Search found 35 matches

by Junxi Feng 3B
Fri Nov 15, 2019 3:52 pm
Forum: Dipole Moments
Topic: London forces
Replies: 9
Views: 37

Re: London forces

London forces exist among all the molecules, because the temporary dipole moment exist in all the molecules due to the random movement of electrons, and therefore it will interact with adjacent molecules.
by Junxi Feng 3B
Fri Nov 15, 2019 3:39 pm
Forum: Determining Molecular Shape (VSEPR)
Topic: Bent shape and angles
Replies: 6
Views: 27

Re: Bent shape and angles

Both VSEPR shape with the formula AX2E and AX2E2 have bent shape. What are the differences in their bond angles?

I think AX2E2 will have a lower bond angle, because the extra lone pair will create a large repulsion which will push the atoms closer to each other and thus a smaller bond angle.
by Junxi Feng 3B
Fri Nov 15, 2019 3:34 pm
Forum: Dipole Moments
Topic: 3f.1
Replies: 3
Views: 17

Re: 3f.1

Dipole-dipole usually exists between polar molecules. Thus, to determine, just draw out the lewis structure of the molecule and see if it's polar or not. To determine whether it's polar, you will need to find its dipole moment and its molecular shape.
by Junxi Feng 3B
Fri Nov 15, 2019 3:32 pm
Forum: Student Social/Study Group
Topic: Chemistry Youtube Channels
Replies: 8
Views: 42

Re: Chemistry Youtube Channels

I would recommend Khan Academy and Bozeman Science.
by Junxi Feng 3B
Fri Nov 15, 2019 3:31 pm
Forum: Polarisability of Anions, The Polarizing Power of Cations
Topic: Polarizing power vs polarizability
Replies: 5
Views: 17

Re: Polarizing power vs polarizability

Polarizing power describes the behavior of a cation pulling, or distorting, the electrons from an anion.
Polarizability describes the behavior of a anion's electrons being pulled towards the cation.
by Junxi Feng 3B
Fri Nov 15, 2019 3:28 pm
Forum: Determining Molecular Shape (VSEPR)
Topic: bond angles
Replies: 9
Views: 22

Re: bond angles

There can be multiple reasons for this. One, for example, is due to the presence of lone pairs that repel electrons from other atoms, making the bond angles lower. Two, it can be the number of electrons on an atom: like the examples in class today-- SO3 2- and NH3. Since O has more electrons than H,...
by Junxi Feng 3B
Fri Nov 15, 2019 3:22 pm
Forum: Student Social/Study Group
Topic: test 2
Replies: 3
Views: 20

Re: test 2

Everything we have learned so far. Good luck!
by Junxi Feng 3B
Fri Nov 15, 2019 3:21 pm
Forum: Determining Molecular Shape (VSEPR)
Topic: structure ?
Replies: 8
Views: 33

Re: structure ?

The best way to do that is simply draw out the lewis structure, count the number of surrounding atoms and lone pairs. And then hopefully you can recall what each shape of molecules should be like.
by Junxi Feng 3B
Fri Nov 15, 2019 3:19 pm
Forum: Interionic and Intermolecular Forces (Ion-Ion, Ion-Dipole, Dipole-Dipole, Dipole-Induced Dipole, Dispersion/Induced Dipole-Induced Dipole/London Forces, Hydrogen Bonding)
Topic: Why does SO2 molecules have dipole-dipole interations?
Replies: 4
Views: 13

Re: Why does SO2 molecules have dipole-dipole interations?

Most of the time, polar molecules will be the molecules with different different elements, such as SO2 in this case, H2O, HCl, and so on. But for the best way, you will have to draw out the lewis structure to determine, such as for CH4, you will have to draw it out to see that all its dipole moment ...
by Junxi Feng 3B
Fri Nov 15, 2019 3:09 pm
Forum: Resonance Structures
Topic: Contribution of each structure?
Replies: 4
Views: 23

Re: Contribution of each structure?

To see which resonance structure is more stable, just look their formal charges, the one closest to 0 will be the most stable. I am not sure what do you mean by which RS contributes more to the molecule, because the resonance structure is just the moving of electrons between different atoms of a mol...
by Junxi Feng 3B
Tue Nov 05, 2019 7:57 pm
Forum: Electronegativity
Topic: How to compare electronegativity difference
Replies: 2
Views: 33

How to compare electronegativity difference

For example, between CH4 and CF4, how do you know which one has a greater electronegativity difference by looking at the periodic table? Please be specific on how to get the answer.

