CHEMISTRY COMMUNITY

AnnaNovoselov1G

Another thing to remember is that single bonds are sigma bonds, double bonds consist of 1 sigma and 1 pi bond, and triple bonds consist of 2 pi bonds and 1 sigma bond. To determine the hybridization, you would consider both the number of lone pairs and the number of bonded atoms.

AnnaNovoselov1G

Hello, Could someone please explain why HCl is a strong acid? I understand that by definition, it's strong because it readily gives off a proton to form H+ and Cl-, but why does it do this? Since Cl have 7 valence electrons and H has 1 valence electrons, aren't they more stable in the combined/depro...

AnnaNovoselov1G

Hello! As explained by the Lowry-Bronsted concept, a strong acid has a weak conjugate base and a weak acid has a strong (more stable) conjugate base. The weaker conjugate base will be less inclined to take up a proton, so the molecule will remain deprotonated and will make the solution more acidic (...

AnnaNovoselov1G

A Lewis acid can accept a pair of nonbonding electrons and a Lewis base can donate a pair of nonbonding electrons. In the example, you can see that NH3 has a lone pair of electrons. The BF3 can react with it to form the stable compound NH3BF3 The NH3 acts as a Lewis acid and the BF3 acts as a Lewis ...

AnnaNovoselov1G

In a neutralization reaction, H+ and OH- ions combine to generate water. Salts are formed from neutralization reactions with acids and bases that are in equal concentrations. If a strong acid combines with a weak acid, the pH will be 7. Strong acid + weak base --> pH less than 7 and weak acid + stro...

AnnaNovoselov1G

Yes, this is correct. This is because the concentration of pH times the concentration of POH must equal to to the equilibrium constant for the ionization of water, which is 1.0 x 10^-14. If you take the log of both sides and simplify, you would get pH + pOH =14. We use pH and pOH because representin...

AnnaNovoselov1G

Could someone please explain why this is incorrect?

AnnaNovoselov1G

It's also important to note that the placement of both atoms and lone electrons helps determine the molecular geometric shape. This is because the location of the lone electron pairs can change the bond angles between atoms (the electrons have a greater repulsion than bonded atoms).

AnnaNovoselov1G

The molecular structure can be linear if there are only electron pairs (no atoms) in the equatorial plane and only the axial atoms remain. In this case, the atoms would be at the max distance apart possible (the bond angle between then would be 180 degrees). Also, the electron repulsion would be min...

AnnaNovoselov1G

Hi! Here is a really helpful pic Your structure is correct. The structure with 2 double bonds minimizes the differences in formal charges because in the all-single bond structure, the I has a +2 charge and the Os all have -1 charges. In the double bond structure, 2 Os has 0 charge, one O has -1 char...

AnnaNovoselov1G

VSEPR helps determine the molecular shape. It is based on the fact that molecules tend to achieve a geometry that minimizes the repulsion of valence electrons. On the other hand, hybridization refers to atomic orbitals mixing to reach the lowest overall energy states. It explains why atomic orbitals...

AnnaNovoselov1G

Hello,

Could someone explain why CO3 (2-) is both mono- and bi-dente?

AnnaNovoselov1G

Here's an example: in [Co(NH3)5)Cl]Cl2
The Cl- inside the brackets has a negative 1 charge and the Cl2 outside of the brackets has a combined -2 charge. -1 + -2 is -3. The overall coordination complex must be neutral so you know that Co must have a +3 charge to counteract the -3 charge.

AnnaNovoselov1G

Could someone please explain what the (en) means in Cd(en)Br2] ?

AnnaNovoselov1G

Could someone please explain this statement from the textbook?

The concept of hybridization enables the description of bond formation to be matched to the observed molecular shape.

AnnaNovoselov1G

Hybridization refers to the mixing of orbitals to create new hybrid orbitals that have an energy that is in between the 2 starting orbitals. For instance, one s and one p can mix to form 1 sp orbital or 2s and 2p^3 can mix to create four 2sp^3 orbitals. In other words, hybridization happens when the...

AnnaNovoselov1G

You can determine negative poles by considering differences in electronegativity. In COF2, for instance, the negative pole will be between the two F atoms because F is more electronegative than O. In COHF, it will be between the O and the F (but closer to the F) because those two atoms are much more...

