CHEMISTRY COMMUNITY

Saima Salam 3J

To add to the previous questions, can someone also explain the conceptual meaning of pKA and pKB?

Saima Salam 3J

What is the polarizing trend in the periodic table?

Saima Salam 3J

The question asks us to write a chemical equation based on the formation of the resulting compound. How do we determine what base and acid we use? I know that we look at the resulting compound to determine but I am confused on exactly how to do so.

Saima Salam 3J

I also had a question about the final. Does anyone know how many questions would be on the final? Would it be similar to the midterm (8 questions)?

Saima Salam 3J

I believe we would have to draw the most stable form which is how test #3 was formatted as well. So I think as long as we can draw with a formal charge of 0 or whatever charge the molecule has on it, we should be fine.

Saima Salam 3J

The problem asks us to explain the difference in the boiling points between ASF3 and ASF5 but the solution manual states that ASF3 is a polar molecule and ASF5 is a nonpolar molecule. Why is it that they are different in polarity characteristics when they are the same atom but different amount?

Saima Salam 3J

Dear Dr. Lavelle, You are truly an amazing professor and I am so grateful to be part of this class. You haven't only made chemistry interesting but made it simple. Even though at times I didn't understand the homework or lecture, but I still had a supporting community such as this one where students...

Saima Salam 3J

When atoms bond to a central atom, they do it in such a way to maximize the difference between two bonds and thus confirming a molecular shape. When there are no lone pairs on the central atom, the electron geometry and molecular geometry is similar. However, when there are lone pairs involved, the ...

Saima Salam 3J

It has to do with electronegativity. The difference in electronegativity between Sulfure and Fluorine is 2.98 and the electronegativity is large enough for it to be a polar molecule.

Saima Salam 3J

What are the significance of sigma and pi bonds and what do they represent? How would we draw sigma and pi bonds?

Saima Salam 3J

Just do the number of things attached to the atom; lone pairs counts as two things and a bond counts as one thing. So do the number of things attached - valence electrons of the atom and that is the shortcut.

Saima Salam 3J

I think memorizing would make it easier because knowing what shape corresponds to how many bonds and lone pairs makes it easier on the test. Also, the bond angles that aren't exact also should be memorized because it's most likely going to be on the test. My tutor told me to make flash cards to memo...

Saima Salam 3J

Think about it this way, if there are a concentration of electrons in one particular side of a molecule and it comes in interaction with another molecule which also has electrons but is less electronegative than the first molecule then the first molecule will push away the electrons because a negati...

Saima Salam 3J

Dipole-dipole interactions are between opposite partial charges on two different molecules attracting each other. It usually forms when there is a permanent dipole. So in case of a water molecule, the Oxygen is partially negative and Hydrogen is partially positive because of their electronegativity ...

Saima Salam 3J

I couldn't make it to class this Wednesday (11/7/18) due to an appointment. It would be wonderful if someone can share their notes and, if not, the topics I should go over in the book, I would greatly appreciate your help.

Thank you very much in advance!

Saima Salam 3J

It has to do with electronegativity. The electronegativity of Nitrogen is greater than Phosphorus so it would pull the electrons closer making the bonds smaller. Also due to the similar sizes of Nitrogen and Fluorine, they make smaller and stronger bonds.

Saima Salam 3J

The 3- is the charge on a Phosphide atom. Since Phosphorus has 5 valence electron in general but when it becomes Phosphide it gains 3 more electrons thus making it 8 valence electrons. Now, if we were to calculate the formal charge it would be #of valence electrons minus the number of electrons/bond...

Saima Salam 3J

Well, Lavelle did say that there will be questions from the homework and since this is a homework problem, I think it would be safer to know how to draw them.

Saima Salam 3J

It depends on what element is given and the number of bonds they can make. If the element can make double or triple bonds and it doesn't exceed the number of bonds they can make then you should be able to use it.

Saima Salam 3J

I think as long as you show work and attempt the problem, most TA's will give you the full grade. Also, you might want to ask your TA how they grade the homework.

