the nature of molecules and the properties of water chapter 2 1

The Nature of Molecules andthe Properties of Water

Chapter 2

1

2.1 Nature of Atoms: Learning Objectives

• Define atoms, elements, and isotopes

• Know basic structure of atoms

• List elements found in living things

• Describe how atomic structure chemical properties

• Explain where e- are found in an atom

3

Nature of Atoms• Matter

• Has mass

• Occupies space

• All matter is composed of atoms

Oxygen atoms on rhodium crystal

Scanning Tunneling Microscopy

4

Atomic Structure• Atoms are composed of

– Protons• Positively charged particles• Located in the nucleus

– Neutrons• Neutral particles• Located in the nucleus

– Electrons • Negatively charged particles• Found in orbitals surrounding the nucleus

http://d1jqu7g1y74ds1.cloudfront.net/wp-content/uploads/2010/02/c-atom_e1.gif

Bohr Atomic Model

5

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

neutron(no charge)

proton(positive charge)

electron(negative charge)

b.

Bohr Atomic Model

6


neutron(no charge)

1 Proton1 Electron

8 Protons8 Neutrons8 Electrons

Hydrogen Oxygen

proton(positive charge)

electron(negative charge)

a.

Quantum Atomic Model

7

Atomic number = Atom’s I.D. #• Atomic number

• number of protons in an atom

• Determines atom’s identity

• Hydrogen = 1 proton

• Helium = 2 protons

8

Atomic mass• Mass or weight?

– Mass – refers to amount of substance– Weight – refers to force gravity exerts on substance

• Sum of protons and neutrons is the atom’s atomic mass

• Each proton and neutron has a mass of approximately 1 Dalton or atomic mass unit (a.m.u.)

Properties of Subatomic Particles

subatomic particle

Mass (in Daltons or

a.m.u.)charge

proton 1 +

neutron 1 neutral

electron almost 0 -

Subatomic Particle Summary

10

Elements• Element

– Any substance that cannot be broken down to any other substance by ordinary chemical means

– A given element is made up one type of atom

Iron is an element because it is made up of only iron atoms

http://www.periodictable.com/Samples/026.32/s9s.JPG

• 90 naturally occurring elements• 12 elements found in living

organisms in substantial amounts

• 4 elements make up 96.3% of human body weight– Carbon, hydrogen, oxygen,

nitrogen

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Mg

Fe

S

P

Ca

Cl

Na

N

H

C

b.

O

Carbon (C)

Oxygen (O)

Hydrogen (H)

Nitrogen (N)

Sodium (Na)

Chlorine (Cl)

Calcium (Ca)

Phosphorus (P)

Potassium (K)K

Sulfur (S)

Iron (Fe)

Magnesium (Mg)


Elements

• 4 elements make up 96.3% of human body weight– Carbon, hydrogen, oxygen,

nitrogen

• Organic molecules contain primarily CHON

• Some trace elements are very important

12

Mg

Fe

S

P

Ca

Cl

Na

N

H

C

b.

O

Carbon (C)

Oxygen (O)

Hydrogen (H)

Nitrogen (N)

Sodium (Na)

Chlorine (Cl)

Calcium (Ca)

Phosphorus (P)

Potassium (K)K

Sulfur (S)

Iron (Fe)

Magnesium (Mg)


Elements

13

Periodic Table of the Elements

1

H

3Li

4Be

19

K

12

Mg

93

Np94

Pu95

Am96

Cm97

Bk98

Cf99

Es100

Fm101

Md102

No103

Lr

37

Rb38

Sr39

Y42

Mo45

Rh46

Pd47

Ag48

Cd49

In50

Sn51

Sb52

Te53

I54

Xe

21

Sc40

Zr

22

Ti23

V24

Cr25

Mn27

Co28

Ni29

Cu30

Zn36

Kr

5

B6 C

8

O 2

He

55

Cs56

Ba72

Hf73

Ta74

W75

Re76

Os77

Ir78

Pt79

Au80

Hg81

Tl82

Pb83

Bi84

Po85

At86

Rn87

Fr88

Ra

57

La89

Ac104 105 106 107 108 109

58

Ce59

Pr60

Nd61

Pm62

Sm63

Eu64

Gd65

Tb66

Dy67

Ho68

Er69

Tm70

Yb71

Lu

90

Th91

Pa92

U(Actinide series)

11

Na20

Ca

41

Nb43

Tc44

Ru

26

Fe

13

Al

31

Ga32

Ge

14

Si

7

N15

P

33

As

16

S35

Br34

Se

9

F

18

Ar

10

Ne17

Cl

110

Rf Ob Sg Bh Hs Mt Ds

111 112 113 114 115 116 117

Rg Cn Uut Fl Uup Lv Uus Uuo

118

Key

1

Hatomic number

chemical symbol

Mg

Fe

S

P

Ca

Cl

Na

N

H

C

a. b.