AnnaNovoselov1G

The valence electrons are the ones responsible for molecular shape because they are the ones that actually determine bonding. The n=1 shell is not the valence shell; the n=2 shell is so we only consider the subshells in that shell.

AnnaNovoselov1G

Another thing to remember is that lone pair electrons contribute to the shape of a molecule, but they are not considered when determining the name of the molecular shape. The lone pairs also have greater repulsion than the bonds. So while both bonds and lone pairs are both considered regions of elec...

AnnaNovoselov1G

Connectivity refers to how atoms are connected/arranged. If 2 molecules have the same molecular formula, but different connectivity, they would be called constitutional isomers. Isomers are molecules that have the same formula but different shapes. Here's an example to illustrate the concept: 2-meth...

AnnaNovoselov1G

The 2p and 2sp^2 orbitals a smaller energy gap between them than 2s and 2p because the 2sp^2 hybridized orbital is found in between the 2s and 2p orbitals. Atoms forms hybridized orbitals because it makes the resulting molecule more stable (lower potential energy) because it allows the regions of el...

AnnaNovoselov1G

CO2 has a total of 4+6+6=16 valence electrons. If we draw the Lewis structure, it would look like this: ::O=C=O:: We see that carbon has 2 regions of electron density, which corresponds to a linear shape. It would be nonpolar because the O and the O are directly opposite each other (form a 180 degre...

AnnaNovoselov1G

It would only be a linear shape if the regions of electron density were confined to a 2D space: a plane. Then, the arrangement would be square planar and the angle between each region of electron density would be about 90 degrees and the angle between the 2 atoms would be 180 degrees (linear). But, ...

AnnaNovoselov1G

The convention is to write that electrons fill spin up first. Make sure that you keep the spin consistent until you have filled all the orbitals with one electron (e.g. in the 3 orbitals of the p subshell, fill them up, up, up, down, down, down and not something like up, down, up --> down, up, down)...

AnnaNovoselov1G

All molecules exhibit London dispersion forces, but nonpolar molecules are the only ones with only London Dispersion Forces because they don't have any permanent dipoles (since the atoms have equal electronegativities). For instance, Cl2 molecules would have LDFs between them. Temporary uneven elect...

AnnaNovoselov1G

Oxygen has the electron configuration 1s^2 2s^2 2p^3, so the p shell is half. Nitrogen, on the other hand, has the electron configuration 1s^2 2s^2 2p^4. In oxygen, each electron in the p shell occupies its own shell while in nitrogen, there are two electrons in one of the orbitals, which results in...

AnnaNovoselov1G

The electrons in shells between the electron of interest and the nucleus can shield the electron from the nucleus's positive charge. This is called effective nuclear charge (zeff) Here's an example: sodium's (Na) nucleus has a charge of 11. There are 2 electrons in the first shell, 8 in the second, ...

AnnaNovoselov1G

Hi,
Is there an answer key to this worksheet?

AnnaNovoselov1G

One other thing that helps me is remembering patterns. For instance, if there is an OH functional group, the oxygen is usually attached to the central atom and the hydrogen is attached to the O. In the COOH functional group, the two Os are attached to the C (one with a double bond and the other with...

AnnaNovoselov1G

Follow Dr. Lavelle! The arrow should be pointing towards the negative dipole, because it indicates where electrons are being pulled. What determines the negative dipole again? The more electronegative atom has the negative dipole because it pulls electrons toward itself more! Electronegativity incr...

AnnaNovoselov1G

Hi! For the Lewis structure of ClO2, how do we determine that the lone electron belongs to the central chlorine atom and not one of the oxygen atoms? There are 7+2(6)=19 valence electrons total, so we know that one atom will have an incomplete octet, but how do we know which one?

AnnaNovoselov1G

F, N, and O are very electronegative because they only need one electron to achieve an octet. Thus, they have a very high affinity for electrons and tend to have a large partial negative charge that attracts the partial charge of a Hydrogen atom.

AnnaNovoselov1G

It has lower energy (a bigger negative value) because it takes that much energy to ionize it. As an electron moves away from the nucleus, its energy approaches 0. Electrons closer to the nucleus are harder to remove because their negative charge is attracted to the positive charge of the protons. It...

