The Chemical Context of Life

Transcription

1 The Chemical Context of Life Chapter 2 MATTER CONSISTS OF CHEMICAL ELEMENTS AND COMBINATIONS CALLED COMPOUNDS 1

2 Elements and Compounds Ma?er is made up of elements Elements cannot be broken down any further by normal chemical reac>ons 92 natural elements recognized by chemists Gold (Au), Copper (Cu), Carbon (C), Oxygen (O) Compounds are two or more elements combined in a fixed ra>o Table salt (NaCl), Water (H 2 O) Proper>es of compounds are different than its individual elements The Elements of Life C, H, O, and N makes up 96% of all living maser EssenEal Elements are required by all organisms Trace Elements Only required in minute quan>>es OUen used as Cofactors for Enzymes 2

3 Check Your Understanding Differen>ate between an element and a compound. Provide examples of each. Which elements make up 96% of all living maser? Differen>ate between an essen>al element and a trace element. Provide example of each. Why are trace elements s>ll important within an organisms diet? AN ELEMENT S PROPERTIES DEPEND ON THE STRUCTURE OF ITS ATOMS 3

4 Subatomic Par>cles Atomic Nucleus Protons (posi>ve charge; mass of 1 Dalton) Neutrons (no charge; mass of 1 Dalton) Orbitals are where an atom s electrons are found 90% of the >me Electrons (nega>ve charge; no mass) Helium Atomic Mass and Atomic Number Atomic Number denotes the number of protons Neutral (uncharged) atoms have equal number of protons and electrons Mass Number denotes the number of protons and neutrons in the nucleus Atomic Mass Mass Number 4

5 Possess more neutrons than normally present Alters the atomic mass Many isotopes are stable RadioacEve Isotopes are inherently unstable Gives off par>cles and energy OUen used to tag proteins, to track the movement of fluids in the body, to iden>fy >ssues (PET scan) Isotopes Energy is the capacity to cause change PotenEal Energy is a type of energy due to posi>on or structure Electrons have poten>al energy due to distance from atomic nucleus Electron Shells Energy Levels 5

6 Electron Distribu>on Valence Electrons are the outermost electrons in an atom s orbital Valence Number is 2 for the first orbital and 8 for the second and third orbital Valence Shell is the outermost orbital of a par>cular atom An atom s chemical behavior is determined by the interac>ons of its valence electrons Check Your Understanding Differen>ate between a proton, a neutron, and an electron. Differen>ate between atomic number and atomic mass. How do you determine an atoms number of protons, electrons, and neutrons if given only those two pieces of informa>on? What is an isotope? What are they commonly used for in medicine? What is meant by the valence number of an atom? What is the valence number of electrons in the first, second, and third electron orbitals? Why is the valence number important to an atom? 6

7 THE FORMATION AND FUNCTION OF MOLECULES DEPENDS ON CHEMICAL BONDS BETWEEN ATOMS Chemical Bonds ASrac>ons that keep atoms close together Due to interac>ons between electrons of neighboring atoms Strongest chemical bonds in Aqueous solu>ons are Covalent Bonds Typical of biological systems Ionic Bonds are generally strong when NOT present in aqueous solu>ons 7

8 Electronega>vity Strength of asrac>on for a given atom to the electrons in a chemical bond Determines if electrons are shared, how they are shared, or if they are transferred completely Covalent Bonds Sharing of a pair of valence electrons between 2 atoms Single Bonds Double Bonds Molecules are created by a covalent bond between 2 or more atoms 8

9 Types of Covalent Bonds Nonpolar Covalent Polar Covalent Equal Sharing Unequal Sharing Ionic Bonds One atom is so electronega>ve, it takes an electron from its partner Result is one nega>vely-charged and one posi>vely-charged atom (Ion) CaEons are posi>vely charged Anions are nega>vely charged Resul>ng ions are held together by electrosta>c interac>ons OUen results in salts such as NaCl, KCl, MgCl 2 9

10 Weak Chemical Bonds Hydrogen Bonds occur between polar molecules Hydrogen of one is asracted to the electronega>ve atom of another van der Waals InteracEons are weak bonds based on the close proximity of molecules Can be significant as the number of interac>ng molecules increases Molecular Shape and Func>on Shape is determined by the way atoms bond to each other Shape determines how molecules interact with other molecules Determines a molecule s func>on 10

11 Check Your Understanding Define electronega>vity and describe how it determines the type of bonds an atom can form. Differen>ate between a covalent and an ionic bond. Differen>ate between a polar covalent and a nonpolar covalent bond. Differen>ate between a ca>on and an anion. What is a hydrogen bond and how does it differ from both covalent and ionic bonds? How do the chemicals endorphin and morphine illustrate the principle of form fits func>on even at the molecular level? CHEMICAL REACTIONS MAKE AND BREAK CHEMICAL BONDS 11

12 Chemical Reac>ons Making and breaking of chemical bonds Reactants are the star>ng materials Products are the end materials Many biological reac>ons are Reversible Most reac>ons occur un>l an Equilibrium is reached Reactants Products 12