Search found 34 matches

by Brian Cook
Tue Jan 08, 2019 6:54 pm
Forum: Ideal Gases
Topic: Pressure units
Replies: 4
Views: 113

Re: Pressure units

I believe for Kp we use bars but for solving for anything using the equation Pv=nRT we use atmospheres. Hope this helps :)
by Brian Cook
Tue Jan 08, 2019 6:49 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: liquid vs aqueous
Replies: 2
Views: 30

Re: liquid vs aqueous

Aqueous means a substance is dissolved in water whereas liquid is a pure substance in its melted state. Hope this helps :)
by Brian Cook
Tue Jan 08, 2019 6:47 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: aqueous solutions
Replies: 2
Views: 26

Re: aqueous solutions

I think it depends on what state the water is in, if it's in a liquid state it can be disregarded and if it's in a gas state like vapor it should be included. This is what I figured from the homework in terms of finding the Kc constant since in lecture we were told to not include solids or liquids. ...
by Brian Cook
Sun Dec 09, 2018 9:29 pm
Forum: Determining Molecular Shape (VSEPR)
Topic: AX3E
Replies: 18
Views: 158

Re: AX3E

The shape is trigonal pyramidal and you base it off of the original tetrahedral shape, for once you remove a bond and add an electron pair to tetrahedral, it becomes trigonal pyramidal.
by Brian Cook
Sun Dec 09, 2018 9:28 pm
Forum: Determining Molecular Shape (VSEPR)
Topic: A.X.E.
Replies: 3
Views: 70

Re: A.X.E.

Lone pairs are included in the E part of the equation, for every lone pair you add an E. 2 Lone pairs is E2
by Brian Cook
Sun Dec 09, 2018 9:27 pm
Forum: Sigma & Pi Bonds
Topic: Amount of sigma bonds
Replies: 6
Views: 134

Re: Amount of sigma bonds

The other 2nd bond would have to be a pi bond since there can only be one sigma bond.
by Brian Cook
Sun Dec 02, 2018 3:38 pm
Forum: Shape, Structure, Coordination Number, Ligands
Topic: chelate
Replies: 4
Views: 45

Re: chelate

Also chelates can only form when the other atom in the initial ring is adjacent, so in a carbon ring the two ligands attached to the carbon ring must be the carbons next to each other or else there would be too much space and the extra ring won't form.
by Brian Cook
Sun Dec 02, 2018 3:31 pm
Forum: Shape, Structure, Coordination Number, Ligands
Topic: Oxidation number
Replies: 3
Views: 61

Re: Oxidation number

The sum of the oxidation numbers in atoms of a neutral compound is always 0, and the sum of the oxidation numbers in a polyatomic ion is equal to the ion's charge. So you would look at the charges of the individual atoms and that would be their oxidation numbers. Free elements, such as C by itself, ...
by Brian Cook
Mon Nov 26, 2018 9:17 pm
Forum: Hybridization
Topic: HW 2.59 Question
Replies: 2
Views: 41

Re: HW 2.59 Question

Hey Vana, so both C and O have 3 2SP^2 orbitals and one unhybridized p orbital. The 3 2SP^2 orbitals initially had 1 electron in each orbital but then they're filled up by each sigma bond, whereas the pi bond fills up the unhybridized p orbital. We know it's 2 in front since C and O are on the secon...
by Brian Cook
Wed Nov 21, 2018 8:31 pm
Forum: Determining Molecular Shape (VSEPR)
Topic: Bond angles for T-shaped, see-saw, and square pyramidal
Replies: 2
Views: 60

Re: Bond angles for T-shaped, see-saw, and square pyramidal

Yes, I believe that you're correct in that the lone pairs push the bonds slightly inward, and that the lone pair's don't have their own bond angles. For T-shaped I think we use <90 degrees as the bond angle because we can't say exactly how much it's pushed in, same with seesaw you would have <90 and...
by Brian Cook
Wed Nov 21, 2018 8:20 pm
Forum: Determining Molecular Shape (VSEPR)
Topic: Square planar shape
Replies: 1
Views: 29

Re: Square planar shape

Trigonal bipyramidal involves five regions of electron density whereas square planar involves six, so I used the octahedral shape as my starting point, and as you can see based off the model you can exchange the "top" and "bottom" atom bonds and make them lone pair electrons, whi...
by Brian Cook
Wed Nov 21, 2018 8:17 pm
Forum: Hybridization
Topic: Help with Confusion
Replies: 6
Views: 100

