Search found 39 matches

by Brian J Cheng 1A
Sun Nov 17, 2019 5:35 pm
Forum: Determining Molecular Shape (VSEPR)
Topic: Preferential
Replies: 3
Views: 27

Re: Preferential

Molecular shape is based on the arrangement of atoms and areas of electron density. Higher or lower Ionization Energies or Electronegativities of atoms will not affect structure.
by Brian J Cheng 1A
Sun Nov 17, 2019 5:31 pm
Forum: Dipole Moments
Topic: Polarity
Replies: 7
Views: 27

Re: Polarity

It's a symmetric molecule and has even distributions of electron density; thus, it is nonpolar.
by Brian J Cheng 1A
Sun Nov 17, 2019 5:29 pm
Forum: Determining Molecular Shape (VSEPR)
Topic: Do we have to memorize the names of shapes and/or the bond angles?
Replies: 7
Views: 26

Re: Do we have to memorize the names of shapes and/or the bond angles?

Yes, we need to memorize the names of the molecular shapes and the rough bond angles. I.e. trigonal planar = shape. 120 degrees = bond angle. OR i.e. trigonal pyramidal = shape, < 109.5 degrees = angle.
by Brian J Cheng 1A
Sun Nov 17, 2019 5:23 pm
Forum: Determining Molecular Shape (VSEPR)
Topic: 2E.13
Replies: 1
Views: 9

Re: 2E.13

I would try to visualize this in 3 dimensions. If there were no lone pairs, the molecule would have a trigonal bipyramidal shape with 180 degree bond angle through the axis and 120 degrees equatorial. But because there are 3 lone pairs, you remove the three equatorial atoms, causing enough repulsion...
by Brian J Cheng 1A
Sun Nov 17, 2019 5:20 pm
Forum: Student Social/Study Group
Topic: test 2
Replies: 8
Views: 31

Re: test 2

50
by Brian J Cheng 1A
Sun Nov 17, 2019 5:19 pm
Forum: SI Units, Unit Conversions
Topic: Memorizing Conversions
Replies: 23
Views: 124

Re: Memorizing Conversions

It's great to memorize the general conversion factors. pm (picometers, 10^-12) and nm (nanometers, 10^-9) are given but it's great to have a handle on the other prefixes in case they pop up in questions.
by Brian J Cheng 1A
Mon Nov 11, 2019 2:52 pm
Forum: Student Social/Study Group
Topic: Post All Chemistry Jokes Here
Replies: 7606
Views: 1018857

Re: Post All Chemistry Jokes Here

An excited electron in this sense may be deadly
by Brian J Cheng 1A
Sun Nov 03, 2019 10:43 pm
Forum: Formal Charge and Oxidation Numbers
Topic: How to know where a double bond should go?
Replies: 10
Views: 49

Re: How to know where a double bond should go?

Check the atoms' octets as well as the formal charge. More electronegative atoms would prefer negative formal charges and thus form more stable structures if this is accomplished via bond rearrangement.
by Brian J Cheng 1A
Sun Nov 03, 2019 10:30 pm
Forum: Electron Configurations for Multi-Electron Atoms
Topic: Electron configuration for D block
Replies: 3
Views: 20

Re: Electron configuration for D block

Venus is correct. But in any case, the 4s orbitals fill first before the 3d orbitals. In copper and chromium, the pre-existing electron from 4s2 fills up a spot in the lower energy 3d5 and 3d10 orbitals, resulting in 4s1 configuration.
by Brian J Cheng 1A
Sun Nov 03, 2019 10:27 pm
Forum: Quantum Numbers and The H-Atom
Topic: Ms and ML
Replies: 6
Views: 28

Re: Ms and ML

Not really sure why ms has -1/2 and +1/2 specifically but the positive and negative values are there to represent opposite electron spins.
by Brian J Cheng 1A
Sun Nov 03, 2019 10:25 pm
Forum: Electron Configurations for Multi-Electron Atoms
Topic: Electron configuration for D block
Replies: 3
Views: 20

