CHEMISTRY COMMUNITY

Eva Becker

Hi! When Dr. Lavelle introduced the myoglobin molecule and heme complex to us, he said it was square planar. He did not elaborate on how we know this but from what we've learned about molecular geometries and the heme complex in general, this is my understanding of why it's square planar: There are ...

Eva Becker

Hi! Since the number of cations/anions outside the coordination sphere is not given via greek prefixes, we must determine the overall charge of the coordination sphere. For potassium hexacyanidochromate(III), we can tell that the 6 cyanides have a charge of -6, and chromate (III) implies chromate ha...

Eva Becker

n(sub)1 should be the final energy level and n(sub)2 should be the initial energy level.

Eva Becker

Hi! The methyl (CH3) group in acetic acid is contributing more electron density to the COOH group. This makes it harder for the OH bond in acetic acid to break. Since formic acid doesn't have that methyl group to stabilize and weaken the acid, it is stronger.

Eva Becker

Looks like an error in the textbook; the name of the molecule (i.e. aqua) determines the (alphabetical) order in the nomenclature of the coordinate compound. The correct name should list diaqua before bisoxalato.

Eva Becker

As stated, radial nodes are n-1, and angular nodes are equal to the value of l (in which l is less than or equal to n-1). Radial nodes won't be on the Final, but quantum numbers (n, l, ml, ms) will be!

Eva Becker

Sulfur acts as a lewis acid in this molecule because of the high electronegativity of the oxygens it is bound to. As the oxygens hog the electrons, sulfur becomes partially positively charged, allowing it to be an electron acceptor (lewis acid).

Eva Becker

Yes; essentially, steric number refers to the number of regions of electron density. This includes bonds and lone pairs.

Eva Becker

Hi! I don't have any tips besides straight up memorization. Strong bases: Group 1 & 2 hydroxides and Group 1 & 2 oxides; a specific list of the more common strong bases you can memorize includes: LiOH, NaOH, KOH, RbOH, CsOH, Ca(OH)2, Sr(OH)2, Ba(OH)2. Strong acids: HCl, HBr, HI, HNO3, H2SO4,...

Eva Becker

As stated, coordination number refers to the number of bonds (within the brackets). Also note whether a ligand is mono or poly dentate, as this changes the coordination number. For example, if given a molecule bonded to ethylenediamine, it may be tempting to note this as one bond. However, because e...

Eva Becker

As mentioned, the high electronegativity of flourine creates an incredibly strong bond between the two atoms. Because of this, the acid cannot dissociate easily in water, hence its status as a weak acid. Note that weak acids are not necessarily closer to 7 on the pH scale, they simply cannot dissoci...

Eva Becker

There are two qualifications that must be met in order for a ligand to be polydentate. 1. It must be able to form at least two coordinate covalent bonds, meaning it has at least 2 lone pairs 2. It must have at least one "spacer atom" (an atom in between and separating the lone pairs). Thes...

Eva Becker

A chelate is formed when at least polydentate ligand forms a coordinate covalent bond to a metal cation. Generally, a ring structure is formed.

Eva Becker

London-based lab, DeepMind, has developed technology that can determine protein structure! This is a huge advancement in the STEM field. Link to the article: https://www.google.com/amp/s/www.nytime ... g.amp.html

Eva Becker

Which of the species contains a delocalized pi bond? HCN, O3, H2O, [CO3]2- How do I approach this? What does it mean to be delocalized? Hi! First we need to identity which molecules have pi bonds which can be easily identified when we draw the molecular structures and look for any double and/or tri...

Eva Becker

Could someone explain the significance of ligands? Also how would we be able to identify if a molecule was an octahedral complex or tetrahedral complex based off of them? Ligands are lewis bases that bind to a central metal atom, and they are often used in medical applications! If a molecule has an...

Eva Becker

How do we know if a ligand forms a chelate? For instance, I'm a bit confused on how EDTA is a chelate as it doesn't appear to have a visible ring of atoms that includes the central metal atom. Hi! We know if a ligand forms a chelate if it binds at 2, 3, or 6 places. I think with the example of EDTA...

