CHEMISTRY COMMUNITY

Chem_Mod

Just for clarification purposes, higher the intermolecular bond strength, higher will be the melting point. This is because you want to break the intermolecular forces within the solid. So higher bond strengths will require more energy to break the bonds, thus will have a higher melting point. There...

Chem_Mod

Can you take all your medical school pre-requisites online or at a community college? If so, is it any less competitive? You can take them wherever you would like. I'm not sure if they accept online courses (that you would need to check with specific schools), but they should accept courses taken a...

Chem_Mod

Is there a way to go to medical school without the pre-requisites such as chemistry classes and physics classes? Unfortunately, you cannot. You need to take these courses because medical school will only build on this material. They don't teach the foundations; they just assume you know it from the...

Chem_Mod

Is there any way to complete medical school pre-requisites while majoring in business economics? Is this a smart move? What do you recommend for an indecisive individual? If you aren't a pre-med, I find that super cool! You end up becoming such a well-rounded applicant and I know from experience th...

Chem_Mod

If you are not enjoying this class or subject but still have dreams of becoming a doctor, what do you do? Do you just go through it and hope it gets better? If it's a course that is a medical pre-requisite then you need to determine if being a doctor is still what you want to be. Medical school wit...

Chem_Mod

You are welcome. :-)

Chem_Mod

CH 2 Cl 2 is polar because it is tetrahedral. The only time a tetrahedral carbon is non-polar is when all 4 atoms connected to the central carbon atom are the same. I did this example in detail in class: CH 4 and CF 4 are non-polar as all the dipoles cancel. I also did variations of CH 3 Cl and disc...

Chem_Mod

Selenic acid is an inorganic compound with the formula H₂SeO₄.

Here is the structure:

: Selenic Acid.jpg (3.79 KiB) Viewed 618 times

In class, when I do more acids and bases, this Lewis structure will be straight forward after I discuss oxoacids.

Chem_Mod

Yes, dipole is permanent and is due to a difference in electronegativity between atoms forming a polar molecule.

Chem_Mod

No, there is only one VSEPR model per molecule.

Chem_Mod

A greater partial charge due to a greater amount of electrons/larger atomic radius.

Chem_Mod

Yes, because london forces are due to random fluctuations of electron density where there is an unequal distribution of electrons on one side of a molecule. All molecules are subject to this random fluctuation.

Chem_Mod

This has to do with the three dimensional structure of the molecule. CH2Cl2 is tetrahedral, therefore you cannot draw the Cl opposite to one another. It is difficult to see this when you draw the tetrahedral structure one dimensionally but if you look at a video of a tetrahedral molecule you'll see ...

Chem_Mod

When referring to the s-character of a hybrid orbital, we look at the percent composition of the hybrid orbital in terms of s and p. For example, an sp3 hybrid orbital has 25% s-character because 1 of the 4 orbitals mixed is an s-orbital. Similarly, an sp2 hybrid orbital has 33% s-character. Hopeful...

Chem_Mod

Do you mean hybridized vs unhybridized orbitals? There is no normalized and unnormalized vocabulary regarding hybridization.

Chem_Mod

Density isosurface shows electron density that is the same (electron density isosurface) and plots electron density at a particular level. Iso means the same Electrostatic potential surface is different in that it shows electric fields representing a partial positive surface or a partial negative su...

Chem_Mod

Look at the strength of the intermolecular forces. NaCl is an ionic salt, it thus experiences ion-ion attractions between Na and Cl ions. Ion-ion forces are the strongest, therefore, NaCl will have the higher melting point. HCl is not an ionic compound; the strongest IMF between its molecules are di...

Chem_Mod

When drawing lewis structures, the arrangement in that case does not matter because everything is attached to the Carbon. Remember that the real structure is 3 dimensional, so any 2 dimensional drawing should be fine.

Chem_Mod

You want to think of sigma and pi bonds more in terms of molecular orbital hybridization theory. Sigma bonds will generally form between s or spx or spxdx orbitals, where x is an integer. Pi bonds generally form between overlapping p orbitals that are not hybridized

Chem_Mod

Multiple VSEPR charts have been posted on Chemistry Community.

Chem_Mod

We accept AX₂E described as bent or v-shaped.

Chem_Mod

Here are the answers to the worksheet from last night. The worksheet is a little ahead of class material as to not fall behind during Thanksgiving break where we will have no session. Test 2 will cover material after the midterm and up to the first 5 minutes of today (Monday) lecture.

