CHEMISTRY COMMUNITY

nicolely2F

I imagine that yes. The syllabus doesn't put any strict limits on choosing exercises for homework, it only says to go for recent topics.

nicolely2F

The textbook mentions vibrational and rotational spectroscopy, and x-ray spectroscopy for larger molecules. Apparently these methods consist of capturing the absorption or emission of energy by atoms in a molecule, and using that data to determine molecular geometry.

nicolely2F

Water molecules are polar (H atoms are slightly positive because the oxygen molecules is pulling their electrons), and so there is an attractive force between molecules with higher electronegativity and the H-atoms in water, increasing the solubility.

nicolely2F

Exercise 2.7 asks to draw all the resonance structures for the salt N_{5}^{+} (a chain structure) and to indicate the most important structure (where there aren't any two like charges side-by-side). I drew the three structures, but all three structures have 2 N-atoms with FC = +1 and 1 N-atom with F...

nicolely2F

Chlorine monoxide is a radical so it's going to have instability

nicolely2F

It's a radical, so it's not going to have the most stable configuration.

nicolely2F

The trend holds true for most of the rest of the table and oxygen was the only exception that was highlighted, so I wouldn't worry about other exceptions or how oxygen affects elements around it. Just remember that it has a lower EN than nitrogen because of its half-filled p-orbital

nicolely2F

I assume that if the EN chart isn't given then we will use the periodic trend. Prof Lavelle did not mention including the chart, though, so I guess we will have to follow the trend, which is what some of the HW questions require.

nicolely2F

We should always draw all electrons. There aren't any lone pair electrons drawn in the answer key to 2.a) because all electrons are in bonds.

nicolely2F

The balanced equation is 4NH3 + 5O2 -> 4NO + 6H2O. We have 1.24 mol of NH3 and 1.32 mol of O2. We know this by calculating that for 1.24 mol of NH3 we would need 1.55 of O2, therefore there is an excess of NH3 and the limiting reagent is O2. For 1.32 mol of O2 we only need 1.056 mol of NH3. NO is fo...

nicolely2F

All increase. a) Increases because outer layers are more energetic. b) Increases because the electron moves from energy level 1 to energy level 2. c) Increases because s is l = 0 and p is l = 1. d) Increases due to electron repulsion.

nicolely2F

In the coordinate, two of the shared electrons come from the same atom. In the polar, a distorted cloud is pulled towards the center of the region between the atoms.

nicolely2F

For the first one just use either Rydberg's equation or Bohr's Frequency Condition (if you choose this, calculate En for n = 3 and n = 1 and plug those into delta E = h.v). For the second, remember that outer layers are more energetic than inner ones, so if an electron moves from an outer shell to a...

nicolely2F

In broad terms, you need to figure out the total energy of one photon from the incident light to then discover the light's frequency. In more detail: 1. You're given the ejected electron's wavelength, and this tells you that there is excess energy (i.e. kinetic energy). Use this wavelength to calcul...

nicolely2F

Because the distance between the center of their positive charge and the anion is smaller. This allows the cation to more strongly distort the anion's cloud

nicolely2F

Spectroscopy in general is the study of how certain particles absorb or emit light. "Atomic spectroscopy" refers to how atoms absorb/emit light; "molecular spectroscopy" refers to how molecules absorb/emit light.

nicolely2F

I think that the options that he wrote in the email were the rescheduled options:

Wednesday, Nov 6, 10-10:50am, CS50, Aamir Shah, Bonding/Structures
Wednesday, Nov 6, 12-12:50pm, CS50, student group discussion
Wednesday, Nov 6, 2-3pm, CS24, Roberto Chavez, Bonding/Structures

nicolely2F

Delta p * delta X is equal to or larger than ℏ / 2. The symbol ℏ (read "h bar") is the reduced version of Planck's constant and it's equal to h/2*pi. Therefore, $\Delta p*\Delta x \geq h/4\pi$

nicolely2F

Yes, we need to know what the Lyman and Balmer series are (but it's basically UV and visible light respectively), as well as their initial n level. As far as I know, we have to know only the visible light range and have a general idea of where the other main ranges (UV, x-ray, gamma, infrared) are.

nicolely2F

Outer levels in the atom are of higher energy, therefore, if an electron transitions from an outer level to an inner level, it needs to get rid of excess energy. In the case that you read about, the electron does that in the form of light. In contrast, the energy of light being shone on a metal surf...

nicolely2F

You multiply the value by 2 to get the total margin of uncertainty in velocity. So you use ∆V = 10 m/s to solve this.

nicolely2F

Dr. Lavelle said that he will keep us posted on the location. In terms of the date, he said there could be possible changes if he is unable to reserve a large enough room for all of us. That was only the case for the review session. The midterm already has a set date and probably set locations as w...

nicolely2F

Yes. The exceptions are the first 4 elements: H, He, Li, Be.

nicolely2F

You used the right formula; you just mixed up the place of the n. The formula is v = R (1/n1^2 - 1/n2^2), where n1 = 16. Do it this way and you should get n2 = approx. 5.99 = 6

nicolely2F

The value of lithium's work function is given at the end of the exercise. It's the last sentence in the prompt, so a bit easy to miss.

