CHEMISTRY COMMUNITY

EricZhao3G

An oxoacid is an acid that has oxygen bonded to a hydrogen atom, along with another element. This bond is able to be dissociated so the hydrogen atom can be donated.

EricZhao3G

A Lewis acid accepts electron pairs while a Lewis base donates electron pairs.

EricZhao3G

I would assume that either it would be given if we needed it or we would be able to calculate it through the charges of the ligands of the coordination compound.

EricZhao3G

HI is a stronger acid because it has a longer bond length so its bond is weaker, thus it is easier for the bond to be broken to donate the H+ compared to HCl.

EricZhao3G

In general, nonmetal oxides are acidic, metal oxides are basic, and semimetal oxides are amphoteric. Sulfur is a nonmetal so it is acidic.

EricZhao3G

You name a coordination compound by listing the ligands in alphabetical order, disregarding the prefix, and then the metal, with -ate if the coordination compound is negatively charged.

EricZhao3G

The oxidation number is the charge the atom would have if the compound was composed of ions. It is the number of electrons gained or loss to form a bond.

EricZhao3G

Cis molecules are polar while trans molecules are nonpolar because of the ligand positioning either on the same or opposite side.

EricZhao3G

The textbook says to list the ligands alphabetically but I think the convention is to put the neutral ligands first and then the anionic ligands.

EricZhao3G

When writing the molecule formula for the coordination compound, should the neutral or negative ligand go first? Here, Dr. Lavelle says to put the anionic ligand first but I think what is conventional has changed since then but I'm not sure: https://lavelle.chem.ucla.edu/forum/viewtopic.php?f=45&...

EricZhao3G

There will not be pi bonds without sigma bonds. A pi bond only occurs for double and triple bonds, where there is 1 sigma bond.

EricZhao3G

DLee_3C wrote:So is the pi bond both the top and bottom electron areas? or are they both separate pi bonds?

They are separate pi bonds. There are 2 pi bonds and 1 sigma bond in a triple bond.

EricZhao3G

The bond angles would be <90, <120, and >180 degrees because the lone pair has a stronger repulsive force than the bond.

EricZhao3G

At least based on what we have learned so far, you are right that dipoles only cancel for a tetrahedral if all the atoms bonded to the central atom are the same. With different atoms in the tetrahedral shape, symmetry is impossible so the molecule would probably be polar.

EricZhao3G

If the lone pair was on the axial plane, it would have a 90 degrees bond angle with 3 atoms. With the lone pair on the equatorial plane, it would have a 90 degrees bond with only 2 atoms. There is less repulsion by putting the lone pair on the equatorial plane so it should be there.

EricZhao3G

A molecule like H2SeO4 has hydrogen bonds right? And hydrogen bonds are dipole dipole forces?

EricZhao3G

With more electrons being involved in the bond, the strength of the pulling attraction is stronger thus the bond length is shorter.

EricZhao3G

A molecule has a dipole moment if there is an unequal sharing of electrons. The arrow points towards the delta negative not delta positive since that is where the electron is being pulled towards.

EricZhao3G

Dipoles occur from the difference in electronegativity between 2 ions causing an unequal sharing of electrons. The dipole moment measures the polarity of the molecule.

EricZhao3G

A dipole moment is a vector measurement of the separation of two opposite electrical charges, calculated by the charge multiplied by the distance between the charges. It comes from a difference in electronegativity between 2 ions and measures the polarity of a molecule.

EricZhao3G

You are right that the atom with the lowest ionization energy is the central atom. In that example, oxygen has a higher electronegativity than chlorine so chlorine is the central atom.

EricZhao3G

The element with the lowest ionization energy goes in the center of the Lewis structure. Ionization energy decreases down a group and increases across a period.

EricZhao3G

You would show resonance by drawing all of the possible Lewis diagrams with the lowest formal charges for the molecule and then by drawing a double-ended arrow between the structures. The double-ended arrow shows resonance between the structures.

EricZhao3G

In reality, the molecule is a resonance hybrid and is a combination of all of the resonance structures. This results in a bond length between a single and double bond since the bonds are defined as neither a single bond nor a double bond.

EricZhao3G

For drawing resonance structures, you would draw every possible Lewis structure with the lowest formal charges that could represent the molecule. Resonance structures are denoted with a double-ended arrow.

EricZhao3G

The octet rule says that elements like to bond so that each element has 8 electrons in its valence shell. Exceptions include H, He, and Li.

EricZhao3G

Formal charge is the charge assigned to an atom assuming the electrons are shared equally. You calculate formal charge with the equation FC = V - (L + S/2) where FC = formal charge, V = valence electrons, L = lone pair electrons, and s = shared electrons of that specific atom.

EricZhao3G

The S in the equation is for shared electrons. For each bond between 2 atoms, there are 2 shared electrons. So if there exists a triple bond, there are a total of 6 shared electrons for those atoms.

EricZhao3G

Resonance is when there are multiple ways of describing bonds through the structure, and thus in real life it is a combination of these contributing structures.

