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Human Anatomy and Physiology I
Chapter 2The Chemical Basis of Life
Instructor: Mary Holman
• Matter
• Elements– Can’t be broken down into simpler
substances– 97 natural elements, >100 known– Organized into a Periodic Table
MajorElements in the Human Body
Oxygen Carbon
HydrogenNitrogenCalcium
Phosphorus
O CHNCaP
% body wt
65.018.5 9.5 3.3 1.5 1.0
Other Important ElementsIn the Human Body
Potassium K
Sulphur S
Sodium Na
Chlorine Cl
Magnesium Mg
Trace Elements
Iodine I Molybdenum MoFluorine F Chromium CrIron Fe Selenium SeCopper Cu Aluminum Al Silicone Si Boron B Vanadium V Tin SnZinc Zn Cobalt CoManganese Mn
Atomic StructureAtom • smallest portion of an element that retains
all the properties of the element• composed of subatomic particles:
• Proton – carries a single positive chargefound in the nucleus
• Neutron – carries no electrical chargefound in the nucleus
• Electron – very small particle that carries a single negative chargefound moving in varying energy
levels around the nucleus
Particle Charge Location
Electron
Proton
Neutron
--
+
none
In nucleus
In nucleus
Outside nucleus
Major Subatomic Particles
Fig. 2.3a
Hydrogen (H)
+
-
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Fig. 2.3b
Helium (He)
-
-
00+
+
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Fig. 2.3c
Lithium (Li)
-
-
-
0
0++
00+
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Atomic number - equal to the number of protons or electrons in an
atom
Atomic mass - equal to the average total number of neutrons plus protons
Isotopes - atoms with differing numbers of neutrons in atoms of the
same element12C 13C 14C
Periodic Table of the Elements
7Nitrogen
N14.0067
Periodic Table Appendix D - Pg 931
Bonding of Atoms
• Bonds form when atoms combine with other atoms through interactions between their electrons
• Electrons of an atom occupy regions of space called electron shells which circle the nucleus
• For atoms with atomic numbers of 18 or less, the following rules apply:
• The first shell can hold up to 2 electrons• The second shell can hold up to 8 electrons• The third shell can hold up to 8 electrons
Valence Number
Number of electrons in outer shell or energy orbital of an element
These electrons participate in bonding with atoms of other elements
Shifting of valence electrons occurs in bonding with other atoms
There are two types of bonds that hold atoms together in a
molecule:
Ionic bond Covalent bond
Valence # determines which kind of bond an atom is likely to make
Bonding of Atoms: Ions
Ion• An atom that gains or loses electrons to become stable• An electrically charged atom
Cation• Positively charged ion• Formed when an atom loses electrons
Anion• Negatively charged ion• Formed when an atom gains electrons
Ionic Bonds
• An attraction between a cation and an anion
• Formed when one atom gives up
one or more electrons to another atom
Fig. 2.4a
11p+
12n0
Sodium atom (Na) Chlorine atom (Cl)
(a) Separate atoms If a sodium atom loses an electron to a chlorine atom, the sodium atom becomes a sodium ion (Na+), and the chlorine atom becomes a chloride ion (Cl–).
17p+
18n0
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Fig. 2.4a Two Atoms Forming An Ionic Bond
Fig. 2.4b
+ -11p+
12n0
Chloride ion (Cl-)Sodium ion (Na+)
(b) Bonded ions These oppositely charged particles attract electrically and join by an ionic bond.
Sodium chloride
17p+
18n0
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Fig. 2.4b Bonded Ions
Important Ions in the Body
Na+
K+
Ca2+
Mg2+
Cl-
PO43-
NH4+
HCO3-
Covalent Bonds
• Formed when atoms share electrons
• Organic compounds contain many covalent bonds
Hydrogen atom +
H
Hydrogen molecule
H2
Hydrogen atom
H
+ + ++
- -
-
-
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Fig. 2.5
=
A Covalent Bond creating a Molecule of Hydrogen
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H
C
O
N
Fig. 2.6
Atomic # - 1 Atomic # - 8
Atomic # - 7 Atomic # - 6
Fig. 2.6a
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HH
H2
Structural Formulasversus
Molecular Formulas
Fig. 2.6b
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OO
O2
The Double Covalent Bond
O : : O . . . .. . . .
Fig. 2.6d
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CO O
CO2
Carbon Dioxide
Fig. 2.6c
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O
HH
H2O
Water - A Polar Molecule(+)
(-)
(+)
Bonding of Atoms:Polar Molecules
Polar Molecules• Molecule with a slightly negative end and a slightly positive end• Results when electrons are not shared equally in covalent bonds• Water is an important polar molecule
Slightly negative end
Slightly positive endsCopyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Fig. 2.8a
O
H H
Hydrogen Bonds
Hydrogen Bonds• A weak attraction between the positive end of one polar molecule and the negative end of another polar molecule• Formed between water molecules• Important for protein and nucleic acid structure
H
H
H
H
H
H
HH
H
H
O
O
O
O
O
Hydrogen bonds
(b)
Fig. 2.8b
Molecular Formulas
Depict the elements present and the number of each atom present in the molecule
H2
H2O
C6H12O6
Acids, Bases, and Salts
Electrolytes – substances that release ions in water
Acids – electrolytes that dissociate to release hydrogen ions in water
HCl H+ + Cl-
Bases – substances that release ions that can combine with hydrogen ions
NaOH Na+ + OH-
Salts – electrolytes formed by the reaction between an acid and a base
NaCl Na+ + Cl-
HCl + NaOH H2O + NaCl
Acid and Base Concentration
pH scale - indicates the concentration of hydrogen ions insolution Neutral pH 7;indicates equal concentrations of H+
and OH-
Acidic pH less than7; indicates a greater concentration of H+
Basic or alkaline pH greater than 7;indicates a greater concentration of OH-
OH– concentration increasesH+ concentration increases
AcidicH+
Relative Amountsof H+ (red)and OH– (blue)
BasicOH–
2.0gastricjuice
6.0corn
7.0Distilledwater
8.0Eggwhite
10.5milk ofmagnesia
11.5Householdammonia
pH 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14Basic (alkaline)NeutralAcidic
3.0applejuice
4.2tomatojuice
5.3cabbage
6.6cow’smilk
7.4Humanblood
8.4Sodiumbiocarbonate
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Pg. 68
Buffers
A buffer solution is one that maintains a constant pH upon the addition of either acid or base.
It consists of a weak acid and a weak base. It can “sponge up” excess H+ if added to a solution, or it can release H+ if the H+ concentration drops.
Inorganic Compounds
• Generally do not contain C*• Usually smaller than organic molecules• Usually dissociate in water, forming ions • Water, oxygen, carbon dioxide, and inorganic salts
* exceptions: CO, CO2, HCO3
Important Inorganic Compounds
Water (H2O) • Most abundant compound in living material• Two-thirds of the weight of an adult human• Major component of all body fluids• Medium for most metabolic reactions• Important role in transporting chemicals in the body• Absorbs and transports heat
Oxygen (O2) • Used by organelles to release energy from nutrients in order to drive cell’s metabolic activities• Necessary for survival
Important Inorganic Compounds
Carbon dioxide (CO2)• Waste product released during metabolic reactions• Must be removed from the body
Inorganic salts• Abundant in body fluids• Sources of necessary ions (Na+, Cl-, K+, Ca2+, etc.)• Play important roles in metabolism
Organic Compounds
• Contain C and H• Usually larger than inorganic molecules• Dissolve in water or organic liquids• Carbohydrates, lipids, proteins,
nucleic acids, and adenosine triphosphate
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