CHEMISTRY COMMUNITY

Junxi Feng 3B

Where is the answer for the Marshmallow Practice???

Junxi Feng 3B

No, we need to memorize the names!

Junxi Feng 3B

I think the best way to determine is to draw out all the lewis structures. And you can see the lewis structure of the final product is still drawn around the sulfur atom, meaning it accepts the electrons. Therefore, it's the Lewis acid.

Junxi Feng 3B

I think you would be fine just to memorize the general trend...The specific values are relatively not important for the exam.

Junxi Feng 3B

AX4 only stands for Tetrahedral, Square Planar is AX4E2.

Junxi Feng 3B

For part A, the hydrogen bonds form like bridges across the nucleic acid between the O, N, H atoms.
For part B, the hydrogen bond between AT is 2, so it is weaker than the hydrogen bond between CG, which is 3.

Junxi Feng 3B

Draw the Lewis structure of boric acid, B(OH)3. (a) Is resonance important for its description? (b) The proton transfer equilibrium for boric acid is given in a footnote to Table 6C.1. In that reaction does boric acid act as a Lewis acid, a Lewis base, or neither? Justify your answer by using Lewis ...

Junxi Feng 3B

I think the best way is to do as many problems as you can, and gain confidence in doing so!

Junxi Feng 3B

I think the best way is to first look at the product and determine which reactant receives protons (the chemical formula is usually given). For example, H2O + CO2=H2CO3, in this case, we look at the product, which is H2CO3, meaning the CO2 accepts protons from H2O. Therefore, water acts as an acid b...

Junxi Feng 3B

First, I think you should check the textbook, there is a picture that draws out all the molecular geometry along with their polarity. Second, the polarity can be determined based on whether the surrounding atoms are the same, if they are the same, then it's likely to be non-polar; if the surrounding...

Junxi Feng 3B

The best way is to do as many practice problems as you can, so that when you are taking the tests, you can react immediately and won't get nervous.

Junxi Feng 3B

The resonance structure is referring to the structures that have electrons constantly shifting between atoms.

Junxi Feng 3B

Since the oxygen has two lone pairs and a double with another atom, it has a total of three bonding regions, and therefore it has a hybridization of sp2.

Junxi Feng 3B

For a linear structure, the central atom must hybridize its sp orbitals to produce valence electrons, which can bond (or overlap) with another two atoms.

Junxi Feng 3B

Guys, I couldn't find which chapter it is in the textbook to review for ligands stuff...

Junxi Feng 3B

The best way to study is first go through your lecture notes, read the corresponding chapters in the textbook. After all these, just practice as many problems as you can depending on what grades you want to get. Hope this helps!

Junxi Feng 3B

Bent and angular are same names of the same shape. This molecular geometry can happen when there is one central atom with two bonding regions and one or two lone pairs. The only difference is that their bond angles are different.

Junxi Feng 3B

London forces exist among all the molecules, because the temporary dipole moment exist in all the molecules due to the random movement of electrons, and therefore it will interact with adjacent molecules.

Junxi Feng 3B

Both VSEPR shape with the formula AX2E and AX2E2 have bent shape. What are the differences in their bond angles?

I think AX2E2 will have a lower bond angle, because the extra lone pair will create a large repulsion which will push the atoms closer to each other and thus a smaller bond angle.

Junxi Feng 3B

Dipole-dipole usually exists between polar molecules. Thus, to determine, just draw out the lewis structure of the molecule and see if it's polar or not. To determine whether it's polar, you will need to find its dipole moment and its molecular shape.

Junxi Feng 3B

I would recommend Khan Academy and Bozeman Science.

Junxi Feng 3B

Polarizing power describes the behavior of a cation pulling, or distorting, the electrons from an anion.
Polarizability describes the behavior of a anion's electrons being pulled towards the cation.

Junxi Feng 3B

There can be multiple reasons for this. One, for example, is due to the presence of lone pairs that repel electrons from other atoms, making the bond angles lower. Two, it can be the number of electrons on an atom: like the examples in class today-- SO3 2- and NH3. Since O has more electrons than H,...

Junxi Feng 3B

Everything we have learned so far. Good luck!

Junxi Feng 3B

The best way to do that is simply draw out the lewis structure, count the number of surrounding atoms and lone pairs. And then hopefully you can recall what each shape of molecules should be like.

Junxi Feng 3B

Most of the time, polar molecules will be the molecules with different different elements, such as SO2 in this case, H2O, HCl, and so on. But for the best way, you will have to draw out the lewis structure to determine, such as for CH4, you will have to draw it out to see that all its dipole moment ...

Junxi Feng 3B

To see which resonance structure is more stable, just look their formal charges, the one closest to 0 will be the most stable. I am not sure what do you mean by which RS contributes more to the molecule, because the resonance structure is just the moving of electrons between different atoms of a mol...

Junxi Feng 3B

For example, between CH4 and CF4, how do you know which one has a greater electronegativity difference by looking at the periodic table? Please be specific on how to get the answer.

What about PH3 and NH3; and SO2 and NO2?

