Search found 31 matches

Mon Dec 03, 2018 2:19 pm
Forum: Calculating pH or pOH for Strong & Weak Acids & Bases
Topic: Negative pH?
Replies: 5
Views: 249

Re: Negative pH?

Since Dr Lavelle said that the regular range of pH is 0-14, that suggests that negative pH or pH greater than 14 would be possible, just unlikely
Mon Dec 03, 2018 2:18 pm
Forum: Calculating pH or pOH for Strong & Weak Acids & Bases
Topic: Ka Calculations
Replies: 3
Views: 173

Re: Ka Calculations

I don't think that we will be asked to calculate Ka/Kb, but keep in mind that they represent the ratio of concentrations of products to reactants. A stronger acid/base will have a greater Ka/Kb
Mon Dec 03, 2018 2:16 pm
Forum: Calculating the pH of Salt Solutions
Topic: Ka Constant
Replies: 4
Views: 448

Re: Ka Constant

Two qualitative things that would be useful to know include
1) Ka and Kb deal with the ratio of concentrations
2) Products sit on top of reactants, meaning a stronger acid/base, which dissociates more easily, will have a greater Ka/Kb
Mon Nov 26, 2018 1:20 pm
Forum: Dipole Moments
Topic: Dipole Moments
Replies: 2
Views: 145

Re: Dipole Moments

More than one type of bond creates dipole moments. Hydrogen bonding, ionic bonding, and polar covalent bonding would create permanent dipole moments. London dispersion forces would create temporary dipole moments.
Mon Nov 26, 2018 1:16 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: Polar Bonds
Replies: 3
Views: 506

Re: Polar Bonds

Consider SiF4. Si-F bond would be ionic (and polar, and have dipoles) because the electronegativity difference is greater than 2. However, since SiF4 is tetrahedral, this same force is exerted in four directions opposite to each other. The vectors would thus cancel out and the molecule would be nonp...
Mon Nov 26, 2018 1:12 pm
Forum: *Molecular Orbital Theory (Bond Order, Diamagnetism, Paramagnetism)
Topic: MO theory
Replies: 2
Views: 201

Re: MO theory

Not sure how much this would help, but:
with regions of electron density:
two: sp // three: sp2 // four: sp3 // five: sp3d // six: sp3d2
with bonding orbitals:
single bond: 1 sigma
double: 1 sigma 1 pi
triple: 1 sigma 2 pi
Mon Nov 19, 2018 4:51 pm
Forum: Hybridization
Topic: hybridization vs VSEPR notation
Replies: 3
Views: 205

Re: hybridization vs VSEPR notation

VSEPR will show us the regions of electron density in a molecule and also the shape that those regions create. Looking at those regions of electron density, we can determine the hybridization orbitals of the molecule.
Mon Nov 19, 2018 4:48 pm
Forum: Hybridization
Topic: Hybridized Orbitals
Replies: 4
Views: 179

Re: Hybridized Orbitals

Consider structures where the central atom has more than four areas of electron density. Looking at VSEPR models, these include octahedral, square pyramid, trigonal bipyramidal, etc. They will need to include d in their hybridization orbitals
Mon Nov 19, 2018 4:45 pm
Forum: Hybridization
Topic: Labeling Compounds
Replies: 4
Views: 182

Re: Labeling Compounds

The first region of electron density will be in the s hybridization orbital since it fills up first just like with regular atomic orbitals
Mon Nov 12, 2018 3:59 pm
Forum: Ionic & Covalent Bonds
Topic: Bonding
Replies: 2
Views: 211

Re: Bonding

When thinking about bonds, think about Coloumb's Law: kQq/r^2=F, where F is force. k is a constant, Q is the charge of one atom, q the charge of the other, and r the radius between them. So, as charge increases or radius decreases (atom gets smaller), force will increase.
Mon Nov 12, 2018 3:56 pm
Forum: Ionic & Covalent Bonds
Topic: Bond Strength
Replies: 2
Views: 243

Re: Bond Strength

Also note that the repulsion of lone pair electrons is stronger than the repulsion of bonding electrons.
Mon Nov 12, 2018 3:55 pm
Forum: Determining Molecular Shape (VSEPR)
Topic: Molecular Shape
Replies: 6
Views: 313

Re: Molecular Shape

Keep in mind that dashed lines are intermolecular interactions. Intermolecular interactions can have huge effects: consider hydrogen bonding in water that gives it surface tension. But, intermolecular interactions can also have tiny effects: van der waals forces only occur sporadically and are broke...
Wed Nov 07, 2018 3:49 pm
Forum: Resonance Structures
Topic: Resonance Hybrids
Replies: 3
Views: 235

Re: Resonance Hybrids

BF3 has a Lewis Structure where the central atom (B) does not have a full octet.
Wed Nov 07, 2018 3:46 pm
Forum: Electronegativity
Topic: Electronegativity
Replies: 5
Views: 239

Re: Electronegativity

When the electronegativity difference is high, the bonding compound will have an ionic bond. Ionic bonded compounds are polar and that influences their behavior with other molecules. Consider H2O which is polar. When ionic compounds (eg NaCl) interact with H2O, they break apart because the negative ...
Wed Nov 07, 2018 3:42 pm
Forum: Bond Lengths & Energies
Topic: Calculating Bond Lengths
Replies: 4
Views: 263

Re: Calculating Bond Lengths

There are tables which give you the length of different bonds and differentiate between single, double, and triple bonds. When you have both a single and double bond, you would find the mean length. Same for other combinations.
Sat Nov 03, 2018 3:11 pm
Forum: Lewis Structures
Topic: H Element
Replies: 2
Views: 126