Re: Electron configuration for D block

The empty 3d block is higher in energy than the 4s block. Because electrons fill up lower energy shells first, the 4s fills before the 3d orbitals. But once one electron is present in the 3d orbitals, it drops to a lower energy than the 4s. This is why an atom with filled 4s and 3d orbitals has 4s e...
by Brian J Cheng 1A
Sun Nov 03, 2019 10:21 pm
Forum: Octet Exceptions
Topic: Expanded Valence Shells
Replies: 6
Views: 25

Re: Expanded Valence Shells

Theoretically speaking, all atoms in the 3rd energy level can break the octet rule because of their unused 3d orbitals that can accommodate extra electrons; however, in nature, only a few atoms consistently do this.
by Brian J Cheng 1A
Sun Nov 03, 2019 10:18 pm
Forum: Electronegativity
Topic: definitions
Replies: 8
Views: 51

Re: definitions

We will not need to know how to calculate the exact values in ionization energy or electronegativity; however, we will need to know what they mean and their respective periodic trends. We'll also need to know how they apply to bonding (i.e. the atom with the highest electronegativity prefers a negat...
by Brian J Cheng 1A
Sun Nov 03, 2019 10:16 pm
Forum: Quantum Numbers and The H-Atom
Topic: Formal names for each letter
Replies: 5
Views: 35

Re: Formal names for each letter

n = principal number
l = orbital angular momentum number
ml = magnetic number

I would just try and hard-code it into my mind. I don't think the full names of the quantum numbers matter very much though--I'm sure the graders will know what you mean if you just use n, l, ml, and ms.
by Brian J Cheng 1A
Sun Oct 27, 2019 5:21 pm
Forum: Trends in The Periodic Table
Topic: Ionization and Electron Affinity
Replies: 5
Views: 19

Re: Ionization and Electron Affinity

Adding on to the posts above, I find it helpful to remember the two separately by thinking of Electron Affinity (energy released when an element gains an electron) as the "affinity" or "attraction" that an elements have for an electron. This increases across a row and decreases d...
by Brian J Cheng 1A
Sun Oct 27, 2019 5:17 pm
Forum: Resonance Structures
Topic: Expanded Octets
Replies: 4
Views: 24

Re: Expanded Octets

Expanded octets (otherwise known as exceptions to the octet rule) exist starting with elements with 4s and 3d orbitals. Due to the nature and arrangement of orbitals, the 4s orbitals fill up before the 3d ones do. This allows additional electrons to be added into the empty 3d orbitals, allowing thes...
by Brian J Cheng 1A
Sun Oct 27, 2019 5:13 pm
Forum: Student Social/Study Group
Topic: Miderm Review
Replies: 10
Views: 83

Re: Miderm Review

I personally have not tried Sapling for myself yet, but I've heard some students are disappointed with what it offers. It's apparently just the same information you can find from the textbook and Dr. Lavelle's webpage. Still open to anything though! I'll give it a look and update my post if I find a...
by Brian J Cheng 1A
Sun Oct 27, 2019 5:11 pm
Forum: Formal Charge and Oxidation Numbers
Topic: Determining # for Formal Charge
Replies: 2
Views: 19

Re: Determining # for Formal Charge

Formal Charge for an element in a compound/molecule is calculated with this formula: FC = # of Valence electrons - (# of lone pair electrons + (#of shared electrons / 2) ) = V - (L + S/2). The S value refers to the # of shared electrons; i.e. the amount of electrons present in bonds. Remember that s...
by Brian J Cheng 1A
Sun Oct 27, 2019 5:03 pm
Forum: Student Social/Study Group
Topic: Study Tips
Replies: 50
Views: 344

Re: Study Tips

I would personally focus on exposing myself to as many problems as possible to get used to applying the information we've learned in lectures in multitudes of ways. External resources (Professor Lavelle's webpage, Youtube, Khanacademy) can help clarify information, but the true essence of understand...
by Brian J Cheng 1A
Sun Oct 27, 2019 4:56 pm
Forum: Resonance Structures
Topic: Bond lenghts.
Replies: 11
Views: 47

Re: Bond lenghts.

