CHEMISTRY COMMUNITY

Yuri Lin 4H

my soul feels destroyed by the final exam

thank you UAs for all you've done for us this quarter and goodbye.

i am deceased.

Yuri Lin 4H

Oxidation number is the charge an atom takes on when it forms a bond with another atom. You can also think of it as the charge an atom would take on to fulfill a full valence shell. Excluding transition metals, which can have multiple oxidation numbers, it usually follows what group the atom is in (...

Yuri Lin 4H

A coordination compound is a complex formed by a transition metal cation and the ligands (which are Lewis bases or e- donors) that bind to the transition metal atom.

Yuri Lin 4H

The coordination number is just how many bonds are connected to the central metal atom, so you would have to draw out the structure before you can determine it. Since Pt has a charge of +4 from the name, and there are two Cl (-1 charge*2=-2) and two C2O4 (-2 charge*2=-4), there must be two Na (+1 ch...

Yuri Lin 4H

A greater acid/base constant value means a stronger acid or base, so it dissociates more in an aqueous solution. So if an acid has a greater Ka value, it has a smaller pKa value and a lower pH. Vice versa for bases: a greater Kb value means a higher pH (or low pOH).

Yuri Lin 4H

You'd have to see the reaction in which the compound is reacting in, and then you can use the Bronsted or Lewis definitions of acids and bases to determine whether it's an acid or base (as in, is it donating or accepting protons, or is it donating or accepting electrons?).

Yuri Lin 4H

Also, the energy to overcome the repulsion from spin-pair in a hybridized orbital is greater than the energy to occupy an unhybridized orbital, so the electron goes to the lower energy option.

Yuri Lin 4H

Hi! Good answer above, and just wanted to add that Bronsted acids are H+ donors and Bronsted bases are H+ acceptors. Most of the time you can tell by looking at the compound which one would donate/accept protons, though there are of course exceptions when a compound can do both. For example, along w...

Yuri Lin 4H

Yes, the molecule should still be linear.

Yuri Lin 4H

I believe there are only 7 strong acids, so it would probably be helpful to just memorize them to eliminate uncertainty. The strong acids are:

HCl: Hydrochloric acid
HNO3: Nitric acid
H2SO4: Sulfuric acid
HBr: Hydrobromic acid
HI: Hydroiodic acid
HClO4: Perchloric acid
HClO3: Chloric acid

Yuri Lin 4H

Clean coal is the one with low sulfur content and high carbon content, and dirty coal has a higher sulfur content. A good way to remember is that sulfur contributes to acid rain, so having less sulfur means "cleaner" emissions.

Yuri Lin 4H

Also, one example of a pentagonal bipyramidal molecule would be IF7.

Yuri Lin 4H

I think certain TAs graded certain questions on the test, but I'm sure that you can ask your TA any question! They should be willing and able to answer.

Yuri Lin 4H

If you can, try to find practice questions to construct your own mock test or try looking at test banks/previous tests and simulate the test day conditions by taking it with the same time constraints. This might help you stay a bit calmer during the actual test, since you'll have a more concrete ide...

Yuri Lin 4H

Yes, all molecules and atoms have Van der Waals interactions (can also be referred to as instantaneous dipoles or london dispersion forces). The strongest forces to weakest forces are ion-dipole, hydrogen bonds, dipole-dipole, and then van der waals/instantaneous dipoles/LDF.

Yuri Lin 4H

Just to add onto what everyone has stated, polarizability is related to the size of an atom (more specifically, how many electrons the atom has). The greater the number of electrons, the more easily the electron cloud can get distorted (higher polarizability). Polarity doesn't relate to polarizabili...

Yuri Lin 4H

A dipole moment means theres a permanent dipole due to uneven electron distribution (you can see this from the shape of the molecule); one example of this would be HCl. Cl is strongly electronegative compared to H, so the Cl side would have a partial negative charge and the H would have a partial po...