Re: H Element

The same is true for He. Since these both are in the 1s (1s1 and 1s2) orbital, so they are not able to form more than one bond since they do not have a p orbital. Keep in mind though that He is a noble gas and unlikely to react.
Sat Nov 03, 2018 3:06 pm
Forum: Lewis Structures
Topic: Stable
Replies: 2
Views: 152

Re: Stable

When formal charge is 0, the structure is most stable (when it is not an ion.) When it is an ion, formal charge should add to the charge. For example, an ion with -1 charge should have a formal charge of -1.
Sat Nov 03, 2018 3:05 pm
Forum: Lewis Structures
Topic: Calculation of bond length
Replies: 3
Views: 189

Re: Calculation of bond length

When a molecule has a single bond and double bond that connect the same element to another element like in NO3-, in reality the double bond won't be shorter than the single bond. Instead, both bonds will have a length somewhere between the length of a double bond and a single bond. Determining this ...
Thu Oct 25, 2018 11:04 am
Forum: Electron Configurations for Multi-Electron Atoms
Topic: Ground vs Excited State
Replies: 3
Views: 231

Re: Ground vs Excited State

In addition, ground state is the "neutral" state of the atom. An example of an excited state is when an electron absorbs a quantum of energy and is artificially raised to a different orbital (as we've been talking about in class).
Thu Oct 25, 2018 10:54 am
Forum: Wave Functions and s-, p-, d-, f- Orbitals
Topic: orbitals and wave functions
Replies: 2
Views: 161

Re: orbitals and wave functions

The first model of the atom that is still used today in basic chemistry is the Bohr model, which looks very similar to the sun (nucleus) with planets (electrons) orbiting around it. However, experiments have shown that electrons behave as waves (double slit experiment etc) so it doesn't make sense t...
Thu Oct 25, 2018 10:41 am
Forum: Trends in The Periodic Table
Topic: Ionization Energies
Replies: 3
Views: 182

Re: Ionization Energies

You're referring to Group 4, which consists of transition metals. Transition metals form cations, although with varying charges. They would lose electrons - not gain electrons, but for most transition metal elements, the number of electrons lost would vary. I believe the other poster is talking abou...
Wed Oct 17, 2018 4:15 pm
Forum: Einstein Equation
Topic: Question on Midterm
Replies: 7
Views: 613

Re: Question on Midterm

"Known" values don't have sig figs (or so I was taught), so any constant given to you isn't going to determine the sig figs in your work. The point of using the long version of the constant is to ensure accurate calculations.
Wed Oct 17, 2018 4:11 pm
Forum: Heisenberg Indeterminacy (Uncertainty) Equation
Topic: H bar
Replies: 5
Views: 274

Re: H bar

What do you mean? H bar is a constant that equals h/2pi. I think it's written this way so it can theoretically be simplified using the values of delta p and delta x.
Wed Oct 17, 2018 4:06 pm
Forum: Properties of Light
Topic: Homework Problem
Replies: 2
Views: 125

Re: Homework Problem

There's part of the problem that it feels like you're missing, and that's that 102.6nm is ultraviolet radiation, which corresponds to the Lyman Series. The Lyman Series also corresponds to the energy level n=1. Treat the unknown n like a variable and solve for it!
Tue Oct 09, 2018 10:41 pm
Forum: Accuracy, Precision, Mole, Other Definitions
Topic: E.23
Replies: 2
Views: 283

Re: E.23

I'll help you through part a! Calculate the amount in moles of Cu2+ ions in 3.00g CuBr2. First, we must go from grams of the molecule to moles of the molecule by dividing by the molar mass. 3.00 g CuBr2 x (1 mol CuBr2/223.35g/mol CuBr2)= 1.34 x 10^2 mol CuBr2 Now you have the moles of the molecule, ...
Tue Oct 09, 2018 10:35 pm
Forum: Balancing Chemical Reactions
Topic: Test 1
Replies: 6
Views: 2611

Re: Test 1

I would say definitely err on showing too much work. That way, your TA will be able to follow your work and award partial credit. Some TAs require you to use pen, so if that's the case for you, definitely make clear what work you want to be graded.
Tue Oct 09, 2018 10:31 pm
Forum: SI Units, Unit Conversions
Topic: Units
Replies: 8
Views: 397

Re: Units

Even if you don't have to use units throughout your work, including them can definitely help. Carrying units throughout will let you see what cancels out and will let you know what units your final answer should be.
Sat Oct 06, 2018 6:20 pm
Forum: Accuracy, Precision, Mole, Other Definitions
Topic: Naming Compounds
Replies: 3
Views: 71

Re: Naming Compounds

When a formula has ---hydrate, the prefix represents the amount of H2O molecules present. So heptahydrate would be 7 H2O, trihydrate would be 3 H2O, and so forth. These are connected to the chemical formula with a dot.
Sat Oct 06, 2018 2:14 pm
Forum: SI Units, Unit Conversions
Topic: Formula Sheet?
Replies: 6
Views: 300

Formula Sheet?

In AP Chemistry, we were given formula sheets that contained formulas of importance and their units, sometimes in different forms. Does anyone have insight into whether we will be given similar sheets on our tests/quizzes here?
Sat Oct 06, 2018 2:10 pm
Forum: Significant Figures
Topic: Sig Figs: Addition and Subtraction
Replies: 3
Views: 266