## Search found 57 matches

Sat Dec 07, 2019 11:25 pm
Forum: Student Social/Study Group
Topic: Ligand help pls
Replies: 3
Views: 150

### Re: Ligand help pls

The ligand is the atom or molecule in the coordination compound acting as a Lewis base to donate lone pair electrons to a transition metal cation.
Sat Dec 07, 2019 12:33 pm
Forum: Calculating pH or pOH for Strong & Weak Acids & Bases
Topic: pH of a solution
Replies: 2
Views: 58

### Re: pH of a solution

This is a strong acid/strong base reaction, so you need to determine whether the resulting solution has an excess hydronium or hydroxide through dimensional analysis with the balanced equations in water. It turns out there is more hydronium and pH=-log[H+]= 2.28.
Sat Dec 07, 2019 12:14 pm
Forum: Naming
Replies: 1
Views: 44

### Re: Adding the word ion

When there is a net charge that is not zero :)
Sat Dec 07, 2019 12:11 pm
Forum: Determining Molecular Shape (VSEPR)
Topic: Polar or Nonpolar
Replies: 13
Views: 220

### Re: Polar or Nonpolar

Correct me if I'm wrong, but I believe square planar is the only VSEPR shape where the molecule may contain lone pairs and still be nonpolar (if every X in AX4E2 is the same element). In any other shape, lone pairs will indicate the net dipole does not cancel and therefore the molecule is polar. Man...
Fri Dec 06, 2019 4:42 pm
Forum: Conjugate Acids & Bases
Topic: oxoacids
Replies: 3
Views: 142

### Re: oxoacids

Oxoacids have an O-H hydrogen bond which dissociates into H+ ions in solution and this is how it acts as an acid. If the H were bonded to the Cl in the example in class this wouldn't happen.
Fri Dec 06, 2019 12:09 pm
Forum: Shape, Structure, Coordination Number, Ligands
Topic: Good resources for learning about coordination compounds?
Replies: 2
Views: 53

### Re: Good resources for learning about coordination compounds?

Tue Dec 03, 2019 1:19 pm
Forum: Acidity & Basicity Constants and The Conjugate Seesaw
Topic: pKa vs Ka
Replies: 6
Views: 92

### Re: pKa vs Ka

Ka is the acid dissociation constant.
Also, this same logic is why pH is preferred over simply quantifying [H+].
Mon Dec 02, 2019 10:41 pm
Forum: Properties & Structures of Inorganic & Organic Acids
Topic: Strength of bases BrO- and C17H19O3N
Replies: 2
Views: 61

### Re: Strength of bases BrO- and C17H19O3N

Just answered this, I'll paste my response here!
HBrO is a weak acid, so its conjugate base BrO- will be a strong base.
Morphine is basic due to the nitrogen with a lone pair, and as Lavelle has stated in lecture, these nitrogen containing compounds are always weak.
Mon Dec 02, 2019 10:35 pm
Forum: Bronsted Acids & Bases
Topic: hw 6c.17
Replies: 1
Views: 36

### Re: hw 6c.17

HBrO is a weak acid, so its conjugate base BrO- will be a strong base.
Morphine is basic due to the nitrogen with a lone pair, and as Lavelle has stated in lecture, these nitrogen containing compounds are always weak.
Mon Dec 02, 2019 7:09 pm
Forum: Shape, Structure, Coordination Number, Ligands
Topic: chelate
Replies: 5
Views: 69

### Re: chelate

A chelating ligand is one that has the bonding motif below that Dr. Lavelle mentioned in class, in order to form multiple bonds to a transition metal cation. This structure is needed in order for the bonds to be physically close enough on the molecule to both/all reach the cation and bond to it. You...
Mon Dec 02, 2019 7:01 pm
Forum: Lewis Acids & Bases
Topic: Acid Strength
Replies: 4
Views: 126

### Re: Acid Strength

To expand, the strength of the acid (or base) is determined by how fully it ionizes in water and how stable the anion is, so weaker bonds like in HI make good strong acids because HI readily dissociates in water into H+ and I-, and I- is a stable anion (electronegative and polarizable).
Wed Nov 27, 2019 3:05 pm
Forum: Bronsted Acids & Bases
Topic: Relative Acidity
Replies: 3
Views: 46

### Re: Relative Acidity

From what I understand, stronger acids are less stable than weaker acids as they readily shed H+ ions in solution. However, the conjugate base (anion) of a stronger acid is more stable (more electronegative) than the conjugate base of a weaker acid. Therefore, the electronegativity/stability of the ...
Tue Nov 26, 2019 4:39 pm
Forum: Shape, Structure, Coordination Number, Ligands
Topic: HW Question 9C.5
Replies: 4
Views: 43

