Chapter 2 The Chemical Basis of Life 4/22/2017 Chapter 2 The Chemical Basis of Life -Part One-

The Chemical Basis of Life 4/22/2017 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

Basic Chemistry Matter, Mass, and Weight Elements and Atoms 4/22/2017 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

Periodic table of the elements 4/22/2017

Atomic Structure Atoms: composed of subatomic particles 4/22/2017 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

Atomic Number and Atomic Mass 4/22/2017 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

Isotopes and Atomic Weight 4/22/2017 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

4/22/2017 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

4/22/2017 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

4/22/2017 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

4/22/2017 Inert Elements Atoms are stable (inert) when the outermost shell is complete These are the element of the periodic table on the furthest right.

4/22/2017 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

4/22/2017 Which are stable?

Types of BONDS 4/22/2017

Electrons and Chemical Bonding 4/22/2017 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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Covalent Bonding Atoms share one or more pairs of electrons 4/22/2017 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

Molecules and Compounds 4/22/2017 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 (22.99 + 35.45)

What is the difference between a compound and a molecule? 4/22/2017 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.

Intermolecular Forces 4/22/2017 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

Intermolecular Forces: Hydrogen Bonds 4/22/2017 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

4/22/2017 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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Intermolecular Forces: Solubility and Dissociation 4/22/2017 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

Electrolytes and Nonelectrolytes 4/22/2017 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

4/22/2017 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

4/22/2017 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

Decomposition Reactions 4/22/2017 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

4/22/2017 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