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BSC 114 Outline of Ch 2

by: bnford1

BSC 114 Outline of Ch 2 BSC 114


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Outline of chapter 2: the chemical context of life. Notes come from both the lecture and the text book materials.
Principles of Biology I
Dr. Lam
Class Notes
Biology, General Chemistry
25 ?




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This 4 page Class Notes was uploaded by bnford1 on Friday September 2, 2016. The Class Notes belongs to BSC 114 at University of Alabama - Tuscaloosa taught by Dr. Lam in Fall 2016. Since its upload, it has received 4 views. For similar materials see Principles of Biology I in Biology at University of Alabama - Tuscaloosa.


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Date Created: 09/02/16
Chapter 2: The Chemical Context of Life 1. Matter consists of chemical elements in pure form and in combinations called compounds. Matter is defined as anything that has mass and takes up space. a. Elements and Compounds i. An element is a substance that cannot be broken down to other substances by chemical reactions. There are 92 naturally occurring elements recognized today. ii. A compound is a substance consisting of two or more different elements combined in a fixed ratio. A compound has characteristics different than those of its elements. b. The Elements of Life i. Essential Elements are needed by organisms in order to live a healthy life and to reproduce. Oxygen, carbon, hydrogen, and nitrogen are four of the main essential elements. Other important ones include calcium, phosphorus, potassium, and sulfur. ii. Trace elements are also required by an organism, but only in minute quantities. 2. An element’s properties depend on the structure of its atoms. An atom is defined as the smallest unit of an element that still maintains its properties. a. Subatomic Particles i. Atoms are composed of protons, neutrons, and electrons. ii. Protons and neutrons are nearly identical in mass at approximately 1.7 x 10 -2g, which is approximately 1 Dalton. The mass of an electron is so minute that it is ignored when computing the total mass of an atom. 1. Because these measurements are so small the unit of measurement called the Dalton (or amu) is used. b. Atomic Number and Atomic Mass i. The atomic number of an element refers to the number of protons in the nucleus, which is a constant number for each element. ii. The mass number is the total number of protons and neutrons iii. The total mass of an atom is also called the atomic mass c. Isotopes i. Isotopes are different forms of the same element. They all have the same number of protons; however, the number of neutrons may vary. Although the isotopes of an element all have slightly different masses, they all behave the same in chemical reactions. ii. A radioactive isotope is one in which the nucleus decays spontaneously. The decay can lead to a change in the number of protons, changing the atom to an atom of a different element. 1. Radioactive isotopes are useful for fossil dating and also as tracers to follow atoms through metabolism. d. The Energy Levels of Electrons i. Electrons are the only subatomic particles directly involved in the chemical reactions between atoms. ii. Energy is the capacity to cause change by doing work. Potential energy is the energy matter possesses because of its location or structure. Matter has a tendency to move to the lowest possible state of potential energy. 1. Electrons have potential energy because of how they are arranged in relation to the nucleus. The more distant an electron is form the nucleus, the greater its potential energy. 2. An electron’s potential energy is determined by its energy level and it cannot exist between energy levels. iii. Electrons are found in different energy shells, each with a characteristic average distance and energy level. An electron can change the shell it occupies by absorbing or losing an amount of energy equal to the difference in potential energy between its position in the old shell and that in the new shell. 1. When it absorbs energy it moves to a shell farther away from the nucleus and when it loses energy it moves closer to the nucleus. This energy lost is usually released to the environment as heat. e. Electron Distribution and Chemical Properties i. The chemical behavior of an element depends mostly on the number of outermost electrons, called valence electrons, which occupy the valence shell. An atom with a complete valence shell is said to be unreactive, or chemically inert. f. Electron Orbitals i. The 3-D space where an electron is found 90% of the time is called an orbital. Each electron shell contains electrons at a particular energy level, distributed among a specific number of orbitals- each with distinctive shapes and orientations. 1. No more than 2 electrons can occupy a single orbital 3. The formation and function of molecules depend on chemical bonding between atoms a. Covalent Bonds i. A covalent bond is the sharing of a pair of valence electrons by two atoms. Two or more atoms held together by covalent bonds make up a molecule. 1. A single bond results from the sharing of a single pair of electrons whereas a double bond is formed by the sharing of two pairs of valence electrons. ii. The bonding capacity of an atom is called its valence and usually equals the number of unpaired electrons required to complete the atom’s valence shell. iii. The attraction of a particular atom for the electrons of a covalent bond is called its electronegativity. The more electronegative an atom is, the more strongly it pulls the shared electrons towards itself. 1. A nonpolar covalent bond occurs when there is a bond between elements of the same electronegativity 2. When one atom is bonded to a more electronegative atom, the electrons are not shared equally resulting in a polar covalent bond. b. Ionic Bonds i. In some cases, two atoms are so unequal in their attraction for valence electrons that the more electronegative atom strips an electron completely away from its partner. ii. A charged atom (or molecule) is called an ion. When the charge is positive it is called a cation and an anion when it is negative. Because of their opposite charges, cations and anions are attracted to each other, resulting in ionic bonds. 1. Compounds formed by ionic bonds are called ionic compounds or salts. a. i.e. Sodium Chloride (table Salt) c. Weak Chemical Bonds i. Hydrogens Bonds 1. The partial positive charge on a hydrogen atom that is covalently bonded to an electronegative atom allows the hydrogen to be attracted to different electronegative atoms nearby, resulting in a hydrogen bond. a. In living cells, the electronegative partners are usually oxygen and nitrogen ii. Van de Waals Interactions 1. Electrons are not always symmetrically distributed in a molecule; they may accumulate by chance in one part of the molecule or another. The results are ever- changing regions of positive and negative charge that enable atoms and molecules to stick to one another. This is called van der Waals interactions and they are individually weak and only occur when atoms and molecules are very close together. However, when they happen they can be very powerful. (They are the reason a lizard can walk straight up a wall) d. Molecular Shape and Function i. Molecular shape is crucial in biology because it determines how biological molecules recognize and respond to one another with specificity. Biological molecules often bind temporarily to each other by forming weak bonds, but this can only happen if their shapes are complementary. 4. Chemical reactions make and break chemical bonds. a. Chemical Reactions i. The making and breaking of chemical bonds, leading to changes in the composition of matter, are called chemical reactions. The starting materials are called the reactants and the resulting in the products.


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