Chapter 2: Atoms, Molecules & Life

What are atoms?

What are molecules?

Why do atoms interact?

How do atoms interact?

Why is water so important to life?

Table 2-1 Biology: Life on Earth 8/e ©2008 Pearson Prentice Hall, Inc.

Living things are composed of chemical elements

Matter is composed of elements

Matter - Elements

Atoms (p. 22)1. Nucleus

a.Protons and neutrons

2. Electronsa. Electron shells,

orbitals, energy levels

Figure 2-1 Biology: Life on Earth 8/e ©2008 Pearson Prentice Hall, Inc.

electronshell

Helium (He)Hydrogen (H)

nucleus

e– e–

e–

p+

p+

p+

nn

Representations of atomic structure

Figure 2-2 Biology: Life on Earth 8/e ©2008 Pearson Prentice Hall, Inc.

Carbon (C) Calcium (Ca)Phosphorus (P)Oxygen (O)

2e–

6p+

6n8p+

8n15p+

16n20p+

20n

4e–

2e–

6e–

2e–

8e–

5e–

2e–

8e–

8e–

2e–

CaPOC

Figure 2-3 Biology: Life on Earth 8/e ©2008 Pearson Prentice Hall, Inc.

lightenergy

3 Electron dropsback into lower-energy shell,releasing energyas light.

2 The energy booststhe electron to ahigher energy level.

1 An electronabsorbs energy.

Electrons are energized moving particles (p. 23)

How do we know orbitals exist?

Atoms of most elements interact with other atoms

Chemical bonds & chemical reactions (p. 25)

H H

Chemically bonded atoms form molecules & compounds (p. 23)

Lactose

Why do atoms form bonds?

ReactiveReactive InertInert

Table 2-2 Biology: Life on Earth 8/e ©2008 Pearson Prentice Hall, Inc.

Matter – Chemical bonds

1.Bonds between individual atomsa. Ionic

b. Covalent

2.Bonds between polar molecules

a. Hydrogen bonds

Ionic bonding (p. 25)

Stable?Stable?

Figure 2-4ab Biology: Life on Earth 8/e ©2008 Pearson Prentice Hall, Inc.

11p+

11n17p+

18n

Electron transferred

Chloride ion (–)Sodium ion (+)

Chlorine atom(neutral)

Sodium atom(neutral)

Attraction betweenopposite charges

(a)

(b)

11p+

11n17p+

18n

Figure 2-4c Biology: Life on Earth 8/e ©2008 Pearson Prentice Hall, Inc.

(c) An ionic compound: NaCl

Na+Cl– Cl–

Na+ Cl– Na+

Na+Cl– Cl–

Covalent bonding (p. 26)

Covalent bonding (p. 28)

Covalent bonding can form polar molecules (p. 26)

Nonpolar covalent bonding (p. 26)

1. 10

2. 11

3. 12

4. 21

5. 22

Sodium (Na), atomic number 11, has a tendency to lose an electron in the presence of chlorine. After losing the electron, Na will have

_________ protons in its nucleus.

Bonds form between atoms because

1.Atoms seek to have an equal number of protons and electrons

2.All atoms form bonds

3.Atoms attempt to become electrically neutral

4.Atoms seek a full outer shell of electrons

Hydrogen bonds

1.Are used to form all molecules involving hydrogen

2.Are only used to form a hydrogen molecule (H2) from two hydrogen atoms

3.Occur between all covalently bonded molecules

4.Occur between polar molecules

1. 2 2. 33. 54. 85. none

How many single covalent bonds can this phosphorus atom form?

1. Because helium has the same number of protons as electrons.

2. Its outermost electron shell has 8 electrons.

3. The outermost electron shell is empty.

4. Because its atomic number is an even number

5. Its outermost electron shell has 2 electrons.

Why is a helium atom (atomic number = 2) more stable than a hydrogen atom (atomic number =1)?

Lithium (Atomic # = 3) can become stable by which of the following types of bonds?1) Ionic

2) Covalent

3) Hydrogen

4) All of these

5) Both 1 and 2

An atom of sulfur (Atomic #16)

1) Is stable and nonreactive

2) Can form a stable compound with beryllium (Be) through a double covalent bond (S=Be)

3) Can become stable by forming 2 single covalent bonds

4) Both 2 & 3

Chemical bonding activity

If your birth month was your atomic number, what would you bond with?

Why is water so important to life?

Water, the solvent of polar and ionic molecules (p. 28)

OO

HH

Water-based solutions can have different pHs (p. 31)

hydrogen ion(H+)

hydroxide ion(OH–)

water(H2O)

(+) (–)

Figure 2-15 Biology: Life on Earth 8/e ©2008 Pearson Prentice Hall, Inc.

H+ concentration in moles/liter

increasingly acidic increasingly basic

neutral(H+ = OH–)

(H+ > OH–) (H+ < OH–)

100 10–1 10–2 10–3 10–4 10–5 10–6 10–7 10–8 10–9 10–10 10–11 10–12 10–13 10–14

1mol

ar s

odiu

mhy

drox

ide

(NaO

H)

1mol

ar h

ydro

chlo

ricac

id (

HC

I)

10 2 3 465 7 8 9

stom

ach

acid

(2)

lem

on ju

ice

(2.3

)"a

cid

rain

" (2

.5–5

.5)

tom

atoe

sbe

er (

4.1)

vine

gar,

col

a (3

.0)

oran

ge (

3.5)

blac

k co

ffee

(5.0

)

norm

al r

ain

(5.6

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wat

er fr

om fa

ucet

urin

e (5

.7)

milk

(6.

4)

pure

wat

er (

7.0)

seaw

ater

(7.

8–8.

3)

saliv

abl

ood,

sw

eat (

7.4)

baki

ng s

oda

(8.4

)

toot

hpas

te (

9.9)

hous

ehol

d am

mon

ia (

11.9

)w

ashi

ng s

oda

(12)

oven

cle

aner

(13

.0)

chlo

rine

blea

ch (

12.6

)ph

osph

ate

dete

rgen

ts

drai

n cl

eane

r (1

4.0)

1110 12 13 14pH

value

Water and life

Water moderates temperature changes (p. 32)

Why is water so important to life?

Water is less dense as a solid than as a liquid (p. 33)

-How is this important for life?

Water and life

Water and chemical reactions1. Hydrolysis

2. Dehydration synthesis

3. Photosynthesis

4. Respiration