nicolely2F

6 – 8pm, Wednesday November 6.

nicolely2F

You have to follow the two rules, the Pauli Exclusion Principle and Hund's Rule. The first states that there cannot be more than 2e- per state, and that if there are two, their spin is paired. The second says that every orbital in a subshell gets one electron before any orbitals get two electrons. U...

nicolely2F

The atomic radius refers to the radius of atoms in ground state (i.e. lowest energy state of an atom, which we can consider electrically neutral). The ionic radius refers to the radius of ions -- atoms with charge -- which are different in size from atoms in neutral state. The ionic radius of an ion...

nicolely2F

For exercise b) you don't need to use the number 6. The possible values for ml can be determined using the subshell "d", which yields the result -2,-1,0,1,2, therefore being 5 possible values for ml -- and you're done!

nicolely2F

Yes. The type of element can be told by their position on the periodic table and every test will have a periodic table at the end.

nicolely2F

They're different, but closely related. A subshell is a subdivision of its shell and is what we label as s, p, d, f, g... etc. The subshell has its own subdivisions, the orbitals, which are the clouds where electrons most likely are. Therefore each subshell can have multiple orbitals (the quantity d...

nicolely2F

"l" represents the shape of each orbital. There are multiple shapes possible, but the ones that are relevant to us as students are the first 4. Each is labeled 0, 1, 2, and 3, but they can also be called s (l=0), p (l=1), d (l=2), and f (l=3); so saying that an orbital has an l = 1 is the ...

nicolely2F

Yes. The work function is the minimum energy to eject the electron, therefore the kinetic energy (which is obtained from the light's excess energy) is 0.

nicolely2F

Here, you can use De Broglie's equation \lambda = h/mV , since you have mass (see the sheet provided on Prof Lavelle's website), wavelength, and Planck's constant (also on Prof Lavelle's sheet), and we only need to figure out the velocity. Plug the numbers in (don't forget to convert picometers to m...

nicolely2F

A vacuum basically has no mass or pressure that can interfere with the waves travelling through. An example, on Earth, our atmosphere isn't a vacuum because it has many gasses that interfere with any waves travelling through it, decreasing their speed, for example, but if we repeated the example in ...

nicolely2F

In the equation \lambda = hc / E , E is the total energy of the photon, so plugging in the value of the ejected electron's kinetic energy was incorrect. To find the wavelength you can simply use De Broglie's Equation, \lambda = h/mV , where m is the mass of the electron and V is the velocity (in met...

nicolely2F

EM waves typically travel at the speed 3x10^-8 m/s. Because light is a type of EM wave (and light waves are used in many scenarios), we call it the speed of light.

nicolely2F

Hz is the unit for 1 cycle/second. The cycle refers to a wave's cycle and it's from the peak of one wave to the trough of the next

nicolely2F

The mass of a neutron can be found in the sheet of Constants and Equations provided on Lavelle's website. It's 1.674 927 × 10−27 kg

nicolely2F

The ratio of moles of this reaction is 6 : 2 : 6 :1. We have 12 moles of the first reactant and 5 of the second, which means that there is enough "material" from each reactant to double the reaction, but not enough to triple it. Since 12 is the next multiple of 6, but 5 surpasses the value...

nicolely2F

We start by calculating the molar mass of KMnO4, which is 158 g/mol. If 5 grams are mixed into 150 mL, this solution will 3.17*10^-2 moles of KMnO4, which means its concentration is 0.21 mol/L. Therefore, 20mL of such solution will have 4.2*10^-3 moles of KMnO4. If we take these 20 mL and mix them i...

nicolely2F

To solve this problem, we'll be using \lambda*v = c and then Rydberg's equation v = \left (1/n_{2}^{2} - 1/n_{1}^{2}\right )*R . The info we have here is the wavelength and the initial level of the electron (n=1 since we know that the H atom emitted energy to reach a new energy level where \...

nicolely2F

They are different. "E" is the overall energy of the photon while "Ek" is the kinetic (movement) energy of that electron when it interacts with a photon.

nicolely2F

You can find that same sheet on the class webpage for Chem 14A. Scroll down and select "Constants, Equations, PT (useful for Chemistry, Physics, Biochemistry, Chem 14A/B, Chem 20A/B, etc.)"

nicolely2F

It's easier to use a 100g sample because we automatically translate the percentages into a mass in grams; there isn't a need to make a calculation. For example: an element X has a 17.8% mass composition. If you give me a 100g sample, I will immediately be able to tell that 17.8% of that sample is 17...

nicolely2F

They won't affect the balancing of the equation (i.e. knowing the state of matter or not, the coefficients we use will be the same), but mostly we're required to write them down for clarity and precision.

nicolely2F

The formula for nitric acid is HNO3. To answer this questions without doing any calculations, we can use our knowledge of atomic masses. We don't need exact numbers for this either, as long as you have a notion on the most common elements, some of which are H, N, and O. If you have some familiarity ...

nicolely2F

You might have problems in terms of numbering of questions, especially when handing in homework. I think it's better to get the 6th or 7th edition!

nicolely2F

It's negative because there is an energy loss. The atom loses energy when transitioning from one level to another that is closer to the nucleus.

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