Re: Help with Confusion

Yeah I think the main concepts of Sigma and Pi bonds that we need to know are that Sigma bonds are always the single bonds where two orbitals overlap, where in Pi bonds it's 2 p orbitals overlapping. So a double bond would have one Sigma and one Pi bond. Also one should note that Pi bonds don't allo...
by Brian Cook
Mon Nov 19, 2018 1:48 pm
Forum: Student Social/Study Group
Topic: Post All Chemistry Jokes Here
Replies: 7337
Views: 802014

Re: Post All Chemistry Jokes Here

How do you post on Chemistry Community?
by Brian Cook
Fri Nov 16, 2018 5:28 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: H-Bonding
Replies: 8
Views: 117

Re: H-Bonding

Hydrogen bonds only form with F O and N because they all have very strong partial negative charges due to their electronegativity, which can also be seen when you look at their location on the periodic table. This allows molecules with H and any of those atoms to bond with the strong partial positiv...
by Brian Cook
Fri Nov 16, 2018 5:25 pm
Forum: Determining Molecular Shape (VSEPR)
Topic: Octahedral Shape
Replies: 4
Views: 59

Re: Octahedral Shape

XeF4 is in fact Square planar. It's VSEPR equation is AX4E2 because it has 4 bonding regions and 2 lone electron pairs. This formula will always yield the square planar shape.
by Brian Cook
Fri Nov 16, 2018 5:22 pm
Forum: Ionic & Covalent Bonds
Topic: Covalent Bond Strength
Replies: 3
Views: 62

Re: Covalent Bond Strength

I believe you are right that as a bond get's longer, it's of weaker strength. Do you have an example which said otherwise? Also note that a double bond would be stronger than a single bond.
by Brian Cook
Sun Nov 11, 2018 10:16 pm
Forum: Ionic & Covalent Bonds
Topic: Ionic Bonds with Covalent Character
Replies: 3
Views: 60

Re: Ionic Bonds with Covalent Character

Yeah, so the electron does't completely transfer to the other side. The positive Na side exerts an attractive force on the Cl electrons, which moves the electron cloud over but isn't a complete transfer of electrons. And that's why there is still some sharing or covalent character between the valenc...
by Brian Cook
Sun Nov 11, 2018 10:06 pm
Forum: Determining Molecular Shape (VSEPR)
Topic: Difference in models
Replies: 2
Views: 35

Re: Difference in models

Building on what Kyleigh has said, pay attention to the VSEPR formula which is based on the central atom, number of atoms sharing bonds, and number of lone pairs on central atom. Structures with the same formula will take on the same shape, so once you solve for one, you can assume that following st...
by Brian Cook
Sun Nov 11, 2018 10:03 pm
Forum: Ionic & Covalent Bonds
Topic: Differentiating between Covalent and Ionic
Replies: 3
Views: 45

Re: Differentiating between Covalent and Ionic

Atoms in covalent bonds are in a liquid or gas state at room temperature whereas atoms in ionic bonds are in a solid state at room temperature. Covalent bonds are low in polarity whereas Ionic bonds are high in polarity.
by Brian Cook
Wed Oct 31, 2018 12:45 am
Forum: Octet Exceptions
Topic: FC and Octet Exceptions
Replies: 1
Views: 52

Re: FC and Octet Exceptions

Using the correct number of e- is most important, then you work on filling the octets. Elements row 3 and below can occupy more electrons than the octet since they have a hidden d block. Then you focus on reducing the formal charges by looking at double bonds you can create and moving lone pairs aro...
by Brian Cook
Wed Oct 31, 2018 12:43 am
Forum: Lewis Structures
Topic: Exception to Octet Rule [ENDORSED]
Replies: 3
Views: 65

Re: Exception to Octet Rule [ENDORSED]

This is because elements in the 3d row and beyond have n=3 which means L can equal 0,1, and 2 (s,p,d). Elements in the 3rd row actually have access to the d block, allowing them to occupy more electrons, up to 10 more than the octet to be exact. Hope this helps :)
by Brian Cook
Wed Oct 31, 2018 12:39 am
Forum: Octet Exceptions
Topic: Octet Exceptions
Replies: 3
Views: 101