O

(Lanthanide series)

Carbon (C)

Oxygen (O)

Hydrogen (H)

Nitrogen (N)

Sodium (Na)

Chlorine (Cl)

Calcium (Ca)

Phosphorus (P)

Potassium (K)K

Sulfur (S)

Iron (Fe)

Magnesium (Mg)


Isotopes• Atoms of a single element

• Different number of neutrons

• Radioactive isotopes are unstable and emit radiation as the nucleus breaks up

Carbon-12 Carbon-13 Carbon-14

6 Protons 6 Neutrons 6 Electrons



**

** radioactive

Uses for Radioactive Isotopes

http://www.scientificamerican.com/article.cfm?id=carbon-dating-gets-reset http://www.rah.sa.gov.au/nucmed/nucmed/ncmd_info.htm

Nuclear MedicineCarbon-Dating

Electrons and Ions

• e- are negatively charged particles

• located in orbitals

• Neutral atoms

• Equal # of protons and e-

• Ions

• Atoms with a charge

• Unbalanced # of protons and e-

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Electrons and Ions

• Types of ions – Cation – more protons than electrons

–positive charge– Anion – fewer protons than electrons

–negative charge

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18

Electron arrangement

• Determines chemical behavior of atom

• Bohr model – electrons in discrete orbits

• Quantum model – orbital as area around a nucleus where an electron is most likely to be found

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One spherical orbital (1s)

Electron Shell Diagram Corresponding Electron Orbital

EnergyLevel K

x

z

y

Neon

Electron Shell Diagram Electron Orbitals

x

y z

One spherical orbital (2s)

Corresponding Electron OrbitalsElectron Shell Diagram

Three dumbbell-shaped orbitals (2kk)

Energylevel L

Electron Orbitals

Each orbital holds a max of 2 electrons

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Reactivity of Elements• Valence electrons (e-) –

• e- in outermost energy level

• Inert (nonreactive) elements have all 8 e-

• Octet rule – atoms with 8 e- (2 e- for small atoms) in outer energy level are stable

Li Ne

1 valence e- 8 valence e-

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Reactivity of Elements• Octet rule –

• Atoms form chemical bonds to obtain stable octet (8 paired e- in outer most energy level)

• Valence e- used in chemical bonding

Review Question

Isotopes are atoms of the same element but differ in the number of

a. Electrons

b. Protons

c. Neutrons

d. Orbitals

e. Bonds

Review Question

Radioactive isotopes –

a. Are unstable

b. Decay over time

c. Emit radiation

d. May occur naturally

e. All of the above

Review Question

An atom with more protons than electrons is –

a. An element

b. An isotope

c. A cation

d. An anion

Review Question

Carbon’s atomic number is 6. How many electrons

are in carbon’s outer shell?

a. 2

b. 4

c. 6

d. 8

Review Question

18O has an atomic number of 8. How many neutrons does 18O have?

a. 8

b. 10

c. 12

d. 18

2.3 The Nature of Chemical Bonds: Learning Objectives

• Describe difference between molecule & compounds

• Explain ionic bonding vs. covalent bonding

• Understand how electronegativity plays a role in bond formation• Polar bonds• Non-polar bonds

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Chemical Bonds• Molecules are groups of atoms held

together in a stable association

• Compounds are molecules containing more than one type of element

• Atoms are held together by chemical bonds

http://en.wikipedia.org/wiki/File:Oxygen_molecule.png https://commons.wikimedia.org/wiki/File:Water_molecule_3D.svg

O2, a diatomic molecule H2O, a compound

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Ionic bonds• Formed by the attraction of oppositely

charged ions

• Gain or loss of electrons forms ions

Sodium atom

Cl

Chlorine atoma.

