Chem 101: Midterm 2

What is electronegativity?

The relative ability of an atom, bonded with a molecule, to attract shared electrons to itself

What happens with electronegativity in a polar covalent bond?

There is an unequal sharing of e- which results in the more electronegative atom taking a partial negative charge and the less electronegative atom taking a partial positive charge

What is the trend of electronegativity?

It increases as you move across a period and decreases as you move down a group

What is a dipole moment?

Molecules aligned in an electric field and creates a polar molecle; each vector of the bonds must cancel to have a non-polar bond, they will not cancel if you have a polar bond

How can you use symmetry to determine polarity of a molecule?

If a moleculel has the same terminal atoms and no lone pairs (or lone pairs direct;y opposing each other) the molecule will be polar

What is a skeletal structure?

An incomplete Lewis structure where all e- are represented and all bonds are to thier most simple form (single bonds)

How do you determine formal charge of an atom in a Lewis structure?

Use the lasso method and subtract the number of e- associated with the atom from the total e- it should have

What is resonance?

When it is possible for more than one Lewis structure to be drawn or a molecule

What is a resonance hybrid?

The true resonance structure of a molecule that has the lowest formal charges, complete octets, seperated like-charges, and the most electronegative atoms have the lowest formal charges

How do you calculate bond order for Lewis structures?

Divide the number of atoms by the number of bonds (double/triple bonds count as one bond)

What is the odd-electron species exception to the octet rule?

For molecules that have an odd number of e-, draw the Lewis structure like you have an extra e- and then remove one e- from the leats electronegative species

What is the incomplete octets exception to the octect rule?

Be, B, and Al may have less than a full octect and therefore, should be left incomplete (no not make double bonds to create a full octec)

What is the expanded valence shells exception to the octect rule?

3rd period (or below the 3rd period) may have 10 or 12 e- surrounding them and therefore, you should reduce the formal chatges for these elements as much as possible by creating double/triple bonds

What is formal charge?

The charge assigned to species assuming all electrons in a bond are shared equally (covalent extremes)

What is oxidation number?

The charge assigned to a species assuming that electrons in a bond are not shared equally, they are associated with the more electronegative atom (ionic extremes)

What is a VESPR model?

A model based of of Valence Shell Electron Repulsion theory that represents the arrangement and shape of a molecule, including electrons around the central atom which minimize repulsions

What does electron group arrangement refer to?

The number of groups/points of electron density (can be determined by counting the number of bonds connecting one species to another)

What does molecular shape refer to?

The specific shape a molecule takes

What is a linear molecule?

A molecule defined by having one central atom and two connecting atoms; repulsion makes the shape a straight line

What is a trigonal planar molecule?

A molecule defined by having one central atom and three connecting atoms; repulsion makes the shape a flat triangle

What is a tetrahedral molecule?

A molecule defined by having one central atom and 4 connecting atoms; repulsion makes this shape a tall 3D pyramid

What is a v-shaped or bent molecule?

A molecule defined by having one central atom, two connecting atoms, and one or two lone pairs; repulsion makes the shape slighly bent

What is a trigonal pyramidal molecule?

A molecal defined by having one central atom, 3 connecting atoms, and one lone pair; repulsion makes the shape a short 3D pyramid

What is the bond angle between linear molecules?

180 degrees

What is the bond angle for trigonal planar molecules?

120 degrees

What is the bond angle for v-shaped/bent molecules with one lone pair?

<120 degrees

What is the bond angle for tetrahedral molecules?

109.5 degrees

What is the bond angle for trigonal pyramidal molecules?

What is the bond angle for v-shaped/bent molecules with two lone pairs?

What is the notation for electron group arrangment?

AXmEn (where A = central atom, X = surrounding atom, and E = lone pairs)

How is repulsion affected if it is between lone pairs or bonding pairs?

Lone pairs are more repelling than bonding pairs (lp-lp > lp-bp > bp-bp)

What does valence bond theory say?

A covalent bond forms when the orbitals of two atoms overlap and a pair of e- is localized in the region between the atoms

According to valence bond theory, what needs to happen for good in-phase overlap to occur?

The phases of the orbital must be the same

What does hybridization in valence bond theory refer to?

Orbitals can form more approriate shapes and orientations to maximize overlap

What hybridized orbtial corresponds to EG 2 and EGA linear?

sp

What hybridized orbtial corresponds to EG 3 and EGA trigonal pyramidal?

sp^2

What hybridized orbtial corresponds to EG 4 and EGA tetrahedral?

sp^3

What hybridized orbtial corresponds to EG 5 and EGA trigonal bipyramidal?

sp^3d

What hybridized orbtial corresponds to EG 6 and EGA octahedral?

sp^3d^2

What is a sigma bond?

End-to-end overlap of orbitals with e- density along axis of bond

What is a pi bond?

Side-to-side overlap of orbitals with e- density above and below the axis of a bond

What does a bonding scheme refer to?

The bond types (sigma/pi), hybridization notation, and atomic orbitals

What are the limitations/failures of valence bond theory/hybridization?

Hybridization schemes involving d-rbitals have been proved to be invalid and bonding schemes from molecules with resonance are misleading

How are double bonds show when drawing a bonding scheme?