Eva Becker

Karen Elrayes 1L wrote:Does anyone know if we can view the questions we got wrong on the midterm?

If you email your TA you should be able to set up a meeting to review your Midterm (in a secure setting to optimize test-safety/prevent cheating/etc.)!

Eva Becker

"An organic compound that is distilled from wood has a molar mass of 32.04 g/mol. Its composition by mass is 37.5% carbon, 12.6% hydrogen, and 49.9% oxygen. Draw the Lewis structure of this compound." Hi! What I did was I multiplied the molar mass by each elements percentage to get an est...

Eva Becker

We have a Sapling for Weeks 7 and * due November 29th at 11:59. Dr. Lavelle was just a little late with posting it at the beginning of Week 7.

Eva Becker

Bc the molecular shape includes the two chlorines in opposing directions, their dipoles cancel out, rendering the molecule nonpolar. Despite being nonpolar, the bonds themselves are still polar bonds.

Eva Becker

Is polarity a characteristic like covalence and ionic? For example, is there any (even if it is negligible) dipole moment between two atoms that generally form a nonpolar bond (C and H)? Yes, dipole moments are always present. In the case of C-H, the dipole moment is, as you said, negligible; it is...

Eva Becker

So I'm trying to sort out my understanding and was wondering if somebody could tell me if this is right. So, a single bond is a sigma bond and that a double bond is one sigma and one pi bond, but a double bond is also just called a pi bond even though its one pi bond and one sigma bond. Right? A pi...

Eva Becker

Hi! Sigma and Pi Bonds are discussed in Dr. Lavelle's most recent lecture from November 20th (Lecture 22).

Eva Becker

Hi! Covalent radius is half the distance of the covalent bond between two atoms' nuclei. Atomic radius is the distance from a neutral atom's nucleus to its outermost valence shell. A key distinction here is that atomic radius refers to ONE atom's distance from its nucleus to valence shell whereas co...

Eva Becker

Hi! A dipole-dipole interaction will occur between the positively and negatively charged portions of 2 polar molecules. A dipole-induced dipole interaction will occur when a polar molecule induces a slight charge (dipole) on an atom or a nonpolar molecule, causing an interaction to occur between the...

Eva Becker

Hi! Polarizing power refers to a cation's ability to attract electrons from an anion. Since cations are positively charged, they will attract electrons to fulfill their valence shell. Thus, cations (not anions) have polarizing power. Polarizability refers to an anion's tendency to become polarized b...

Eva Becker

When indicating the charge of an anion or cation, the order (i.e. -2 vs 2-) does not matter. Hope this helps!

Eva Becker

Hi! The only error you have in this model is the charge on C. Carbon likes to make 4 covalent bonds, sharing 8 electrons and fulfilling its octet. However, given that it only has 2 covalent bonds, the 2 lone pairs indicate that Carbon should have a charge of -2. Hope this helps!

Eva Becker

Hund's Rule is saying that electrons will fill the orbitals alone before doubling up. An orbital can house 2 electrons spinning in opposing directions, however each orbital will fill with one singular electron before 2 occupy the same one. To draw an analogy: if a house has 3 rooms and a family with...

Eva Becker

In simplest terms, there are only 2 electrons per orbital because, due to their magnetism, they must have opposing spins. Thus, there are 2 electrons (maximum) in each orbital, and they spin in opposing directions. This is notated via up and down arrows.

Eva Becker

Yes because formal charge refers to the charge of a compound. You must calculate it using the number of bound and lone electrons, proving that a bond is needed.

Eva Becker

Atomic radius refers to the length from the nucleus to the valence shell. Similarly, ionic radius measures this, however it more specifically measures the length from the nucleus to the outermost electrons when an atom is in its ionized state. Therefore, an atom's ionic radius can be longer or short...

Eva Becker

I think it more refers to the relationship between the two molecules and which is donating versus accepting the electron. They're not necessarily Bronsted acids or bases, those refer to the movement of protons. Instead, Lewis acids and bases refer to the movement of electrons.