What about PH3 and NH3; and SO2 and NO2?
by Junxi Feng 3B
Sat Nov 02, 2019 5:02 pm
Forum: Trends in The Periodic Table
Topic: How to compare the electronic affinity between two atoms
Replies: 2
Views: 25

How to compare the electronic affinity between two atoms

Can someone explain a general way to do so? I see lots of exceptions in electronic affinity.
Also, can someone answer this question?
Which has a higher electron affinity, chlorine (Cl) or Neon (Ne)

Thanks!
by Junxi Feng 3B
Fri Nov 01, 2019 12:49 pm
Forum: Bond Lengths & Energies
Topic: bond lengths
Replies: 10
Views: 43

Re: bond lengths

Obviously, they do not have the same length. Single bond has the longest bond length, and triple bond has the shortest bond length. This also has something to do with bond strength.
by Junxi Feng 3B
Fri Nov 01, 2019 12:46 pm
Forum: Electronegativity
Topic: Electronegativity
Replies: 11
Views: 41

Re: Electronegativity

Electronegativity is a measure of the tendency of an atom to attract a bonding pair of electrons. In the periodic table, it decreases down a group and increases across a period.
by Junxi Feng 3B
Fri Nov 01, 2019 12:41 pm
Forum: Electronegativity
Topic: Electronegativity on Test
Replies: 7
Views: 26

Re: Electronegativity on Test

We will not need to know how to calculate the electronegativity, but we need to know the trend of it in the periodic table. And we need to compare the relative electronegativity between different atoms.
by Junxi Feng 3B
Fri Nov 01, 2019 12:39 pm
Forum: Lewis Structures
Topic: Central atom
Replies: 6
Views: 18

Re: Central atom

The central atom is always the one with the least electronegativity. Also, central atom will be the one that has the most unpaired valence electrons. In most of the cases, it should be fairly easy to find the central atom, such as CO2, BF4, SO4., etc., apparently you cannot put oxygen or fluorine in...
by Junxi Feng 3B
Fri Nov 01, 2019 12:33 pm
Forum: Ionic & Covalent Bonds
Topic: Radicals
Replies: 9
Views: 42

Re: Radicals

Radicals have unpaired electrons. A rough guideline: any total electron number that cannot be divided by 2 is a radical. They are important because midterm or final will ask questions about radicals and they might relate to your future field of study. More practically speaking, radicals are highly r...
by Junxi Feng 3B
Fri Nov 01, 2019 12:29 pm
Forum: Ionic & Covalent Bonds
Topic: How does one find a most likely charge for ions for a given element?
Replies: 6
Views: 33

Re: How does one find a most likely charge for ions for a given element?

It depends on the valence electrons of the atom. For instance, if the atom has 6 valence electrons in its outer shell, it tends to gain 2 e- to form its most stable form, which means its ion will -2. With the same idea, if the atom has only 2 valence electrons, it tends to lose 2 e- and form ion wit...
by Junxi Feng 3B
Fri Oct 18, 2019 8:16 pm
Forum: Quantum Numbers and The H-Atom
Topic: 1D 13 Part A
Replies: 2
Views: 29

Re: 1D 13 Part A

By definition, l=0,1,....,n-1.
Since n=7, then l=0,1,2,3,4,5,6.
There are exactly 7 possible values for l.
by Junxi Feng 3B
Fri Oct 18, 2019 8:14 pm
Forum: Quantum Numbers and The H-Atom
Topic: Quantum vs Classical
Replies: 5
Views: 36

Re: Quantum vs Classical

I think classical mechanics describes the objects that are have a continuous movement--movements that are predictable, like a trajectory. But quantum mechanics study tiny particles like electrons, photons that we talked about in class. Theses particles are usually moving in unpredictable paths: say,...
by Junxi Feng 3B
Fri Oct 18, 2019 8:08 pm
Forum: Quantum Numbers and The H-Atom
Topic: Spectral Series
Replies: 3
Views: 30

Re: Spectral Series

Each series correspond to a different range of wavelengths. When you calculate the wavelength, just match it to the range of the series.
by Junxi Feng 3B
Fri Oct 18, 2019 8:05 pm
Forum: Wave Functions and s-, p-, d-, f- Orbitals
Topic: Geometric description of shell, subshell, and orbitals
Replies: 2
Views: 44

Geometric description of shell, subshell, and orbitals

How to think of the shell, sub-shell and orbitals geometrically? What do they look like if a picture of them is drawn?
by Junxi Feng 3B
Fri Oct 18, 2019 8:01 pm
Forum: Wave Functions and s-, p-, d-, f- Orbitals
Topic: Orbitals in relation to arrows
Replies: 10
Views: 62

Re: Orbitals in relation to arrows

The number of arrows is equal to the number of electrons an atom has. The first arrow you draw will always be pointing upwards, then the second one can either be up or down depending on the number of electrons.
by Junxi Feng 3B
Fri Oct 18, 2019 7:58 pm
Forum: Wave Functions and s-, p-, d-, f- Orbitals
Topic: quantum number n, l, m
Replies: 13
Views: 72

