Search found 25 matches

Fri Dec 08, 2017 9:21 am
Forum: Acidity & Basicity Constants and The Conjugate Seesaw
Topic: Relationship between pka, ka, and acidity strength
Replies: 5
Views: 7068

Re: Relationship between pka, ka, and acidity strength

A way to remember that acids are stronger when pKa is smaller is to remember that the smaller/lower the pH, the stronger an acid is. I think Dr. Lavelle mentioned this way to remember that the low pKa = strong acid relationship is similar to pH during lecture
Fri Dec 01, 2017 9:09 pm
Forum: Dipole Moments
Topic: Determining polar or non polar: 4.27
Replies: 2
Views: 404

Re: Determining polar or non polar: 4.27

Also, it's also important to note that a molecule can still have polar bonds and end up being nonpolar if the dipole moments cancel. Simply put: nonpolar molecules have no net dipole moments. Dipole moments cancel out due to symmetry. For example, if the molecule has a symmetrical shape like a tetra...
Thu Nov 30, 2017 11:00 am
Forum: Applying Le Chatelier's Principle to Changes in Chemical & Physical Conditions
Topic: Exothermic vs. Endothermic?!
Replies: 5
Views: 2139

Re: Exothermic vs. Endothermic?!

I don't know if you need to know this, but a problem in the Ch.11 homework distinguished exothermic and endothermic using Gibbs Free Energy (delta G). An exothermic reaction has a negative delta G and and endothermic reaction has a positive delta G. I think the main idea you need to know is that exo...
Thu Nov 30, 2017 10:49 am
Forum: Equilibrium Constants & Calculating Concentrations
Topic: Calculating the Equilibrium Constant with Coefficients
Replies: 2
Views: 273

Re: Calculating the Equilibrium Constant with Coefficients

The coefficient before the x, like 3x for NH3, is referring to the number of moles of NH3. When using x in the ICE chart for equilibrium, make sure to remember the number of moles of each component and tack it on as a coefficient to x. Also, you don't always add x to the reactants side. When Q (reac...
Sat Nov 25, 2017 10:57 pm
Forum: Determining Molecular Shape (VSEPR)
Topic: Expanded octet
Replies: 6
Views: 387

Re: Expanded octet

The d orbital starts in period 3. Period 3 and beyond is where expanded octets can be observed
Sat Nov 25, 2017 10:55 pm
Forum: Determining Molecular Shape (VSEPR)
Topic: Electronegativity
Replies: 3
Views: 286

Re: Electronegativity

It's also important to note that 2 atoms (diatomic molecule) with a high difference in electronegagivity will form a polar bond. However, when you have a polyatomic molecule (multiple atoms bonding) symmetry and dipole moments cancelling determines whether a molecule is polar. For polyatomic molecul...
Sat Nov 25, 2017 10:51 pm
Forum: Determining Molecular Shape (VSEPR)
Topic: Molecular Shape Memorization
Replies: 6
Views: 524

Re: Molecular Shape Memorization

Some of the bond angles are straightforward. For example, trigonal pyramidal has bond angles of 120 degrees (360 degree divided by 3) and linear has bond angles of 180 degrees (360 divided by 2). There are some bond angles that we purely need to memorize, like tetrahedral (bond angle of 109.5 degree...
Tue Nov 14, 2017 10:27 pm
Forum: Determining Molecular Shape (VSEPR)
Topic: Sigma vs. Pi Bonds
Replies: 5
Views: 352

Re: Sigma vs. Pi Bonds

if you want a more visual example of pi bonds think about Dr.Lavelle's example in lecture with the 2 chalk pieces between his two pointer fingers. When he moved his finger, one of the chalks fell. The chalks represent the pi bonds' regions of electron density, and rotating would break one of the two...
Tue Nov 14, 2017 9:39 pm
Forum: Determining Molecular Shape (VSEPR)
Topic: How to Find Bond Angle
Replies: 2
Views: 202

How to Find Bond Angle

How do you find the bond angle for a molecule or compound?
Sun Nov 12, 2017 9:25 pm
Forum: Octet Exceptions
Topic: Expanded Octet
Replies: 4
Views: 381

Re: Expanded Octet

An expanded octet is due to the existence of a "d orbital" which allows for more than 8 electrons.
Sun Nov 12, 2017 9:23 pm
Forum: Ionic & Covalent Bonds
Topic: oxidation state
Replies: 3
Views: 315

Re: oxidation state

To add to the above response, I learned in my biology class that when an atom loses electrons and becomes a cation (positive) then it is reduced. When an atom gains electrons it becomes an anion (negative). When an atom gains electrons, it is referred to as being "oxidized".
Sun Nov 12, 2017 9:20 pm
Forum: Electronegativity
Topic: oxygen and nitrogen
Replies: 3
Views: 441

Re: oxygen and nitrogen

To add to the other responses, remember Hund's rule. You need to fill all the orbitals with one electron (fill all with the up pointing arrow representing the spin up of the electron) before you double up on electrons. Then, make sure the 2 electrons in each orbital have opposite spins (drawn arrows...
Tue Nov 07, 2017 1:05 pm
Forum: Formal Charge and Oxidation Numbers
Topic: Formal Charge and stability [ENDORSED]
Replies: 7
Views: 4081

Re: Formal Charge and stability[ENDORSED]

