Search found 34 matches

by Beverly Shih 1K
Mon Jun 04, 2018 4:38 pm
Forum: Hybridization
Topic: Meaning of hybridization
Replies: 2
Views: 94

Re: Meaning of hybridization

Carbon with its unhybridized atomic orbitals can only form 2 bonds because it only has 2 unpaired electrons (unpaired electrons are necessary to form bonds; just having an empty orbital doesn't let an atom form a bond). The overall purpose of hybridization is to lower the energy of the molecule over...
by Beverly Shih 1K
Mon Jun 04, 2018 4:27 pm
Forum: Bond Lengths & Energies
Topic: Ionic Character
Replies: 3
Views: 237

Re: Ionic Character

To respond to the two replies above, the first person is correct that a greater difference in electronegativities causes a greater ionic character. In the case of NaBr vs NaI, Na has a low electronegativity, I has a high electronegativity, and Br has an even higher electronegativity. Therefore, NaBr...
by Beverly Shih 1K
Mon Jun 04, 2018 4:15 pm
Forum: Hybridization
Topic: Why # regions of e density= # atomic orbitals?
Replies: 3
Views: 76

Re: Why # regions of e density= # atomic orbitals?

The 4 hybrid orbitals (sp3) is just one example of how orbitals can hybridize. In a molecule like HCONH2, the carbon actually has 3 hybrid orbitals (sp2) because it has a single bond with hydrogen, a single bond with nitrogen, and a double bond with oxygen. In the double bond with oxygen, the sigma ...
by Beverly Shih 1K
Thu May 31, 2018 5:56 pm
Forum: Hybridization
Topic: Hybridization
Replies: 2
Views: 72

Re: Hybridization

Hybridization has to occur for an atom to have the correct number of hybridized orbitals to make the correct number of bonds in a molecule. For example, carbon as an atom has a full 2s orbital, two 2p orbitals with unpaired electrons, and one empty 2p orbital. Therefore, it has 2 unpaired electrons ...
by Beverly Shih 1K
Thu May 31, 2018 5:53 pm
Forum: Determining Molecular Shape (VSEPR)
Topic: HW Question 4.25
Replies: 1
Views: 47

Re: HW Question 4.25

A molecule is polar if it has one or more polar bonds with dipoles that don't cancel. From the Lewis structure, you can infer that the C-Cl bonds are polar, but you can't determine if the dipoles cancel out until you determine the molecular shape. CH2Cl2 has the formula AX4, so it has a tetrahedral ...
by Beverly Shih 1K
Thu May 31, 2018 5:46 pm
Forum: Hybridization
Topic: sp^3 orbitals
Replies: 3
Views: 84

Re: sp^3 orbitals

I agree with Nabila--empty orbitals can't form bonds, unpaired electrons in 2p3 orbitals form sigma bonds. You might be thinking about unhybridized p-orbitals, which form pi bonds.
by Beverly Shih 1K
Thu May 31, 2018 5:42 pm
Forum: Hybridization
Topic: Why # regions of e density= # atomic orbitals?
Replies: 3
Views: 76

Re: Why # regions of e density= # atomic orbitals?

I think what you're referring to is the line from the lecture slide that "regions of e- density = number of hybrid orbitals". When hybridization occurs, atomic orbitals are mixed to become hybridized orbitals and electrons are redistributed among the hybridized orbitals. For example, when ...
by Beverly Shih 1K
Fri May 25, 2018 10:24 pm
Forum: Lewis Structures
Topic: Why Resonance for SO2?
Replies: 3
Views: 210

Re: Why Resonance for SO2?

