CHEMISTRY COMMUNITY

Qilan Li 4I

I did not quite understand the second question Lavelle went over in his review of past exam questions. What is the Heisenberg equation and how do we use it?

Qilan Li 4I

For 6D.11, I understand that the ions in the salt would indicate whether the pH will be less or more than 7 (or neutral). However, I used the charts in the textbook to see whether they are ions from strong/weak acids or bases. Do you memorize the different cations and anions for the final? Does anyo...

Qilan Li 4I

I don't know if this is extremely helpful but you can refer to Table 6D.1 in the textbook and it shows all the small, highly charged metal cations that are written with (H2O)6. This is how I know when and where to include it.

Qilan Li 4I

The question was: Magnesium ions are a known cofactor in over 300 enzymatic reactions. What are the possible angular momentum quantum numbers of the highest energy electrons in these magnesium ions? Indicate the corresponding subshell of each angular momentum quantum number. I understand that the hi...

Qilan Li 4I

Our TA mentioned that Ka and Kb won't be in the final, but we spent a considerable amount of time on it and it is in our outline. What do we really need to know about it besides its relationship to acidic/basic strengths?

Qilan Li 4I

I am confused about the concept of pKa, pKw, and pKb. What exactly are they and what is their relationship to each other? What type of calculations are involved?

Qilan Li 4I

I believe the final is cumulative but the material we learned after the midterm will probably be heavily emphasized. I also heard that the final is more conceptual than the exams we've had so far.

Qilan Li 4I

Is the best way to remember how to name coordinate compounds is to memorize all the rules? Does anyone have any tips?

Qilan Li 4I

My grade for Test 2 is also a 0. The grades will probably be released Monday or Tuesday this coming week.

Qilan Li 4I

I believe so. Lavelle will most likely provide us a list of review sessions from TAs, UAs, and himself for the final.

Qilan Li 4I

I heard that the final is very conceptual. I used to do all the homework problems to study for the tests and midterm and I have done alright, not super well. What study strategies would be best for the final?

Qilan Li 4I

For me, I usually don't have many questions to ask. I like to look at other students' questions and if I don't know how to answer them, I look for the answers. I find that this is the most productive way to learn. As a result, I get to learn something I don't know AND answer someone's posts as part ...

Qilan Li 4I

They are both covalent bonds formed by the overlap of atomic orbitals. Sigma bonds are formed by end-to-end overlaps and pi bonds are formed by side-to-side overlaps (the lobes of the orbitals overlapping one another). Sigma bonds are stronger because there is generally more overlap compared to pi b...

Qilan Li 4I

I attached a picture of a molecular geometry chart. It includes the names, the bond angles, and pictures. You can also google "molecular geometry chart" and see many examples that include bond angles, pictures of the shapes, and the corresponding names.

Qilan Li 4I

How do we attach pictures in our posts for chemistry community? I see the Img option on the top of the text box but how does it work?

Qilan Li 4I

Lewis acids accept an electron pair and will have vacant orbitals. I think this goes for all common “acids” if that is what you mean by “regular.”

Qilan Li 4I

It can have one lone pair or two lone pairs. This is a link to an image showing the two different molecular shapes: http://intro.chem.okstate.edu/1314F97/C ... PMain.html

Qilan Li 4I

On homework questions, 2E.5, 2E.7, and 2E.9, the answers to the bond angles are all "less than blank." Is this because they all have lone pairs that push the bonded pairs together creating a "less than" degree. Why is that? Does this "less than" degree occur between onl...

Qilan Li 4I

Since bond angles are affected by the presence of lone pairs of electrons at the central atom, we can tell if there are lone pairs when a picture only shows bonded pairs/atoms. A lone pair of electrons at the central atom would always repel the shared pair/bonded pair which is why the 120-degree ang...

Qilan Li 4I

Ion-ion interactions are an attractive force between ions with opposite charges. An ion-dipole interaction is the result of an electrostatic interaction between a charged ion and a neutral molecule that has a dipole (temporarily charged dipole). For example, a positive ion (cation) attracting the pa...

Qilan Li 4I

The Lewis Structure can help you visualize the bonded pairs and the lone pairs so I personally believe it is very helpful to draw it out while using the VSEPR model. I think once you are familiar with the shape of a molecule, you wouldn't need to draw out the Lewis Structure.

Qilan Li 4I

On homework problem 2E.9, ICL3 is T-shaped but what is the difference between trigonal bipyramidal and T-shaped?

Qilan Li 4I

I think a good example would be XeF2 where it has 2 bound atoms and 3 lone pairs. Another example would be I3.

Qilan Li 4I

You would have to find out the formal charge of both atoms. I usually do this by comparing the number of electrons that are surrounding an atom with the number of electrons the neutral atom normally has. However, the atom with greater electronegativity usually has a negative charge or at least that ...

Qilan Li 4I

The electronegative atom must have one or more unshared electron pairs (which oxygen and nitrogen have). The atoms must also have a partial negative charge. The hydrogen (has a partial positive charge) is attracted to the partial negative charge of oxygen or nitrogen which has excess electrons to sh...

Qilan Li 4I

Dipole-dipole interactions occur when the positively charged part of a molecule interacts with the negatively charged part of another molecule. Induced dipole-induced dipole or London dispersion forces exist between all types of molecules (polar or nonpolar). Electrons constantly move so an atom or ...