Chem_Mod

In addition to the examples listed here, there are induced dipole-induced dipole interactions between two nonpolar molecules. This arises from a temporary dipole moment in a nonpolar molecule resulting from random uneven electron distribution, which in turn can induce another temporary dipole in a n...

Chem_Mod

You have to take into account the 3D molecular geometry instead of just looking at the 2D Lewis structure. A carbon with 4 bonds is tetrahedral, so all the positions of the atoms are all equivalent at approximately 109.5 degrees away from each other. So there is not cis or trans isomer for tetrahedr...

Chem_Mod

You can first relate it to its structure, which is a tetrahedral. Since there are two chlorine atoms on opposite sides of each other, the two dipole moments will cancel each other out. However, since there is a third chlorine atom, that dipole moment will not be cancelled out, meaning that there is...

Chem_Mod

The molecular formula does not always give you the exact molecular shape, as shape depends on the location of bonding and lone pairs of electrons. This is especially true with organic compounds, where multiple molecules have the same molecular formula (number of each atom). This is why in problems, ...

Chem_Mod

Attached is the worksheet for tomorrow!

Chem_Mod

Answer key for test 2 problems

Chem_Mod

Here are some practice problems for test 2 for you to enjoy your weekend with, mostly focusing on geometry/bond angle stuff.

Chem_Mod

Correct; to expand on that, bonding pair electrons are more restricted in their domain because they experience attractive forces from both atom's nuclei, so are localized between the two nuclei. Lone pairs only experience attraction from one atom's nuclei, so they are not pulled as tightly. Therefor...

Chem_Mod

A dipole-dipole force involves two permanent dipole moments, so typically between two polar bonds. On the other hand, a dipole-induced dipole force involves a permanent dipole moment inducing, or causing, a temporary dipole moment on another bond that was not there before the interaction, so typical...

Chem_Mod

Not necessarily. All bonds, regardless of multiplicity (e.g. single bond, double bond) or polarity, all have the same amount of electron repulsion because they are all confined to the spaces between atoms. However, lone pairs cause more electron repulsion because they are not bonded to anything and ...

Chem_Mod

Because of the lone pairs on H2O2 the shape will always be bent (regardless if they are drawn linear in a lewis structure). Since a lone pair is required on N, O, or F molecules to form hydrogen bonds, they are typically nonlinear.

Chem_Mod

Since SO₄ exists as SO₄^2- this is actually a case of ion-dipole interaction. An example of dipole-induced dipole would be between CCl4 and water

Chem_Mod

For deciding which atom is the central atom, a good rule to go by is choosing the element with the lowest ionization energy as the central atom. For (a) S has a lower ionization energy compared to O and for (b), Be would be at the center since it has the lower ionization energy. From there, symmetry...

Chem_Mod

Since C2H4 has a carbon with a double bond and two hydrogen molecules one each side, there are no lone pairs on carbon. Therefore, each carbon will have a trigonal planar shape meaning the H-C-H bond angle will be 120 degrees and the H-C-C will also be 120 degrees.

Chem_Mod

Hope this was helpful.

Chem_Mod

Hope this was helpful.

Chem_Mod

Hope this was helpful.

Chem_Mod

Use Sapling as it has many great problems as assignments.

Chem_Mod

Hi scholars, I wanted to share a great resource that I helped contribute to during my time at UC Davis. The following is a link to Chemistry Libre Text, which is like a Wikipedia page for all topics chemistry. This particular link is for the page that goes over VSEPR geometry, bond angles, lone pair...

Chem_Mod

Hi! I have attached a word doc with some helpful links / homework problems!

Julia

Chem_Mod

Answer key

Chem_Mod

F19 WEEK 7 1k

Chem_Mod

Draw the lewis structure first, if you can identify a dipole (difference in electronegativity between two atoms), it will have dipole dipole interactions and dipole - induced dipole, especially if another molecule that has no dipole is present (induced). If it does not have those properties, then th...

Chem_Mod

All molecules have london forces to a certain extent, those that have a dipole will have dipole - dipole interactions in addition to the already present london dispersion forces. The N - H bonds have a dipole pointed towards the nitrogen, and the O - H bonds have a dipole pointed towards to the oxyg...

Chem_Mod

SO2 should have a higher boiling point as it will have dipole interactions, whereas O3 will only have induced dipole. Dipole interactions are stronger than induced dipole.