Re: quantum number n, l, m

n is the principal quantum number, which determines the energy and size of the electrons (also called the shell), and it can be any whole numbers such as 1,2,3....n; l is the angular momentum quantum number, which describes the shape of the electrons (also called the sub-shell), and it can be whole ...
by Junxi Feng 3B
Fri Oct 18, 2019 7:50 pm
Forum: Properties of Light
Topic: Equations and Constants
Replies: 6
Views: 40

Re: Equations and Constants

Most of the equations and constants will be given in the tests and exams, but the derivation equations are not given. Such as E= hc/wavelength, this is an important equation but not given directly in the formula sheet.
by Junxi Feng 3B
Thu Oct 10, 2019 11:46 am
Forum: Einstein Equation
Topic: Planack's constant
Replies: 8
Views: 87

Re: Planack's constant

The Planck's constant is used in the Einstein equation E=hv, where h is the Planck's constant and v is the frequency of the light. With the constant, we can calculate the energy per photon.
by Junxi Feng 3B
Thu Oct 10, 2019 11:42 am
Forum: Einstein Equation
Topic: 1B.9 HW
Replies: 2
Views: 44

Re: 1B.9 HW

I think the best way to solve the problem is dimensional analysis. First, multiply the time 2 sec to the 32W, and notice how the units of time cancel out each other, do the calculation and the result is simply 64 J. Now, use the given wavelength of violet light to find out the frequency by using the...
by Junxi Feng 3B
Thu Oct 10, 2019 11:28 am
Forum: Einstein Equation
Topic: Energy Problem
Replies: 4
Views: 53

Re: Energy Problem

To eject an electron from the surface of a metal, the incoming photo must have enough energy. Given the frequency, we can use the Einstein Equation E=hv to solve for energy E. Plug the frequency and the constant h, the resulting value will be the minimum energy required.
by Junxi Feng 3B
Thu Oct 10, 2019 10:51 am
Forum: Einstein Equation
Topic: Numbers to memorize [ENDORSED]
Replies: 37
Views: 996

Re: Numbers to memorize [ENDORSED]

The answer is no. The tests and exams will provide you with these numbers, because the point is not about whether you can memorize the numbers, but whether you understand the materials and are able to do the calculations.
by Junxi Feng 3B
Thu Oct 10, 2019 10:49 am
Forum: Properties of Light
Topic: Atomic Spectra
Replies: 7
Views: 58

Re: Atomic Spectra

Yes for both of the questions.
Going from n=6 to n=2 gives the purple light, from n= 5 to n=2 gives the blue, and so on. All these lights are in visible regions.
But going from n=2 to n=1 will give a even shorter wavelength, which is in the UV region.
by Junxi Feng 3B
Fri Sep 27, 2019 6:40 pm
Forum: Accuracy, Precision, Mole, Other Definitions
Topic: MOLARITY
Replies: 17
Views: 650

Re: MOLARITY

Molarity is number of moles per liter of solution. Molarity is important in experiments because it acts like the specific dosage that is needed in different reactions. Different molarity may result in different amount of products in a reaction.
by Junxi Feng 3B
Fri Sep 27, 2019 6:35 pm
Forum: Empirical & Molecular Formulas
Topic: Formulas
Replies: 10
Views: 737

Re: Formulas

First of all, I think the actual molecular mass of the compound must be given. And then you simply divide the actual molecular mass by the molecular mass of its empirical formula. The number you get will be the answer.
by Junxi Feng 3B
Fri Sep 27, 2019 6:31 pm
Forum: Significant Figures
Topic: How does Significant Figures work? [ENDORSED]
Replies: 12
Views: 121

How does Significant Figures work? [ENDORSED]

I don't remember how all the sig figs work... Can somebody explain it to me? Like if 1.25 multiply 3.1, how many sig figs should I keep? What about division?

Also, do I have to keep the sig figs for the problems in the homework?
by Junxi Feng 3B
Fri Sep 27, 2019 6:25 pm
Forum: Accuracy, Precision, Mole, Other Definitions
Topic: Stoichiometric reactions
Replies: 5
Views: 499

Re: Stoichiometric reactions

Just need to make sure that the coefficients of each element on both sides of the chemical equation is equivalent (or balanced).
by Junxi Feng 3B
Fri Sep 27, 2019 6:20 pm
Forum: Molarity, Solutions, Dilutions
Topic: Questions about Homework Problem G5
Replies: 3
Views: 76

Questions about Homework Problem G5

A student prepared a solution of sodium carbonate by adding 2.111 g of the solid to a 250.0-mL volumetric fl ask and adding water to the mark. Some of this solution was transferred to a buret. What volume of solution should the student transfer into a fl ask to obtain (a) 2.15 mmol Na+; (b) 4.98 mm...

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