We haven't been taught how exactly to obtain measurements for bond lengths as of now. Professor Lavelle specified the different lengths to prove that double and triple bonds have higher attraction and thus shorter lengths than single bonds, and the bonds for resonance structures have lengths between...
by Brian J Cheng 1A
Sun Oct 27, 2019 4:52 pm
Forum: Ionic & Covalent Bonds
Topic: Valence Electrons
Replies: 16
Views: 68

Re: Valence Electrons

Valence electrons of a specific element are based on the position the element is inside its period (row). For example, Oxygen is the 6th element in its period (not counting elements in d and f blocks), which means it has 6 valence electrons. Chlorine is the 7th element in its period so it has 7 vale...
by Brian J Cheng 1A
Sat Oct 19, 2019 11:23 pm
Forum: Wave Functions and s-, p-, d-, f- Orbitals
Topic: 1D.17
Replies: 1
Views: 10

Re: 1D.17

Question: 1D.15: What are the principal and orbital angular momentum quantum numbers for each of the following orbitals:(a)6p,(b)3d,(c)2p,(d)5f?

principal # n = energy level
Angular momentum # l = 0,1,2,3,.... n-1

a) 6p: n = 6, l = 1
b) 3d: n = 3, l = 2
c) 2p: n = 2, l = 1
d) 5f: n = 5, l = 3
by Brian J Cheng 1A
Sat Oct 19, 2019 11:18 pm
Forum: Quantum Numbers and The H-Atom
Topic: 1D.19
Replies: 6
Views: 32

Re: 1D.19

Below always holds true:
s: 1 orbital
p: 3 orbitals
d: 5 orbitals
f: 7 orbitals
g: 9 orbitals
by Brian J Cheng 1A
Sat Oct 19, 2019 11:16 pm
Forum: Accuracy, Precision, Mole, Other Definitions
Topic: Unit for Avogadro's Number
Replies: 10
Views: 77

Re: Unit for Avogadro's Number

Avogadro's number is used to convert mols to virtually any unit. Think of it as the number of "something" in one mole of this "something". It can be the amount of atoms in 1 mole of atoms, or even the amount of jelly beans in one mole of jelly beans.
by Brian J Cheng 1A
Sat Oct 19, 2019 11:09 pm
Forum: Wave Functions and s-, p-, d-, f- Orbitals
Topic: Inner e- and Outer e-
Replies: 14
Views: 69

Re: Inner e- and Outer e-

Just another reimagining of the same story: The different positions of the electrons cause electrons closer to the nucleus to "shield" outer electrons from the nucleus' attractive forces. This affects the energy needed to use electrons in bonding or to remove electrons entirely. For atoms ...
by Brian J Cheng 1A
Sat Oct 19, 2019 11:06 pm
Forum: Properties of Light
Topic: Homework due Next Week
Replies: 9
Views: 67

Re: Homework due Next Week

Yes, this should be the correct homework.
by Brian J Cheng 1A
Sat Oct 19, 2019 11:05 pm
Forum: General Science Questions
Topic: Tests
Replies: 9
Views: 55

Re: Tests

It would be great to memorize them! There are a few that are used extensively in life-science applications, and it would be wonderful in my opinion to streamline our calculations by committing some of these prefixes to memory.
by Brian J Cheng 1A
Sat Oct 19, 2019 10:54 pm
Forum: Student Social/Study Group
Topic: Post All Chemistry Jokes Here
Replies: 7606
Views: 1018857

Re: Post All Chemistry Jokes Here

Here's a good one:

What is the chemical formula of coffee?

