1724374923_1707410101_1695303557_BIOL111_L5.pdf

COURSE: INTRODUCTION TO BIOLOGICAL CONCEPTS COURSE CODE: BIOL 111 CREDIT HOURS: 3 LECTURER : GERLISA VIGILANT SEPTEMBER 2022/2023 SEMESTER Chemistry of living organisms  Learning Objectives 1. Define ionic, covalent, hydrogen and polar covalent bonds. 2. Draw simple molecules t...

COURSE: INTRODUCTION TO BIOLOGICAL CONCEPTS COURSE CODE: BIOL 111 CREDIT HOURS: 3 LECTURER : GERLISA VIGILANT SEPTEMBER 2022/2023 SEMESTER Chemistry of living organisms  Learning Objectives 1. Define ionic, covalent, hydrogen and polar covalent bonds. 2. Draw simple molecules to demonstrate the types of bonds state above  Videos! https://www.youtube.com/watch?v=zpaHPXVR8WU https://www.youtube.com/watch?v=TxHi5FtMYKk https://www.youtube.com/watch?v=h24UmH38_LI  Matter Takes up space and has mass Exists as elements (pure form) and in chemical combinations called compounds Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings 5  Elements Can’t be broken down into simpler substances by chemical reaction Composed of atoms Essential elements in living things include carbon C, hydrogen H, oxygen O, and nitrogen N making up 96% of an organism Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings 6  Compounds Are substances consisting of two or more elements combined in a fixed ratio Have characteristics different from those of their elements + Figure 2.2 Sodium Chloride Sodium Chloride Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings 7  Properties of Matter An element’s properties depend on the structure of its atoms Each element consists of a certain kind of atom that is different from those of other elements An atom is the smallest unit of matter that still retains the properties of an element Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings 8  Subatomic Particles Atoms of each element Are composed of even smaller parts called subatomic particles Neutrons, which have no electrical charge Protons, which are positively charged Electrons, which are negatively charged Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings 9  Subatomic Particle Location Protons and neutrons – Are found in the atomic nucleus Electrons – Surround the nucleus in a “cloud” Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings 10  Atomic Number & Atomic Mass Atoms of the various elements Differ in their number of subatomic particles The number of protons in the nucleus = atomic number The number of protons + neutrons = atomic mass Neutral atoms have equal numbers of protons & electrons (+ and – charges) Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings 11  Atomic Number Is unique to each element and is used to arrange atoms on the Periodic table Carbon = 12 Oxygen = 16 Hydrogen = 1 Nitrogen = 17 Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings 12  Atomic Mass Is an approximation of the atomic mass of an atom It is the average of the mass of all isotopes of that particular element Can be used to find the number of neutrons (Subtract atomic number from atomic mass) Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings 13  Periodic table – Shows the electron distribution for all the elements Hydrogen 2 Atomic number Helium He 2 He 1 H 4.00 Element symbol Atomic mass First Electron-shell shell diagram Lithium Beryllium Boron Carbon Nitrogen Oxygen Fluorine Neon 3 Li 4 Be 3 B 6 C 7 N 8 O 9 F 10 Ne Second shell Sodium Magnesium Aluminum Silicon Phosphorus Sulfur Chlorine Argon 11 Na 12 Mg 13 Al 14 Si 15 P 16 S 17 Cl 18 Ar Third shell igure 2.8 Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings 14  Why do some elements react? Valence electrons – Are those in the outermost, or valence shell – Determine the chemical behavior of an atom Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings 15  Chemical Bonding Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings 16  Covalent Bonds Hydrogen atoms (2 H) Sharing of a pair of valence 1 In each hydrogen atom, the single electron electrons is held in its orbital by its attraction to the + + proton in the nucleus. Examples: H2 2 When two hydrogen atoms approach each other, the electron of each atom is also + + attracted to the proton in the other nucleus. 3 The two electrons become shared in a covalent bond, forming an H2 + + molecule. Hydrogen Figure 2.10 molecule (H2) Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings 17  Covalent Bonding A molecule – Consists of two or more atoms held together by covalent bonds A single bond – Is the sharing of one pair of valence electrons A double bond – Is the sharing of two pairs of valence electrons Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings 18 Fig. 2-UN5 Single Double covalent bond covalent bond  Multiple Covalent Bonds Name Electron- Structural Space- (molecular shell formula filling formula) diagram model (a) Hydrogen (H2). Two hydrogen H H atoms can form a single bond. (b) Oxygen (O2). Two oxygen atoms share two pairs of O O electrons to form a double bond. Figure 2.11 A, B Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings 20  Compounds & Covalent Bonds Name Electron- Structural Space- (molecular shell formula filling formula) diagram model (c) Water (H2O). Two hydrogen atoms and one O H oxygen atom are joined by covalent H bonds to produce a molecule of water. (d) Methane (CH4). Four hydrogen atoms can satisfy H the valence of one carbon atom, forming H C H methane. H Figure 2.11 C, D Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings 21  Covalent Bonding Electronegativity – Is the attraction of a particular kind of atom for the electrons in a covalent bond The more electronegative an atom – The more strongly it pulls shared electrons toward itself Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings 22  Covalent Bonding In a nonpolar covalent bond – The atoms have similar electronegativit ies – Share the electron equally Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings 23  Covalent Bonding In a polar covalent bond – The atoms have differing electronegativities – Share the electrons unequally Because oxygen (O) is more electronegative than hydrogen (H), shared electrons are pulled more toward oxygen. δ– This results in a partial negative charge on the oxygen and a partial positive O charge on the hydrogens. Figure 2.12 H H δ+ δ+ H2O Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings 24 Ionic Bonds Atoms sometimes strip electrons from their bonding partners An example is the transfer of an electron from sodium to chlorine After the transfer of an electron, both atoms have charges A charged atom (or molecule) is called an ion Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings  Ionic Bonds In some cases, atoms strip electrons away from their bonding partners Electron transfer between two atoms creates ions Ions – Are atoms with more or fewer electrons than usual – Are charged atoms Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings 26 Fig. 2-14-1 Na Cl Na Cl Sodium atom Chlorine atom Fig. 2-14-2 Na Cl Na Cl Na Cl Na+ Cl– Sodium atom Chlorine atom Sodium ion Chloride ion (a cation) (an anion) Sodium chloride (NaCl)  Ions An anion – Is negatively charged ions A cation – Is positively charged Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings 29  A cation is a positively charged ion An anion is a negatively charged ion An ionic bond is an attraction between an anion and a cation Animation: Ionic Bonds 2005 Pearson Education, Inc., Copyright © 2008 Inc. publishing publishingas asBenjamin BenjaminCummings Cummings  Compounds formed by ionic bonds are called ionic compounds, or salts Salts, such as sodium chloride (table salt), are often found in nature as crystals Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings Hydrogen Bonds A hydrogen bond forms when a hydrogen atom covalently bonded to one electronegative atom is also attracted to another electronegative atom In living cells, the electronegative partners are usually oxygen or nitrogen atoms Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings Fig. 2-16 δ− δ+ Water (H2O) δ + Hydrogen bond δ− Ammonia (NH3) δ δ + + δ +