CHEMISTRY COMMUNITY

Alan Wu

NaOH, the entire compound, is considered a base (a STRONG base, even). A bronsted base is defined as anything that accepts a proton. But the textbook explicitly states that Na+ is the spectator ion and OH- alone is the Bronsted Base. It warns us to not confuse it with what you said about NaOH being...

Alan Wu

NaOH, the entire compound, is considered a base (a STRONG base, even). A bronsted base is defined as anything that accepts a proton. But the textbook explicitly states that Na+ is the spectator ion and OH- alone is the Bronsted Base. It warns us to not confuse it with what you said about NaOH being...

Alan Wu

Are we required to memorize all the amphoteric oxides shown in Figure 6A.7 on page 450 for the final exam? And what exactly do we have to know about amphoteric compounds? Is it the fact that they can react with both acids and bases? Let's say we're given an oxide and we're unsure if it's amphoteric ...

Alan Wu

For the upcoming final, which definition of acids and bases are we supposed to use by default?

Also, for Bronsted Bases, are we allowed to refer to NaOH (the entire compound) as a base? Or do we have to specifically point out that OH- is the Bronsted Base while Na+ is just a spectator ion?

Alan Wu

Yes, just take the grams of Na3AsO4 and divide it by its molar mass. Then remember to multiply the result by 3, because there are 3 moles of Na for every mole of the compound.

Alan Wu

Yes.
A Bronsted Acid donates a proton. (It is the entire compound that donates the H+ proton, e.g. HCl)
A Bronsted Base accepts a proton. (It is just the species that accepts the H+ proton, not including the spectator ion, e.g. OH-, not NaOH)

Alan Wu

Regarding industrial examples of coordination compounds, is Cis-platin as the chemotherapy drug the only example we need to know for the final?
Are there any other industrial examples of coordination compounds that we should know?

Alan Wu

How many hydrogen bonding sites are on caffeine? https://us-static.z-dn.net/files/dfd/7d0fd265f1e9dddec8043e926cfb1571.png There are 8 lone pairs of electrons in total on N and O atoms in caffeine. There are no H atoms bonded to N, O, or F atoms in caffeine. Therefore, shouldn't the number of hydrog...

Alan Wu

BenJohnson1H wrote:Without myoglobin, is hemoglobin square planer about Fe?

Isn't hemoglobin just 4 myoglobin-like molecules joined together? It should have the same shape I believe?

Alan Wu

Fe is always at the center of the Heme Complex. The reason he talked about the heme complex is because it is a coordination complex. And all coordination complexes are made up of a transition metal as the central atom, which is then bonded to numerous ligands.

Alan Wu

How do we precisely know if a ligand is polydentate? For example, the O in water has 2 lone pairs of electrons, but it is monodentate. Then oxalate has 4 Os, each with 2 lone pairs of electrons, but it is bidentate. Why is that the case?

Alan Wu

There's one water molecule ligand and 5 cyanide ligands (cyano) surrounding cobalt (III) in the coordination sphere.

Alan Wu

If the orbitals that form sigma bonds overlap more than the pi bonds, how is it that sigma bonds can rotate and have more flexibility than the pi bonds? Sigma bonds overlap in a different way. Use the dumbbell example I mentioned above. If 2 dumbbells are merged together on one end (like orbitals i...

Alan Wu

Yes, this can happen. The number of electron density regions equals the number of hybrid orbitals created. However, the lone pairs would be already-paired electrons in these hybrid orbitals. The unpaired electrons, on the other hand, are responsible for forming bonds with the orbitals of other atoms.

Alan Wu

The orbitals forming a sigma bond overlap end to end. Just imagine 2 dumbbells flat on the floor, with one of their ends completely merged together. The orbitals forming a pi bond overlap side to side. Just imagine 2 dumbbells standing side by side on the floor, with each of their ends touching each...

Alan Wu

As the hybridized orbital has more s character (meaning less p character), the less regions of electron density are around a particular atom. For instance, if we compare sp3 to sp2, the s character increased (25% to 33%) and there is one less region of electron density, so the shape went from a tet...

Alan Wu

No. It's important to remember that in molecules with both single and multiple bonds, there only exist hybrid bonds of equal energy, and the localized double bonds depicted in lewis structures only exist as a limitation of lewis structures. This is why resonance structures exist: because the multip...

Alan Wu

This isn't really an exception, but consider AX2E3. This will give you a linear molecule, with bond angle 180 degrees, as opposed to angular or bent.

Alan Wu

Definitely the one with the double bond between S and O. That gives O a formal charge of zero. In general, you should always try giving O or any Group 16 element a double bond and 2 lone pairs if possible.