Sodium ion (+)

Cl–

Chloride ion (–)

NaNa Na+Na+

b. NaCl crystal

Cl– Cl–

Cl– Cl–

Cl–

NaNa++

NaNa++

NaNa++

NaNa++


30

Covalent bonds

• Form when atoms share 2 or more valence electrons

http://cnx.org/content/m47181/latest/

31


NN

N2N N

H H

O2O O

H2

O O

Single covalent bondHydrogen gas

covalent bond

Double covalent bondoxygen gas

Triple covalent bondNitrogen gas

H H

Structural vs. Molecular Formulas

• Molecular formulas• Shows number and types of elements

• Structural formulas• Shows arrangement of atoms and types of bonds present

http://www.cliffsnotes.com/assets/276058.png

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33

Carbon and Organic Compunds

• Carbon can form up to 4 single covalent bonds

• Carbon atoms can form linear chains or rings

• These carbon “backbones” form basis of organic molecules

http://www.nutritionalhq.com/wp-content/uploads/2011/08/Glucose-molecule-model.jpg

Glucose (C6H12O6)

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Electronegativity

• Atom’s affinity for electrons• Differences in electronegativity dictate how

electrons are distributed in covalent bonds– Nonpolar covalent bonds = equal sharing of

electrons– Polar covalent bonds = unequal sharing of

electrons

http://www.chem.ubc.ca/courseware/pH/section10/eshift1.jpg

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Chemical reactions

• Chemical reactions involve the formation or breaking of chemical bonds

• Reactants = original molecules• Products = molecules resulting from reaction

6H2O + 6CO2 → C6H12O6 + 6O2

reactants products

37

• Extent of chemical reaction influenced by1. Temperature2. Concentration of reactants and products3. Catalysts

• Many reactions are reversible

Chemical reactions

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Review Question

What property of an atom determines how it forms bonds?

a. Atomic Mass

b. Atomic number

c. Valance electrons

d. Orbits

e. Neutrons

Review Question

What kind of chemical bond is formed when atoms share one or more pairs of electrons?

a. Covalent bond

b. Ionic bond

c. Hydrogen bond

d. Polar bond

Review Question

Typically an increase in temperature causes the rate of a chemical reaction to –

a. Decrease

b. Increase

c. Remain the same

2.4 Water: A Vital Compound: Learning Objectives

• Describe hydrogen bonding

• Explain how hydrogen bonding gives H2O very important properties• Cohesiveness and adhesiveness• High specific heat• High heat of vaporization• Ice floating on liquid water• Universal solvent

43

Water

• Single most outstanding chemical property of water is its ability to form hydrogen bonds– Weak chemical associations that form

between the partially negative O atoms and the partially positive H atoms of two water molecules


a. Solid b. Liquid c. Gas

a: © Glen Allison/Getty Images RF; b: © PhotoLink/Getty Images RF; c: © Jeff Vanuga/Corbis

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Polarity of water• Within a water molecule, the bonds

between oxygen and hydrogen are highly polar

• Partial electrical charges develop– Oxygen is partially negative δ+

– Hydrogen is partially positive δ–

δ+ δ+δ+

δ

http://academic.brooklyn.cuny.edu/biology/bio4fv/page/image15.gif


+

–

+

+

a. b.

c.

Bohr Model

Space-Filling Model

8p

Ball-and-Stick Model

8n

–

+

+

–

–

+

+

–

104.5

+

45

46

Hydrogen bonds

• Each individual H-bond is weak and transitory

• Cumulative effects are enormous

• Responsible for many of water’s important physical properties

47


+

a.

b.

Water moleculeHydrogen atom

–Hydrogen bond

Oxygen atom

Hydrogen atom

Hydrogen bond+

–

An organic compound

Oxygen atom

• Cohesion – water molecules stick to other water molecules by hydrogen bonding

• Adhesion – water molecules stick to other polar molecules by hydrogen bonding

48

49

Properties of water1. Water has a high specific heat

– A large amount of energy is required to change the temperature of water

http://commons.wikimedia.org/wiki/File:Boiling_water.jpg

50

Properties of water2. Water has a high heat of vaporization

- The evaporation of water from a surface causes cooling of that surface

http://www.baltimoresun.com/media/photo/2012-05/70086876.jpg

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Properties of water

3. Solid water is less dense than liquid water

- Bodies of water freeze from the top down

http://www.hdwallpapersplus.com/wp-content/uploads/2012/10/iceberg_2.jpg

http://sailboatdiaries.com/wp-content/uploads/iceHbonds.gif52

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4. Water is a good solvent– Water dissolves polar molecules and ions

