CHEMISTRY COMMUNITY

Andrew Evans - 1G

That is because Ca has a lower electronegativity than Mg, producing a greater electronegativity difference between that metal and the Cl.

Andrew Evans - 1G

This is solely a matter of balancing the equation, given the normal combustion layout: the organic molecule and O² as reactants with CO₂ and H₂O as the products

Andrew Evans - 1G

A polar covalent bond has a an unequal distribution of charge, meaning one of the bonded atoms has a higher electronegativity than the other. So the guideline is that if the electronegativity difference > 2 the bond is ionic. If the difference is <1.5 the bond is covalent. And that in between area f...

Andrew Evans - 1G

In this situation the C already has 4 bonds and wouldn't be able to accept another.

But more importantly this molecule is a base, which means it has a LONE PAIR that takes on the proton. N is the only atom with a lone pair so it has to be the one that takes on the H⁺ proton.

Andrew Evans - 1G

Yes and H₂SO₄ is a polyprotonic acid and has the possibility to donate both protons to form an acidic solution, but only H₂SO₄ is a strong acid. The following HSO₄ is only a weak acid.

So for a problem like this just consider the first proton dissociating.

Andrew Evans - 1G

NH₃ has no charge, so the Cl's charge is neutralized by the metal's +2 charge

Yes the coordination number = 4

Andrew Evans - 1G

A ligand is described as chelating, but the chelate's ring must include the transition metal or else it wouldn't be a ring it would just be an arch

Andrew Evans - 1G

When I draw lewis structures I try to satisfy formal charges before considering octet rule honestly, so since P has 5 valence electrons, give it 3 bonds with each of the Cl and a double bond with the Oxygen. All atoms have a formal charge of 0. Now you can see that P would then have a total of 10 su...

Andrew Evans - 1G

Yeah they make it sure to not say "metalloid" because the diagonal band of amphoteric oxides is not the metalloids themselves but a diagonal band right next to the metalloids.

So don't get caught up in terminology, Be is part of that band of amphoteric oxides.

Andrew Evans - 1G

No NaBr definitely has more ionic character. Br is above I on the periodic table and therefore Br is more electronegative and there is a greater difference between Na and Br than there is between Na and I.

Andrew Evans - 1G

You don't need to find the concentration of H₃O⁺. Instead you can find the value of pOH using the concentration of OH^- and find pH using the following:

pH + pOH = 14

Andrew Evans - 1G

A ligand chelates with the transition metal when it binds at two different sites. So it forms a ring of atoms from the transition metal, through one binding site, through the ligand, through to the second binding site, and back to the transition metal. So chelating ligands, any polydentate ligand fo...

Andrew Evans - 1G

More electronegative what I would call "accessory atoms" would cause a stronger base . So when an H + proton dissociates from an oxygen lets say, are there other electronegative atoms attached to that original molecule that will be able to pull that charge away from the O and distribute it...

Andrew Evans - 1G

There's the double bond between the two carbons, so each carbon is bound to only three other atoms -> 3 regions of e^- density -> trigonal planar 120º

Andrew Evans - 1G

SO 3 is acidic because the nonmetal will not "let go" of the Oxygen in the same way a metal oxide would. Instead the whole molecule reacts with water to form a molecule that can then donate an H + proton into the solution. SO 3 + H 2 O -> H 2 SO 4 So basically the two molecules merge. Now ...

Andrew Evans - 1G

Each ligand is an individual molecule that binds to the transition metal. So a single ligand can bind to a transition metal multiple times if it is polydentate . You can tell that it is polydentate if it has an multiple atoms with a lone pairs with at least two atoms between: In edta, the ligand has...

Andrew Evans - 1G

I thought of it as Na is smaller, so has the same charge as K, but in a smaller volume (so it has greater charge density). Since it has a greater charge density, it has greater polarizing power, which pulls on Br's electron cloud more, causing greater distortion making the bond have more covalent ch...

Andrew Evans - 1G

Okay hi Briana, So Dr. Lavelle DIDN'T say salts do not change pH of water. In fact the entire lecture was giving examples of how salts can change pH. Where you're mistaken is that at the beginning of lecture he said how TABLE SALT (NaCl) doesn't affect pH. That's a specific case and is similar to mo...

