Search found 40 matches

by Shutong Hou_3I
Thu Nov 14, 2019 11:52 am
Forum: Determining Molecular Shape (VSEPR)
Topic: 4.3 Draw the structures and name the shapes of the following molecules: (a) HCN; (b) CH2F2.
Replies: 4
Views: 98

Re: 4.3 Draw the structures and name the shapes of the following molecules: (a) HCN; (b) CH2F2.

How do you know that the two bonds with hydrogen are next to each other, versus across the molecule from each other? I think that it does't matter, and there are 2 reasons. 1) they are all single bonds, so arranging the hydrogen atoms next to each other or across from each other doesn't make differ...
by Shutong Hou_3I
Wed Nov 13, 2019 3:30 pm
Forum: Determining Molecular Shape (VSEPR)
Topic: Shape
Replies: 8
Views: 21

Re: Shape

Yes, because we are only trying to name the shape of molecules.
by Shutong Hou_3I
Wed Nov 13, 2019 3:24 pm
Forum: Determining Molecular Shape (VSEPR)
Topic: molecular shape
Replies: 5
Views: 20

Re: molecular shape

There are several general rules to help determine, and thus memorization is required. To determine the molecular shape, both lone pair electrons and bonding pair electrons need to be considered; professor Lavelle hasn't discussed this in lecture yet. However, to name the shape of the molecule, only ...
by Shutong Hou_3I
Wed Nov 13, 2019 3:16 pm
Forum: Determining Molecular Shape (VSEPR)
Topic: Methane VSEPR
Replies: 7
Views: 20

Re: Methane VSEPR

In order for the amount of repulsion to be minimized, the distance between bonding pair should be maximized, that is, keeping the bonding regions of electrons as far apart from each other as possible. Unlike Lewis structure that is 2-dimensional, VSEPR model is actually 3-D, allowing bonding regions...
by Shutong Hou_3I
Tue Nov 12, 2019 12:36 am
Forum: DeBroglie Equation
Topic: De Broglie Wavelength
Replies: 17
Views: 1026

Re: De Broglie Wavelength

De Broglie's wavelength equation applies to any moving particle with momentum so that the particle has wavelike properties, such as electrons, neutrons, and protons. However, only when the particle has extremely small mass would the wavelike property be noticeable.
by Shutong Hou_3I
Tue Nov 12, 2019 12:23 am
Forum: Quantum Numbers and The H-Atom
Topic: Rydberg equation
Replies: 7
Views: 27

Re: Rydberg equation

We are actually totally allowed to use the Rydberg equation, whereas using the (final - initial) form of the the Rydberg equation could give us a better understanding of the concept and therefore what we are doing. And I believe that using the form of equation recommended by professor Lavelle elimin...
by Shutong Hou_3I
Tue Nov 12, 2019 12:15 am
Forum: Quantum Numbers and The H-Atom
Topic: Orbital angular momentum
Replies: 3
Views: 25

Re: Orbital angular momentum

The angular momentum quantum number (l) describes the shape of the atomic orbital.
Allowed values: l = 0 (s-orbital), 1(p-orbital), 2(d-orbital), ..., n-1; each l is called a subshell.
by Shutong Hou_3I
Mon Nov 11, 2019 11:11 pm
Forum: Determining Molecular Shape (VSEPR)
Topic: central atoms
Replies: 7
Views: 23

Re: central atoms

According to the information I collected online, the first ionization energy of oxygen is 1313.94 kJ/mol and that of chlorine is 1251.19 kJ/mol. So the ionization energy of Cl is lower than that of oxygen, making Cl reasonable to be put as the central atom.
by Shutong Hou_3I
Mon Nov 11, 2019 10:58 pm
Forum: Determining Molecular Shape (VSEPR)
Topic: Difference Between Lewis Structure and VSEPR Model
Replies: 3
Views: 12

Re: Difference Between Lewis Structure and VSEPR Model

Lewis structure clearly shows number of atoms, valence electrons, and types of bonds in a simple way. However, unlike the VSEPR model, Lewis structure doesn't represent the shape of the molecule or bond angles.
by Shutong Hou_3I
Mon Nov 11, 2019 10:52 pm
Forum: Determining Molecular Shape (VSEPR)
Topic: Hydrogen Bonding
Replies: 3
Views: 12

