Orgo I Chapter 2: Polar Covalent Bonds; Acids and Bases

polar covalent bonds

bond characterized by asymmetrical electron distribution between atoms

electronegativity

the ability of an atom to attract the shared electrons in a covalent bond

what element is the most electronegativity

Fluorine

what element is the least electronegativity

Cesium

what is the electronegativity of carbon

2

bonds between atoms whose electronegativities differ by less than 0.5 are __________________

nonpolar covalent bonds

bonds between atoms whose electronegativity differ by 0.5 to 2 are _________________

polar covalent

bonds between atoms whose electronegativities differ by more than 2 are larger ______________

ionic

True or False: Carbon can only have a partial positive charge

False; it can also be partially negative if it is more electronegative than the other element (ex C--Li)

inductive effect

the shifting of electrons in a sigma bond in response to the electronegativity of nearby atoms

dipole moment =

charge Q at either end of the molecular dipole times the distance r between charges

what is the dipole moment of CH4 (a nonpolar molecule)

0

What makes oxygen and nitrogen strongly electronegative

lone pair electron which stick out away from the nuclei giving rise to considerable charge separation which contributes to dipole moment

formal charge =

# valence electrons in free atom - (# nonbonding electrons + (1/2 # bonding electrons))

resonance hybrid

the actual structure of a molecule that is intermediate between two or more resonance structures

resonance structure

one of the two or more equally valid electron dot structures of a molecule or polyatomic ion

what changes in different resonance forms

the placement of the pi bond or nonbonding electrons

what do curved arrows indicate

the movement of electrons in different resonance forms

True or False: Any 3-atom grouping with a p orbital on each atom has two resonance forms

True

Brønsted-Lowry acid

substance that donates a hydrogen ion

Brønsted-Lowry base

a substance that accepts a hydrogen ion

conjugate base

product that results from an acid losing a proton

conjugate acid

the product that results when the base gains a proton

Ka (acidity constant)

the exact strength of a given acid HA in water solution. (The stronger the acid the larger the Ka)

Ka =

([H3O+][A-])/[HA]

in which direction is stronger acids equilibria?

the right

pKa =

-log Ka

what is the relationship between Ka and pKa

larger Ka has a smaller pKa

what is the ion product constant for water (Kw)

1.00 x 10^-14

what is the relationship between acid strength of an acid and base strength of the conjugate base

strong acid has weak conjugate base

how are organic acids characterized

the presence of positively polarized hydrogen atoms

what are the two main kinds of organic acids

acids that contain a hydrogen atom bonded to an electronegative oxygen atom and acids that contain a hydrogen atom bonded to a carbon atom next to a C(double bond)O bond

carboxylic acids

acids with --CO2H grouping

how are organic bases characterized

the presence of an atom with a lone pair of electrons that can bond to H+

why are amino acids name that way

they are both amines (--NH2) and carboxylic acids (--CO2H)

lewis acid

substance that accepts an electron pair

lewis base

substance that donates an electron pair; a compound with a pair of nonbonding electrons that it can use to bond to a lewis acid

what do lewis acids have

a vacant, low energy orbital or a polar bond to hydrogen (so it can donate H+ which has an empty 1s orbital)

intermolecular forces, van der Waals forces, noncovalent interactions

interactions between molecules that strongly affect molecular properties

types of intermolecular forces

London dispersion, dipole-dipole, hydrogen bonding

dipole dipole forces

forces between polar molecules as a result of electrostatic interactions among dipoles which can be attractive or repulsive

dispersion forces

forces that occur between all neighboring molecules and arise because the electron distribution within molecules is constantly changing

what can the cumulative effect of dispersion forces be if strong enough

allowing substances to be liquid or solid

hydrogen bond

attractive interaction between a hydrogen bonded to an electronegative O, or N and an unshared electron pair on another O or N atom

what are some consequences of hydrogen bonding

DNA coiling into a double helix, adhesion and cohesion of water, holding enzymes in shapes necessary for catalyzing reactions