Qilan Li 4I

So to clarify, hydrogen bonding is a type of dipole-dipole interaction, but it is only between hydrogen and oxygen, nitrogen, or fluorine atom. While dipole-dipole is the strongest interaction between atoms and molecules, hydrogen bonding is the strongest which makes it THE strongest interaction?

Qilan Li 4I

Dipole-dipole interactions occur when the positively charged part of a molecule interacts with the negatively charged part of another molecule. Induced dipole-induced dipole exists between all types of molecules (polar or nonpolar). Electrons constantly move so an atom or molecule can develop a temp...

Qilan Li 4I

They are examples of expanded octets (expanded its valence shell). For phosphorus, there is the 3d subshell available and the d-orbitals that can accommodate for more valence electrons. This allows for extra pair of electrons to occupy the valence shell which means there are more than 8 valence elec...

Qilan Li 4I

Most likely, there will be one question (with multiple parts) on fundamentals out of 8 since we already had a test on it. The other questions would probably be split equally between the other topics.

Qilan Li 4I

Do we need to know how to calculate the exact number for electronegativity for the midterm and all the tests afterward? If not, is there anything else to know about electronegativity besides the general trends and information?

Qilan Li 4I

Your way is the process that I use when I draw Lewis structures. I also think as you draw more and more, you get used to it and begin to remember how certain structures look like. The two tips commented under this post are also very helpful.

Qilan Li 4I

I believe the classes are not Bruincasted, but the video modules on the chem 14A website seem to be past lectures. However, the video modules only cover certain subjects and not all.

Qilan Li 4I

In double bonds, there are four bonding electrons between two atoms instead of two in single bonds so there is more attraction between the atoms when there is a double bond. Stronger Attraction = Shorter Bond

Qilan Li 4I

Electron affinity reflects the ability of an atom to accept an electron. When an electron is added to a gaseous atom, an energy change occurs which is the electron affinity. Atoms with greater effective nuclear charge have greater electron affinity.

Qilan Li 4I

The atom with the lowest ionization energy is usually the central atom because it is able to create the most bonds. You can also look for the atom with the lowest electron affinity since they share the same trend.

Qilan Li 4I

The Lewis structure is a simplification for the structure of the molecule but it is helpful to visualize it. The bonds can be written in as many ways as the bonds can be arranged which indicates resonance. The actual molecule is an average of the resonance structures.

Qilan Li 4I

Lone pairs are valence electrons that are not shared with another atom in a bond. They are found in the outermost electron shell of atoms.

Qilan Li 4I

The Balmer series corresponds to the region of visible light on the spectrum and the electrons drop to n=2. The Lyman series corresponds to the region of ultraviolet light and electrons drop to n=1.

Qilan Li 4I

If the energy of the photon is equal to that of the work function, it means that the energy threshold will be met and the electron will be ejected.

Qilan Li 4I

The step-up sessions consist of the UA going over topics and problems that were covered in past lectures. Usually, at the end of the session, the UA is open to any questions pertaining to the course. You can drop into any session and there’s no need to register and you can leave any time.

Qilan Li 4I

My TA told us that the best study method would be to do all the homework problems that are assigned and really try to understand the concept behind them. For me, I also like to review my notes, watch the video modules, and go through the checklist on the outlines to make sure I understand everything...

Qilan Li 4I

It all depends on what you are looking for and what the problem gives you. Like others have said, the formulas can be rewritten or combined to yield the correct results.

Qilan Li 4I

After an electron reaches an excited state, does it fall down to its original energy level because it cannot maintain it? What are the results?

Qilan Li 4I

Photons with shorter wavelengths have greater energy (higher frequency). Is this why they eject electrons more than photons with longer wavelengths? If it is, why is that so?

Qilan Li 4I

The energy of light is related to its frequency, but what is the relationship between Planck's Constant to frequency and energy? How does it affect the two?

Qilan Li 4I

The color of light is determined by its wavelength. Is this what establishes the relationship between the color of light and the energy level electrons jumps from and to?

Qilan Li 4I

Can someone explain more in-depth what wave-particle duality is and how light can be both?

Qilan Li 4I

I think if the problem gives you the same unit throughout, you can keep it as is, but I don't think it'll hurt to convert it to base units. I usually use the most “standard” one or SI base units if there are more than two units involved with the problem so mol instead of mmol or meter instead of mil...

Qilan Li 4I

It would be very unlikely for there to be two limiting reactants because they would have to be of the same amount.

Qilan Li 4I

Why is it easier to imagine the sample mass as 100 grams when calculating the empirical formula? Also, I just want to confirm that it will only work if we calculated the mass percentage already? And this will work as long as we calculate the mass percentages from the original mass given in the probl...

Qilan Li 4I

Exactly what you said, the limiting reagent or limiting reactant determines how much of the products are made because if a reaction runs out of any reactant, the amount of product is limited as a result. And the theoretical yield is the maximum amount of product that can be produced calculated with ...

Qilan Li 4I

The first is usually used to find the molarity of a solution when the moles of solute (n) and the volume of solution (v) are given. The formula can also be rearranged to find moles or volume if the other two values are given. The second formula is used when dilution is occurring (adding more solvent...

Qilan Li 4I

First, you have to find the molarity of the sodium carbonate which is 0.08mol/L. For a), I converted mmol to moles (1 mmol = .001 mol). Since there are 2 Na’s in sodium carbonate, the molarity will be twice that of the solution which means 0.08 x 2 (the molarity will be 0.16mol/L). Then it will be (...

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