Re: Hydrogen Bonding

When a compound melts, it goes from solid to liquid, increasing the distance between molecules. Hydrogen bonding is a strong intermolecular force, so with hydrogen bonding, increasing the distance between molecules within a compound is harder, requiring more energy, thereby resulting in a higher mel...
by Shutong Hou_3I
Sun Nov 03, 2019 5:32 pm
Forum: Bond Lengths & Energies
Topic: HW: 2D Q5c
Replies: 2
Views: 12

Re: HW: 2D Q5c

The electronegativity of O is greater than that of S, because they have the same number of valence electrons, but O has more effective nuclear charge, because O has more protons, therefore more positive charges, in the nucleus.
by Shutong Hou_3I
Sun Nov 03, 2019 4:27 pm
Forum: Octet Exceptions
Topic: 2C.3
Replies: 3
Views: 33

Re: 2C.3

The most favorable structure should be the one with 0 formal charges on each atom. If it is impossible to have each atom with 0 formal charge, then the atoms with negative formal charge should be the ones with greatest electronegativity.
by Shutong Hou_3I
Sun Nov 03, 2019 9:20 am
Forum: Polarisability of Anions, The Polarizing Power of Cations
Topic: Polarizable vs Polarizing
Replies: 6
Views: 36

Re: Polarizable vs Polarizing

Since in forming covalent bonds, electrons are shared between neighboring atoms, an increase in covalent character means that even though in forming ionic bonds, electrons from the less electronegative atom are taken by the more electronegative atom, the less electronegative atom would actually attr...
by Shutong Hou_3I
Sun Nov 03, 2019 9:04 am
Forum: Dipole Moments
Topic: Dipole Moments
Replies: 3
Views: 19

Re: Dipole Moments

The difference in electronegativity between neighboring atoms leads to difference in charge, which generates an electric field and could be measured.
dipole moment = charge * distance between atoms (bond length)
by Shutong Hou_3I
Sun Nov 03, 2019 1:03 am
Forum: Formal Charge and Oxidation Numbers
Topic: Formal charge equation
Replies: 3
Views: 12

Re: Formal charge equation

Yes, it works, because it is actually equivalent to the formal formula, numerically. As long as not written formally in exams, I think that using this equation instead is much faster in calculation and harder to make mistakes.
by Shutong Hou_3I
Sun Nov 03, 2019 12:19 am
Forum: Ionic & Covalent Bonds
Topic: Bond Strength
Replies: 3
Views: 18

Re: Bond Strength

Indeed, F has greater electronegativity than Cl. I think it is because of greater electronegativity, electrons are pulled to F by a greater electrostatic force than to Cl.
by Shutong Hou_3I
Fri Oct 25, 2019 11:26 am
Forum: Ionic & Covalent Bonds
Topic: Isoelectronic Atoms
Replies: 6
Views: 37

Re: Isoelectronic Atoms

Being isoelectronic elements means that they have the same number of valence electrons. However, this doesn't mean that they have similar chemical properties, partially because they have different nuclear charges. I think that when mentioning isoelectronic, the elements aren't in the state of atom. ...
by Shutong Hou_3I
Fri Oct 25, 2019 11:12 am
Forum: Resonance Structures
Topic: Formal Charge
Replies: 13
Views: 454

Re: Formal Charge

Yes, it matters. The most ideal situation is to have 0 formal charges on each atom. If it cannot be 0, then it is best to have the least absolute sum value of formal charges with the most negative on the most electronegative element.
by Shutong Hou_3I
Thu Oct 24, 2019 8:50 pm
Forum: Ionic & Covalent Bonds
Topic: octet rule
Replies: 6
Views: 83

Re: octet rule

There are many exceptions to the octet rule. The octet rule works mainly well for elements in the first three periods, because they don't have d-orbitals. Since the 4th period, the electron cloud become relatively big (having d-orbitals), therefore allowing electrons more than eight as valence elect...
by Shutong Hou_3I
Thu Oct 24, 2019 8:28 pm
Forum: Trends in The Periodic Table
Topic: blocks
Replies: 13
Views: 68

Re: blocks

I think that remembering that s is on the left, p is on the right, d is in the middle, and f is at the bottom would be enough for this course. And remember that f-block is actually inserted in the 6th and 7th period, between s-block and d-block.
by Shutong Hou_3I
Thu Oct 24, 2019 8:19 pm
Forum: Trends in The Periodic Table
Topic: bond length
Replies: 9
Views: 50

