Chem 120

What is the behaviour of energy and size of on orbital as nuclear Charge increases? Why? What is nuclear charge?

Nuclear charge is the total positive charge of an atom’s nucleus (determined by the # of protons)

The energy and size of an orbital decrease. This is because as Z increases, the attraction between the nucleus and electrons increases.

More + attracts more -

What is the Pauli Exclusion Principle

• No two electrons can have the same set of quantum numbers

• Ex. If n, l, and ml are the same, the spin must be different

What is Hund’s Rule? What does energetically degenerate mean?

Energetically degenerate means two or more orbitals have the same energy level

If there are not enough electrons to fill completely a set of energetically degenerate, the lowest energy arrangement is the one which has the maximum number of parallel spins

How would you determine the ground state electron configurations for positive monatomic ions? What is the special exception?

Write the configuration of the neutral atom first, and then remove electrons from orbitals with the highest n value first. Remove the e with the highest value of l if they have the same value of n

The special exception is that for atoms in the d block, the ns electrons should be removed first.

Example:

Neutral Fe: [Ar] 4s² 3d^6

Fe2+ ion: [Ar] 3d^6

How can you determine if an atom is paramagnetic? How will it react with a magnetic field?

One or more unpaired electrons. This will make the atom strongly interact with an external magnetic field

How can you determine that an atom is diamagnetic. How does it react with a magnetic field.

All electrons are paired. Reactor weakly with an external magnetic field.

What is a magnetic moment

When there are unpaired electrons, and the magnetic fields of each electron do not cancel. Recall, electron spin = magnetic field

Describe the trend of Atomic Radii.

Decrease across a period, because as electrons are added to empty shells, the nuclear charge increases.

Increase down a group because each atom down is a new shell. Each shell has it maximum electron density at a greater distance from the nucleus.

Describe the trend of Ionization Energy. What are the exceptions?

Decrease down a group, as valence electrons of larger atoms are easier to remove as they’re farther from the nucleus

Increases across a period (with some exceptions), because the pull of nucleus on electrons is stronger (opposite attraction).

Exceptions:

B vs. Be - 2p electron in boron is in a higher energy orbital and easier to remove than the 2s electron in beryllium. This effect outweighs the increase in nuclear charge from Be to B

N vs. O - The 2p subshell in N is half-filled, so it is stable, while removing an electron from O would be removing a paired 2p electron so that it becomes half-filled, like N

What is electron affinity? Describe the trend for electron affinity

Electron affinity is the energy change when an electron is added to a gaseous atom to form a negative ion.

For atoms near the right-hand side end of a period (except noble gasses), a large amount of energy is released when adding an electron

For atoms near the left-hand side, a small amount of energy is released

For group 2, energy is required to add an electron because they already have a full s-orbital

Also, adding an electron to a negative monatomic ion will require energy due to electron electron repulsion. So, it does not release energy, it requires it.

What is electronegativity. Describe the trend.

Electronegativity is the measure of the pull an atom has on the electrons in its bonds

Generally, electronegativity values increase from left to right across a period And decrease from top to bottom in a group

Describe the trend of covalent radius. What is covalent radius?

Covalent radius is half the distance between the nuclei of two identical bonded atoms. Increases down a group, and decreases across a period

What is the special exception when determining the electron configuration of positive monatomic ions?

For transition metals (d block), remove electrons from the s orbital first.

What is the de broglie wavelength formula and why is it significant?

de broglie wavelength = h/mv

m = 9.109 × 10^-31 (mass of an electron)

h = planck’s constant = 6.626×10^-34

v = velocity

It describes how a particle can move as wave.
De broglie knew that light could exhibit wave and particle like behaviour, and thought particles could also exhibit wave-particle duality

“A complete description of the behaviour of an electron in an atom must incorporate wave-particle duality.”

What is the heisenberg uncertainty principle?

it is impossible to know simultaneously both the position and the momentum of a particle with absolute certainty. the more certain we are about a particle’s position, the less certain we are about where it’s going.

What is the concept of electron repulsion

Simply put, electrons are all negative, and they all want to be as far away from each other as possible. It can help explain some atomic trends, ex. ionization energy, sometimes its easier to take away from a paired electron so that electron has more space. It can affect atomic radius, as the repulsion works against proton pull which is why more electrons = bigger radius.