I thought that for structures to have resonance, they had to have the same energy level. Does this mean resonant structures can have different levels of energy?
by Beverly Shih 1K
Fri May 25, 2018 10:21 pm
Forum: Bond Lengths & Energies
Topic: bond length and charge
Replies: 3
Views: 189

Re: bond length and charge

Bond length is also related to bond strength. The stronger the bond, the shorter it is. Single bonds are longer than double bonds which are longer than triple bonds.
by Beverly Shih 1K
Fri May 25, 2018 10:14 pm
Forum: Determining Molecular Shape (VSEPR)
Topic: VSEPR
Replies: 3
Views: 83

Re: VSEPR

The number of bonds doesn't affect how you use the VSEPR model to draw molecular shapes. Single, double, and triple bonds are all treated as one region of electron density. Therefore, it doesn't matter which resonance structure you use to draw a molecular structure because you'll get the same result...
by Beverly Shih 1K
Sat May 19, 2018 11:25 pm
Forum: Formal Charge and Oxidation Numbers
Topic: Formal charge in (S2CO)2-
Replies: 3
Views: 454

Re: Formal charge in (S2CO)2-

I think you're right, that it would be preferable (lower energy) to put the formal charges of -1 both on sulfur atoms, instead of one on sulfur and one on oxygen. I think that's why there's a > sign pointing towards the structure with the formal charges on sulfur--it means that structure is preferre...
by Beverly Shih 1K
Sat May 19, 2018 11:13 pm
Forum: Ionic & Covalent Bonds
Topic: Bonds between 1.5 and 2 [ENDORSED]
Replies: 5
Views: 125

Re: Bonds between 1.5 and 2 [ENDORSED]

The numbers 1.5 and 2 are just guidelines. There are exceptions, like Mg-Cl bonds which have a difference in electronegativity of 1.85 but are ionic. For bonds between 1.5 and 2, it is just even harder to determine what type a bond is based solely on its electronegativity.
by Beverly Shih 1K
Sat May 19, 2018 11:09 pm
Forum: Dipole Moments
Topic: Meaning of an induced dipole
Replies: 3
Views: 147

Re: Meaning of an induced dipole

A dipole is a molecule with a positive charge on one end and a negative charge on the other. One example is H2O, which has a partial positive charge on the hydrogens and a partial negative charge on the oxygen. An induced dipole is when interactions between two molecules cause one or both of them to...
by Beverly Shih 1K
Thu May 10, 2018 3:17 pm
Forum: Bohr Frequency Condition, H-Atom , Atomic Spectroscopy
Topic: Relationship between Electromagnetic Radiation and Enrgy of the photon
Replies: 2
Views: 120

Re: Relationship between Electromagnetic Radiation and Enrgy of the photon

Correct me if I'm wrong, but I think electromagnetic radiation has to do with the wave-like properties of light, and photons have to do with the particle-like properties of light. You can still use properties of electromagnetic radiation (like frequency, wavelength) to calculate the energy of photon...
by Beverly Shih 1K
Thu May 10, 2018 3:04 pm
Forum: Trends in The Periodic Table
Topic: Relationship between Ionic Radius, Atomic RdiuIonization Enrgy, Electron Affinity
Replies: 3
Views: 173

Re: Relationship between Ionic Radius, Atomic RdiuIonization Enrgy, Electron Affinity

It's also important to remember that these are trends, not rules, so there are several exceptions that may break the patterns between them. For example, boron is to the right of beryllium in the periodic table, so its electron affinity is bigger but its ionization energy is smaller instead of larger...
by Beverly Shih 1K
Thu May 10, 2018 2:57 pm
Forum: Ionic & Covalent Bonds
Topic: Difference between anions and cations?
Replies: 3
Views: 90

Re: Difference between anions and cations?