Re: bond length

I believe that we don't need to know how to calculate bond length throughout chem 14A. However, I think it is necessary to know that the bond length of triple bond is shorted than double bond, which is shorter than single bond. There are three pairs of shared electrons in triple bond, so the forces ...
by Shutong Hou_3I
Thu Oct 24, 2019 8:01 pm
Forum: Trends in The Periodic Table
Topic: Effective Nuclear Charge
Replies: 5
Views: 37

Re: Effective Nuclear Charge

Because the inner electrons shield outer electrons from electrostatic attraction of the positive nucleus, the outer electrons feel a reduced electrostatic attraction, resulting in an effective nuclear charge. In my opinion, the larger the effective nuclear charge, the higher the first ionization ene...
by Shutong Hou_3I
Sun Oct 20, 2019 12:08 am
Forum: Trends in The Periodic Table
Topic: Electronegativity vs. Electron Affinity?
Replies: 11
Views: 378

Re: Electronegativity vs. Electron Affinity?

If an element has a high electronegativity, does that mean it has higher electron affinity? I believe so because for one of our practice questions, the answer was something along the lines "If an element has a high ionization energy and a higher electron affinity, it is also highly electronega...
by Shutong Hou_3I
Sat Oct 19, 2019 11:56 pm
Forum: Wave Functions and s-, p-, d-, f- Orbitals
Topic: Inner e- and Outer e-
Replies: 14
Views: 65

Re: Inner e- and Outer e-

The following sentence is actually a quote that well explains the reasons that lead to difference between inner and outer electrons from professor Lavelle's ppt: "Since inner electrons shield outer electrons from electrostatic attraction of positive nucleus, outer electrons feel a reduced elect...
by Shutong Hou_3I
Sat Oct 19, 2019 11:42 pm
Forum: Wave Functions and s-, p-, d-, f- Orbitals
Topic: Shell, Subshell, Orbital Terminology
Replies: 8
Views: 66

Re: Shell, Subshell, Orbital Terminology

Thanks a lot for your clarification for these clarification of terminologies. I have been confused by these terms while reading questions to solve for days.
by Shutong Hou_3I
Sat Oct 19, 2019 11:37 pm
Forum: Wave Functions and s-, p-, d-, f- Orbitals
Topic: Nodal Planes
Replies: 6
Views: 24

Re: Nodal Planes

Nodal plane means that the wave function = 0, meaning that the probability of finding electrons in that plane is zero. I am not sure about why s-orbitals don't have nodal plane, but I think that it is because there is no node when depicting the math model of the s-orbital.
by Shutong Hou_3I
Sat Oct 19, 2019 11:27 pm
Forum: Properties of Light
Topic: 1A.9 Energy of Photon
Replies: 12
Views: 68

Re: 1A.9 Energy of Photon

In finding the energy of photons, we generally consider E = (Plank's constant) * (frequency) as the key equation. However, the equation c = (wavelength) * (frequency) is also important in a way that sometimes we only know the wavelength, rather than the expected frequency of photons. By utilizing E ...
by Shutong Hou_3I
Fri Oct 18, 2019 4:29 pm
Forum: Heisenberg Indeterminacy (Uncertainty) Equation
Topic: General question 1B.27
Replies: 4
Views: 27

Re: General question 1B.27

± 5.00 m*s^-1 means that the uncertainty (the range of possible values of speed) in speed is 5.00 m*s^-1, rather than that the speed is really positive or, unreasonably, negative.
by Shutong Hou_3I
Fri Oct 11, 2019 12:04 pm
Forum: Photoelectric Effect
Topic: Photoelectric Effect Intensity of Light
Replies: 7
Views: 41

Re: Photoelectric Effect Intensity of Light

When the experiment changed the intensity of the light on the metal, the frequency didn't increase. When the intensity of light increases, the number of photons per unit of area increase.
by Shutong Hou_3I
Fri Oct 11, 2019 11:35 am
Forum: Properties of Electrons
Topic: Kinetic Energy
Replies: 4
Views: 43

Re: Kinetic Energy

Yes, the kinetic energy does increase if we were to increase the frequency. In solving photoelectric effect problem, we generally don't directly use this equation (Ek = (1/2) Me- * Ve-^2) to get the kinetic energy, probably because the Ve is hard to directly measure and thus unknown to us in problem...
by Shutong Hou_3I
Fri Oct 11, 2019 11:17 am
Forum: Properties of Electrons
Topic: Energy Levels
Replies: 8
Views: 47

