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Chapter 2

Lecture Outline

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Matter, Energy, and Life

Matter is anything that has mass and occupies space.

Energy is the ability to do work.– There are two types of energy:

Potential energy– Stored energy, available to do work

Kinetic energy– Energy of motion

– Potential energy can be converted to kinetic energy to do work.

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Law of Conservation of Energy

Energy is never created or destroyed.– The first law of thermodynamics

Energy can be converted from one form to another, but the total energy remains constant.– An object at the top of a hill has potential energy

based on its location.– When the object rolls down the hill, the potential

energy is converted to kinetic energy.

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Forms of Energy

There are five forms of energy:1. Mechanical energy

• Energy of movement

2. Nuclear energy• Energy from reactions involving atomic nuclei

3. Electrical energy• Flow of charged particles

4. Radiant energy• Energy in heat, light, x-rays and microwaves

5. Chemical energy• Energy in chemical bonds

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What is the nature of matter?

Atoms– The smallest units of matter that can exist

separately Elements

– Chemical substances composed of the same kind of atoms

– Listed on the periodic table– Each element is represented by a symbol of one

or two letters.– The principal elements that comprise living things

are: C, H, O, P, K, I, N, S, Ca, Fe, and Mg.

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The Periodic Table of the Elements

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Atomic Structure

Atoms are composed of:– The atomic nucleus

Protons - positively charged

– Atomic numberthe number of protons

– All atoms of the same element have the same number of protons.

Neutrons – no charge

– Electrons Orbit the nucleus in energy

levels Are constantly in motion

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Atomic Structure

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Elements

Atoms of the same element have equal numbers of electrons and protons. – Thus, they have a neutral charge.

Isotopes– Atoms of the same element that have different

numbers of neutrons.– Atomic weightthe average of all of the isotopes in a

mixture. Mass number

– The sum of protons and neutrons in the nucleus.

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Isotopes of Hydrogen

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Electrons

Electrons occupy specific energy levels around the nucleus.

– Electrons closest to the nucleus have the lowest energy.

Energy levels hold specific numbers of electrons.– The first energy level can have up to 2 electrons.– All other energy levels can have up to 8 electrons.

Atoms seek to have a full outer energy level.– Atoms that have full outer energy levels are inert.– Other atoms seek to fill their outer energy levels through

chemical bonds.

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Electrons

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The Formation of Molecules

Molecules consist of two or more atoms joined by a chemical bond.

A compound is a chemical substance made of two or more elements combined in chemical bonds.– The formula of a compound describes the nature

and proportions of the elements that comprise the compound.

H2O

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Molecules and Kinetic Energy

Molecules are constantly in motion. Temperature is a measure of the average speed of

the molecules in a substance.– The greater the speed, the higher the temperature.– Measured in Fahrenheit or Celsius

Heat is a measure of the total kinetic energy of molecules.

– Measured in calories (amount of heat that will raise 1g of water 1 degree Celsius).

Heat and Temperature are related.– Add heat energy to a substance and the molecules will

speed up, and the temperature will rise.

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Kinetic Energy, Physical Changes and Phases of Matter

Three phases of matter– Solid– Liquid– Gas

The phase in which a substance exists depends on its kinetic energy and the strength of its attractive forces.

– Solidsstrong attractive forces, low kinetic energy, little to no molecular movement.

– Liquidenough kinetic energy to overcome the attractive forces; more molecular movement.

– Gashigh kinetic energy, little to no attractive forces; maximum movement.

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Chemical Changes—Forming New Kinds of Matter

Chemical reactions– Creating different chemical substances by forming

and breaking chemical bonds.– Remember: Atoms form chemical bonds to fill

their outermost electron energy levels, achieving stability.

There are several types of chemical bonds.– We will discuss:

Ionic bonds Covalent bonds

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Ionic Bonds

Atoms can gain or lose electrons to achieve a full outermost energy level.

– Atoms with charge are called ions.– When an atom gives away an electron, it ends up with more protons than

electrons and gains a positive charge; cation.– When an atom accepts an electron, it ends up with more electrons than

protons and gains a negative charge; anion.– This process is called ionization.

An ionic bond– The attraction between oppositely charged ions

Example: NaCl– Sodium (Na) has one electron in its outer energy level.– Chloride has seven electrons in its outer energy level.– Sodium donates an electron to chloride, each achieving stability.– The positively charged sodium is attracted to the negatively charged

chloride.

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Ion Formation

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Covalent Bonds

Atoms can achieve full outermost energy levels by sharing electrons instead of exchanging them.

A covalent bond is formed by the sharing of electrons.– The atoms sharing electrons sit close enough together so that

their outer energy levels overlap.– Single covalent bondone pair of electrons is shared.

H2

– Double covalent bondtwo pairs of electrons are shared. ethylene

– Triple covalent bondthree pairs of electrons are shared. N2

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Covalent Bonds

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Hydrogen Bonds

The positive hydrogen end of one polar molecule is attracted to the negative end of another polar molecule.

– This attraction is a hydrogen bond. Hydrogen bonds hold molecules together.

– Since they do not hold atoms together, they are not considered true chemical bonds.

Hydrogen bonds are very important in biology.– They stabilize the structure of DNA and proteins.– Water molecules can “stick” together with hydrogen bonds.

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Water: The Essence of Life

Water has special properties that make it an essential molecule for life.– H2O– Electrons are shared unequally by hydrogen and

oxygen. This is a polar covalent bond. Oxygen has more protons than hydrogen.