Andrew Evans - 1G

Hello Sharon... again So in questions that involve actual vs. theoretical yield it goes as such: Actual yield will be specified by the context as "during an experiment, this much product formed" or some experimental observation. However experimental observations are hardly ever exactly wha...

Andrew Evans - 1G

Hi Sharon, From my understanding the mere property of a salt is that it is formed of two ions that dissociate when dissolved in water. So that's it. All salts dissociate when aqueous. And in reality as a reactant, it exists as two separate aqueous ions. Now how well it dissociates goes back to the i...

Andrew Evans - 1G

Yeah the lone pair is essentially what makes the molecule the ligand.
The ligand provides the lone pair to bond with the transition metal when the transition metal doesn't have an electron of its own to share.

-Andrew Evans
Section 1G

Andrew Evans - 1G

So when we draw resonance structures, we draw multiple structures in which a double bond can be in various locations. For that one on the right, the double bonds could be on the ones shown, or it could be on the other two. Actually, there are 6 different resonance structures in which the double bond...

Andrew Evans - 1G

Yeah, as Susu said, the two Cl's dissociate form the complex and instead the coordination complex forms with lone pairs associated with the DNA. This is only possible with the cis formation of the complex because the Cl-binding locations are on the same side of the transition metal, so the DNA can p...

Andrew Evans - 1G

Yes, Since lone pairs are considered regions of electron density, they factor in to the shape and arrangement of bonds around an atom. However, as Octavia said, two electrons within one bubble are going to create greater repulsion than just another bonded atom, so a lone pair of electrons are going ...

Andrew Evans - 1G

Yeah, as mr. chem_mod said, polarity comes from an uneven sharing of electrons (from a slight, not drastic, difference in electronegativity). This gives the molecule a dipole moment, where one end has a partial negative charge and one has a partial positive charge (no actual full charge). So this pa...

Andrew Evans - 1G

I would assume the carbon and nitrogen share a triple bond, just like carbon monoxide. While nitrogen's octet is now full, but the carbon's octet is not, you add the extra electron (given by the negatively charged ion) to fill that one lone pair on carbon. This would give carbon a formal charge of -...

Andrew Evans - 1G

It's the formal charge! Basically the formal charges are in fact the charge on each individual atom within a molecule as evaluated using the lewis structure arrangement of electrons. That's why by adding up the total formal charges you can find/confirm the charge of the molecule. So basically, if an...

Andrew Evans - 1G

Hi Ellen, I didn't hear him say that molecules that are less tightly packed have higher melting points. In fact, I think your intuitions are correct. Since pentane is a long and thin chain of carbons, they can lie right up against one another with a small distance r, and therefore pentane will have ...

Andrew Evans - 1G

Heyo, I'm a tad bit confused. Problem 3.67 asks to identify the atom that violates the octet rule. However, for ClO2 I drew the lewis structure with both oxygens bound by double bonds with two lone pairs each, meanwhile the solution manual has each oxygen bound by single bonds with three lone pairs ...

Andrew Evans - 1G

Imagine a bear. Most bears have one two to cubs, right. We'll say mommy has 2. Mamma bear is living a free and happy life in Alaska, cruising the wilderness, no man to tie her down, just her and her happy baby furballs. Mamma bear has no threats. So she lets her cubs go play around in the field, mun...

Andrew Evans - 1G

Heyo, So basically the "expected charges" bit is just asking you to assume what charge an atom/molecule will adopt based off of its properties. For the ones that have roman numerals next to it, that gives it right away, saying how much positive charge that ion has. Otherwise, you just add ...

Andrew Evans - 1G

Regardless, for d you basically do the same process as you do for c: Since you have some 7s electrons, you'll be looking at the 7th period (row). And basically you go to the second element in the d-block which is Rutherfordium. The only problem here is that the question doesn't include the 5f elemen...