Junxi Feng 3B

Can someone explain a general way to do so? I see lots of exceptions in electronic affinity.
Also, can someone answer this question?
Which has a higher electron affinity, chlorine (Cl) or Neon (Ne)

Thanks!

Junxi Feng 3B

Obviously, they do not have the same length. Single bond has the longest bond length, and triple bond has the shortest bond length. This also has something to do with bond strength.

Junxi Feng 3B

Electronegativity is a measure of the tendency of an atom to attract a bonding pair of electrons. In the periodic table, it decreases down a group and increases across a period.

Junxi Feng 3B

We will not need to know how to calculate the electronegativity, but we need to know the trend of it in the periodic table. And we need to compare the relative electronegativity between different atoms.

Junxi Feng 3B

The central atom is always the one with the least electronegativity. Also, central atom will be the one that has the most unpaired valence electrons. In most of the cases, it should be fairly easy to find the central atom, such as CO2, BF4, SO4., etc., apparently you cannot put oxygen or fluorine in...

Junxi Feng 3B

Radicals have unpaired electrons. A rough guideline: any total electron number that cannot be divided by 2 is a radical. They are important because midterm or final will ask questions about radicals and they might relate to your future field of study. More practically speaking, radicals are highly r...

Junxi Feng 3B

It depends on the valence electrons of the atom. For instance, if the atom has 6 valence electrons in its outer shell, it tends to gain 2 e- to form its most stable form, which means its ion will -2. With the same idea, if the atom has only 2 valence electrons, it tends to lose 2 e- and form ion wit...

Junxi Feng 3B

By definition, l=0,1,....,n-1.
Since n=7, then l=0,1,2,3,4,5,6.
There are exactly 7 possible values for l.

Junxi Feng 3B

I think classical mechanics describes the objects that are have a continuous movement--movements that are predictable, like a trajectory. But quantum mechanics study tiny particles like electrons, photons that we talked about in class. Theses particles are usually moving in unpredictable paths: say,...

Junxi Feng 3B

Each series correspond to a different range of wavelengths. When you calculate the wavelength, just match it to the range of the series.

Junxi Feng 3B

How to think of the shell, sub-shell and orbitals geometrically? What do they look like if a picture of them is drawn?

Junxi Feng 3B

The number of arrows is equal to the number of electrons an atom has. The first arrow you draw will always be pointing upwards, then the second one can either be up or down depending on the number of electrons.

Junxi Feng 3B

n is the principal quantum number, which determines the energy and size of the electrons (also called the shell), and it can be any whole numbers such as 1,2,3....n; l is the angular momentum quantum number, which describes the shape of the electrons (also called the sub-shell), and it can be whole ...

Junxi Feng 3B

Most of the equations and constants will be given in the tests and exams, but the derivation equations are not given. Such as E= hc/wavelength, this is an important equation but not given directly in the formula sheet.

Junxi Feng 3B

The Planck's constant is used in the Einstein equation E=hv, where h is the Planck's constant and v is the frequency of the light. With the constant, we can calculate the energy per photon.

Junxi Feng 3B

I think the best way to solve the problem is dimensional analysis. First, multiply the time 2 sec to the 32W, and notice how the units of time cancel out each other, do the calculation and the result is simply 64 J. Now, use the given wavelength of violet light to find out the frequency by using the...

Junxi Feng 3B

To eject an electron from the surface of a metal, the incoming photo must have enough energy. Given the frequency, we can use the Einstein Equation E=hv to solve for energy E. Plug the frequency and the constant h, the resulting value will be the minimum energy required.

Junxi Feng 3B

The answer is no. The tests and exams will provide you with these numbers, because the point is not about whether you can memorize the numbers, but whether you understand the materials and are able to do the calculations.

Junxi Feng 3B

Yes for both of the questions.
Going from n=6 to n=2 gives the purple light, from n= 5 to n=2 gives the blue, and so on. All these lights are in visible regions.
But going from n=2 to n=1 will give a even shorter wavelength, which is in the UV region.

Junxi Feng 3B

Molarity is number of moles per liter of solution. Molarity is important in experiments because it acts like the specific dosage that is needed in different reactions. Different molarity may result in different amount of products in a reaction.

Junxi Feng 3B

First of all, I think the actual molecular mass of the compound must be given. And then you simply divide the actual molecular mass by the molecular mass of its empirical formula. The number you get will be the answer.

Junxi Feng 3B

I don't remember how all the sig figs work... Can somebody explain it to me? Like if 1.25 multiply 3.1, how many sig figs should I keep? What about division?

Also, do I have to keep the sig figs for the problems in the homework?

Junxi Feng 3B

Just need to make sure that the coefficients of each element on both sides of the chemical equation is equivalent (or balanced).

Junxi Feng 3B

A student prepared a solution of sodium carbonate by adding 2.111 g of the solid to a 250.0-mL volumetric fl ask and adding water to the mark. Some of this solution was transferred to a buret. What volume of solution should the student transfer into a fl ask to obtain (a) 2.15 mmol Na+; (b) 4.98 mm...

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