1. Chapter 2 The Chemical Basis of Life
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Chapter 2 The Chemical Basis of Life
-Part One-

2. The Chemical Basis of Life
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The Chemical Basis of Life
Key to understanding normal structure and function and understanding disease processes
The information in this chapter will help in the understanding of how different organ systems function

3. Basic Chemistry Matter, Mass, and Weight Elements and Atoms
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Basic Chemistry
Matter, Mass, and Weight
Matter: anything that occupies space and has mass
Mass: the amount of matter in an object
Weight: the gravitational force acting on an object of a given mass
Elements and Atoms
Element: the simplest type of matter with unique chemical properties; composed of atoms of only one kind
Atom: smallest particle of an element that has chemical characteristics of that element
Compounds: combination of two or more elements

4. Periodic table of the elements
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5. Atomic Structure Atoms: composed of subatomic particles
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Atomic Structure
Atoms: composed of subatomic particles
Neutrons: no electrical charge
Protons: one positive charge
Electrons: one negative charge
Nucleus: formed by protons and neutrons
Most of the volume of an atom occupied by electrons

6. Atomic Number and Atomic Mass
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Atomic Number and Atomic Mass
Atomic Number: equal to number of protons in each atom. Has a neutral charge. Thus, has an equal number of electrons
Atomic Mass: number of protons plus number of neutrons

7. Isotopes and Atomic Weight
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Isotopes and Atomic Weight
Isotopes: two or more forms of same element with same number of protons and electrons but different neutron number
For example; there are three types of hydrogen
Denoted by using symbol of element preceded by mass number as 1H, 2H, 3H
Atomic Weight: average masses of naturally occurring isotopes

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Radioactive Isotopes
Forms of atoms that emit radioactivity such as gamma rays, which can then be measured
Unstable isotopes which undergo nuclear decay
Used clinically and in research
Examples of uses
Tracking hormone uptake
Treating cancer
Sterilization of materials to be used in surgery

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Electrons and Bonding
Electrons occupy energy levels called electron shells
Electrons closest to the nucleus are most strongly attracted
Each shell has distinct properties
The number of electrons has an upper limit
Shells closest to the nucleus fill first

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Electrons and Bonding
Bonding involves interactions between electrons in the outer shell (valence shell) These valence electrons of elements interact with each other to form chemical reactions
Full valence shells do not form bonds

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Inert Elements
Atoms are stable (inert) when the outermost shell is complete
These are the element of the periodic table on the furthest right.

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Inert Elements
Atoms will gain, lose, or share electrons to complete their outermost orbitals and reach a stable state
Octet Rule
Atoms are considered stable when their outermost orbital has 8 electrons
The exception to this rule is Shell 1, which can only hold 2 electrons

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Which are stable?

14. Types of BONDS
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15. Electrons and Chemical Bonding
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Electrons and Chemical Bonding
Intramolecular bonding occurs when outermost electrons are either shared with or transferred to another atom
Ionic Bonding: atoms exchange electrons
Covalent Bonding: two or more atoms share electron pairs
Ion: an atom loses or gains electrons and becomes charged
Cation: positively charged ion
Anion: negatively charged ion
In an ionic bond, cations and anions are attracted to each other and remain close to each other

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17. Covalent Bonding Atoms share one or more pairs of electrons
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Covalent Bonding
Atoms share one or more pairs of electrons
Single covalent: two atoms share one pair of electrons
Double covalent: Two atoms share 4 electrons
Nonpolar covalent: Electrons shared equally because nuclei attract the electrons equally
Polar covalent: Electrons not shared equally because one nucleus attracts the electrons more than the other does

18. Molecules and Compounds
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Molecules and Compounds
Molecules: two or more atoms chemically combine to form an independent unit
Example: a hydrogen molecule (H2)
Compounds: a substance composed of two or more different types of atoms chemically combined
Example: water (H2O)
Molecular Mass: determined by adding up atomic weights of its atoms or ions
Example: NaCl ( )

19. What is the difference between a compound and a molecule?
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What is the difference between a compound and a molecule?
A molecule is formed when two or more atoms join together chemically. A compound is a molecule that contains at least two different elements. All compounds are molecules but not all molecules are compounds.
Molecular hydrogen (H2), molecular oxygen (O2) and molecular nitrogen (N2) are not compounds because each is composed of a single element. Water (H2O), carbon dioxide (CO2) and methane (CH4) are compounds because each is made from more than one element. The smallest bit of each of these substances would be referred to as a molecule. For example, a single molecule of molecular hydrogen is made from two atoms of hydrogen while a single molecule of water is made from two atoms of hydrogen and one atom of oxygen.

20. Intermolecular Forces
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Intermolecular Forces
Forces between molecules
Result from weak electrostatic attractions between oppositely charged parts or molecules, or between ions and molecules
Weaker than forces producing chemical bonding

21. Intermolecular Forces: Hydrogen Bonds
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Occur when the positively charged H of one molecule is attracted to the negatively charged O, N or F of another molecule
For example, in water the positively charged hydrogen atoms of one water molecule bond with the negatively charged oxygen atoms of other water molecules
Hydrogen bonds play an important role in determining the shape of complex molecules

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Polar vs Non polar This is a very important concept that is used in biology every day!
Polar molecules
Have a charge because the electrons are NOT equally shared
Dissolve in water
Ionic bond, polar covalent bond and hydrogen bonding
Example is Water
Hydrophilic
Non-polar
Do not have a charge
Nonpolar covalent bonding where the charges are distributed evenly
Do NOT dissolve in water
Example is Oil
Hydrophobic

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24. Intermolecular Forces: Solubility and Dissociation
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Solubility: ability of one substance to dissolve in another
For example, sugar or salt dissolves in water
Dissociation or Separation: in ionic compounds, cations are attracted to negative end and anions attracted to positive end of water molecules; the ions separate and each becomes surrounded by water molecules
Electrolyte: dissociation of an ionic compound in water

25. Electrolytes and Nonelectrolytes
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Electrolytes: solutions made by the dissociation of cations (+) and anions (-) in water
Have the capacity to conduct an electric current
Currents can be detected by electrodes
Nonelectrolytes: solutions made by molecules that dissolve in water, but do not dissociate; do not conduct electricity

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Chemical Reactions
Atoms, ions, molecules or compounds interact to form or break chemical bonds
Reactants: substances that enter into a chemical reaction.
Products: substances that result from the reaction
Chemical bonds are made (synthesis; anabolism) and broken (decomposition; catabolism) during chemical reactions
Metabolism: collective term used for the sum of all of the anabolic and catabolic reactions in the body

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Synthetic Reactions
Two or more reactants chemically combine to form a new and larger product. Anabolism.
Chemical bonds made; energy stored in the bonds.
Responsible for growth, maintenance and repair
Dehydration: synthetic reaction where water is a product
Produce chemicals characteristic of life: carbohydrates, proteins, lipids, and nucleic acids

28. Decomposition Reactions
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Decomposition Reactions
A large reactant is broken down to form smaller products. Catabolism.
Chemical bonds broken; energy released.
Hydrolysis: water is split into two parts that contribute to the formation of the products
Example: the breakdown of ATP to form ADP and inorganic phosphate with a concomitant release of free energy

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Reversible Reactions
Chemical reactions in which the reaction can proceed either from reactants to products or from products to reactants.
Equilibrium: rate of product formation is equal to rate of reactant formation
Example: CO2 and H+ formation in plasma