CHEM 51A -- GRIFFIN (UCI) EXAM QUESTIONS WELL ANSWERED LATEST UPDATE 2026
1. Ionic bond - Answers bonds formed by electron transfer from one element to another
1. electronegativity - Answers the tendency for an atom of a given chemical element to attract shared
electrons when forming a chemical bond; determines ionic character of bonding
1. covalent bond - Answers bonds formed by electron sharing between two nuclei; used in molecules
(<1.6 electronegativity difference)
1. valence electrons - Answers electrons in highest principal energy level / outermost electrons ; can
bond (same as group #)
1. Lewis structure - Answers electron dot representation for molecules
1. formal charge - Answers Charge on individual atoms in lewis structure (Not the net charge of the
molecule as a whole)
FC = (valence electrons) - (# of lone pair electrons) - 0.5 x (bonding electrons)
1. carbocation - Answers positively charged carbon atoms; unstable intermediates bc they contain a
carbon atom that is lacking an octet of electrons
1. carbanion - Answers An ion with a negative charge on a carbon atom
1. oxonium - Answers any cation containing an oxygen atom that has three bonds and 1+ formal
charge (?)
1. oxyanion - Answers an anion containing one or more oxygen atoms bonded to another element (as
in the sulfate and carbonate ions). (?)
2. Isomer - Answers different molecules having the same molecular formula (different arrangement
of atoms & electrons)
2. constitutional isomer - Answers two compounds that have the same molecular formula, but differ
in the way the atoms are connected to each other; aka "structural isomers"
2. resonance structure - Answers two Lewis structures having the same placement of atoms but a
*different arrangement of electrons*; the true structure is a hybrid (not in equilibrium! no movement
of electrons) of these (shown by double headed arrow)
2. curved arrow notation - Answers shows the movement/reposition of an electron pair. the tail of
the arrow always begins at an electron pair, in either a bond or lone pair. the head points to where
the electron pair "moves" (an atom or bond)
2. major and minor contributors - Answers when resonance structures are different, the "better" one
contributes more to the hybrid (the major contributor)
"better" = more bonds & fewer charges
3. VSEPR - Answers "valence shell electron pair repulsion" theory; electron pairs repel each other &
thus the most stable arrangement keeps the groups around an atom as far away from each other as
possible
3. steric number - Answers Steric number: # of bonds* & lone pairs attached to an atom
note*: "bonds" are more like substituents
ex. =C= ; 1 double bond on one side & 1 double bond on another side gives a SN of 2
steric # helps in assigning shape to molecules
- 2 = linear
- 3 = trigonal planar
- 4 = tetrahedral (0 lone pairs included), trigonal pyramidal (1 lone pair included), or bent (2 lone pairs
included)
3. orbital - Answers are the spaces that electrons occupy around the atomic nucleus
Bonding orbitals are created from the combination of atomic orbitals (AO) into molecular orbitals
3. hybridization - Answers the combination of 2+ atomic orbitals to form parts of molecular orbital
that are equal in energy
Can figure out hybridization from steric #
ex. Steric # of 4 → sp3 hybridized
, 3. sigma (σ) bond - Answers a cylindrically symmetrical bond that concentrates the electron density
on the axis that joins two nuclei. all single bonds (made from hybridized orbitals) are sigma bonds.
- can rotate
- end-on overlap
- stronger than pi bonds
3. π bond - Answers usually weaker/more easily broken than sigma bonds (bc electron density in a pi
bond is farther from the 2 nuclei); unhybridized orbitals make double/triple bonds (which are pi
bonds)
- can't rotate (bc pi bond has to break + reform, which requires energy)
- side by side overlap
- again, weaker than sigma bonds
3. polar covalent bond - Answers occur between atoms w/ a electronegativity difference > ~0.3
3. dipole moment - Answers The overall dipole moment of a molecule is the sum of all individual
bond dipole moments
- dipoles are indicated by an arrow (less electroneg. atom to the more electroneg. atom)
- Dipoles can cancel out → making molecule nonpolar, since there is no NET dipole
- Dipoles can reinforce one another / be additive → getting an overall dipole moment + making
molecule polar
3. condensed structure - Answers used for compounds having a chain of atoms bonded together
- all atoms drawn in but two-electron bond lines are generally omitted
- atoms are usually drawn next to the atoms to which they are bonded
- parentheses are used around similar groups bonded to the same atom
- lone pairs are omitted (must add them in if converting to Lewis structure)
all Cs are tetravalent
3. skeletal structure - Answers used for organic compounds containing both rings (drawn as polygons)
& chains of atoms (drawn as zigzags)
- assume a carbon atom is located at the junction of any two lines or at the end of any line
- assume each carbon has enough hydrogens to make it tetravalent
- draw in all heteroatoms & the hydrogens directly bonded to them
4. Bronsted-Lowry acid - Answers proton donor (HA)
4. Bronsted-Lowry base - Answers proton acceptor (B)
must have an "available" electron pair that can easily be donated to make a bond (lone pair or pi
bond)
4. conjugate acid - Answers what is formed when a base gains a proton (BH+)
strong base forms weak conj. acid
weak base forms strong conj. acid
4. conjugate base - Answers what is formed when an acid loses a proton (A-)
strong acid forms weak conj. base
weak acid forms strong conj. base
4. Ka - Answers acid dissociation constant
[H3O+][A-] / [HA]
the stronger the acid = larger Ka; also the further the equilibrium lies to the right
4. pKa - Answers pKa = -logKa
1. Ionic bond - Answers bonds formed by electron transfer from one element to another
1. electronegativity - Answers the tendency for an atom of a given chemical element to attract shared
electrons when forming a chemical bond; determines ionic character of bonding
1. covalent bond - Answers bonds formed by electron sharing between two nuclei; used in molecules
(<1.6 electronegativity difference)
1. valence electrons - Answers electrons in highest principal energy level / outermost electrons ; can
bond (same as group #)
1. Lewis structure - Answers electron dot representation for molecules
1. formal charge - Answers Charge on individual atoms in lewis structure (Not the net charge of the
molecule as a whole)
FC = (valence electrons) - (# of lone pair electrons) - 0.5 x (bonding electrons)
1. carbocation - Answers positively charged carbon atoms; unstable intermediates bc they contain a
carbon atom that is lacking an octet of electrons
1. carbanion - Answers An ion with a negative charge on a carbon atom
1. oxonium - Answers any cation containing an oxygen atom that has three bonds and 1+ formal
charge (?)