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Hydration shells

Water molecules

Salt crystal

Cl–

Na+

Cl–

+

+

+

++

–

–

–

–

–

Na+


54

4. Water is a good solvent– When H2O dissolves a polar or ionic compounds like NaCl

– water is the solvent–NaCl is the solute

• Both solvent and solute make up a solution

http://bio1151.nicerweb.com/Locked/media/ch03/03_07DissolvingSalt-L.jpg

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5. Water organizes nonpolar molecules– Hydrophilic “water-loving”– Hydrophobic “water-fearing”– Water causes hydrophobic molecules to

aggregate or assume specific shapes

http://www.uic.edu/classes/bios/bios100/lecturesf04am/hydrophobic.jpg

Hydrophobic molecule

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6. Water can form ions

H2O OH– + H+

hydroxide ion hydrogen ion

• H+ ions also known as protons

http://www.kmacgill.com/lecture_notes/lecture_notes_17_files/image003.jpg

Review Question

Which of the following types of chemical bonds is the strongest?

a. Hydrogen bond

b. Ionic bond

c. Covalent bond

d. All are equal strength

2.6: Acids and Bases: Learning Objectives

• Define mole and molar concentration

• Describe acids, bases, and pH scale

• Relate changes in pH to changes in [H+]

• Understand how buffers work

•The molar concentration of H+ or OH- ions in a solution is the basis of pH scale

•Molar concentration = 1 mole of solute ÷ 1 Liter of solution (mol/L)

• Amount of substance (in grams) in 1 mole = its molecular weight (mass)

• 1 mole of sodium ion Na+ = 23 g

• 1 mole of sodium chloride (NaCl) = 58.44g

Molar Concentrations

59

60

Acids and bases• Pure water

– [H+] of 10–7 mol/L– Considered to be neutral – Neither acidic nor basic– [H+] = [OH-]

• pH is the negative logarithm of hydrogen ion concentration of solution

pH = -log[H+]pH= –log 10-7 = -(-7)=7

Acids and Bases - pH

• Acid (pH < 7)– Any substance that dissociates in water to

increase the [H+] (and lower the pH)– The stronger an acid is, the more hydrogen

ions it produces and the lower its pH

• Base (pH > 7)– Substance that combines with H+ dissolved in

water, and thus lowers the [H+]

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62


Hydrogen IonConcentration [H+] Examples of Solutions

Stomach acid, lemon juice

pH Value

Hydrochloric acid

Acidic

Basic

10–2

10–3 Vinegar, cola, beer

10–4 Tomatoes

10–5 Black coffee

10–6 Urine

10–7 Pure water

10–8 Seawater

10–9 Baking soda

10–10 Great Salt Lake

10–11 Household ammonia

10–12

Household bleach10–13

10–14 Sodium hydroxide

0

1

2

3

4

5

6

8

9

10

11

12

13

14

100

10–1

Review Question

Which of the following properties of water is not a consequence of its ability to form H bonds?

a. Cohesion

b. High specific heat

c. Adhesion

d. Ability to function as a solvent

e. Neutral pH

Review Question

Paleontologists distinguish rocks from dinosaur bones by touching their tongues to the object. If their tongue sticks, it is considered bone. This occurs because the water from the tongue moves up the porous spaces of bone. What property of water is allowing this to occur?

a. Cohesion

b. Capillary action

c. Water ionization

d. Heat of vaporization

Review Question

A water strider is an insect that can walk on water. How is this possible?

a. Capillary action

b. Hydration shells

c. Hydrophobic exclusion

d. Surface tension

Review Question

Hydrogen bonding between water molecules makes them tend to stick together. How does this affect the specific heat (SH) and heat of vaporization (HOV) of water?

a. The SH and HOV of water are high

b. The SH and HOV of water are low

c. SH is high but HOV is low

d. HOV is high but SH is low

e. None of these answers are correct

Review Question

Which of the following has the lowest concentration of H+ ions?

a. pH = 2

b. pH = 6

c. pH = 8

d. pH = 12

e. pH = 14

Buffers

• Substance that resists changes in pH

• Act by – Releasing H+ when a base is added– Absorbing H+ when acid is added

• Overall effect of keeping [H+] relatively constant

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69

• Most biological buffers consist of a pair of molecules, one an acid and one a base


+Bicarbonate

ion(HCO3

–)+

++

–

+

Water(H2O)

Carbondioxide(CO2)

Carbonicacid

(H2CO3)

Hydrogenion(H+)

Buffers

70


1X0 3X 4X 5X2X

pH

9

876543210

Amount of base added

Buffering range

Buffers Minimize pH Changes

the nature of molecules and the properties of water chapter 2 1

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