Re: Energy Levels

When an electron drops two energy levels, only one photon will be released, but the photon would have more energy than that released from an electron dropping one energy level. In the photoelectric effect, electrons exhibit properties of one sort of particles called photons. When thinking this way, ...
by Shutong Hou_3I
Fri Oct 11, 2019 11:05 am
Forum: Properties of Electrons
Topic: Polar vs Non polar
Replies: 15
Views: 592

Re: Polar vs Non polar

If the electronegativity difference between two atoms is large, the molecular formed by the two atoms would be polar; if he difference is subtle or zero, then the molecule is nonpolar. If the molecule is a long chain composed of many (mostly four or more) carbons and hydrogens, as well as very few (...
by Shutong Hou_3I
Fri Oct 11, 2019 10:48 am
Forum: Properties of Light
Topic: Waves/Particles
Replies: 14
Views: 103

Re: Waves/Particles

It is actually light that has wave-particle duality, rather than photons. Instead, photons are used to represent the particle properties of light.
by Shutong Hou_3I
Fri Oct 11, 2019 10:24 am
Forum: Properties of Light
Topic: Converting units
Replies: 8
Views: 30

Re: Converting units

To convert length units, we could always use meter (m) as the basic reference, that is, we could convert any unit into meter (m) first. Generally, we remember the meaning of the prefix of length units by remembering that adding the prefix means meter (m) multiplied by x power to 10. Specifically in ...
by Shutong Hou_3I
Wed Oct 02, 2019 9:43 pm
Forum: Properties of Light
Topic: Speed of Light
Replies: 41
Views: 745

Re: Speed of Light

The speed of light is constant in vacuum, and the speed is 3*10^8 m*s^-1, which would also be generally used in solving general problems. However, the speed would actually be a little bit slower when there is air, whereas we generally ignore this difference between the idea and the fact in our calcu...
by Shutong Hou_3I
Wed Oct 02, 2019 9:34 pm
Forum: SI Units, Unit Conversions
Topic: Units
Replies: 5
Views: 71

Re: Units

According to today's lecture: PREFIX. NAME Meaning G giga 10^9 M mega 10^6 k kilo 10^3 d deci 10^-1 c centi 10^-2 m milli 10^-3 u (it's Greek) micro 10^-6 n nano 10^-9 p pico 10^-12
by Shutong Hou_3I
Wed Oct 02, 2019 8:29 pm
Forum: Empirical & Molecular Formulas
Topic: 5 Homework Problems Due
Replies: 21
Views: 183

Re: 5 Homework Problems Due

I was confused with the same thing as you are. However, after consideration and careful reading, I think we could select any five questions to answer for the weekly homework. There are three main reasons for me to think this way. First, I have carefully read the syllabus, and it occurs to me that it...
by Shutong Hou_3I
Wed Oct 02, 2019 8:18 pm
Forum: Molarity, Solutions, Dilutions
Topic: Question on E27
Replies: 4
Views: 34

Re: Question on E27

For this question, we should calculate the mass of one mole of water in grams first, because the only information, known to us, about water's mass is water's molar mass (because we know the molar mass of hydrogen and oxygen). Second, we should divide the mass of one mole of water, in grams, by Avoga...
by Shutong Hou_3I
Wed Oct 02, 2019 8:06 pm
Forum: Accuracy, Precision, Mole, Other Definitions
Topic: E.7 calculate atoms in moles
Replies: 4
Views: 32

Re: E.7 calculate atoms in moles

1 mole is the number of atoms in 12 grams of carbon 12, which equals 6.022 * 10^23 (Avogadro constant).
Specifically for this question, I think that it could be solved by dividing the number of carbon atoms by Avogadro constant, according to the definition of 1 mole.
by Shutong Hou_3I
Wed Oct 02, 2019 7:54 pm
Forum: General Science Questions
Topic: Rusty on High School Chem [ENDORSED]
Replies: 166
Views: 100747

Re: Rusty on High School Chem [ENDORSED]

I took my AP chemistry class as a senior in my senior high, and I'm a freshman now, so study techniques for chemistry is still fresh for me. Personally, I would recommend the strategy that keeping asking "why", especially when the professor is introducing a new concept or explaining how to...

Go to advanced search