BIOL 1107 1nd Edition Final Exam Study Guide Each section below includes material from the lecture homework and textbook Test 1 Chapter 2 The Chemical Context of Life 2 1 2 2 Matter Elements properties atoms Organisms are composed of matter which is anything that takes up space and has mass Matter made up of elements Element substance that cannot be broken down Compound substance consisting of two or more different elements combined in a fixed ratio A compound has different characteristics than the elements that make it Of 92 elements that exist today 20 25 are essential elements that organisms need to live and reproduce Oxygen O carbon C hydrogen H and nitrogen N make up 96 of living organisms Calcium Ca phosphorous P potassium K sulfur S and a few others make up most of the rest Trace elements only required in small amounts in organisms An element is defined by the number of protons it has but some elements have different numbers of neutrons These different extreme forms are called isotopes Atoms are mostly empty space An atom s electrons possess energy Energy is defined as the capacity to cause change through work Potential energy is the energy that matter possess because of its location or structure Matter has a tendency to move to the lowest point state of potential energy Electrons have potential energy The more distant an electron is from the nucleus the greater its potential energy An electron s potential energy is determined by its energy level An electron cannot exist between energy levels They are found in electron shells When an electron absorbs energy it moves away from the nucleus The chemical behavior of an atom is determined by the distribution of electrons Electrons tend to exist in the lowest available state of potential energy However the first shell only holds 2 electrons 2 3 Chemical bonding and molecules Atoms either share or transfer valence electrons This sharing or transferring created chemical bonds The two strongest are covalent and ionic A covalent bond is the sharing of a pair of valence electrons between 2 atoms Two or more atoms held together by a covalent bond creates a molecule There are two ways to represent a molecule structure Lewis dot structure or structural formula In a structural formula a straight line represents a single bond Two pairs of shared electrons create a double bond An atom s valence is its bonding capacity equals the number of unpaired electrons Atoms share electrons to a varying degree Attraction of electrons to a covalent bond is electronegativity Greater electronegativity means a greater attraction pull to electrons In a covalent bond where electrons are shared equally the bond is nonpolar However when bonding elements have different electronegativities the bond is polar In some elements the electronegativity difference is so great electrons are transferred rather than shared This creates net electrical charges A charged atom molecule is called an ion When an ion is positive it is a cation A negative ion is called an anion The bond formed between the two is an ionic bond Compounds formed by ionic bonds are ionic compounds or salts Besides covalent and ionic bonding there are also weaker bonds and attractions One of which is the hydrogen bond It is a noncovalent attraction between hydrogen and an electronegative atom There are also van der Waals interactions which are caused by distortions in the electron cloud These are usually very weak Chapter 3 Water and Life 3 1 Polar bonds water and hydrogen bonding Water s unique behavior can be traced to its structure and interactions It has polar covalent bonds because oxygen is more electronegative This makes this molecule polar because the overall charge is unequally distributed Water molecules can also hydrogen bond with each other up to 4 H bonds Hydrogen bonds are very fragile about 1 20 as strong as a covalent bond They form and break very easily They last very shortly but new ones form very quickly A lot of qualities of water are due to hydrogen bonding 3 2 Four emergent properties of water 4 properties cohesion behavior ability to moderate temperature expansion upon freezing and versatility as a solvent Water molecules stay close to each other due to H bonding These kinks make water more structured than most other liquids Collectively H bonds hold a substance together through cohesion This contributes to the transport of water and dissolved nutrients against gravity Water from the roots reaches leaves through water conducting cells As water evaporates from the leaves H bonds cause it to tug on molecules further down and pull upward Adhesion is the clinging of one substance to another also plays a role Adhesion helps counter gravity Related to cohesion is surface tension measure of how difficult it is to stretch or break surface of a liquid Water has a greater surface tension than most liquids Anything that moves has kinetic energy KE energy of motion Faster a molecule moves greater its KE Heat form of energy The amount of heat is a measure of matter s total kinetic energy Heat also depends on volume of the matter Heat and temperature not the same thing Temperature measure of heat intensity that represents the average KE of molecules regardless of volume Whenever two objects of different temps are brought together heat passes from the warmer object to the cooler one KE of cooler object increases Water is less dense frozen ice floats Water expands instead of contracting when it freezes This is because of hydrogen bonding Due to the cold when water freezes it gets locked into a crystal lattice A liquid that is completely homogenous of 2 or more substances is a solution The dissolving agent is the solvent A dissolved substance is the solute An aqueous solution is one where water is the solvent A substance that has an affinity for water is said to be hydrophilic Some substances are hydrophobic but do not dissolve in water They end up suspended in the water These are colloids stable suspension of fine particles in a liquid Some non ionic and nonpolar substances are actually repelled by water they are said to be hydrophobic 3 3 Acidic and basic conditions Occasionally during an H bond a hydrogen atom leaves its electron behind and a hydrogen ion H a single proton The water molecules with the last proton is now a hydroxide ion OH The proton binds to another water molecules and it becomes a hydronium ion H3O or H When acids dissolve in water they donate H s to the solution An acid