AnnaNovoselov1G

Electron deficient means (at least for the elements we're focusing on) that the atom doesn't have a full octet of valence electrons. Boron and Aluminum are electron deficient because they only receive 6 electrons when they bond with other atoms to form molecules. For instance, in AlH3, the Al only h...

AnnaNovoselov1G

I love going on runs, especially on hiking trails with pretty viewpoints or during sunset. I also stretch.

AnnaNovoselov1G

I think a coordinate covalent bond is when one atom donates both electrons (for instance in the bond between BF3 and NH3, the the two electrons in the bond both come from NH3. On the other hand, in the bond between two oxygen atoms, the oxygen atoms contribute 1 electron each (regular covalent bond).

AnnaNovoselov1G

If the value is between 1.5 and 2, we have to examine the bond more closely to determine whether is is more ionic or covalent. But, since the electronegativity for one of the atoms is much greater, the partial charges will be more defined/distinct and the molecule will be more polar.

AnnaNovoselov1G

Another thing to remember is that full orbitals are generally more stable than half filled ones, which are generally more stable than partially filled ones. For instance, Zn, which has the electron configuration [Ar] 4s^2 3p^10, will be more likely to lose 2 electrons from 4s^2 than 3p^10. Also, eac...

AnnaNovoselov1G

Here are some additional details: Double and triple bonds are also stronger because they restrict electron mobility around the nucleus, thus increasing stability (because of their pi bonds). This is because pi bonds are created by p orbitals (lobe shaped) Single bonds (sigma bonds) however, permit t...

AnnaNovoselov1G

Here are the common ones we should know: H, He, Li, and Be all want the He noble gas configuration (which only has 2 valence electrons since it only has the n=1 shell). B and Al often only need 6 electrons. compounds with 7 valence electrons (notably, N) can form free radicals with an unpaired elect...

AnnaNovoselov1G

The electron configuration for Sulfur is1s^2 2s^2 2p^6 3s^2 3p^4. Sulfur thus has 6 valence electrons because that's how many are in the third shell (when n=3). The electrons in the 1st and the 2nd shell won't participate in bonding. I think you meant to say the fourth period. Let's use scandium as ...

AnnaNovoselov1G

This means that the electrons aren't strictly associated with a single atom or a single covalent bond. Delocalized electrons are sometimes indicated by a circle (like for benzene). On the other hand, localized electrons tend to stick around a single atom. Delocalized electrons are seen when a molecu...

AnnaNovoselov1G

One way to know is by examining the formal charge, which is FC= V (L+ s/2). L represents lone pair electrons and s represents shared electrons. The closer the formal charge is to 0, the more stable the element is. Usually, elements with an atomic number less than 20 form an octet (based on their orb...

AnnaNovoselov1G

Can someone elaborate more on what radicals are? From what I understand, they are just atoms that are electron-deficient, but if I am missing another essential part of its definition, please let me know! To answer your question, radicals are compounds with unpaired electrons. As a guideline, we kno...

AnnaNovoselov1G

Some causes of free radical formation inside out body are toxic chemicals (like pollutants and pesticides), smoking, alcohol and fried foods. Fats and oils (especially saturated ones) can undergo oxidation when they're exposed to light, air, or heat (for instance, during the frying process). The fat...

AnnaNovoselov1G

Phosphorus is in the third row of the periodic table (where n=3). Going back to last week, we talked about how the third shell can have three possible sublevels (l=0, l=1, and l=2). The l=0 orbital corresponds to 1 orbital, l=2 is 3 orbitals, and l=3 is 5 orbitals). The s-and p- orbitals (correspond...

AnnaNovoselov1G

Another thing to remember is that noble gases have 0 electron affinity because they don't want to gain an electron (since they already have a full shell). However, they have the highest ionization energy because it takes the most energy to remove an electron from them. Besides that, noble gases have...

AnnaNovoselov1G

To add on, electron affinity is reported as a negative value because it represents the energy released when an atom gains an electron. In other words, it represents how favorable it is for an atom to gain an electron (e.g. it is favorable if it helps the atom reach a noble gas electron configuration...

