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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
)
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