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The Chemical Context of Life & Water and the Fitness of the Environment Chapters 2 & 3
The Chemical Context of Life
&Water and the Fitness of the Environment
Chapters 2 & 3
Chapter 2-3 Chemistry / Water
Learning Objectives• Identify subatomic particles and their properties
• Use the periodic table to draw Bohr electron configurations
• Utilize Bohr electron configurations to draw and describe ionic and covalent bonds
• Identify and describe polar compounds and polar interactions such as hydrogen bonds
• Convert pH values to hydrogen and hydroxide ion concentraton values
• Describe and explain buffer interactions such as carbonic acid
2
Chapter 2-3 Chemistry / Water 3
Outline
Chemical ElementsAtoms IsotopesMolecules and Compounds
Chemical Bonding Ionic and CovalentHydrogen
Properties of WaterAcids and Bases
Chapter 2-3 Chemistry / Water 4
Elements Important for Biology
Why were thesetwo not includedin the previous list?
Chapter 2-3 Chemistry / Water 5
Composition of Earth’s Crust versus Organisms
Organic vs Inorganic matter
Chapter 2-3 Chemistry / Water 6
Atomic SymbolsKey
H1.008
1+1-1
Hydrogen
Atomic Number
Atomic Mass
Chapter 2-3 Chemistry / Water 7
Periodic Table12
Chapter 2-3 Chemistry / Water 8
Periodic TableElements grouped in periodic table based on characteristicsVertical columns = groups; chemically similarHorizontal rows = periods; larger larger
1
H1.008
3
Li6.941
11
Na22.99
19
K39.10
4
Be9.012
12
Mg24.31
20
Ca40.08
5
B10.81
13
Al26.98
21
Ga69.72
6
C12.01
14
Si28.09
22
Ge72.59
7
N14.01
15
P30.97
23
As74.92
8
O16.00
16
S32.07
24
Se78.96
9
F19.00
17
Cl35.45
25
Br79.90
10
Ne20.18
18
Ar39.95
26
Kr83.60
2
He4.003
I
II III IV V VI VII
VIII1
2
3
4
Groups
Perio
ds
Chapter 2-3 Chemistry / Water 9
The Bohr Model of The Atom(CHNOPS)
1
2
3
1H
9F
15P
9F
Figure 2.9 , page 36
Chapter 2-3 Chemistry / Water 10
Updated model – Energy levels!Quantum mechanics requires a more versatile model
Showing probability domains in 3 dimensions
Electrons have the ability to move between these Orbitals !!This movement is very important for the use and Transfer of energy in biological systems !! ex: Photosythesis and cellular Respiration.
Chapter 2-3 Chemistry / Water 11
Octet Rule of atomic bondingAtoms with fewer than 8 electrons in outermost shell (except Hydrogen and Helium) are chemically reactive! If 3 or less – Tendency to donate electrons If 5 or more – Tendency to receive electrons This dictates what and how many atoms will form bonds!!!
Chapter 2-3 Chemistry / Water 12Groups of Elements
Semi-metals
Elements on this side lose electronsto complete octet
Elements on this sideGain electrons
Chapter 2-3 Chemistry / Water 13
Chemical Bonding
Bonds are the result of either:A. Donating and Accepting electrons = Ionic bonds
OR
B. Sharing electrons = Covalent bonds
Chapter 2-3 Chemistry / Water 14Formation of Sodium Chloride
Ionically bonded sodium and chloride ionswhere the electron has been donated ,forming the new compound sodium chloride
Chapter 2-3 Chemistry / Water 15Types of Bonds:B. Covalent Bonds
Covalent bonds form between non-metals and other non-metals (elements on the right hand side of the periodic table)
In this type of bonding electrons are shared and ions do not form.
Chapter 2-3 Chemistry / Water 16Covalently Bonded Molecules
Figure 2.12 page 38
Chapter 2-3 Chemistry / Water 17The concept of polarity
Polar means to have very different characteristics or to be opposites like the North and South poles of the earth.
The concept of polarity is very important in biology. A molecule is said to be polar if it has two different characteristics at either end. The difference in characteristics is a difference in charge (+ or -) that results from an unequal distribution of electrons or an ionized subgroup.
Chapter 2-3 Chemistry / Water 18
Nonpolar Covalent Bonds
Note: When non-metals bond (C, O, N, P, S) they tend to form non-polar bonds (of course we are talking about covalent bonds here because we are talking about non-metals)
Electrons are shared equally between the bonded elements
Chapter 2-3 Chemistry / Water 19
Polar Covalent Bonds
But, when non-metals bond with hydrogen they tend to form polar covalent bonds. (This is essentially because their charge density from protons (+) is much, much greater than hydrogen.)
Electrons are not shared equally in polar covalent bonds.
Chapter 2-3 Chemistry / Water 20Types of Bonds:Hydrogen Bonds
Water (H2O or H–O–H) is a polar moleculeElectrons spend more time with O than H’sH’s become slightly +, O slightly –
When polar molecules are dissolved in waterThe H’s of water molecules are attracted to the negative parts of the solute molecules
Results in a weak bond – the hydrogen bondEasily broken, but many together can be quite strong
Chapter 2-3 Chemistry / Water 21Water Molecule
e--
e-- e--
e--
Fig. 2.13 p39
Chapter 2-3 Chemistry / Water 22Hydrogen Bonding