Yuri Lin 4H

The dipole-dipole attraction comes from the shape of the SO2 molecule. It has a bent molecular structure (same shape as H2O), so the S has a lone pair and a partial positive charge whereas the oxygens have a partial negative charge. The uneven electron distribution means there's a permanent dipole, ...

Yuri Lin 4H

electron distortion describes how much an electron cloud can be influenced or pulled in a direction by the charge of an external atom or molecule. It has just about the same meaning as polarizability.

Yuri Lin 4H

the strength of LDF is dependent on the distance (r) between the molecules and the polarizability (alpha) of each molecule. The formula for the potential energy is (alpha1*alpha2)/r^6.

Yuri Lin 4H

The equation as a whole describes the potential energy. Alpha represents the polarizability of the atom or molecule and r is the distance between the two atoms or molecules. Since r is raised to the 6, this just means that any small change in distance will result in a large change in the potential e...

Yuri Lin 4H

Look at the shape of the molecule as well as the atoms present. An induced dipole (induced dipole-induced dipole) means that the molecule had no dipole to begin with but has an induced partial negative or positive charge as the result of interacting with a second molecule. Induced-induced dipoles ar...

Yuri Lin 4H

Degenerate orbitals are just orbitals with the same energy. So for a p orbital, px py and pz are all degenerate. The significance of all of this is degenerate orbitals fill evenly per Aufbau's principle, so there should be one electron in every degenerate orbital before there are two.

Yuri Lin 4H

Larger atoms with more electrons that are also more loosely bound due to shielding have a higher polarizability, so they get more distorted in bonding. In ionic bonding, this means that the electron cloud of the anion is pulled toward the cation, which resembles the 'sharing' of electrons in covalen...

Yuri Lin 4H

I think the rule of thumb is that the central atom is the least electronegative atom, not the one with the lowest ionization energy, though I might be wrong. Nitrogen has a lower electronegativity than oxygen, so it would be the central atom.

Yuri Lin 4H

Oxygen has a lower first ionization energy than nitrogen even though nitrogen is further right on the PT because oxygen has one fully filled orbital and two half filled orbitals whereas nitrogen has three half filled orbitals. Nitrogen's half-filled orbitals are more stable, so it's harder to pull a...

Yuri Lin 4H

Someone also asked this question in my discussion, and our TA said that you should be given the formula for anything that's not super simple or common knowledge (like H20 for water or CO2 for carbon dioxide), since we never covered nomenclature. He said if this happens, raise your hand and the TA wa...

Yuri Lin 4H

more covalent character means a more highly polarizable electron cloud that is more easily "pulled" toward the other atom (therefore the cloud is shared, sort of like the sharing of electrons in covalent bonds). In this case, Br has more electrons than F and is more highly polarizable, so ...

Yuri Lin 4H

I think it's just a general principle of atomic bonding that atoms want to fill up orbitals to reach a stable state. Noble gas configuration just means that all the orbitals are filled, so covalent bonding and sharing of electrons is a way to get that stability. Hope that was helpful in some way!

Yuri Lin 4H

Ionization energy is the energy it takes to remove an electron. It usually increases left to right because the atomic radius gets smaller in that direction, so electrons experience more attraction to the positive nucleus and therefore are harder to pull away.

Yuri Lin 4H

Yes, spins are only up (+1/2) or down (-1/2)

Yuri Lin 4H

I'm not quite sure if this answers your question, but there are 8 electrons in 2s2,2p6.

Yuri Lin 4H

I think my TA did a problem with this, and the 'h' has a bar through it and is pronounced "h bar"

H bar stands for h/2pi

Yuri Lin 4H

d10 represents a full d orbital with two electrons in each of the five orbitals. THis should be more stable than d9, which is four full orbitals and one half filled one, which is unstable because it's trying to fill the last orbital.

Yuri Lin 4H

Electrons fill up orbitals one at a time with parallel spin before going back and filling in the second electron in the orbital, which would be paired spin with the first electron in the orbital.