Alan Wu

In C2H4, consider each carbon as a central atom by itself. Each carbon atom has 3 electron density regions around it, so each carbon can have the VSEPR formula AX3. Therefore, there's essentially 2 trigonal planar molecules joined together in C2H4, so the bond angles are around 120 degrees.

Alan Wu

If the dipole moments in a lewis structure cancel out, then the molecule will be nonpolar.
If there are lone pairs of e-, the molecule is almost always polar.
If the dipole moments don't cancel out and point in one general direction, then the molecule is polar.

Alan Wu

Why if a molecule has AX2E1 or AX2E2, the bond angle is slightly less than 120 degrees and not 180 degrees?

Isn't a linear shape 180 degrees??

Alan Wu

It is negative because the attractive forces are lowering the energy of the molecule by pulling them closer together. In contrast, the energy you put in to break the bonds would have a positive value.

Alan Wu

Vapor pressure is a measure of the pressure exerted by a gas above a liquid in a sealed container. Strong intermolecular forces produce a lower rate of evaporation and a lower vapor pressure. Weak intermolecular forces produce a higher rate of evaporation and a higher vapor pressure.

Alan Wu

The terms induced dipole - induced dipole, London, Dispersion, and Van der Waals forces all describe the same force in this class.

Alan Wu

Only highly electronegative atoms are strong enough (negative in charge) to attract the H atom, which has a positive dipole and literally acts like a proton.

Alan Wu

Yes, these intermolecular forces are inherently different from each other. Dipole-dipole: an attractive force between 2 polar covalent molecules exhibiting dipoles. Hydrogen bonding: an attractive force between H connected to an electronegative atom and a lone pair of e- on N, O, or F. London Forces...

Alan Wu

Wait are you sure? Because in class we learned that there are 3 pairs of hydrogen bonds between G and C compared to 2 pairs between A and T. Therefore, G and C are harder to break apart.

Alan Wu

Usually viscosity or any property in liquid/solid form is determined by the intermolecular forces between the individual molecules. In that case, single bonds and double bonds don't apply to intermolecular forces. We learned in class that having a rod shape compared to a spherical shape greatly incr...

Alan Wu

Point the arrow toward the more negative region. You can also put a + on the arrow at the more positive side.

Alan Wu

Polarizability, or polarizing power depends solely on the anion's electronegativity. I is bigger and less electronegative than the other halogens, so it has a greater polarizability. Polarizing power, on the other hand, is determined by the cation's charge and size. These are separate things.

Alan Wu

An example of a covalent bond would simply be F + F --> F2. In this molecule, each F donates one electron to share with the other. An example of a coordinate covalent bond would be BF3 + F- --> BF4. In this molecule, F- provides 2 electrons to share with the central atom B and to complete its octet....

Alan Wu

Formal charge for an atom = # of valence electrons - (# of lone electrons + # of bonds)

This should be easier than counting the number of shared electrons and the dividing it by 2. Just count the number of bonds that atom has in the lewis structure instead.

Alan Wu

In a resonance structure, the formal charges for same atoms should all be equal in reality. This is because in reality, the structure is a hybrid of all the resonance structures. For example, in the SO4 2- resonance structures with 2 Os connected to S with double bonds and 2 Os connected to S with s...

Alan Wu

A perfect, complete, 100% ionic bond would mean that the cation has lost its valence electrons completely and the anion has gained those electrons completely. In a 100% ionic bond, there should be no electrons entering the cation's electron cloud. However, the cation having a positive charge, tends ...

Alan Wu

Another way to determine the most likely charge for an ion of a given element is to look at that element's successive ionization energies. For example, Mg's 1st IE = 737.7 KJ/mol, 2nd IE = 1450.6 KJ/mol, and 3rd IE = 7732.6 KJ/mol. The huge increase from the second to third IE for Mg means that afte...

Alan Wu

Difference in electronegativity:
0.0 - 0.4: non-polar covalent bond
0.4 - 1.8: polar covalent bond
>1.8: ionic bond

These numbers can vary from source to source, but you get the general idea.

Alan Wu

What is the significance of sigma and pi bonds? How do they affect the properties of a compound?

Alan Wu

Is electron affinity only important/ only affects Group 17 (according to Lavelle) and noble gases? Or why is it important to know the electron affinity? It's important to know the electron affinity of elements probably because we can use that to measure how much energy is released or gained in reac...

Alan Wu

Why is electron affinity negative in some textbooks and positive in this one? I learned in high school that if energy is released when an electron is added to an atom, it should be represented by a negative value. So are the positive values of electron affinity in this book just the direct opposite ...

