Chemistry of Life

Chemistry Life depends on chemistry Living things are made from chemical compounds Inside cells there are continuous chemical reactions taking place that are necessary for survival

Review Matter – anything that has mass and takes up space Atoms – basic unit of matter –Protons – (+); in nucleus –Neutrons – (0); in nucleus –Electrons – (-); in electron shells outside nucleus

Properties of Atoms Atomic Number - # of protons; determines the element Mass Number – sum of protons and neutrons Atomic Mass – average mass of an atom

Atoms Atoms are neutral: protons (+) = electrons (-) Electrons can be lost or gained in bonding creating charged particles called ions –Cation – positive ion (lost electrons) –Anion – negative ion (gained electrons)

Isotopes Atoms of the same element that have different numbers of neutrons –Similar chemical properties –Identified by mass number (p+n)

Radioactive Isotopes Have unstable nucleus and break down releasing radiation The nucleus decays spontaneously, giving off particles and energy –May lead to a change in protons and a new element Can be used for –Determining age of rocks and fossils –Treating cancer and killing bacteria –Tracers to follow substances in the body

Elements Element – pure substance that cannot be broken down –92 natural elements –About 25 essential to life –C, O, H, and N make up 96% of living matter –O – 65%, C – 18.5%, H – 9.5%, N – 3.3% –Trace elements – those that are required by organisms in only minute quantities (less than 0.01%) Iron, iodine, chromium, copper, etc.

Other Elements in the Human Body ElementSymbol% human body weight CalciumCa1.5 PhosphorusP1.0 PotassiumK0.4 SulfurS0.3 SodiumNa0.2 ChlorineCl0.2 MagnesiumMg0.1

Molecules and Compounds Molecule – two or more atoms bonded –H 2, O 2, NaCl Compound – two or more elements combined in definite proportions –H 2 O, NaCl, C 6 H 12 O 6 Remember…..All compounds are molecules, but not all molecules are compounds

Electrons Directly involved in chemical reactions Vary in amount of energy they possess –Created energy levels or electron shells –Energy increases the farther from the nucleus –May change shell, but have to absorb or lose energy

Valence Electrons Chemical behavior of an atom is determined by electron configuration Valence electrons – those that are in the outermost shell –Atoms with the same # of valence electrons exhibit similar chemical properties –Valence electrons play a major role in bonding

Covalent Bonds Electrons are shared between atoms = STRONG –Single: share two electrons –Double: share four electrons The moving electrons actually travel in the orbitals of both atoms Example is water H 2 O

Covalent Bonds Electronegativity – attraction of an atom for the electrons in a covalent bond –The higher the electronegativity, the more an atom pulls the electrons toward it –Ex: oxygen has a very high electronegativity Can cause atoms to become polar

Nonpolar vs. Polar Nonpolar covalent bond – electrons are shared equally –Often bonds between the same element like H2 and O2; another example CH4 –Symmetrical Polar covalent bond – one atom that is more electronegative causes an unequal sharing of electrons –Atoms within the molecule will have partial charges –asymmetrical

Polar and Nonpolar

Ionic Bonds The attraction between oppositely charged ions One or more electrons are transferred to another atom –More electronegative atom strips an electron(s) from less electronegative atom –Creates ions when electrons are lost or gained Ionic compounds also called salts –Example is NaCl – Na loses and Cl gains –Forms sodium chloride or table salt

Ionic Bonds

Hydrogen Bonds Both covalent and ionic bonds are strong intramolecular bonds (within molecules) Hydrogen bonds are weak intermolecular bonds (between molecules) Form between partially (+) H and partially (-) atoms in polar covalent bonds Example is bond between two water molecules

Hydrogen Bonds

Van der Waals Interactions Intermolecular forces of attraction –Can occur between nonpolar molecules A slight attraction can develop between oppositely charged regions of nearby molecules

Chemical Reactions The making and breaking of chemical bonds Reactants  Products Matter is not created or destroyed; simply rearranged Chemical equilibrium – no net effect on reactant and product concentrations; concentrations are stabilized (not necessarily equal)

Organic Chemistry Compounds containing carbon Carbon usually shares electrons in four covalent bonds (tetravalence) Carbon chains form the skeletons of most organic molecules Hydrocarbons –molecules that consist of carbon and hydrogen only –May be the backbone of many important organic molecules

Carbon Skeletons May vary in length May be straight, branched or unbranched, or may be arranged in closed rings May have double bonds that vary in number and location

Isomers Compounds with the same molecular formula but different structures and properties Structural isomers – differ in covalent arrangements (butane and isobutane )

Isomers Geometric isomers – same covalent partnerships, but different spatial arrangements Enantiomers – mirror images of each other

Functional Groups Components of organic molecules that are most commonly involved in chemical reactions –“attached” in a sense to the carbon skeletons –Number and arrangement of groups gives the molecule its unique properties – acidic, basic, polar, hydrophilic Most important are: hydroxyl, carbonyl, carboxyl, amino, sulfhydryl, and phosphate groups