What is the VSPER Geometry for 2 groups attached to the central atom

Linear

What is the VSPER electronic geometry for 3 groups attached to the central atom

Trigonal planar

What is the VSPER electronic geometry for 4 groups attached to the central atom

Tetrahedral

What is the VSPER electronic geometry for 5 groups attached to the central atom

Trigonal bipyramidal

What is the VSPER electronic geometry for 6 groups attached to the central atom

Octahedral

What is the molecular geometry for 3 groups attached to the central atom but one is a lone pair

Bent/V-shaped

What is the molecular geometry for 4 groups attached to the central atom but one is a lone pair

Trigonal pyramidal

What is the molecular geometry for 4 groups attached to the central atom but two of them are lone pairs

Bent

What is the molecular geometry for 5 groups attached to the central atom but two of them are lone pairs

T-shaped

What is the molecular geometry for 5 groups attached to the central atom but one is a lone pair

See-saw

What is the molecular geometry for 5 groups attached to the central atom but three of them are lone pairs

Linear

What is the molecular geometry for 6 groups attached to the central atom but three of them are lone pairs

T-shaped

What is the molecular geometry for 6 groups attached to the central atom but two of them are lone pairs

Square planar

What is the molecular geometry for 6 groups attached to the central atom but one is a lone pair

Square pyramidal

What are partial charges? What is a bond dipole moment?

When bonded atoms have different electronegativities and the shared electrons are pulled more towards the more electronegative atom

A bond dipole moment is a measure of how polar a specific chemical bond is, basically a number that tells us how unevenly the electrons are being shared.

What is a polar covalent bond?

When one end of the covalent bond is slight positive and the other is slightly negative, meaning they both a dipole moments

What does the magnitude of a dipole moment depend on?

The magnitude of the partial charges on each atom and how far away they are from each other

How do you determine if a molecule is polar?

For non-polar molecules, the bond dipole cancel out = symmetrical distribution of electron density

Polar molecules = asymmetrical distribution

We can see this by looking at the VSEPR shaper of a molecule

What is the difference between valence bond theory and molecular orbital theory?

VB Theory:

• Theory is localized (electron is fixed between to atomic nuclei)

• Bonds form when atomic orbitals on atoms overlap and share the same region in order to share electrons

• Explains bond angles and shapes using VSEPR theory

MO Theory:

• Atomic orbitals combine to form new molecular orbitals that are spread out over the entire molecule

• Delocalized

• Electrons fill orbitals

• Explains magnetism

What are the types of bonds/overlap to consider in VB theory?

Sigma bond

• when orbitals overlap between the two nuclei. This region is called the INA

Pi bond

• Side by side overlap of p-orbitals after a sigma bond has already been formed

• Pi bonds only arise when double or triple bonds are formed

What is orbital hybridization

Taking “n” atomic orbitals and mixing the to generate “n” hybrid orbitals

• When two atoms come together in a multi atom molecule, the center atom needs to change somehow in order for proper overlapping

Explain how orbital hybridization works. What does an sp, sp² and sp³ mean?

You can think of it like making new paint. In CH4, C hybridizes to create for new half-filled orbitals in between the 2p and 2s level in order to accommodate for the 4 hydrogen atom’s that it wants to bond with. By hybridizing each orbital for this accommodation, we get a new orbital in between 2p and 2s called sp orbital. Since we need 4 hybridized orbitals, and we have three 2p orbitals and one 2s orbital, we blend up all four in order to create four new orbitals where each new orbital is made up of 75% 2p, and 25% 2s

What happens to the unhybridized 2p orbitals in sp²?

It will be used to form one pi bond

What does a double bond = in terms of sigma and pi. What about a triple bond

1 sigma bond + 1 pi bond

Triple bond = 1 sigma bond and 2 pi bonds

How does the energy level of a bonding MO compare to an AO

It is lower energy

What is the order for the molecular orbital aufbau

Like the regular aufbau principle, it’s an order of how you need to fill out the molecular orbitals from lowest energy level to highest. The molecular orbital aufbau is as follows:

Sigma 2s, sigma 2s (antibonding), pi 2p, pi 2p (antibonding), sigma 2p (antibonding)

The exception is that pi 2p and sigma 2p switch for the elements O2 and F2

Idk if you need to know that tbh

How can you find bond order

Fill out all the molecular orbitals just like a regular orbital

Find all the electrons that are part of bonding orbitals, and subtract them from the all the electrons that are part of antibonding orbitals, then multiply by 0.5

What are the 6 assumptions of Kinetic Molecular Theory

1) Gas molecules are tiny, and the space between them is vast

2) Molecules are always moving randomly in all directions

3) Collisions between molecules and with the container walls are responsible for the gas’s pressure

4) When molecules collide the bounce of each other perfectly so the gas doesn’t spontaneously lose energy and cool down. This is so the total kinetic energy of the system remains constant without external influence

5) No intermolecular forces: molecules don’t attract or repel each other except during collisions

6) Kinetic energy is proportional to temperature KE (average) = (3/2) RT

Why is molecular motion random?