### Re: HW Question 9C.5

Yes, only the oxygens that are attached with single bonds are negatively charged, these are the 2 binding points making oxalate bidentate.
Tue Nov 26, 2019 11:41 am
Forum: Properties & Structures of Inorganic & Organic Acids
Topic: Structure of H2SO4
Replies: 2
Views: 46

### Re: Structure of H2SO4

Very simply, it does consist of these H+ and HSO4- like you say, so the bond between this H+ and HSO4- has high ionic character. However, the other bonds in the sulfate ion, particularly S-O bonds, have high covalent character. It has an 'ionic nature' in that it will readily separate into H+ and HS...
Mon Nov 25, 2019 7:30 pm
Forum: Shape, Structure, Coordination Number, Ligands
Topic: Polydentate Ligands
Replies: 2
Views: 50

### Re: Polydentate Ligands

I think this would be valid, as I found online that ligands with more than one bonded atom are referred to as polydentate.
Wed Nov 20, 2019 11:16 pm
Forum: Dipole Moments
Topic: Polar or Nonpolar
Replies: 5
Views: 143

### Re: Polar or Nonpolar

If the molecule has mirror symmetry, the dipoles will cancel and the net dipole will be zero, therefore it'll be nonpolar. Monatomic compounds will be nonpolar since there's no electronegativity difference. If there's not symmetry and it's polyatomic, often the more electronegative species will pull...
Wed Nov 20, 2019 10:46 pm
Forum: Sigma & Pi Bonds
Topic: Resonance Structures
Replies: 2
Views: 43

### Re: Resonance Structures

Khan Academy has a detailed video on SO2 that I found useful: https://www.khanacademy.org/science/che ... ur-dioxide
Tue Nov 19, 2019 8:41 pm
Forum: Dipole Moments
Topic: Dipole Moment
Replies: 10
Views: 275

### Re: Dipole Moment

You know electronegativity trends from the periodic table, so unless you want the exact numerical value, you can just follow the trend. The larger the difference in electronegativity, the larger the dipole moment. Polar molecules have permanent dipole moments, and nonpolar molecules can have induced...
Tue Nov 19, 2019 12:37 pm
Forum: Dipole Moments
Topic: Polar or nonpolar
Replies: 8
Views: 152

### Re: Polar or nonpolar

Nonpolar. Draw the Lewis structure and you will see there's no net dipole.
Tue Nov 19, 2019 12:22 pm
Forum: Hybridization
Topic: What are pi bonds in relation to sigma?
Replies: 2
Views: 26

### Re: What are pi bonds in relation to sigma?

Sigma bonds are the more favorable configuration due to increased stability so they will always form first, and pi bonds form when sigma bonds cannot (i.e., in double and triple bonds).
Tue Nov 19, 2019 12:21 pm
Forum: Determining Molecular Shape (VSEPR)
Topic: Square Planar Shape
Replies: 2
Views: 51

### Re: Square Planar Shape

I believe they are just 90 and 180. The square planar shape has two lone pairs on each side of the equatorial plane, so the distortions effectively 'cancel' each other, resulting in the expected bond angles of 90 and 180, unlike shapes that just have 1 lone pair distorting bond angles.
Tue Nov 19, 2019 12:04 am
Forum: Lewis Structures
Topic: Cis- vs Trans- bonds
Replies: 5
Views: 108

### Re: Cis- vs Trans- bonds

Dr. Lavelle did mention the concept before the content cutoff for Test 2, so I think we should know it. From what I understand of the example given in class, the cis molecule has a less symmetric Lewis structure you could say, with the same atoms or functional groups on the same side of the molecule...
Wed Nov 06, 2019 12:01 pm
Forum: Lewis Structures
Topic: Lewis acids vs Lewis bases
Replies: 3
Views: 51

### Re: Lewis acids vs Lewis bases

Lewis base: electron donator (examples: anions like F-, molecules with lone pairs, complex anions)
Lewis acid: electron acceptor (examples: cations like H+, complex cations, molecules w/ incomplete octet)
Water (H2O) can be both a Lewis base (OH-) and a Lewis acid (H3O+)
Wed Nov 06, 2019 11:48 am
Forum: Bond Lengths & Energies
Topic: 1B on Dino Nuggets
Replies: 2
Views: 54