I think you may have gotten mixed up about anions vs. cations. You're right that anions have a negative charge, but that's because they have gained an extra electron--remember that electrons have a negative charge so having extra electrons would make the atom more negative. Cations therefore have a ...
by Beverly Shih 1K
Fri May 04, 2018 1:38 pm
Forum: Trends in The Periodic Table
Topic: Removing the 2nd electron is always harder [ENDORSED]
Replies: 5
Views: 126

Re: Removing the 2nd electron is always harder [ENDORSED]

Removing the second electron is always harder because once you remove the first electron, the atom becomes a cation (positive charge) and will exert a greater electrostatic pull on its remaining electrons.
by Beverly Shih 1K
Fri May 04, 2018 1:16 pm
Forum: Properties of Electrons
Topic: Exciting Electrons
Replies: 2
Views: 184

Re: Exciting Electrons

When the electron goes from 1s to 2p, its principal quantum number (n) goes from 1 to 2, meaning it goes from the first shell to the second shell. The shell directly corresponds to the size of the orbital, so a higher value of n means a larger size of atom.
by Beverly Shih 1K
Fri May 04, 2018 1:14 pm
Forum: Properties of Light
Topic: Higher Work Function and Electron Velocity?
Replies: 1
Views: 69

Re: Higher Work Function and Electron Velocity?

The work function is how much energy it takes to remove an electron from a metal, and the velocity of the removed electron depends on how much energy is left after being removed. The equation that relates these two concepts is: Energy of photon - work function = kinetic energy of electron, and kinet...
by Beverly Shih 1K
Fri Apr 27, 2018 1:05 pm
Forum: Quantum Numbers and The H-Atom
Topic: Angular Momentum Quantum Numbers
Replies: 1
Views: 69

Re: Angular Momentum Quantum Numbers

You're right that the angular momentum quantum number describes shape. If l is 0, for example, the orbital is an s-orbital with a spherical shape. If l is 1, the orbital is a p-orbital. The n-1 is used to calculate what possible l values an orbital may have, based on its principal quantum number n. ...
by Beverly Shih 1K
Fri Apr 27, 2018 1:01 pm
Forum: Einstein Equation
Topic: Hw problem 1.59 [ENDORSED]
Replies: 3
Views: 204

Re: Hw problem 1.59 [ENDORSED]

You're right that you have to use E = hc/lambda. Plugging in the constants for h, c, and the given wavelength for lambda will give you the energy per photon. Then you multiply by the given number of photons to get the total energy produced.
by Beverly Shih 1K
Fri Apr 27, 2018 11:05 am
Forum: Properties of Light
Topic: Homework question 1.27 [ENDORSED]
Replies: 3
Views: 103

Re: Homework question 1.27 [ENDORSED]

Once you have the number of electrons emitted in 2 seconds, you can just divide that by Avogadro's constant to get the moles of electrons emitted in 2 seconds.
by Beverly Shih 1K
Wed Apr 25, 2018 11:29 pm
Forum: Einstein Equation
Topic: Difference Between Equations [ENDORSED]
Replies: 4
Views: 180

Re: Difference Between Equations [ENDORSED]

Yes, they are just different pathways to solve for the same thing based on what information you are given.
This is because frequency (v) and wavelength (lambda) have an inverse relationship where v = c/lambda. So the two equations for energy are equivalent.
by Beverly Shih 1K
Fri Apr 20, 2018 9:38 am
Forum: Properties of Light
Topic: units for frequency and wavelength [ENDORSED]
Replies: 9
Views: 192

Re: units for frequency and wavelength [ENDORSED]

I have seen questions that asked for both frequency and wavelengths, or just one. If you have one but not the other, it is easy enough to convert between frequency and wavelength using v = c/lambda, so it doesn't really matter which order you find them.
by Beverly Shih 1K
Fri Apr 20, 2018 9:35 am
Forum: Photoelectric Effect
Topic: 1.9
Replies: 6
Views: 130

Re: 1.9

I think what you calculated was actually frequency, not wavelength. In the equation E = hv, v stands for frequency so you would want to use E = hc/lambda and solve for lambda instead. A wavelength of 4.980x10^14 Hz seems more than reasonable. For reference, red light has a frequency of about 4.3x10^...
by Beverly Shih 1K
Fri Apr 20, 2018 9:28 am
Forum: Properties of Light
Topic: 1.3 Atomic Spectra- Rydberg's equation
Replies: 3
Views: 88