Another detail that might prove useful in assigning formal charge in lewis structures is that negative charge should be assigned to the more electronegative atom, and positive charge should be assigned to the less electronegative atom.
Mon Nov 06, 2017 12:00 am
Forum: Photoelectric Effect
Topic: Post Module #17 [ENDORSED]
Replies: 3
Views: 395

Re: Post Module #17[ENDORSED]

Just like the above two posts, remember that one photon will eject one electron. This photon must have enough energy to eject the electron (energy must be greater than or equal to the work function). Increasing intensity refers to increasing the number of photons. If you add more photons that are we...
Sat Nov 04, 2017 1:11 pm
Forum: Resonance Structures
Topic: Efficiency [ENDORSED]
Replies: 2
Views: 277

Re: Efficiency[ENDORSED]

The structure with the lowest formal charge is the most effective structure.
Thu Nov 02, 2017 1:25 pm
Forum: Resonance Structures
Topic: Resonance
Replies: 3
Views: 411

Re: Resonance

To add onto the previous response, the best structure is also determined by the formal charge. Use the formal charge equation to calculate the charge of each atom in the bond, and see which one has the lowest formal charge.
Wed Oct 25, 2017 12:20 pm
Forum: Wave Functions and s-, p-, d-, f- Orbitals
Topic: Writing Electron Configuration for Excited element [ENDORSED]
Replies: 2
Views: 406

Writing Electron Configuration for Excited element[ENDORSED]

How do you write the electron configuration for an excited atom? Is it any different from how you would write the electron configuration of an atom in its ground state?
Wed Oct 25, 2017 12:18 pm
Forum: Wave Functions and s-, p-, d-, f- Orbitals
Topic: Shells, Subshells, and Orbitals
Replies: 4
Views: 426

Re: Shells, Subshells, and Orbitals

Each of the "subshells" (s,p,d,f) have a different number of nodes or orientations (ml). For the s subshell, there is only 1 orbital. For the p subshell there are 3 orbitals. The d subshell has 5, and the f subshell has 7. The number of orbitals there are increase with the angular quantum ...
Tue Oct 17, 2017 9:47 pm
Forum: Bohr Frequency Condition, H-Atom , Atomic Spectroscopy
Topic: Why don't we use the Rydberg equation from the book?
Replies: 8
Views: 514

Re: Why don't we use the Rydberg equation from the book?

I think Dr. Lavelle said he doesn't want us to use it because it doesn't make conceptual sense. You can derive the one from the textbook from the formula from class though and plug it into the change of energy = energy(final) - energy(initial). If you wanna use the one from the textbook I've heard y...
Tue Oct 17, 2017 9:45 pm
Forum: DeBroglie Equation
Topic: De Broglie Wavelength
Replies: 23
Views: 1874

Re: De Broglie Wavelength

An important thing to note: photons don't have mass! That's why none of the other formulas include mass or velocity. You'll know when to use de broglie because you'll be given mass or velocity and it's the only formula that you can plug this into to find wavelength. Hope this helps!
Sun Oct 15, 2017 2:00 pm
Forum: Photoelectric Effect
Topic: Kinetic energy equal to zero?
Replies: 4
Views: 972

Re: Kinetic energy equal to zero?

I was confused about this concept at first too. It can be confusing to think that an ejected electron(e-) can have a kinetic energy of zero. Like the other responses have been saying, when the work function/threshold energy is equal to the energy of the photon, the kinetic energy of the ejected e- w...
Thu Oct 12, 2017 1:29 pm
Forum: Properties of Light
Topic: Wavelengths and Frequency of Electromagnetic Radiation [ENDORSED]
Replies: 7
Views: 624

Re: Wavelengths and Frequency of Electromagnetic Radiation[ENDORSED]

Hi Shannon, I remember Dr. Lavelle stating in lecture that we should remember that visible light is about 500 nm. However, I certainly think it would be helpful to know the wavelength spectrum of visible light (400nm-700nm) for your own understanding and knowing what answer to anticipate on a test o...
Thu Oct 12, 2017 1:18 pm
Forum: DeBroglie Equation
Topic: Should velocity always be in m.s. when solving? [ENDORSED]
Replies: 11
Views: 1030

Re: Should velocity always be in m.s. when solving?[ENDORSED]

The SI units (standard units) are meters per second (m/s). If you're confused on what units to use, just use m/s because it will most likely be correct. However, if the problem specifies the units, then make sure to stick with those. I hope this helps!
Thu Oct 05, 2017 10:35 pm
Forum: Empirical & Molecular Formulas
Topic: Trouble in finding the Molecular Formula
Replies: 6
Views: 1093

Re: Trouble in finding the Molecular Formula

If the molar ratio is 0.1 off then you can round up. For example, if the number is 1.9, then it can be rounded up to 2.0. If the number is 1.86, even rounding up seems to be fine, but if you'd like to be safe you can multiply it by the number 6 to get a closer whole number. Honestly, I think as long...
Thu Oct 05, 2017 11:34 am
Forum: Accuracy, Precision, Mole, Other Definitions
Topic: Significance of delta sign
Replies: 2
Views: 481

Re: Significance of delta sign

The significance of a delta sign is to show that a reaction is heated or that it is a combustion reaction. I think it's also important to mention that in a combustion reaction, it's common to have oxygen gas (O2) as a reactant and the products of carbon dioxide (CO2) and water (H2O). During discussi...