Saima Salam 3J

I have talked to my counselor as well and she advised me that if you want to take them simultaneously it could be difficult and time-consuming since labs are mostly about writing long lab reports. It's not recommended unless you feel very good at chemistry. However, it is your choice and completely ...

Saima Salam 3J

Which of these compounds has bonds that are primarily ionic? a) BBr3 b)BaBr2 c)BeBr2 I understand the first two and why they are covalent and ionic but BeBr2 is covalent and I don't understand why because it's a metal forming a bond with a nonmetal. The solution manual says that its due to the high ...

Saima Salam 3J

When we write the ground state for an ion such as Tl^3+ it is [Xe] 4f^145d^106s^26p^1 but then we lose 3 electrons so the final configuration would be [Xe]4f^145d^10. Why do we only remove electrons from the p-subshell and the s-subshell but never the d or f subshells?

Thank you in advance!

Saima Salam 3J

Actually, I read some of the older post from Lavelle about curving. He said in that post "curves vary from quarter to quarter" and students can expect a 3-5% curve from the standard point scale. I hope he still continues this grade curving.

Saima Salam 3J

1 eV = 1.6x10^-19 Joules. So if we are given a certain number of electron volt (eV) and want it in Joules, you would set up a conversion factor. For example, 2eV to Joules would be: 2eV x ((1.6 x 10^-19 J)/1 eV)) = 3.2 x 10^-19 J. I don't think we have to memorize it, he will probably give it to us ...

Saima Salam 3J

As the others have said, meters is the standard use in solving for the wavelength of the photon. When we use the formula, c is the speed of light in m/s and turning nanometer into meter cancels out the meters. Finally, to represent energy we usually write it in Joules because when we use Planck's co...

Saima Salam 3J

As the replies above me have already stated, it is safer to use the entire molar mass given in the periodic table. However, every periodic table differs in the molar mass they provide on the chart. If you have a periodic table that gives the molar mass to 5 decimal places as opposed to one that give...

Saima Salam 3J

Even though I have not taken the test yet, I have talked to others who have. They told me that the test has 8 questions and they were able to finish it fairly quickly leaving them time in the end. I recommend focusing on practicing the problems assigned by professor Lavelle so you know exactly what ...

Saima Salam 3J

It depends on how many significant numbers the problem is asking for but in this case, 4.45 would be rounded to 4.5 because if you are just rounding to 4.4 it means you are rounding down which is incorrect. The .05 makes a difference in the answer so we can't disregard it by rounding down so the bes...

Saima Salam 3J

When we are trying to find the empirical formula, we usually take the mass percent composition and turn it into grams because percent is usually out of 100. In most cases,100 gram is convenient because it reflects the mass of each element in conjunction with the percent composition which is a fracti...

Saima Salam 3J

When balancing an equation, the state of matter might be provided by the equation but if not then there are some common ones that we should know. For example, if we have H2, O2 or N2 then we know that they are gaseous elements. However, in the case of I2, the state is solid in room temperature and B...

Saima Salam 3J

When you have 1 mole of H2, the molar mass will be the molar mass of Hydrogen times 2 because you have 2 atoms of hydrogen in this molecule. However, in HCl, you will only use 1.007 because there is only one atom of Hydrogen. The subscript next to the Hydrogen will indicate how much of that atom the...

CHEMISTRY COMMUNITY

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Re: Final Exam

Polarizability

Problem J.7 - 7th Ed.

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Re: 2F.3b (7th Edition)

7th Edition 3F.15

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Re: 4.25 6th edition: Polarity of SF4

Sigma bond and Pi bonds

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Re: Test 3

Re: electron distortion

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Wednesay - 11/7 Notes

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Re: 7th edition 2b9

Re: Lewis Structure of Glycine

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Focus 2D #3 - HW Problem

Electron Configuratin

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Re: Periodic Table

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Re: When to use H vs H2