Re: Octet Exceptions

13th column, doesn't need complete octet

3rd row and below, can have up to 10 extra electrons in addition to octet

First 4 elements in periodic table don't have octets to complete

hope this helps :)
by Brian Cook
Wed Oct 31, 2018 12:38 am
Forum: Lewis Structures
Topic: Lewis Structures
Replies: 4
Views: 88

Re: Lewis Structures

Boron doesn't need a full octet because it's in the 13th column, and elements there have stable electron states already.
by Brian Cook
Sun Oct 21, 2018 6:22 pm
Forum: Quantum Numbers and The H-Atom
Topic: KJ/mol-->J
Replies: 1
Views: 36

Re: KJ/mol-->J

Divide the number by Avogadro's number to convert to Kj, then multiply by 1000 to convert to J. Hope this helps :).
by Brian Cook
Sun Oct 21, 2018 6:19 pm
Forum: Properties of Electrons
Topic: Atomic Spectra
Replies: 2
Views: 42

Re: Atomic Spectra

The Lyman series involves UV light, and thus it has a higher energy drop and moves all the way down to n=1, whereas Balmer series involves visible energy which is why it only moves to n=2, thus less energy involved as well.
by Brian Cook
Sun Oct 21, 2018 6:15 pm
Forum: Wave Functions and s-, p-, d-, f- Orbitals
Topic: Shape of Orbitals
Replies: 3
Views: 48

Re: Shape of Orbitals

I think we just need to know the basic shapes and understand the concepts. For doing a simple drawing, s is a sphere, p has the two balloons up and down, and d has 4 long balloons going north south east and west. I think you'll only need to know those three, and you can see that as the orbital numbe...
by Brian Cook
Sat Oct 13, 2018 7:49 pm
Forum: Administrative Questions and Class Announcements
Topic: Writing in Pen
Replies: 13
Views: 266

Re: Writing in Pen

I would say just practice by doing your homework in pen. Getting used to it now will help you in the long run I think. I use to only work in pencil, so I know how you feel, but I would say don't worry too much about making mistakes as you can always cross them out, and focus on solving the Chem prob...
by Brian Cook
Sat Oct 13, 2018 7:43 pm
Forum: Properties of Light
Topic: Wave vs. Photon
Replies: 2
Views: 38

Re: Wave vs. Photon

I think the important takeaway is that light has both the properties of a wave and a particle/photon, depending on the situation. The photoelectric experiment showed that light cannot eject electrons without the correct frequency, showing that it doesn't act like a wave, because if it always acted l...
by Brian Cook
Sat Oct 13, 2018 7:34 pm
Forum: Properties of Light
Topic: Rydberg Equation
Replies: 3
Views: 41

Re: Rydberg Equation

Let's say a question asks to find the wavelength of the electromagnetic radiation that is emitted from an electron which changes from n = 3 to n = 1. You would plug in the two ns' and then solve for wavelength. Sometimes the question would ask for the frequency, which you would have to solve for by ...
by Brian Cook
Sat Oct 06, 2018 7:22 pm
Forum: Limiting Reactant Calculations
Topic: Limiting Reactants M11
Replies: 2
Views: 63

Re: Limiting Reactants M11

Hey there, wow this was quite the question. So basically, you take the masses you are given of P4 and O2 and convert them to moles by dividing by their respective molar masses. You also compare the P4 moles to the O2 moles by multiplying the P4 moles by 3 since the ratio of P4 to O2 atoms is 1:3. Th...
by Brian Cook
Sat Oct 06, 2018 7:10 pm
Forum: Empirical & Molecular Formulas
Topic: homework problem E23
Replies: 2
Views: 54

Re: homework problem E23

Hi, I believe it is asking for the number of F- ions in moles, they textbook may have just stated the question in a confusing way. Hope this helps :)
by Brian Cook
Thu Oct 04, 2018 12:24 pm
Forum: Empirical & Molecular Formulas
Topic: Polyatomic Ions
Replies: 1
Views: 54

Re: Polyatomic Ions

I think over time we will get use to the most common polyatomic ions. Also if you consider the polyatomic ions that end in -ate as your main ones, different prefixes and suffixes will tell you the different number of oxygen atoms. Per___ate (1 more oxygen) , __ate (most common form), ___ite (1 less ...

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