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Biology 240

by: Fadumo Abdullahi

Biology 240 Biology 240-01

Fadumo Abdullahi
U of L

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Chapter 2 Notes: The Chemical Context of Life
Biology Unity of Life
Dr. Shira Rabin
Class Notes
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This 2 page Class Notes was uploaded by Fadumo Abdullahi on Monday September 5, 2016. The Class Notes belongs to Biology 240-01 at University of Louisville taught by Dr. Shira Rabin in Fall 2016. Since its upload, it has received 31 views.


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Date Created: 09/05/16
Chapter 2: The Chemical context of Life Matter is anything that can take up space  - Organisms are composed of matter - Matter is made up of elements - An element a substance that cannot be broken down to other substance by  chemical reactions.  - A compound is a substance consisting of two or more different elements  combined.  There are 92 natural elements that are essential for organisms to live a healthy life and  reproduce.  - Just four elements make up 96% of living matter: oxygen, carbon, hydrogen and  nitrogen.  - Calcium, phosphorus, potassium, sulfur and other elements account for the  remaining 4%.  Atom is the smallest unit with properties of an element. - Protons and neutron are packed together in the atomic nucleus of an atom. - The electrons move rapidly around the nucleus.  - Atomic number is the number of protons unique to that element. - Mass number is the sum of protons plus neutrons. - Isotope is an element with same proton but different neutron Electron shell is the fixed level of potential energy that electrons exist at.  - Electron are found I different electron shells. - Each shell has a characteristic average distance and energy level  - The first shell is closest to the nucleus and has the lowest potential energy An atom’s electrons vary in the amount of energy they possess.  - Energy is the capacity to cause change. - Potential energy is the energy that matter possesses because of its location or  structure.  - An electron can move from one shell to another only if the energy it gains or loses  is exactly equal to the difference in energy between the energy levels of two  shells.  The chemical behavior of an atom depends mostly on the number of electron in its  outermost shell.  - The outermost shell is called the valence electron The formation and function of molecules depend on chemical bonding between atoms - A covalent bond is the sharing of pair of valence electrons by two atoms - Two or more atoms held together by covalent bond constitute a molecule in this  case a hydrogen molecule.  o Atom in a molecule attract shred bonding electron to varying degrees, depending  on the element. o Electronegativity is the attraction of a particular atom for electrons of covalent  bond.  o The more electronegative an atom is, the more strongly it pulls shared electrons  toward itself. o Nonpolar covalent bond is the bond between two atoms of the same element.          o The electrons are shared equally because the two atoms have the same  electronegativity. o Polar covalent bond is when an atom is bonded to a more electronegative atom, the electrons of the bond are not shared equally.  - Ionic bonds: o The positive and the negative attraction of cations and anions.  A positively charged ion is called cation  A negatively charged ion is called anion o Compounds formed by ionic bonds are called ionic compound - Weak Chemical Bonds o In organisms the strongest chemical bond is the covalent bond o Hydrogen bond and van der Waals interaction are among the weak bonds - Hydrogen bond o The attraction between hydrogen and an electronegative atom o When the hydrogen atom is covalently bonded to an electronegative atom,  the hydrogen atom has a partial positive charge - Van der Waals interaction occur between transiently positive and negative regions  of molecules - A molecule’s shape is determined by the position of its atoms’ valence orbitals.  Covalent bonds result in hybrid orbitals, which are responsible for the shapes of  H2O and CH4.  - Chemical reactions change the reactants into products - All chemical reactions are theoretically reversible


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