Re: 1.3 Atomic Spectra- Rydberg's equation

Rydberg's equation is derived from the equation we used in class (E = -hR / n^2) with the main difference that Rydberg's equation has two n values, n1 and n2, so it can be used as a shortcut when you calculate the energy needed or released when transitioning between two energy levels. E = -hR / n^2 ...
by Beverly Shih 1K
Sat Apr 14, 2018 3:54 pm
Forum: Bohr Frequency Condition, H-Atom , Atomic Spectroscopy
Topic: 1.3 Atomic Spectra- Spectral lines
Replies: 4
Views: 78

Re: 1.3 Atomic Spectra- Spectral lines

That's right. They also use different values for n1 (Balmer series uses n1 = 2, Lymer uses n1 = 1).
by Beverly Shih 1K
Sat Apr 14, 2018 2:26 pm
Forum: Bohr Frequency Condition, H-Atom , Atomic Spectroscopy
Topic: Line absorption spectrum vs. line emission spectrum [ENDORSED]
Replies: 1
Views: 39

Line absorption spectrum vs. line emission spectrum [ENDORSED]

What is the difference between a line absorption spectrum and line emission spectrum (if any), other than the fact that they measure light absorption vs. light emission? Would a line absorption spectrum for a particular element necessarily have the same wavelengths as its line emission spectrum?
by Beverly Shih 1K
Sat Apr 14, 2018 12:38 am
Forum: Photoelectric Effect
Topic: Post module quiz #25
Replies: 6
Views: 134

Re: Post module quiz #25

Option A contains v (frequency of light), but c is the speed of light, not the energy of light. Option B has to do with kinetic energy. Option C is the equation we used in class, relating the energy of an incoming photon to the threshold energy needed to eject an electron and the resulting kinetic e...
by Beverly Shih 1K
Sat Apr 14, 2018 12:22 am
Forum: Bohr Frequency Condition, H-Atom , Atomic Spectroscopy
Topic: 1.3 Atomic Spectra- Spectral lines
Replies: 4
Views: 78

Re: 1.3 Atomic Spectra- Spectral lines

n is used as a counting number, so it doesn't stand for anything in particular. It is just used to generate values of lambda. In the Balmer series, for example, the equation for lambda contains the variable n, which is specified to be 3, 4, and all whole numbers after that. That means for the first ...
by Beverly Shih 1K
Sat Apr 14, 2018 12:17 am
Forum: Properties of Light
Topic: Light frequency and photons [ENDORSED]
Replies: 2
Views: 56

Re: Light frequency and photons [ENDORSED]

Increasing the frequency of light increases the energy each photon has. Due to the equation E = h * v, when v (frequency of light) increases, E (energy per photon) increases proportionally.
by Beverly Shih 1K
Sat Apr 07, 2018 1:54 pm
Forum: Molarity, Solutions, Dilutions
Topic: HW G.25
Replies: 1
Views: 75

Re: HW G.25

You're right that just diluting a solution doesn't change the total number of solute molecules in the solution, so after diluting the solution 90 times there is the same number of solute molecules you started with. But the question asks how many solute molecules would be present in 10. mL of the fin...
by Beverly Shih 1K
Sat Apr 07, 2018 1:43 pm
Forum: Limiting Reactant Calculations
Topic: Video 3 Post- assessment
Replies: 1
Views: 74

Re: Video 3 Post- assessment

There was one partially confusing piece of information provided on that question that changed my answer the first time around--the molar mass provided for 3AgNO3 (169.88 g/mol) is for one mol of AgNO3, not 3. With that in mind: Find the moles of C6H9Cl3 by dividing its mass by mass per mole: 0.750g ...
by Beverly Shih 1K
Fri Apr 06, 2018 1:42 pm
Forum: Significant Figures
Topic: Questions F11
Replies: 4
Views: 178

Re: Questions F11

I was confused about this too. Since the mass percent compositions and mass of O2 are given to 3 sfs, wouldn't the answer have to have 3 sfs, not 4?

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