biological science · 2017. 7. 28. · freeman quillin allison © 2014 pearson education, inc....

Freeman Quillin Allison

© 2014 Pearson Education, Inc.

BIOLOGICAL SCIENCEFIFTH EDITION

2

Lecture Presentation by

Cindy S. Malone, PhD, California State University Northridge


Roadmap 2

In this chapter you will learn that

How are atoms

bonded together

in molecules?

The structure of

atoms, ions, and

molecules

How do chemical

reactions occur?

The unique

properties of water

Current models

for chemical

evolution

Carbon: The most

versatile atom

on Earth

Chemistry is intimately linked to the evolution of life

andasking

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then examiningthenexamining

by reviewing

2.1

2.2

2.3

2.4 2.5


▪ Atoms are composed of

– —positively charged

particles

– —neutral particles

– —negatively

charged particles

▪ Protons and neutrons are located in the

▪ Electrons are found in

surrounding the nucleus

(a) Diagrams of atoms

(b) Most of an atom’s volume is empty space.

Hydrogen

Carbon

Electron

Proton

NeutronNucleus

If an atom occupied the samevolume as this stadium, the nucleuswould be about the size of a pea


▪ The

– Every different atom has

a characteristic number

of protons in the nucleus

▪ Atoms with the same

atomic number

– Have the same chemical

properties

– Belong to the same

▪ are

– Forms of an element

with different

numbers of neutrons

▪ The is

– The number of

protons neutrons of

the most common

isotope


Figure 2.2

Mass number

(number of protons

+ neutrons)

Atomic number

(number of protons)


Figure 2.3

Hydrogen

Lithium

Sodium

Beryllium

Magnesium

Boron

Aluminum

Carbon

Silicon

Nitrogen

Phosphorus

Oxygen

Sulfur

Fluorine

Chlorine

Helium

Neon

Argon

Valence = 1 2 3 4 3 2 1 0

Electron shell

Nucleus

The highlightedelements are the most

abundant elementsfound in organisms

Number of unpairedelectrons = valence


▪ Unfilled electron orbitals allow formation of

–

– Are most stable when each electron orbital is filled

–

– Are substances held together by covalent bonds

–

– Each atom’s unpaired valence electrons are shared by both nuclei to fill their orbitals

–

– Electrons are transferred from one atom to another


▪ Electrons are not always shared equally

▪ An atom in a molecule with a high

– Holds electrons more tightly—has a partial negative

charge (–)

– The other atom will have a partial positive charge

()

Hydrogen atoms eachhave one unpairedelectron

Covalent bond

H2 molecule hastwo sharedelectrons


▪ Differences in electronegativity dictate how electrons are

distributed in covalent bonds

–

– Electrons are evenly shared between two atoms

– The bond is symmetrical

–

– Electrons are asymmetrically shared

(a) Nonpolar covalent bond in hydrogen molecule

(b) Polar covalent bonds in water molecule

Electrons are halfway betweenthe two atoms, shared equally

Electrons are not shared equally(O is more electronegative thanH), so partial charges exist onthe O and H atoms


▪ Ion -An atom or molecule that carries a charge

▪ Cation -An atom that loses an electron and becomes positively charged

▪ Anion -An atom that gains an electron and becomes negatively charged

▪ Ionic bond-The resulting attraction between oppositely charged ions

(a) A sodium ion being formed

Loss of electron

Cation formation

(b) A chloride ion

being formed

Sodium ionhas positivecharge

Gain of electron

Anion formation

Chloride ionhas negativecharge

(c) Table salt (NaCl) is a crystal composedof two ions.