A sigma bond will be formed AND a pi bond will be formed

How are triple bonds show when drawing a bonding scheme?

A sigma bond will be formed AND two pi bonds will be formed

What does Molecular Orbital Theory address?

How quantum mechanics can be applied to molecules

What does part of molecular orbital theory does the Schrodinger equation solve for?

It solves for the e- in a molecule, which results in moecular orbitals that show e- delocalization over an entire molecule

What are atomic orbitals?

Orbitals associated with a singular atom

What are molecular orbiatsl?

Orbitals associated with an entire molecule

What are the characteristics of molecular orbitals?

They each hold two e- with opposite spins; the square of the molecular orbital wavefunction gives the probability density

How does the energy level between bonding and antibonding molecular orbitals compare?

Antibonding MOs are higher in energy than bonding MOs; this is unfavourable

Why are antibonding MOs higher in energy?

Their nuclei repel each other

Whay are bonding MOs lower in energy?

Their e- density is spread out beteen nuclei, minimizing repulsions; this is favourable

How do you calculate bond order for molecular orbitals?

1/2 (MO - MO*)

What does a bond order that is non-zero tell you?

The molecule will form/will exist and is stable

What does a bond order of zero tell you?

The molecule will be too unstable and therefore does not form/does not exist

What is the relationship betwene bond order and bond energy?

Bond energy increases with bond order

What is the relationship between bond length and bond energy?

Bond energy increases as bond length decreases

What is the relationship between bond length and bond order?

As bond order increases, bond length decreases (because stronger bonds pull its atoms tighter)

What is the relationship between atomic radii, bond length, and bond order?

As atomic radii increases, bond length increases, and bond energy decreases

What is the format of a molecular orbital diagram?

Atomic orbitals on the side with the combined molecular orbitals in between

What overlap, sigma or pi, is more effective?

Sigma overlap

How can you relate energy of a molecular orbital to the number of nodes?

More nodes means depletion of e- density between nuclei resulting in a less stable molecular orbital; more nodes = higher energy

What is the rule for drawing MOs of diamtomic early (leftmost) second-period elements?

Use the two triangle rule (order of orbitals is pi2p, sigma2p, pi2p*, sigma2p*)

What is the rule for drawing MOs of diamtomic late (rightmost) second-period elements?

Use the oval rule (order of orbitals is sigma2p, pi2p, pi2p*, sigma2p*)

What does it mean for substances to be paramagnetic?

It has unpaired e- and it is attracted to an external magnetic field

What does it mean for substances to be diamagnetic?

All of it's e- are paired and it is weakly repelled by a magnetic field

What does HOMO refer to?

Highest Occupied Molecular Orbital (refers to the highest energy orbital electrons occupy)

What does LUMO refer to?

Lowest Occupied Molecular Orital (refers to the lowest energy orbital electrons occupy)

What is the Arrhenius acid definition?

Acid: a substance that produces H+ ions in aqueous solutions

What is the Arrhenius base definition?

Base: a substance that produces OH- ions in aqueous solutions

What is the Bronsted-lowry acid definition?

Acid: proton (H+) donor

What is the Bronsted-lowry base definition?

Proton (H+) acceptor

What are conjugate acid-base pairs?

Ions/compounds related by the transfer of H+

What does it mean for a compound to be amphoteric?

It is able to react as a base and an acid

What is the Lewis acid definition?

Electron-pair acceptor

What is the Lewis base definition?

Electron-pair donor

What are adducts?

The products of a reaction

What is an equlibrium constant and how is it calculated?

A measure of the strength of an acid/base; K = Products / Reactants

What does a large Ka mean?

Strong acid

What does a large Kb mean?

Strong base

What does a small Ka mean?

Weak acid

What does a small Kb mean?

Weak base

What is the relationship between the strength of acids/base conjugate pairs?

The stronger the acid, the weaker the base (and vice versa)

What is the formula for a carboxylic acid?

COOH

What is the formula for a carboxylate ion?

COO-

What is the formula for ammonium ions?

NH+ (has an N with an H attached seperately)

What is the formula for amines?

N (has an N in the middle of it somewhere)

What kind of reaction do ionic compounds result from?

Acid/base neutralization reactions (produces salt + water)

How do you identify whether a salt is acidic or basic?

Evalute the individual ions

What are carboxylic acids, weak acids or weak bases?

Weak acids

What are ammonium ions, weak acids or weak bases?

Weak acids

What are carboxylate ions, weak acids or weak bases?

Weak bases

What are amines, weak acids or weak bases?

Weak bases

What are binary acids?

An acid where the acidic proton is bonded directly to a non-metal atom (H-X)

What is the trend of acid strength for binary acids?

An acid gets stronger as you go down a group and stronger as you go across a period

What is the relationship between acid strength and bond length?

The longer the bond, the stronger the acid

What makes soemhting a stronger acid (regarding dissociation)?

The easier it is to dissociate the H+ in an acid, the stronger the acid is

What is the relationship between polarity and acid strength for binary acids?

More polar equals a weaker acid

What are oxyacids?

Acids where the acidic proton is bonded to an O atom is bonded to another element (H-O-X)