Chem_Mod

There a few different cutoffs. Using the pauling scale of electronegativity (link below), generally we can say if the difference in electronegativity is about 0.5 or greater we can say it's a polar bond and the molecule may be polar. If it's greater than 1.5 - 2 or greater, it becomes ionic. However...

Chem_Mod

Yes, if molecules have the same general structure, then the bigger one or one with more molecular weight will have the higher boiling or melting point.

Chem_Mod

Chem_Mod wrote:Here's this week's worksheet. Answer key will be posted after discussion tomorrow.

Question 6 should ask "why does nitrogen to carbon bond not freely rotate?" You may think of sp3 hydbridized atoms as having only single bonds, and sp2 hybridized atoms as having a double bond.

Chem_Mod

Here's this week's worksheet. Answer key will be posted after discussion tomorrow.

Chem_Mod

! week 7 1a

Chem_Mod

Diethyl ether is not capable of hydrogen bonding. If you draw the lewis structure, the oxygen is bonded to the carbons of two ethyl groups (abbreviated as C2H5 or CH3CH2), not the hydrogens. For hydrogen bonding to occur, there must be a hydrogen directly bonded to an O, N, or F, which is not the ca...

Chem_Mod

Polar bonds do not affect molecular shape. However, molecular shape does affect the polarity of a molecule when there are polar bonds. Since we can think of dipole moments as vectors, if they do not cancel based on the shape of the molecule, then the molecule will be polar. If they do cancel, then t...

Chem_Mod

Since you all had your midterm on Wednesday, there is not too much material to review this weekend. Today's workshop will be a drop-in where you can bring in questions about past material or homework. Have a great 3-day weekend!

-Karen

Chem_Mod

Because they have some covalent character.

Chem_Mod

Search Chemistry Community. Several have been posted.

Figure 2E.1 is lists the shapes, names, and clear visual examples.

Chem_Mod

This becomes a very detailed topic beyond general chemistry.

For those interested read:

https://en.wikipedia.org/wiki/London_dispersion_force

https://en.wikipedia.org/wiki/Van_der_Waals_force

Chem_Mod

discussion worksheet

Chem_Mod

Hello, the key doesn't have a radical as a resonance structure. A radical is when you have one lone pair electron that is not paired with another one. The resonance structure provided in the key has a separation of charge where one atom has a formal charge of +1 and one -1, but this does not make it...

Chem_Mod

You can always try to get answers at future sessions!

Chem_Mod

Topics covered from the midterm to test 2.

Chem_Mod

correct

Chem_Mod

It is working fine.

Chem_Mod

Chem_Mod wrote:Rip, sorry forgot to post the answer key yesterday

There's an error for number one, the highest frequency is i but the highest wavelength is iiii.

Chem_Mod

For number 4 part b on the extra practice problems, why doesn't boron have to complete it's octet? In your answer key, boron only has 6 electrons accounted for in the lewis structure Boron's a weird one where giving it an octet would require it have a negative one charge or greater. Since it is not...

Chem_Mod

Wish there was. I have asked the publisher to offer this.

Chem_Mod

Electrons in atoms can be excited to higher atomic orbitals.
Electrons in molecules can be excited to higher molecular orbitals.

The energy difference for the above transitions typically occur in the visible and UV region.

Chem_Mod

Valid solutions from Schrodinger's equation give wave functions, psi, that give the energy, E, of the electron (that the wave function is modelling).
These valid wave functions (math functions) are orbitals.

As discussed in class, students need to know where 'orbitals' come from.

Chem_Mod

Valid solutions from Schrodinger's equation give wave functions, psi, that give the energy, E, of the electron (that the wave function is modelling).
These valid wave functions (math functions) are orbitals.

As discussed in class, students need to know where 'orbitals' come from.

Chem_Mod

Valid solutions from Schrodinger's equation give wave functions, psi, that give the energy, E, of the electron (that the wave function is modelling).
These valid wave functions (math functions) are orbitals.

Chem_Mod

Rip, sorry forgot to post the answer key yesterday

Chem_Mod

I concur.

Unless you really, really want it on the midterm … :-(

Chem_Mod

As I discussed several times in class, the f-block elements are not covered in general chemistry.

In class we discussed the visible and UV regions several times so they should be known.

Chem_Mod

I have not yet covered coordination compounds.
I don't think students would want it …

Chem_Mod

Here's the worksheet, answer key coming soon!

Chem_Mod

Coordinate covalent bonds are when a bond is formed from a lone pair from only ONE atom donating BOTH electrons. Remember a bond is two electrons. Take for example NH3 and BF3 bonding to NH3BF3. The bond between the N and B comes from the two electrons from the N, not 1 from N and 1 from B.