Because the surfaces of the container walls aren’t perfectly flat, meaning all the molecules won’t be moving in parallel. The irregular surfaces of the container walls would deflect molecules, and these deflected molecules would collide with others causing motion to be random

What does ideal gas law predict?

1) As T increases (keeping P and n constant) » V increases

2) As V increases (keeping T and n constant) » P decreases

3) As n increases (keeping T and V constant) » P increases

When would deviations from ideal behaviour of ideal gas laws be the most significant?

When the pressure is very high or the temperature is very low

What are some flaws of the ideal gas model? What is different in real gases compared to the ideal gas?`

1) It neglects the size of the molecules themselves

2) Intermolecular forces

For real gases, they behave most ideally at high temperature and low pressure, where molecular volume and intermolecular forces become negligible

• Low pressure gives molecules lots of space and high temp gives them enough energy to ignore each other’s presence

How can we account for real gases being most ideal at low pressure and high temp?

We can use Van der Waals’ equation

What R constants can you use and when can you use them?

R = 0.08206 when atm

R = 0.083144 when bar

What is vapour pressure

Pressure of vapour that forms above a liquid in a closed container

What is normal boiling point (Tvap)

Temperature at which the vapour pressure of the liquid equal 1 atm

What is surface tension

Energy required to increase the surface area of a liquid

What is viscosity

A measure of a fluid’s resistance to flow

• The speed of flow through a tub is inversely proportional to the viscosity (when one increases, the other decreases)

Generally, what happens when intermolecular attractions are strong?

The stronger the intermolecular attractions, the higher the boiling point, the greater the surface tension, the higher the viscosity, and the lower the vapour pressure

What is the molecular property of a dipole moment?

If two atoms’ electrons in a bond have a tug of war over the electrons, and one is winning = dipole moment

If the electrons stay in the middle then there is no dipole

• A dipole is the separation of positive and negative charge, but the dipole moment is the measure of how strong that dipole is

What is a non-zero dipole moment? Aren’t all dipoles non zero numberical values?

No, a molecule can have a numerical value of zero while still having a tug of war, when the bond dipoles cancel out due to molecular symmetry, or there are no polar bonds at all

• If a dipole moment is equal to 0, then it is a nonpolar molecule

• If it is non-zero than it is a polar molecule

What is polarizability? What is the trend?

Polarizability of a molecule provides a measure of how much its charge cloud can be distorted/polarized by another molecule

• The bigger the molecule, the larger the polarizability

Dipole dipole forces

• Polar molecules tend to orient themselves head to tail

  • The charge distribution of a polar molecule is represented by an arrow that points from the positive end to the negative end

Describe London dispersion forces

Because electrons in a molecule are constantly in motion, at any moment, there might be an asymmetric distribution of electrons in a molecule (means a bunch of electrons might be at one end). This gives us an instantaneous and temporary dipole moment, which causes a dipole in a neighbouring molecule.

• Strength of the force increases with increasing polarizability

• LDFs are most attractive when the molecules are large = more polarizable charge clouds

• LDFs always contribute to the molecular interactions because all molecules have charge clouds and there have polarizability

Describe hydrogen bonding forces. Why are they important?

A special type of interaction that occurs between molecules have and H atom bonded to N, O or F.

• In all, the H has a significant positive charge and is strongly attracted to a lone pair on another molecule

• When an H atom that is covalently bonded to one atom is simultaneously attracted to the lone pair of another atom is called “bridging” the two molecules

  • This is a hydrogen bond

  • An intermolecular hydrogen bond bridges two molecules, and an intramoleculr hydrogen bond bridges two parts of the same molecule

• Stronger than LDF, but weaker than covalent and ionic

Important because

• Give the solid ice an open structure (why it floats)

• Give liquid water high boiling point, high surface tension and large heat capacity

• Important in biology (DNA)

What classifies an acid to be strong? What are the common strong acids and bases>

An acid is classified as a strong acid if very acid molecule reacts with water.

HCL

HBR

HI

HClO4

HBrO4

HIO4

HNO3

H2SO4

Bases

Group 1 hydroxides, group 2 hydroxides, and hydride ions, and oxide ions