### Re: 1B on Dino Nuggets

To add on to this, if you draw the Lewis structure for carbonate you'll notice 2 single C-O bonds and 1 C=O double bond. Now this might not be experimentally accurate, but a safe way to get an approximation for the resonance hybrid bond length would be to calculate the 'mean bond length': length of ...
Mon Nov 04, 2019 10:32 pm
Forum: Limiting Reactant Calculations
Topic: missed question test 1
Replies: 4
Views: 277

### Re: missed question test 1

Take the given value of grams, divide by the molar mass. Now you have Si3N4 in moles. Use the molar ratio from the balanced equation to multiply by moles of Si. Now you have Si in moles. Multiply by the molar mass of Si. Now you have Si in grams, your answer. The process is dimensional analysis, usi...
Mon Nov 04, 2019 10:28 pm
Forum: Quantum Numbers and The H-Atom
Topic: Quantum number
Replies: 1
Views: 40

### Re: Quantum number

This question is purely conceptual to test your understanding that values of l range from 0 to n-1. For our practical purposes we shouldn't be dealing with any atoms having any value bigger than l=3 corresponding to the f subshell.
Mon Nov 04, 2019 10:10 pm
Forum: Ionic & Covalent Bonds
Topic: Question 2D.5
Replies: 2
Views: 60

### Re: Question 2D.5

You just have to look at the electronegativity difference between the two atoms, which can be found using the periodic trend. You'll be given the periodic table on the test to use, it can be helpful to circle the atoms and look at their physical distance on the periodic table while thinking about el...
Mon Nov 04, 2019 10:05 pm
Forum: Polarisability of Anions, The Polarizing Power of Cations
Topic: Polar Covalent VS Ionic
Replies: 11
Views: 213

### Re: Polar Covalent VS Ionic

You can try to logically reason it out looking at the electronegativity difference between the atoms in the bond. The larger the difference, the more ionic character the bond will likely express. However, without calculating electronegativity (X) using the equation X= .5(I+Ea) where I is ionization ...
Mon Nov 04, 2019 9:52 pm
Forum: Properties of Light
Topic: When do you use light equations?
Replies: 3
Views: 123

### Re: When do you use light equations?

If the value given is wavelength for an electron, frequency cannot be calculated with this equation because the constant c is the speed of light, and it is impossible for an electron to move at the speed of light. If the value given is wavelength for a photon, go ahead and use it. For electrons, we ...
Mon Nov 04, 2019 9:47 pm
Forum: Wave Functions and s-, p-, d-, f- Orbitals
Topic: 1D.23 Number of Orbitals question
Replies: 2
Views: 162

### Re: 1D.23 Number of Orbitals question

S, p, d, and f are subshells. The orbital is specified by the first 3 quantum numbers, as 2 electrons occupy an orbital. Therefore, you need the first 3 quantum numbers to be given in order for the answer to be 1.
Mon Nov 04, 2019 9:43 pm
Forum: Lewis Structures
Topic: Double Bonds
Replies: 3
Views: 77

### Re: Double Bonds

You need to look at electronegativity. You can see which atoms are more electronegative based on the periodic trend. Calculating formal charge will also be helpful in determining where to put double bonds, as highly electronegative atoms are able to have a negative formal charge.
Sat Nov 02, 2019 1:40 pm
Forum: Resonance Structures
Topic: Delocalization
Replies: 4
Views: 81

### Re: Delocalization

I believe you are correct! Delocalized electrons increase stability in a molecule, which is why those with resonance are also more stable.
Wed Oct 30, 2019 2:47 pm
Forum: Ionic & Covalent Bonds
Topic: 2D.9
Replies: 1
Views: 33

### Re: 2D.9

Polarizing power increases with higher cation charge (more lost e-). Ions with a +2 charge will have a greater polarizing power than those with a charge of +1, so it's safe to say the Rb+ will be the smaller of the two.
Wed Oct 30, 2019 2:41 pm
Forum: Electron Configurations for Multi-Electron Atoms
Topic: S to D orbital?
Replies: 1
Views: 40

### Re: S to D orbital?

The s (4s) subshell fills first because it is a lower energy than d (3d) until the d subshell begins to fill. At that point, the d orbital then becomes the lower energy configuration. Atoms will favor full or half full shells, so whenever there's 9 electrons in the d subshell, you can be sure that t...
Tue Oct 29, 2019 10:24 pm
Forum: Octet Exceptions
Topic: Octet Rule Exceptions
Replies: 4
Views: 70

### Re: Octet Rule Exceptions

Atoms in the first two groups must follow the octet rule. The octet rule really applies to those atoms with atomic numbers below 20, because they want the configuration of a noble gas.
Tue Oct 29, 2019 10:21 pm
Forum: Ionic & Covalent Bonds
Topic: Formal Charge
Replies: 2
Views: 32