Chem_Mod

I'm assuming c is concentration (ie Molarity), M is also molarity, n= number of moles, and v= volume. Can you elaborate on what "m" refers to?

Chem_Mod

The strength of the interactions between the anion and cation, which can be determined by electronegativity differences as well as atomic radius. As eneg difference increases and atomic radius decreases, melting point increases.

Chem_Mod

For further clarification: The two other resonance structures you mentioned are viable resonance structures; however they are what we call minor resonance contributors because they do not have the best formal charges assigned to the atoms. There is only one major (best) resonance contributor, which ...

Chem_Mod

You are correct in saying that B is more electronegative than C, and so the B-O should be more polar. The answer key is wrong, thank you for pointing that out! We will be sure to fix it.

Chem_Mod

Because you only look at the number of protons when you are comparing two elements in the same row, however because selenium is in a higher row than the other three elements there is less shielding associated with it. Therefore, selenium's positively charged nucleus is able to attract electrons more...

Chem_Mod

Electrons are constantly moving, resulting in formation of resonance structures when empty p orbitals are available. These other resonance structures are likely only minor contributors, as they are less stable than the main contributing structure. You will learn more about this and "arrow-pushi...

Chem_Mod

The same principles for all Lewis structures applies, using formal charge, etc. to determine a reasonable structure.
Organic and Biological molecules normally have Carbon and Nitrogen elements.

Chem_Mod

In comparing electronegativity of two atoms it is important to think about their respective atomic radii. Oxygen is in the same column as S but it is higher, therefore it has less shielding and a smaller atomic radius. Because this is the case, oxygen's positively charged nucleus is able to attract ...

Chem_Mod

If you can get into 14BL next quarter then great. 14BL doesn't have to be taken along with 14B, you can take it later as well. It just depends on you, whatever you are more comfortable doing.

Chem_Mod

Just kidding, remember the order of priorities. Make sure you have the correct number of electrons, then pay attention to the octet rule. After that, double bonds can be created to ensure you have the lowest energy lewis structure meaning fewest formal charges, and with any negative formal charges o...

Chem_Mod

You just kinda know.

Chem_Mod

These terms simply refer to the sharing of the two electrons that make up a bond between two atoms. Greater unequal sharing or distribution of electrons means greater ionic character and more equal sharing means more covalent character. It follows that when there is a greater electronegativity diffe...

Chem_Mod

Black Body radiation is not part of the syllabus.

Chem_Mod

If a certain frequency of radiation is not ejecting electrons from the surface of a metal, is it possible to eject electrons by increasing the intensity of the incident radiation? How would we solve a question such as the question stated above? Does the intensity refer to the wavelength of the radi...

Chem_Mod

Key for today's workshop.

Chem_Mod

ayushibanerjee06 wrote:
Ada Chung 1C wrote:Will the mini dino nuggets answer key be posted as well?

Will they be posted? pls help us out

Posted :) Apologies for the wait.

Chem_Mod

You won't need to calculate dipole moments but you will need to know how to identify if one exists (using relative electronegativities) and be able to draw the arrow and partial charges on the Lewis structure.

Chem_Mod

We isolated frequency because the question asked to find the frequency of the light. It's generally good practice to manipulate the variables you are working with to isolate the one that you are solving for. This is more efficient but not necessary; if you don't feel comfortable doing that you can s...

Chem_Mod

Yes, but there is also Test 2 after the midterm.

Chem_Mod

The resonance hybrid is the blending of all possible resonance contributors and represents the true structure of the molecule.

Chem_Mod

Thanks for answering this.

See my detailed answer here: viewtopic.php?f=23&t=47967&p=170473&hilit=tungsten&sid=0e5b17cc2a1046c645bd802eed503cad#p170473

I have removed part e of this problem as it is not part of the Chem 14A syllabus.

Chem_Mod

See my detailed answer here: viewtopic.php?f=23&t=47967&p=170473&hilit=tungsten&sid=0e5b17cc2a1046c645bd802eed503cad#p170473

I have removed part e of this problem as it is not part of the Chem 14A syllabus.

Chem_Mod

See my detailed answer here: viewtopic.php?f=23&t=47967&p=170473&hilit=tungsten&sid=0e5b17cc2a1046c645bd802eed503cad#p170473

I have removed part e of this problem as it is not part of the Chem 14A syllabus.

Search found 17668 matches