AnnaNovoselov1G

To get the energy of the electron, first use the DeBroglie equation (wavelength= h/(mv)) to calculate the velocity of the electron (convert 2.3 μm into meters first and use 9.109 x 10^31 for the mass of the electron). Then, use the equation E= 0.5m (v^2) to solve for the energy. Good luck! An import...

AnnaNovoselov1G

Hi! The first shell (when n=1) has 1 subshell (s) The second shell (when n=2) has 2 subshells (s and l) The third shell (when n=3) has 3 subshells (s, l and d) The fourth shell (when n=4) has 4 subshells (s, l, d and f) As a result, we can't have a 2d subshell because the 2nd shell doesn't have the ...

AnnaNovoselov1G

I also wanted to add that you can use c=vλ and E=hv when calculating whether an electron can be ejected because electrons absorb the energy of a photon that strikes them. For instance, an energy of light (hv) that equals the work threshold of a metal could eject the electrons (= the energy the elect...

AnnaNovoselov1G

Hi! 4s is written first in the filling order because it gets filled before 3d (you can tell because the 4s section is before the 3d section on the periodic table). However, 4s would be written first in the proper order. Electrons would be lost from the proper order. Here's an example: [Ar] 3d^10 4s^...

AnnaNovoselov1G

For question 1E.5 in the textbook, it says that electrons in an s-orbital are more effective than those in other orbitals at shielding other electrons from the nuclear charge because an electron in an s-orbital can penetrate to the nucleus of the atom. Can someone please explain how an electron can ...

AnnaNovoselov1G

Hello, Could someone please clarify why exactly the wavefunction squared is equal to the probability density of electrons? I understand what wave function squared means "the probability of finding a particle described by a specific wave function at a given point and time", but I'm not sure...

AnnaNovoselov1G

The textbook says "a particle in a container cannot have zero energy. Because the lowest allowed value of n is 1 (corresponding to a wave of one-half wavelength fitting into the box), the lowest energy is E 1 = h^2 / 8mL^2. This lowest possible energy is called the zero-point energy. The existe...

AnnaNovoselov1G

When using the equation 1/λ = RZ^2(1/n1^2 - 1/n2^2) , you would plug in R=1.097 x 10^7/m. When using the equation v=R[1/n12-1/n22, you would plug in R= 3.29 x 10^15 Hz. I think there are different variations because the units are different. I found that this question was also asked on Chem Community...

AnnaNovoselov1G

4.86x10^-20 is not the energy per photon; it is the combined energy of all the photons in the light. So, it is equal to hv times the number of photons. E=h x frequency (for one electron), but E (total for all electrons) = hv times the number of photons. 15.77 J = 4.86x10^-20/x Solving for x would gi...

AnnaNovoselov1G

The emission of visible light corresponds to a photon dropping from an excited state to the 2nd orbital (the Balmer series). Thus, you know that the final/lower n value would be n=2. Now you need to find the initial/higher n value. To find this, you can use the equation frequency= R(1/(n1)^2 -(1/(n2...

AnnaNovoselov1G

The photoelectric effect helped revolutionize our understanding about the behavior/structure of light and subatomic particles. It helped lead to technologies such as: -imaging technology, like television camera tubes or image intensifiers -photocopiers -light meters -photocells, photoconductive devi...

AnnaNovoselov1G

Hello! 1. Consider the equation E (kinetic) = E (photon) - work function. E (photon) is h x frequency. You know that the kinetic energy of the electrons would be 1.25 eV. Convert that to Joules by using the relationship 1eV=1.62 x 10^-19 Joules. You can also find the energy of the photon since you k...

AnnaNovoselov1G

During the lecture, Professor Lavelle described that an electron can be modeled as a circular standing wave. Could someone please clarify how this model was derived? I understand that the circular model fits the prediction that waves must be in phase if only certain quantized energy levels are allow...

AnnaNovoselov1G

Intensity corresponds to the amplitude of the wave (how high it is). It is defined as the distance from the crest or trough of a wave to the baseline (center line). For a classical wave, an increase in amplitude would correspond to an increase in energy. Frequency, on the other hand, is the number o...

AnnaNovoselov1G

The UV spectrum of the hydrogen atom corresponds to the Lyman series, which represents a jump to the principle quantum energy level n=1. first, you would find the frequency of the 102.6 nm wave using the equation: frequency= c/lambda. Then, you can solve for the initial energy level (from which the ...