Cl–

Na+


Figure 2.8(a) Single bonds

WaterH2O

AmmoniaNH3

MethaneCH4

(b) Double bonds

Carbon dioxideCO2

(c) Triple bonds

Molecular nitrogenN2


▪ occur when

– One substance is combined with another

– Atoms are rearranged in molecules

– Or small molecules combine to form larger molecules

– One substance is broken down into another

substance

– Molecules are split into atoms or smaller molecules

▪ In most chemical reactions

– Chemical bonds are broken and new bonds form

– This event is called a coupled reaction


▪ Life is based on water because water is a great

▪ The covalent bonds in water are polar, because

oxygen has a greater electronegativity than

hydrogen

– Oxygen has a partial negative charge (–)

– Hydrogen has a partial positive charge ()


▪ atoms and

molecules

– Are ions and polar

molecules that stay in

solution

– They stay in solution

because of their

interactions with water’s

partial charges

▪ makes it

possible for almost any

charged or polar molecule to

dissolve in water

▪ molecules

– Are uncharged and

nonpolar compounds

– They do not dissolve

in water


▪ is unique due to

its structure

– Small size

– Bent shape

– Highly polar covalent

bonds

– Overall polarity

▪

– Binding between like

molecules

– Binding to itself

– Results in high surface

tension

▪

– Binding between unlike

molecules

– Binding to plastic or

epithelial layers


Figure 2.15(a) A meniscus forms where water meets a solid surface,as a result of two forces.

(b) Water has high surface tension.

Adhesion: Watermolecules thatadhere to theglass pull upwardat the perimeter.

Cohesion: Watermolecules at thesurface form hydrogenbonds with nearbywater molecules andresist the upward pullof adhesion.

Because of surfacetension, lightobjects do notfall through thewater’s surface


▪ Proton [hydrogen ion (H)] concentration is the basis of the pH scale

– pH expresses proton concentration in a solution

▪ The pH of pure water is 7

– Acids have a pH of less than 7

– Bases have a pH of greater than 7

▪ In –

– A proton donor (acid) transfers a proton to

– A proton acceptor (base)

–

Oven cleaner

Household bleachHousehold ammonia

Milk of magnesia

Baking sodaSeawater

Human bloodPure waterMilkUrine

Black coffee

Tomatoes

WineVinegar, soft drinks, beer

Lemon juice

Stomach acid

Neutral

Acidic

Basic


▪ The pH scale is logarithmic:

pH = −log [H]

– Greater H concentration more acidic

– Lower H concentration more

basic/alkaline

▪ are compounds that

minimize changes in pH

Oven cleaner

Household bleachHousehold ammonia

Milk of magnesia

Baking sodaSeawater

Human bloodPure waterMilkUrine

Black coffee

Tomatoes

WineVinegar, soft drinks, beer

Lemon juice

Stomach acid

Neutral

Acidic

Basic


▪ have and

– For example:

CO2(g) H2O(l) H2CO3(aq)

▪ occurs

– When the forward and reverse reactions proceed at the same rate

– The quantities of reactants and products remain constant

▪ must absorb heat to

proceed

▪ release heat


▪

– Stored energy

– An object’s position

determines its ability to

store energy, for example

– Electrons in an outer

shell (farther from the

charged nucleus)

have more potential

energy than do

electrons in an inner

shell

▪ is the capacity

to do work or supply

heat

▪ This capacity exists in

one of two ways:

– As a stored potential

– As an active motion


▪ The or

– Is energy of movement

– Is measured as temperature

– If an object has a low temperature:

– Its molecules are moving slowly

– We perceive this as “cold”

– If an object has a high temperature:

– Its molecules are moving rapidly

– We perceive this as “hot”


▪ Heat is the thermal

energy transferred

between objects of

different temperatures

▪ The first law of

thermodynamics

– Energy is conserved

– It cannot be created or

destroyed

– It can be transferred or

transformed

▪ The second law of thermodynamics

– Entropy always increases

– Chemical reactions result in products with

– Less ordered energy

– Less usable energy

▪ Entropy (S)

– The amount of disorder in a group of molecules

▪ Physical and chemical processes proceed in the direction that results in lower potential energy and increased disorder


Figure 2.24

(a) Carbons linked in a chain (b) Carbons linked in a ring

C8H18 Octane

C6H12O6 Glucose

biological science · 2017. 7. 28. · freeman quillin allison © 2014 pearson education, inc....

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