### Re: Formal Charge

You'd want to favor lower formal charge in order to make stable molecules. However, there are many atoms that must obey the octet rule. Molecules with atoms in groups I and II can't have an expanded octet. Other than this, I can't see why not to favor formal charge.
Fri Oct 25, 2019 8:48 pm
Forum: Electron Configurations for Multi-Electron Atoms
Topic: Electron Configurations
Replies: 2
Views: 21

### Re: Electron Configurations

3p comes before 4s, the logical sequential order. The d subshell is where things begin to get tricky. This is because the 4s subshell fills first, because it is much smaller and therefore has lower energy making it the optimal (experimentally observed) configuration. However, once the 3d subshell be...
Wed Oct 23, 2019 12:04 pm
Forum: Trends in The Periodic Table
Topic: Shielding
Replies: 8
Views: 234

### Re: Shielding

Electrons repel each other because of their negative charge. Electrons are attracted to the positively charged nucleus, but outer subshells experience shielding due to electron-electron repulsion. Valence shell electrons experience the most shielding.
Tue Oct 22, 2019 11:14 pm
Forum: Electron Configurations for Multi-Electron Atoms
Topic: Electron Configurations
Replies: 13
Views: 636

### Re: Electron Configurations

The 'trick' would probably just be having a copy of the periodic table handy, as if you know where the s- and p- blocks are, it is easy to see which subshells fill up before the others. Also, since the order is always the same, a bit of practice will make the order seem more intuitive, but you can a...
Tue Oct 22, 2019 11:09 pm
Forum: Einstein Equation
Topic: 1B.9
Replies: 3
Views: 63

### Re: 1B.9

The question asks for number (and moles) of photons. First, you need to use the E=hc/lambda formula to solve for the number of Joules one photon of such wattage would produce. Then, you need to find the number of photons. This is where the other equation is used, because you need to use the watts gi...
Tue Oct 22, 2019 1:36 pm
Forum: Trends in The Periodic Table
Replies: 3
Views: 36

### Re: 1F.1 Atomic Radius Differences

On a test, I don't believe you will be given these values. In accordance with the reply above, I think that this question is checking your understanding of general periodic trends. You should be able to figure out or recall the periodic trends for atomic radii, electron affinity, ionization energy, ...
Tue Oct 22, 2019 1:31 pm
Forum: Properties of Electrons
Topic: x,y,z for Electrons
Replies: 10
Views: 154

### Re: x,y,z for Electrons

In class, Dr. Lavelle said it is a better answer when this is specified, but electrons fill orbitals within a subshell randomly, so you could just pick one orbital to specify.
Thu Oct 17, 2019 8:31 pm
Forum: Wave Functions and s-, p-, d-, f- Orbitals
Topic: Orbital v. Subshell
Replies: 1
Views: 33

### Re: Orbital v. Subshell

The four subshells are s, p, d, and f. Orbitals are within subshells and are the regions where electrons are found (up to two per orbital). You can refer to them, for example, as an "s orbital within an s subshell". The question you are referring to asks for the number of subshells in the ...
Thu Oct 17, 2019 8:22 pm
Forum: Properties of Electrons
Topic: 1D.15
Replies: 2
Views: 58

### Re: 1D.15

Each atomic sublevel has a specific l value associated with it: for s, l=0, for p, l=1, for d, l=2, and for f, l=3. You simply apply this to the given letters.
Thu Oct 17, 2019 8:13 pm
Forum: Properties of Electrons
Topic: x,y,z for Electrons
Replies: 10
Views: 154

### Re: x,y,z for Electrons

I think you have the right idea. I found the visuals in Dr. Lavelle's slides helpful so maybe you should look up visual representations of the various orbitals. For the p subshell, there are 3 orbitals (the x, y, and z you mentioned) and each is in relation to the orientation with a coordinate axis....
Wed Oct 16, 2019 3:02 pm
Forum: SI Units, Unit Conversions
Topic: Fundamentals Problem Question
Replies: 2
Views: 80

### Re: Fundamentals Problem Question

Additionally, for net ionic reactions, I find it most helpful to write the complete molecular reaction including the spectator ions, and from there, determine the net ionic equation by eliminating the species that aren't reacting.
Wed Oct 16, 2019 11:04 am
Forum: Bohr Frequency Condition, H-Atom , Atomic Spectroscopy
Topic: Question upon 1A15
Replies: 1
Views: 63

