Chemistry of Life

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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