodium and completes the chlorine atom’s outer shell Outer shell has 7 electrons

Cl Chlorine atom

Complete outer shells

Na+ Sodium ion

Cl− Chlorine ion

The attraction between the ions—an ionic bond—holds them together

Sodium chloride (NaCl)

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Hydrogen Bonds – Water is a compound in which the electrons in its covalent bonds are shared unequally. • This causes water to be a polar molecule, one with opposite charges on opposite ends. (slightly +)

(slightly +)

H

H O

(slightly –)

Hydrogen bonding • Weak bonds formed between hydrogen and another atom – Surface tension of water

• Important p as intramolecular bonds, giving shape to proteins and other biomolecules

WATER AND LIFE – Life on Earth began in water and evolved there for 3 billion years. • Modern life remains tied to water. • Your cells are composed of 70%–95% water.

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Properties of Water • Numerous properties due to the hydrogen bonding

Properties of Water • Cohesion • Adhesion Evaporation from the leaves

Microscopic tubes

SEM

Cohesion due to hydrogen bonds between water molecules

Properties of Water – Heat and temperature – Water can absorb and store large amounts of heat while only changing a few degrees in temperature. – Water can moderate temperatures.

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Properties of Water – Surface tension is the measure of how difficult it is to stretch or break the surface of a liquid.

Water is the solvent of life *solution *solvent *solute *aqueous solution

The Chemical Basis of Life Hydrophilic and hydrophobic substances *hydrophilic *hydrophobic

The dissociation of water molecules

H2O

H+ + OH-

Acids and bases *acid

*base

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Acids, Bases and pH

14 Increasingly basic (lower H+ concentration)

Oven cleaner

Basic solution

Increasingly acidic (greater H+ concentration)

Neutral [H+] = [OH–]

Neutral solution

Acidic solution

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Household

12 bleach Household ammonia 11 Milk of magnesia 10 9 Seawater 8 Human blood 7 Pure water 6 Urine 5 4 Tomato juice 3 Grapefruit juice, soft drink 2 Lemon juice, gastric juice 1

0 pH scale

Carbon and Organic Chemistry – Carbon is a versatile atom. – Carbon forms large, complex, and diverse molecules necessary for life’s functions. – Organic compounds are carbon-based molecules. Structural formula

Ball-and-stick model

Space-filling model

Carbon and Organic Chemistry • Variations in Carbon skeletons

Carbon skeletons vary in length

Carbon skeletons may be unbranched or branched

Carbon skeletons may have double bonds, which can vary in location

Carbon skeletons may be arranged in rings

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Chemical Components of Cells *structural isomers *geometric isomers *enantiomers Example of enantiomers:

Hydrocarbons – Larger hydrocarbons form fuels for engines. – Hydrocarbons of fat molecules fuel our bodies.

Carbon and Organic Chemistry • The unique properties of an organic compound depend not only on its carbon skeleton but also on the atoms attached to the skeleton – These atoms are called functional groups – Some common functional groups include: Hydroxyl group

Carbonyl group

Found in alcohols and sugars

Found in sugars

Amino group

Carboxyl group

Found in amino acids and urea in urine (from protein breakdown)

Found in amino acids, fatty acids, and some vitamins

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