### Re: Question upon 1A15

I think this is just a bit of tricky semantics-- The n1 value should indeed be equal to 1 since the question states it is in the UV spectrum (therefore you use Lyman series like you said). I suppose the issue with the textbook solutions is that in this case, n1 is the final energy state and you're t...
Sat Oct 12, 2019 2:29 pm
Forum: Properties of Electrons
Topic: Diffraction
Replies: 4
Views: 40

### Re: Diffraction

The famous experiment regarding this is the Davisson–Germer experiment, so doing some research on that name may help your understanding. Basically, diffraction is the concept of waves bending or shifting, causing (constructive or destructive) interference, so any light or matter that can exhibit dif...
Sat Oct 12, 2019 2:19 pm
Forum: Properties of Electrons
Topic: wave properties of electrons
Replies: 4
Views: 34

### Re: wave properties of electrons

It would be considered to not exhibit measurable wavelike properties past the 10^-15 cutoff, but I think this will not be the case for most electrons, as the mass of an electron is 9.10938356 × 10-31 kilograms which is so small that typically electrons are considered to possess both wave and particl...
Sat Oct 12, 2019 2:11 pm
Forum: Properties of Electrons
Topic: Wavelike properties of electrons
Replies: 3
Views: 69

### Re: Wavelike properties of electrons

Experimentally, electrons passing through a crystal show diffraction just as light does (for example, X-rays). Therefore, it has been shows that electrons have wavelike properties in addition to their particle-like properties. De Broglie was the one who suggested this, building upon Einstein's quant...
Tue Oct 08, 2019 10:08 pm
Forum: Empirical & Molecular Formulas
Topic: Estimating the greatest mass percentage
Replies: 2
Views: 66

### Re: Estimating the greatest mass percentage

Essentially, yes this is a good way to think about it. Once you have the formula for nitric acid, it should be pretty evident which atom has the greatest mass percentage. Having a good idea of the atomic masses of the atoms is important too.
Tue Oct 08, 2019 10:05 pm
Forum: Balancing Chemical Reactions
Topic: Balancing Chemical Equations (Question L.35)
Replies: 3
Views: 82

### Re: Balancing Chemical Equations (Question L.35)

From the Comments and Errors file found on the Chem 14A site:
"L.35 in the textbook question:
In the third reaction step the compound "FeBr2" needs to be "Fe3Br8"."
Thu Oct 03, 2019 11:10 am
Forum: SI Units, Unit Conversions
Topic: Dimensional Analysis Question
Replies: 6
Views: 106

### Re: Dimensional Analysis Question

Hi! So dimensional analysis is really just a fancy name for a math concept we learned a long time ago-- multiplying by 1 does not change a value. Essentially, we are doing what you stated and using ratios to convert, by creating fractions that are equivalent to one (such as molar ratios, moles to gr...
Wed Oct 02, 2019 10:47 pm
Forum: Significant Figures
Topic: Question About Significant Figures and Rounding
Replies: 22
Views: 1213

### Re: Question About Significant Figures and Rounding

For this follow-up question, I don't believe that a question saying 1 mol is used would limit sig figs because it is a exact measurement. Sometimes the question will try to guide you towards the correct number of sig figs, by writing it as 1. mol or 1.00 mol, but I wouldn't think this measurement as...
Wed Oct 02, 2019 10:34 pm
Forum: Limiting Reactant Calculations
Topic: Module: limiting chemical reactions
Replies: 3
Views: 102

### Re: Module: limiting chemical reactions

This is a limiting reactant problem, so you follow the procedure we used in class. First, convert CaCO3 from kg to g to moles. From the equation given, you can see the molar ratio of CaCO3:CO2 is 1:1 (look at the stoichiometric coefficients), so however many moles of CaCO3 are produced is equivalent...
Wed Oct 02, 2019 10:24 pm
Forum: Molarity, Solutions, Dilutions
Topic: G5
Replies: 1
Views: 44

### Re: G5

I am looking specifically at (a), but it's a similar procedure for all three. First, we see we are looking for the volume of solution. So you have to know how much solute you have in moles, using the molar mass of NaCO3 and the given grams. Once you calculate this, find molarity (M) by dividing by 0...
Wed Oct 02, 2019 10:10 pm
Forum: Limiting Reactant Calculations
Topic: limiting reactant
Replies: 5
Views: 180

### Re: limiting reactant

The only reactant given in the problem is CaCO3 so this must be the limiting reactant per se. So you just need to calculate the theoretical yield of CO2 from the 42.73 grams CaCO3 given in the problem, and compare that to the actual yield which is given as 17.5 grams CO2. The percent yield is then (...