1. oxyanion - Answers an anion containing one or more oxygen atoms bonded to another element (as
in the sulfate and carbonate ions). (?)
2. Isomer - Answers different molecules having the same molecular formula (different arrangement
of atoms & electrons)
2. constitutional isomer - Answers two compounds that have the same molecular formula, but differ
in the way the atoms are connected to each other; aka "structural isomers"
2. resonance structure - Answers two Lewis structures having the same placement of atoms but a
*different arrangement of electrons*; the true structure is a hybrid (not in equilibrium! no movement
of electrons) of these (shown by double headed arrow)
2. curved arrow notation - Answers shows the movement/reposition of an electron pair. the tail of
the arrow always begins at an electron pair, in either a bond or lone pair. the head points to where
the electron pair "moves" (an atom or bond)
2. major and minor contributors - Answers when resonance structures are different, the "better" one
contributes more to the hybrid (the major contributor)
"better" = more bonds & fewer charges
3. VSEPR - Answers "valence shell electron pair repulsion" theory; electron pairs repel each other &
thus the most stable arrangement keeps the groups around an atom as far away from each other as
possible
3. steric number - Answers Steric number: # of bonds* & lone pairs attached to an atom
note*: "bonds" are more like substituents
ex. =C= ; 1 double bond on one side & 1 double bond on another side gives a SN of 2
steric # helps in assigning shape to molecules
- 2 = linear
- 3 = trigonal planar
- 4 = tetrahedral (0 lone pairs included), trigonal pyramidal (1 lone pair included), or bent (2 lone pairs
included)
3. orbital - Answers are the spaces that electrons occupy around the atomic nucleus
Bonding orbitals are created from the combination of atomic orbitals (AO) into molecular orbitals
3. hybridization - Answers the combination of 2+ atomic orbitals to form parts of molecular orbital
that are equal in energy
Can figure out hybridization from steric #
ex. Steric # of 4 → sp3 hybridized
, 3. sigma (σ) bond - Answers a cylindrically symmetrical bond that concentrates the electron density
on the axis that joins two nuclei. all single bonds (made from hybridized orbitals) are sigma bonds.
- can rotate
- end-on overlap
- stronger than pi bonds
3. π bond - Answers usually weaker/more easily broken than sigma bonds (bc electron density in a pi
bond is farther from the 2 nuclei); unhybridized orbitals make double/triple bonds (which are pi
bonds)
- can't rotate (bc pi bond has to break + reform, which requires energy)
- side by side overlap
- again, weaker than sigma bonds
3. polar covalent bond - Answers occur between atoms w/ a electronegativity difference > ~0.3
3. dipole moment - Answers The overall dipole moment of a molecule is the sum of all individual
bond dipole moments
- dipoles are indicated by an arrow (less electroneg. atom to the more electroneg. atom)
- Dipoles can cancel out → making molecule nonpolar, since there is no NET dipole
- Dipoles can reinforce one another / be additive → getting an overall dipole moment + making
molecule polar
3. condensed structure - Answers used for compounds having a chain of atoms bonded together
- all atoms drawn in but two-electron bond lines are generally omitted
- atoms are usually drawn next to the atoms to which they are bonded
- parentheses are used around similar groups bonded to the same atom
- lone pairs are omitted (must add them in if converting to Lewis structure)
all Cs are tetravalent
3. skeletal structure - Answers used for organic compounds containing both rings (drawn as polygons)
& chains of atoms (drawn as zigzags)
- assume a carbon atom is located at the junction of any two lines or at the end of any line
- assume each carbon has enough hydrogens to make it tetravalent
- draw in all heteroatoms & the hydrogens directly bonded to them
4. Bronsted-Lowry acid - Answers proton donor (HA)
4. Bronsted-Lowry base - Answers proton acceptor (B)
must have an "available" electron pair that can easily be donated to make a bond (lone pair or pi
bond)
4. conjugate acid - Answers what is formed when a base gains a proton (BH+)
strong base forms weak conj. acid
weak base forms strong conj. acid
4. conjugate base - Answers what is formed when an acid loses a proton (A-)
strong acid forms weak conj. base
weak acid forms strong conj. base
4. Ka - Answers acid dissociation constant
[H3O+][A-] / [HA]
the stronger the acid = larger Ka; also the further the equilibrium lies to the right
4. pKa - Answers pKa = -logKa