Alan Wu

The atoms of elements toward the right of a period (except for the noble gases) are more electronegative because they have more protons and the same amount of shielding compared to the other elements in the same period. Therefore, their nuclear charge is higher and it's easier for them to pull an el...

Alan Wu

This is all a result of electron repulsion. Since electrons are all negatively charged, they repel each other and would want to occupy separate orbitals (they are farther from each other that way).

Alan Wu

I don't think you can just write [Ar] for Argon. You won't be writing any actual configuration then. I'm pretty sure for noble gases, you have to use the previous one and write out all the valence electrons.

Alan Wu

These Px, Py, and Pz states are not associated with any of the magnetic quantum numbers (-1,0,1) for the p subshell, unless otherwise stated. Electrons in reality can fill in these orbitals in any order; Px, Py, and Pz are just the names we give these orbitals.

Alan Wu

I remember there were exceptions in periodic trends in ionization energy and something else. They are due to penetration of the s-orbital over the p-orbital and Hund's Rule. May someone please give a recap on these exceptions?

Alan Wu

How exactly does Schrodinger's Wave Function equation relate to the orbitals (1s, 2s, 2p... etc.)? I know the orbitals are solutions to the Wave Function, but what exactly does that mean? Like do the orbitals have energies corresponding to the ones calculated by this equation?

Alan Wu

Amplitude, or intensity, for waves are measured by the height of the waves from their base to their peak. However, if light is regarded as a photon, amplitude, or intensity, is simply the number of photon particles emitted. That's why light with higher intensity resulted in more electron emissions b...

Alan Wu

E(photon) = hv, whereas Ek or E(electron) = 1/2 mv^2

E(photon) = threshold energy + Ek

Alan Wu

Can someone explain why electrons bound to the various energy levels of hydrogen have negative energies as calculated by Rydberg's equation?

Alan Wu

This may not be the best way to explain it, but it can help you understand this phenomenon better. Elements toward the left of each period have less valence electrons and are more likely to lose them to establish a stable octet. For example, Na only needs to get rid of one electron to achieve a stab...

Alan Wu

I believe for the sake of this class, there's no need to break down the unit for hertz. It's simply s^-1 and that works perfectly in equations such as E=hv because it cancels out with Planck's constant to get the final answer in Joules.

Alan Wu

The answer is D.

Simply use the equation E=hv to solve this.

E = 6.63x10^-34 JS * 3.00x10^15 Hz = 1.99x10^-18 J

Alan Wu

Placnk's constant is used to find the energy of a photon given its frequency or wavelength.

These 2 equations are very handy:
Energy of photon = planck's constant (h) * frequency
Energy of photon = planck's constant (h) * (speed of light (c) / wavelength)

Alan Wu

I don't get why only EMs of specific wavelengths can be absorbed by Hydrogen atoms. I understand that the Emission Spectrum is a result of electrons falling back from one specific energy level to another. However, why can only specific wavelengths be absorbed? If the EM has a short wavelength and th...

Alan Wu

How would we calculate Zeff in this class? Do we subtract the number of shielding electrons from the atomic number Z? Or do we need to know Slater's Rule? If that's the case, can someone please explain Slater's Rule?

Alan Wu

1B.11 The star Antares emits light with maximum intensity at 850 nm. What is the temperature at the surface of Antares?

What is the relationship between wavelength and temperature? Can someone explain the equation needed to solve this question?

Alan Wu

When dilution occurs, you are only adding water (or solvent) to the solution. Whatever the solute is remains unchanged in amount. Only solvent has been added. Therefore, the moles of solute remains the same prior to and after dilution. This means that M1V1 = M2V2, and by knowing 3 of those values, y...

Alan Wu

1 mole just means 6.022 * 10^23 number of things. It is just like how you would say I have a dozen eggs, where dozen refers to "12". You can have 1 mole of atoms, 1 mole of eggs, or in this case, 1 mole of humans. For this question, to find how many moles of humans there are on Earth, simp...

Alan Wu

Since tin can have multiple charges, SnO2 must be named as Tin (II) Oxide. This is how you name any ionic compound in which the metal can have multiple charges. Whereas an element like magnesium with only one possible charge (2+) would combine with oxygen to form magnesium oxide.

Alan Wu

Formula units are typically used to describe one unit of an ionic compound. Ionic compounds are often found in huge lattice structures, where the positive and negative ions alternate. The formula unit would describe the most basic unit that makes up the ionic compound (e.g. NaCl). A molecule is used...

Alan Wu

Another thing you should remember to do is to not round intermediate answers to the desired sig figs. Directly take whatever number you got from your calculator and copy it onto the next line to perform the calculation. Many often round the intermediate answers and that could result in undesirable f...

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