Chapter 2 :Chapter 2 The Chemical Context of Life


Slide 2:Overview: Chemical Foundations of Biology


Slide 3:The bombardier beetle uses chemistry to defend itself Figure 2.1


Slide 4:Concept 2.1: Matter consists of chemicalelements in pure form and in combinationscalled compounds


Elements and Compounds :Elements and Compounds Organisms are composed of matter, whichis anything that takes up space and hasmass


Slide 6:Matter is made up of elements, substancesthat cannot be broken down to other substances by chemical reactions


Slide 7:A compound Is a substance consisting of two or more elements combined in a fixed ratio Has characteristics different from those of its elements Figure 2.2


Essential Elements of Life :Essential Elements of Life Essential elements Include carbon, hydrogen, oxygen, and nitrogen Make up 96% of living matter


Slide 9:A few other elements Make up the remaining 4% of living matter Table 2.1


Slide 10:The effects of essential element deficiencies Figure 2.3


Slide 11:Trace elements Are required by an organism in only minute quantities


Slide 12:Concept 2.2: An element’s propertiesdepend on the structure of its atoms


Slide 13: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


Subatomic Particles :Subatomic Particles Atoms of each element Are composed of even smaller parts called subatomic particles


Slide 15:Relevant subatomic particles include Neutrons, which have no electrical charge Protons, which are positively charged Electrons, which are negatively charged


Slide 16:Protons and neutrons Are found in the atomic nucleus Electrons Surround the nucleus in a “cloud”


Slide 17:Simplified models of an atom Figure 2.4


Atomic Number and Atomic Mass :Atomic Number and Atomic Mass Atoms of the various elements Differ in their number of subatomic particles


Slide 19:The atomic number of an element Is the number of protons Is unique to each element


Slide 20:The mass number of an element Is the sum of protons plus neutrons in the nucleus of an atom Is an approximation of the atomic mass of an atom


Isotopes :Isotopes Atoms of a given element May occur in different forms


Slide 22:Isotopes of a given element Differ in the number of neutrons in the atomic nucleus Have the same number of protons


Slide 23:Radioactive isotopes Spontaneously give off particles and energy


Slide 24:Can be used in biology


Slide 25:Figure 2.5


Slide 26:Can be used in biology


The Energy Levels of Electrons :The Energy Levels of Electrons An atom’s electrons Vary in the amount of energy they possess


Slide 28:Energy Is defined as the capacity to cause change Potential energy Is the energy that matter possesses because of its location or structure


Slide 29:The electrons of an atom Differ in the amounts of potential energy they possess


Slide 30:Energy levels Are represented by electron shells


Electron Configuration and Chemical Properties :Electron Configuration and Chemical Properties The chemical behavior of an atom Is defined by its electron configuration and distribution


Slide 32:The periodic table of the elements Shows the electron distribution for all the elements


Slide 33:Valence electrons Are those in the outermost, or valence shell Determine the chemical behavior of an atom


Electron Orbitals :Electron Orbitals An orbital Is the three-dimensional space where an electron is found 90% of the time


Slide 35:Each electron shell Consists of a specific number of orbitals


Slide 36:Concept 2.3: The formation and function of molecules depend on chemical bonding between atoms


Covalent Bonds :Covalent Bonds A covalent bond Is the sharing of a pair of valence electrons


Slide 38:Figure 2.10 Formation of a covalent bond


Slide 39: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


Slide 40:(a) (b) Single and double covalent bonds


Slide 41:Covalent bonding in compounds


Slide 42: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


Slide 43:In a nonpolar covalent bond The atoms have similar electronegativities Share the electron equally


Slide 44:Figure 2.12 In a polar covalent bond The atoms have differing electronegativities Share the electrons unequally


Ionic Bonds :Ionic Bonds In some cases, atoms strip electrons away from their bonding partners


Slide 46:Electron transfer between two atoms creates ions Ions Are atoms with more or fewer electrons than usual Are charged atoms


Slide 47:An anion Is negatively charged ions A cation Is positively charged


Slide 48:Figure 2.13 An ionic bond Is an attraction between anions and cations


Slide 49:Ionic compounds Are often called salts, which may form crystals


Weak Chemical Bonds :Weak Chemical Bonds Several types of weak chemical bonds are important in living systems


Hydrogen Bonds :Hydrogen Bonds  –  +  + A hydrogen bond Forms when a hydrogen atom covalently bonded to one electronegative atom is also attracted to another electronegative atom


Van der Waals Interactions :Van der Waals Interactions Van der Waals interactions Occur when transiently positive and negative regions of molecules attract each other


Slide 53:Weak chemical bonds Reinforce the shapes of large molecules Help molecules adhere to each other


Molecular Shape and Function :Molecular Shape and Function The precise shape of a molecule Is usually very important to its function in the living cell Is determined by the positions of its atoms’ valence orbitals


Slide 55:In a covalent bond The s and p orbitals may hybridize, creating specific molecular shapes


Slide 57:Molecular shape Determines how biological molecules recognize and respond to one another with specificity


Slide 58:Figure 2.17


Slide 59:Concept 2.4: Chemical reactions make and break chemical bonds


Slide 60:A Chemical reaction Is the making and breaking of chemical bonds Leads to changes in the composition of matter


Slide 61:Chemical reactions Convert reactants to products


Slide 62:Photosynthesis Is an example of a chemical reaction Figure 2.18


Slide 63:Chemical equilibrium Is reached when the forward and reverse reaction rates are equal