CoFe2
by Brian J Cheng 1A
Sat Oct 12, 2019 10:05 pm
Forum: Properties of Light
Topic: Speed of Light
Replies: 41
Views: 785

Re: Speed of Light

For the purpose of this class we'll assume the speed of light (c) to be roughly 3.00 x 10^8 m/s. Light travels at different speeds through different mediums, but we'll use the vacuum measurement for our calculations
by Brian J Cheng 1A
Sat Oct 12, 2019 6:51 pm
Forum: Properties of Light
Topic: Balmer vs Lyman series
Replies: 4
Views: 42

Re: Balmer vs Lyman series

The respective series form because the electron absorption "pathways" all have the lowest energy level (n) involved. For the Lyman series n=1, and the Balmer series has electrons starting from n=2.
by Brian J Cheng 1A
Sat Oct 12, 2019 6:44 pm
Forum: SI Units, Unit Conversions
Topic: Weekly Posts
Replies: 7
Views: 49

Re: Weekly Posts

Before Sunday would be best.
by Brian J Cheng 1A
Fri Oct 11, 2019 11:55 pm
Forum: Significant Figures
Topic: Sig Figs
Replies: 5
Views: 41

Re: Sig Figs

If you wanted to be really precise, I would suggest not rounding until the very end. However, I've found that rounding from time-to-time within the calculations don't make that much of a difference, so make of it what you will.
by Brian J Cheng 1A
Sun Oct 06, 2019 10:52 am
Forum: Student Social/Study Group
Topic: Post All Chemistry Jokes Here
Replies: 7606
Views: 1018857

Re: Post All Chemistry Jokes Here

Friend: What's H2O?

Me: Water.

Friend: Ok, what's 100000000000000000000000000000000000H2O?

Me: IDK, a flood??
by Brian J Cheng 1A
Sat Oct 05, 2019 10:55 am
Forum: Properties of Light
Topic: "n" variable
Replies: 3
Views: 33

Re: "n" variable

"n" refers to the energy level of a particular electron. Because energy is "quantized" at the quantum level, electrons can only exist in specific energy values, hence "n" being limited to 1, 2, 3, etc etc.
by Brian J Cheng 1A
Sat Oct 05, 2019 10:53 am
Forum: Student Social/Study Group
Topic: Study Group Fall 2019
Replies: 32
Views: 296

Re: Study Group Fall 2019

Yes please! Thank you so much for this! I'm fully onboard with this idea.
by Brian J Cheng 1A
Fri Oct 04, 2019 9:18 am
Forum: Accuracy, Precision, Mole, Other Definitions
Topic: Formula Units
Replies: 4
Views: 48

Re: Formula Units

A google search told me that "formula units" is equal to the number of molecules of that specific compound present. I would use the same method as finding the amount of atoms (1 mol == 6.022 x 10^23 atoms or formula units). Please correct me if I'm wrong, thanks!
by Brian J Cheng 1A
Fri Oct 04, 2019 9:15 am
Forum: SI Units, Unit Conversions
Topic: Homework
Replies: 9
Views: 120

Re: Homework

I wrote mine in pencil; I might catch calculation errors in my work, so erasing my writing from time to time is always welcome :)
by Brian J Cheng 1A
Fri Oct 04, 2019 9:13 am
Forum: General Science Questions
Topic: Rusty on High School Chem [ENDORSED]
Replies: 166
Views: 100968

Re: Rusty on High School Chem [ENDORSED]

Same here! I haven't taken Chemistry in a few years, but Lavelle's modules and Fundamentals reviews really help out in making the information come back to me! I suppose if we read ahead periodically and used his office hours/external resources, we would all do well :) Good luck to all of us!
by Brian J Cheng 1A
Sun Sep 29, 2019 9:24 am
Forum: Administrative Questions and Class Announcements
Topic: Advice from a Medical Student - Part II [ENDORSED]
Replies: 117
Views: 1704

Re: Advice from a Medical Student - Part II [ENDORSED]

Thank you for sharing your experiences--it was amazing to hear about what to expect from med school and beyond! Highly looking forward to Dr. Lavelle's classes! Did you have your mind set on a medical occupation from the start, or would there be an alternate universe where you would pursue something...

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