EricZhao3G

So far, we have not covered bond angles yet so I would assume it is not to be expected from us unless Dr. Lavelle goes over it in a future lecture.

EricZhao3G

For example for 3d, would an element like Mn have 2 or 7 valence electrons? Would Cu have 1 or 11 valence electron? I'm pretty sure that Ga has 3 valence electrons right? Can someone explain when 3d is included in valence electrons?

EricZhao3G

I know the 4s orbital fills first before the 3d orbital because the 4s orbital is lower in energy, but are electrons always removed from the 4s orbital first as well?

EricZhao3G

The 4s orbital initially has lower energy than the 3d orbital so according to the Aufbau principle it would fill first. However, as the 3d orbital is filled it begins to have less energy than the 4d orbital so electrons are removed from the 4d orbital.

EricZhao3G

Ionization energy is just the minimum amount of energy needed to remove an electron from a gaseous atom. The second ionization energy is always larger than the first ionization energy because there is a stronger nuclear charge once an electron is already missing.

EricZhao3G

I know that nodal planes are areas where the probability of finding electrons is 0 and that they depend on the orbital. Is there more significance to these planes or do we just need to memorize the shapes of orbitals?

EricZhao3G

I know that Dr. Lavelle mentioned that Cr and Cu are exceptions to the rules and have electron configurations of [Ar] 3d5 4s1 and [Ar] 3d10 4s1 respectively. Does this extrapolate to the whole group 6 and group 11 where an electron is always taken from the 4s orbital?

EricZhao3G

Part a asks for the wavelength of the ejected electron which can be found using the kinetic energy of the ejected electron and E = hv and c = vλ. Part c asks for the wavelength of the proton that caused the electron to be ejected which would be solved in a similar fashion after finding the energy of...

EricZhao3G

The equation comes in handy whenever you need to find the energy of a photon if you know the it's frequency, or vice versa. In a lot of photoelectric effect problems, often you will need to use E = hv first to find the energy of the photon in order to solve for the other components of the problem.

EricZhao3G

Heisenberg's indeterminacy equation was simply mentioned Friday and is explained a lot more in-depth today in lecture. There is also a module on Heisenberg's indeterminacy equation on Dr. Lavelle's website if you want more explanation or practice on the subject.

EricZhao3G

Constructive interference occurs when two waves are in phase and "add" to each other. This happens when both waves are positive or negative at the same time so their amplitudes will increase after they collide. Destructive interference is the opposite and occurs when two waves are out of p...

EricZhao3G

Threshold energy is the least amount of energy needed to eject an electron off of a surface. Threshold energy is important when using Einstein's photoelectric equation since it is one of the three components of his equation: E(photon) - E(threshold) = E(kinetic).

EricZhao3G

If it is 0.8, I believe you would have to multiply all of the elements of the compound by 5 in order to find the empirical formula since that is the smallest number you can multiply by to get a whole number. Rounding 0.8 to 1 is a bit of a stretch even if you rounded in your work.

EricZhao3G

First, you would add the convert the grams of the 2 solutes to moles using the molar masses. Then, add those 2 moles to find the total moles of solute. Finally, divide the moles of solute by the volume of the solution in order to find the molarity and compare that to 5.30 x 10^-3 M to see whether or...

EricZhao3G

Electrons and protons have mass as well so based off of the law of conservation of mass, the number of electrons and protons must stay the same in a chemical equation. That's just one way to think about it, because there's also charge conservation as well.

EricZhao3G

You're right that mass and the number of atoms are conserved. Electrons and protons are also conserved because remember that they have mass as well. If the equation were to gain or lose electrons or protons then the mass wouldn't be balanced between the 2 sides of the equation.

EricZhao3G

I don't think he ever mentioned knowing the states so I wouldn't be too worried about including them. Obviously if they're given in the unbalanced chemical equation you should keep it in your work, but in general I don't think we are writing our own chemical equations from the names of chemical comp...

EricZhao3G

I just switched into this class and was wondering if Dr. Lavelle ever mentioned how he wanted answers formatted. Are we supposed to use scientific notation or SI prefixes or does it not matter?

EricZhao3G

I doubt TA's are spending the time to record exactly what questions everyone has done so I wouldn't be too stressed about it. However, these problems are for practice so you should be a little more conscious with the questions you work on and be sure that they are helping you learn the material cove...

EricZhao3G

Changing the subscript would change the molecule. The chemical equation has specific molecules and changing them would result in a totally different chemical equation. Any differences in the solutions manual should be a typo or misprint since the only things you can change in order to balance chemic...

EricZhao3G

Just using all of the significant digits provided by the periodic table would be the best, which for the periodic table provided to us is only 3-4 decimal places depending on the element. I believe in class Dr. Lavelle usually uses 4 decimal places as well to solve problems.

EricZhao3G

Let's say I didn't have one long line of dimensional analysis and instead first found one number before later using it again to calculate a final answer. Is it fine to show my work as rounded, even if I keep it exact in my calculator?

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