Yuri Lin 4H

If you visualize it with drawing arrows to represent electrons in orbitals, you draw one up arrow (+1/2 spin) to represent the first electron in each orbital in that shell before going back and filling in down arrows (-1/2 spin). So for example in a p orbital, electrons 1, 2, and 3 would have +1/2 s...

Yuri Lin 4H

The Pauli Exclusion principle says that each orbital can only have two electrons, and if two electrons are in the same orbital, they must have opposite spins. I think the 'exclusion' part of the principle simply means that once you know the spin of one electron, the other cannot be the same and is t...

Yuri Lin 4H

Electron affinity usually increases going up the periodic table and going left to right, but I believe there are a lot of exceptions to this (such as F having less electron affinity than Cl), especially moving horizontally. For example, Be has less electron affinity than Li because beryllium's elect...

Yuri Lin 4H

What exactly is a nodal plane and how does it relate to electron distribution?

Yuri Lin 4H

Hello! To my understanding, potential energy is the stored energy of something (in this case a charge or an electron) to do work, due to its position or place. Electrostatic potential energy (otherwise known as Coloumbic potential energy) is the stored energy between two charges due to the distance ...

Yuri Lin 4H

Hi! 3.29x10^15 s^-1 is the Rydberg constant. If you notice in the solution, the line above where that number appears shows (1/1^2)-v/R. R is the Rydberg constant! Hope that helps :)

Yuri Lin 4H

No, we cannot always assume that the initial state is n=1. The reason why they use n 1 =1 is because the spectral line is observed at 102.6 nm. This wavelength falls within the UV region, suggesting that the spectral line is a part of the Lyman series which, by definition, transitions where the n 1...

Yuri Lin 4H

Light behaves like a wave in examples such as reflection (reflects at the same angle it hits, which is a property of a wave), refraction (light bends like a wave when passing from one medium to another), and diffraction (going around an obstacle and then spreading out again to form interference patt...

Yuri Lin 4H

In the solutions manual, it looks like it's assumed that the first n in 1/n^2 of the Rydberg equation (the n^2 with a 1 subscript) is 1. Can you always assume that the smaller n is always 1 for the Rydberg equation? How did they arrive at this conclusion, and how do we know it's not some other energ...

Yuri Lin 4H

I understand that in order for an electron to be ejected, the electron hitting the metal must have energy equal to or greater than the work function. However, I also understand that the energy must be greater than the work function for the electron to have kinetic energy. So what about the electrons...

Yuri Lin 4H

For N, you would divide 4.37 by 14.007 g/mol to get the moles and then multiply that by 6.022*10^23 to get the number of N atoms in 4.37 grams. This should get you 1.88*10^23 For N2, you would divide 4.37 by 28.014 g/mol to get the moles and then once again multiply that by 6.022*10^23 to get number...

Yuri Lin 4H

If the transition to energy level n=1 takes the most energy (UV spectrum), transition to n=2 takes less energy (visible light), and transition to n=3 even less (infrared), can this trend continue beyond these three levels? These were the only three mentioned in lecture, but following the trend, coul...

Yuri Lin 4H

Knowing an ion's charge when writing formulas helps you know how many ions are present in the compound. For example, if you're asked to give the formula of potassium chloride, knowing that K is +1 charge and Cl is -1 charge allows you to know there is one of each in the compound, so the net charge i...

Yuri Lin 4H

Hi guys, this may have been mentioned already but I just wanted to note that there's an error in the textbook for L35. FeBr2 in the third line of the reaction is actually supposed to be Fe3Br8. It's displayed correctly in the solutions manual.

Yuri Lin 4H

Only use sig figs for your final answer! You want to keep your calculations as accurate as possible, so the continuous rounding in each step would mess up the accuracy of your final result.

Yuri Lin 4H

I second the trial and error method. From what I've encountered, the decimals are usually the simpler ones you've listed that can be easily multiplied into whole numbers (or close to whole numbers). But trial and error has worked well for me in the past, and other than that, I'm not sure if there ar...

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