covalent bonding of shapes and molecules & acids and bases

pre-orgochem in orgochem book

ionic bond

a chemical bond resulting in the electrostatic attraction of an anion and a cation

covalent bond

a chemical bond resulting from the sharing of one or more pairs of electrons with a

electronegativity

a measure of the force of an atom’s attraction for electrons it shares in a chemical bond with another atom

non-polar covalent bonds

electrons are shared equally

polar covalent bonds

electrons are shared unequally

the more electronegative atom gains…

a fraction of the shared electrons and acquires a partially negative charge

the seperation of charge produces a

dipole

formal charge

the charge of an atom in a molecule or polyatomic ion

nonbonding electrons

valance electrons not involved in forming covalent bonds (unshared electrons)

bonding electrons

valance electrons shared in a covalent bond

resonance contributing structures

respresentation of a molecule or ion that differ only in the distribution of valance electrons

resonance hybrid

a molecule or ion that is the best described as a composite of a number of contributing structures

a covalent bond is formed when

a portion of an atomic orbital of one atom overlaps a portion of an atomic orbital of another atom

a sigma bond

a covalent bond in which the overlap of atomic orbitals is concentrated along the bond axis

hybrid orbitals

an orbital produced from the combination of two or more atomic orbitals

pi bond

a covalent bond formed by the overlap of parallel p orbitals

why are pi bonds weaker than sigma bonds?

because of the lesser degree of overlap of orbitals forming pi bonds compared to those forming sigma bonds

functional groups

an atom or a group of atoms within a molecule that shows a characteristic set of physical and chemical properties

amino group

an sp³ hybridized nitrogen atom bonded to one, two or three carbon groups

carbonyl group

C=O

carboxyl group

-COOH

arrhenius acid

a substance that dissolves in water to produce H+ ions

arrhenius base

a substance that dissolves in water to produce -OH ions

Why does the arrhenius theory have limits?

1 - it cannot explain why substances lacking hydroxide ions are bases

2 - doesn’t take into account the role of solvent in the process

3 - doesn’t describe accurately the H+ ion state, that doesn’t exist such as in water, but rather in form of an oxonium (hydronium) ion

brownsted-lowry acid

a proton (H+) donor

brownsted-lowry base

a proton (H+) acceptor

conjugate base

the species formed when an acid donates a proton

conjugate acid

the species formed when a base accepts a proton

the stronger the acid

strong acid

an acid that is completely ionized in aqueous solutions

strong base

a base that is completely ionized in aqueous solutions

weak acid

an acid that only partially ionizes in aqueous solutions

weak base

a base that only partially ionizes in aqueous solutions

pKa

measure of the acids strength

the equilibrium favors the side with the weaker acid and weaker base. why?

because they are more stable and represent the lower-energy state of the system. since reactions proceed toward minimum Gibbs free energy (ΔG < 0), the system shifts toward forming the weaker conjugate acid–base pair.

the greater the electronegativity of an atom

higher electronegativity of an atom leads to

lower energy of the anion

delocalized means

that the negative charge is spread over multiple atoms, so each atom carries only a fraction of the total negative charge rather than one atom holding it all

the spreading out of charge reduces electron–electron repulsion which makes the species…

more stable than if the charge were localized on a single atom

if the anion is very stable…

it doesn’t mind being separated from the H+. and the equilibrium shifts to the right

more H+ released

a stronger acid

more electronegative and more stable anion…

a stronger acid

alcohols are slightly weaker acids than water

because alcohols lack resonance stabilization of their conjugate base, so the negative charge remains localized on oxygen, making them weaker acids than species whose conjugate bases are resonance-stabilized.

ranking of stabilization effects

resonance > induction > size > electronegativity> hybridization

inductive effect

the polarization of electron density transmitted through covalent bonds caused by a nearby atom of higher electronegativity

a larger atom can disperse the negative charge better because

the electron cloud is larger and more polarizable

why is HI a very strong acid?

because the iodide ion is the most stable anion since its large and the negative charge can spread over the large volume

lewis acid

any molecule or ion that can form a new covalent bond by accepting a pair of electrons

lewis base

any molecule or ion that can form a new covalent bond by donating a pair of electrons

the proton

attaches itself to the strongest available lewis base

an oxonium ion

an ion that contains an oxygen atom bonded to three other atoms or groups of atoms and bears a positive charge

all bronsted acids are lewis bases but

not all lewis acids are bronstead bases

carbocations

a carbon bonded to only three atoms and bears a positive formal charge, has an empty orbital that can accept an electron pair

neutralization reaction

acid + base —> salt + water

buffers

a buffer solution maintains the pH by neutralizing small amounts of added acid or base