– The electrons spend more time around oxygen than around hydrogen.

– The oxygen end of water is more negative.– The hydrogen end of water is more positive.

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Hydrogen Bonds

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Mixtures and Solutions

A mixture – Matter that contains two or more substances that are not in set

proportions A solution is a homogeneous mixture of ions or

molecules of two or more substances. – Components are distributed equally throughout.– The process of making a solution is called dissolving.– The solvent is the substance present in the largest amount.

Frequently the solvent is a liquid.– The solutes are the substances present in smaller amounts.

Aqueous solutions are solids, liquids or gases dissolved in water.

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Mixtures vs. Pure Substances

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Water and Life

The following properties of water make it essential for life:

– High surface tension Water molecules stick to each other via hydrogen bonds. Capillary action moves water through streams, soil, animals

and plants.

– High heat of vaporization A lot of heat is required to break the hydrogen bonds holding

water together. Large bodies of water absorb a lot of heat.

– Temperate climates– Evaporative cooling

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Water and Life

Unusual density properties– Ice is less dense than water, so ice floats.– Allows aquatic life to survive in cold climates.

The universal solvent– Water can form hydrogen bonds with any polar or

ionic compound.– Therefore, many things can be dissolved in water.

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Chemical Reactions

A chemical change:– When the bonds of compounds are made or

broken, new materials with new properties are produced.

– Happens via chemical reactions.

In a chemical reaction the elements remain the same, but the compounds they form and their properties are different.

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Chemical Reactions and Energy

Chemical reactions produce new compounds with less or more potential energy.– Energy is released when compounds are made with

less potential energy.– Energy is used to make compounds with more

potential energy.

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Chemical Equations

A chemical equation is a method of describing what happens in a chemical reaction. – For example, photosynthesis is described by the

following equation:

Energy + 6CO2 + 6H2O → C6H12O6 + 6H2O

Reactantssubstances that are changed, usually on the left side of the equation.

Productsnew chemical substances formed, usually on the right side of the equation.

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Five Important Chemical Reactions in Biology

1. Oxidation–reduction

2. Dehydration synthesis

3. Hydrolysis

4. Phosphorylation

5. Acid–base reactions

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Oxidation-Reduction Reactions

Oxidationreduction reactions – Reactions in which electrons (and their energy) are transferred from

one atom to another.– Oxidation

An atom loses an electron.– Reduction

An atom gains an electron. For oxidation to occur, reduction must also occur. Example:

– Respiration Sugar is oxidized to form carbon dioxide and oxygen is reduced to form

water. Energy is released in the process.

C6H12O6 + 6O2 → 6H2O + 6CO2+ Energy Sugar + oxygen → water+ carbon dioxide + energy

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Dehydration Synthesis Reaction

When two small molecules are joined to form a larger molecule,– A molecule of water is released.

Example:– Joining amino acids to form proteins.

NH2CH2CO-OH + H-NH CH2CO-OH NH2CH2CO-NH CH2CO-OH + H-OH

amino acid 1 + amino acid 2 = protein + water

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Hydrolysis Reactions

When a larger molecule is broken down into smaller parts,– A water molecule is split– Opposite of a dehydration synthesis

Example:– Digesting proteins into amino acids.NH2CH2CO-NH CH2CO-OH + H-OH NH2CH2CO-OH + H-NH CH2CO-OH

Protein + water = amino acid 1 + amino acid 2

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Phosphorylation Reactions

When phosphate groups are added to other molecules,– Phosphate groups are clusters of oxygen and phosphate

atoms.

Bonds between phosphate groups and other molecules contain high potential energy.

– When these bonds are broken, the energy that is released can be used by the cell to do work.

– Phosphorylation reactions are commonly used to transfer potential energy.

Q-P + Z Q + Z-P

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Acid-Base Reactions

Occurs when ions from an acid interact with ions from a base.

This type of reaction allows harmful acids and bases to neutralize one another.

H+Cl- + Na+OH- → Na+Cl- + H+OH-

Hydrocloric + Sodium Sodium + Water acid hydroxide chloride

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Acids, Bases and Salts

An acid – Ionic compounds that release hydrogen ions (H+) into a solution – Phosphoric acid, hydrochloric acid

A base– Compounds that release hydroxide ions (OH-) into a solution– Sodium hydroxide, ammonia

Because bases are negatively charged, they will react with a positively charged hydrogen in solution.

The strength of an acid or base is determined by how completely it will dissociate in water.

– Strong acids release almost all of their hydrogen ions into water.– Strong bases release almost all of their hydroxide ions into water.

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Some Common Acids, Bases and Salts

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Salts

Neither acids nor bases Usually formed when acids and bases react

– The dissociated hydrogen ions and hydroxide ions join to form water.

– The remaining ions form ionic bonds, creating a salt.– This is an example of neutralization:

H+Cl- + Na+OH- → Na+Cl- + H+OH-

Hydrocloric + Sodium Sodium + Water

acid hydroxide chloride

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pH

A measure of hydrogen ion concentration Solutions with high hydrogen ion concentrations

– Have low pH– Are acidic

Solutions with low hydrogen ion concentrations– Have a high pH– Are basic

There is a 10-fold difference in hydrogen ion concentration between solutions that differ by one pH unit.

– A solution with pH 4 has ten times as many hydrogen ions as a solution with pH 5.

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The pH Scale