Andrew Evans - 1G

You’re correct in that n=2 now has p orbitals, but that is in addition to the s orbital in the n=2 shell. So you have the 6 electrons from the 2p orbitals and the other two electrons are from the 2s orbital (since you need to count all the orbitals s and p within n=2).

-Andrew Evans
Section 1G

Andrew Evans - 1G

Hi Jimmy, I don’t know what the problem was, or whether you had to find the energy levels, but I’m just gonna answer your question anyway. Essentially if you’re given the wavelength, you can find the energy (E=h*c/λ). However to find the energy levels it changes to and from, calculated through ΔE. B...

Andrew Evans - 1G

Cindy explained how interaction waves work, now diffraction patterns are basically what form as a result of interacting waves. Two sets of waves are being emitted from slightly different locations so they send, essentially, two different ripples. Now when measured against a straight line further awa...

Andrew Evans - 1G

Each of the first three quantum numbers are related and depend on the values of the other. n (shell) just depends on what the energy level is, so that must be given to you for the most part. l (subshell) is given as a series of possible values starting from 0 until n-1. ex: for n=3 -> l=0,1,2 where ...

Andrew Evans - 1G

I’m assuming we can use the shorthand unless otherwise stated, since that’s how they have it in the solutions manual.

-Andrew Evans
Section 1G

Andrew Evans - 1G

I don’t know the specifics of how they got each variable or constant, but conceptually the electron’s diffraction pattern displayed how a particle with a mass can show wavelike properties. De Broglie’s equation relates the electron with its mass and velocity (p) to a wavelike property (wavelength). ...

Andrew Evans - 1G

You would just plug in 10 m/s for the uncertainty in velocity (Δv) and solve for the uncertainty of position (Δx) using the Heisenberg Uncertainty Equation:

m * Δv = Δp ------> mass hydrogen * 10 m/s = Δp
------> Δp * Δx >= h / 4π -------> Δx >= h / (4π)(Δp)

-Andrew Evans
Section 1G

Andrew Evans - 1G

Yeah, like Madison said, the photoelectric experiment provided an example of electromagnetic radiation (light) behaving unlike a wave. For a wave, you can increase the energy by increasing the intensity (increasing the amplitude). However, in the experiment, shining brighter light did not eject elec...

Andrew Evans - 1G

Yeah, but please don't bother memorizing that number, they give it on the front page of the test with all the other constants and equations.
;)
-Andrew Evans
Section 1G

Andrew Evans - 1G

Once you know the limiting reactant to be HCl, you just have to use the moles of HCl and convert it to moles of AlCl3. Since you know the molar ratio from the balanced equation (6 HCl : 2 AlCl3), you use that to convert from moles HCl to moles AlCl3. And then, yes, multiply the moles of AlCl3 produc...

Andrew Evans - 1G

So the relation between light and energy is what is magically revealed through the Photoelectric Experiment: As Dr. Lavelle was saying in class, if light was only to be considered as a wave, its energy should be proportional to its intensity, or its amplitude. Therefore, by increasing the brightness...

Andrew Evans - 1G

Once you have the wavelength in the standard SI unit (meters), you just have to use dimensional analysis to convert it to nanometers or picometers: _____ m * (10^9 nm / 1 m) = ______ nm _____ m * (10^12 pm / 1 m) = _______ pm .... since there are 10^9 nanometers in every meter and 10^12 picometers i...

Andrew Evans - 1G

Yo. I do dimensional analysis for basically everything on the homework so far. It’s my way of doing what Mr. Dr. Prof. Lavelle said where you use what you know to find what you don’t. So you start with some value and use any sort of relationships you know to find what you’re looking for. So I’m just...

Andrew Evans - 1G

Basically, you start with this original compound M(OH)2 which has a molar mass of 74.10 g/mol. In compounds we know that the total molar mass is simply the sum of the molar masses of the atom components (molar mass of M + 2*molar mass of O + 2*molar mass of H). Since you know the molar masses of O a...

Andrew Evans - 1G

I would always use units in your calculations just so you can check yourself and see that your units are properly canceling out to give you the desired resulting unit. Also in dimensional analysis, where you start with one value and use value relationships (stoichiometry, molarity, molar masses, ect...

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