AnnaNovoselov1G

You would divide the total energy of the photons by the work function. The equation Ek= hv - phi gives us the kinetic energy that one ejected electron will have. The energy to eject one of this electrons from the metal, however, is simply phi. It takes 7.23×10−7 J to eject an unknown number of elect...

AnnaNovoselov1G

When you increase the number of photons, you are increasing the intensity (amplitude of the light). However, you aren't actually changing the wavelength or the frequency. As a result, those values will stay the same. The energy of a photon is E= planck's constant times the frequency. Since there are...

AnnaNovoselov1G

From the atomic spectra focus module on Professor Lavelle's website, I wrote down that the Rydberg constant is equal to 3.29 x 10^15/sec when used in the equation En=(-hR/n^2). However, in other resources like https://ch301.cm.utexas.edu/section2.php?target=atomic/H-atom/rydberg.html it says that R ...

AnnaNovoselov1G

The number in front of the name refers to what carbon in the organic molecule chain an additional molecule/group is bonded to. For instance, the organic molecule pentene would be a straight chain of 5 carbons with hydrogens bonded to them. However, 2-methylpentane would be a pentene molecule with a ...

AnnaNovoselov1G

Thomas Vu: I also got 461.66 kg but the textbook says that the answer is 509 kg.

Did anyone else also get 461.66 for the answer?

AnnaNovoselov1G

One eV (electrovolt) is equal to 1.602×10−19 Joules. Good luck!

AnnaNovoselov1G

How can the Hydrogen atom have an infinite number of energy levels available (as seen by the equation En= -R (1/n)^2 where n=1,2,3... and En is the energy of an individual quantum level)? I understand that the atom has a finite energy range because it takes 13.6 eV to fully discharge an electron, so...

AnnaNovoselov1G

I was really confused about this one as well because I wasn't able to balance the last chemical equation. But, I checked Professor Lavelle's website and there's actually an error in the textbook. Here's what the solution manual correction PDF says: L.35 in the textbook question: In the third reactio...

AnnaNovoselov1G

Here is info from an email sent a few hours ago: Due to the bookstore delays in shipping your Ebook/Sapling access card (with the access code) I have organized that you have Ebook/Sapling access via a free trial period (for details see https://docs.google.com/document/d/1t0ExeH8Rruxp0GKgB-KdSmsNDk0f...

AnnaNovoselov1G

Hi Annabel, I'm noticing 2 mistakes: 1) H20 has only one mole of oxygen, not two. 2) In the 0.06056 g of oxygen calculation, you accounted for the fact that some of the mass of the oxygen in the products didn't come from caffeine. When you converted to moles first, you forgot to do that. Hope this h...

AnnaNovoselov1G

This is true. For instance, J.J Thomsons's experiment determined the charge to mass ratio of an electron by sending electrons into a positively charged plate. Millikan's oil drop experiment helped determine the mass of an electron. Furthermore, Wilson's cloud chamber can be used to study an electron...

AnnaNovoselov1G

1 angstrom is equal to 10−10 meters = 0.1 nm
visible light ranges from about 380nm-700nm.
1 nanometer = 10^-9 m
so 380nm x (1 angstrom/0.1 nm) = 3800 angstroms
and 700 nm x (1 angstrom/0.1 nm) = 7000 angstroms

AnnaNovoselov1G

Here is the information from the email he sent tonight: "the Fundamental section should be finished by the end of week 1 (as we will finish it week 1). The quantum section we will finish by the end of week 3. Therefore, readings and questions from the textbook should be finished by the end of w...

AnnaNovoselov1G

Energy levels are different for different atoms because they depend on the number of protons and neutrons in the nucleus. Thus, there isn't a universal value that will cause excitation vs emission in every single atoms. In hydrogen, for instance, electrons in the first energy level have a value of -...

AnnaNovoselov1G

Hello, While trying to understand why an electron's energy is quantized, I stumbled on an article published by the University of Nebraska-Lincoln that clarified some points for me. https://astro.unl.edu/naap/hydrogen/transitions.html#:~:text=The%20formula%20defining%20the%20energy,the%20electron%20f...

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