Eva Becker

n refers to the total number of orbitals (i think).

for the s subshell: l=0
p subshell: l=1
d: l=2

ml is the negative value of l to the positive value (i.e. if l=2, ml=-2, -1, 0, 1, 2)

Eva Becker

To help you with n=3, keep in mind that the s, p, and d orbitals are included, so make sure to add up all the electrons that occupy those orbitals.

Eva Becker

I used the de Broglie equation lambda=h(Planck's constant)/mv(mass*velocity). Since we're given the wavelength, h is a constant, and we know the masses of an electron, neutron, and proton, we need to put the equation in terms of velocity, our unknown. Thus, v=h/m*lambda. Make sure you convert the gi...

Eva Becker

Some questions may ask you to list the noble gas first. Others will want you to write out the entire configuration. One is not more correct than the other. Generally, including the noble gas first is just time-efficient! :-)

Eva Becker

Though seemingly similar, there is a distinction between the atomic and ionic radii. Atomic radius refers to the distance from the nucleus to the normal valence electrons of an atom. Ionic radius, however, refers to the distance from the nucleus to the outermost electrons. For example, the atomic ra...

Eva Becker

I agree. To add, I think we say it "approaches" zero because though it's highly, highly unlikely an electron will be that close to the nucleus, we cannot say definitively that it's impossible or never happens.

Eva Becker

Yes, use that value as the wavelength! :-)

Eva Becker

Yes; as frequency increases, energy does too. Conversely, as frequency increases, wavelength decreases.

Eva Becker

Essentially, yes. The Bohr Theory of the Atom states that electrons occupy energy orbitals (the lower levels/orbitals are closer to the nucleus), and when electrons jump to higher energy levels, light is emitted.

Eva Becker

No; apparently different TAs have been saying different numbers, anywhere from 10 to 30 questions. I doubt it's as few as 10 questions, but also probably less than 30. 15-20 questions is probably a fair assumption.

Eva Becker

I think it's because as n-->infinity, E becomes so small it approaches 0 (E-->0). When we look at the equation E=-(hR)/(n^2), we can see that as n were to increase and get so large (infinity), E would be equal to a fraction so small it would, in theory, approach 0. I think?

Eva Becker

Zeros are counted in sig figs when they occur after a decimal, assuming there is an integer that comes first. 0.0050 has 2 sig figs because even though there are 2 zeros that came after a decimal, the only zero that should be counted is the zero that came after the integer (5) following the decimal....

Eva Becker

An electron is at its ground state when it is occupying its normal energy level; when excited, the electron can jump up to higher energy levels.

Eva Becker

I think the order does matter, at least that's what my previous chemistry teachers have always said. For your follow up question, the second option was correct (3s^2p^2).

Eva Becker

The audio visual modules are great review for the midterm, as they cover the same information (I found them to be SUPER helpful this week because I didn't feel like I totally understood the lectures). As for review problems, both are good study tools! The textbook problems aren't assigned for homewo...

Eva Becker

Hi! All zeros before the first integer (8) are leading zeros and do not count towards the number of sig figs, but all zeros following the integers after the decimal DO count. Therefore, there are 3 sig figs.

Eva Becker

Both responders have done a great job explaining, but I wanted to add that the lack of a decimal at the end of 5000 does not imply specificity because the number could have been rounded. When we put a decimal at the end of 5000., we are specifically stating that this number is EXACTLY 5000 with 4 si...

Eva Becker

Scientific notation can be used whenever you deem necessary. My past chem teachers have said that as a rule of thumb, scientific notation should be used from 10^-3 or smaller (10^-4, 10^-5, etc.) and from 10^3 or larger (10^4, 10^5, etc.). Both forms are technically correct, but scientific notation ...

Eva Becker

Like everyone before has stated, 32g/mol would be the value in this context. I wanted to mention though that the reason we should use 32g/mol and not 16g/mol is because we have to take into account the mass of both atoms of oxygen (O2) which are present. This is important because, like Dr. Lavelle h...

Eva Becker

I think we can post 5 times during the week, including the weekend! As long as we post 5 times before Sunday, we get credit.

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