CHEMISTRY COMMUNITY

BryantChung_4B

An acid is generally specific to its conjugate base, and a base is specific to its conjugate acid. Whether it is a Lewis or Bronsted base won't change what conjugate it forms.

BryantChung_4B

In a reaction with acid containing hydrogen and a base containing hydroxide, the two will neutralize each other and give off their ions, meaning the H+ and OH- ions can now combine into H2O. The remaining ions can combine into a salt.

BryantChung_4B

Lewis and Bronsted definitions have been explained above already, but just know that a conjugate base occurs when an acid donates an H+ and thus the product is now able to accept an H+ back in the reverse reaction.

BryantChung_4B

Ligands are found in coordination compounds, meaning they donate an electron pair to a central atom.

BryantChung_4B

Conjugate acids and bases can arise in reversible reactions. For example, an acid donates an H+ to another molecule, and then turns into a product with one less H+. This is now a conjugate base, because in the reverse reaction, it can accept an H+.

BryantChung_4B

There are just certain periodic trends to know. In basic terms, electronegativity is mainly reliant on an atom's positive charge and the "shielding" of electrons. N is more electronegative than C because it has one more proton, allowing it to attract electrons more tightly. F is more elect...

BryantChung_4B

Some atoms can't complete their octet unless another atom donates a whole electron pair (2 electrons instead of 1). This is known as a coordinate covalent bond.

BryantChung_4B

Simple formal charge calculations. The carbon atom, for example, has 4 valence electrons, but if you take the electrons in a CO molecule (2 lone electrons and 3 bonded electron pairs) you will get 4 - 5 = -1 formal charge.

BryantChung_4B

Coordinate covalent bonds allow certain atoms to complete the octet. Boron, a big example, needs to accept a whole lone pair from another atom to complete its octet.

BryantChung_4B

BeCl2. As stated, the molecule with smaller electronegativity difference has more covalent character. A larger difference becomes more ionic.

BryantChung_4B

The electron geometry is considering all areas of electron density. Because this molecule has 5 such areas, it would be a trigonal bipyramidal shape. However, because one of the areas is a lone pair, the actual shape is a see-saw

BryantChung_4B

Should be fine, it makes sense to do homework on whatever you studied.

BryantChung_4B

The goal of the VSEPR model is showing how each region of electron density repels others. You do not always remove non-axis electrons first, it depends on whatever creates the farthest distance between each electron density region.

BryantChung_4B

Diatomic molecules like NO are always linear, as there's only one way to connect them. But this molecule is indeed polar because of the electronegativity difference between N and O.

BryantChung_4B

The shape is always linear, just make sure not to confuse it with polarity. Diatomic molecules are not always nonpolar.

BryantChung_4B

Atomic radius only affects bond length. For VSEPR, you don't need to worry about atomic radius, just look at the areas of electron density.

BryantChung_4B

Dipole moment is just a term to describe attraction between molecules. Atoms in a molecule like H2O are unequal in electronegativity; the O atom pulls electrons more strongly, obtaining a partial negative charge, while the H atoms become partially positive. This creates a dipole.

BryantChung_4B

Whether the bond is single, double, or triple, it is still grouped as one area of electron density, so it can be treated the same as a different type of bond.

BryantChung_4B

There are resources and charts to show the bond angles of specific shapes. The angles themselves though are determined by the areas of electron density repelling each other.

BryantChung_4B

The basis of VSEPR is that areas of electron density repel each other and try to get as far from each other as possible. This repulsion determines the shape of the molecule and how the atoms are positioned.

BryantChung_4B

You probably already tried, but just make sure you use LL14A19, which is the password he gave us.

BryantChung_4B

If there can be a resonance structure with no formal charges on any atoms, that will be the most stable structure. However, if this is not possible, you would indeed place the charge on the more electronegative atom.

BryantChung_4B

The exam already passed but for future reference, it's good to draw the different resonance structures. Usually the question will ask for this.

BryantChung_4B

Like the above post says, probably about a week. It mostly depends on how fast the TA's will grade the tests.

BryantChung_4B

One tip is that in most examples I've seen, the central atom will NOT have the single electron. This is not the specific rule, but we've learned that the central atom is least electronegative, so that one will not pull electrons as strongly as the outer, more electronegative atoms.

BryantChung_4B

The lowest energy is basically just a way of saying which bond is likely to form. NaCl, for example has a large electronegativity difference between Na and Cl, making it ionic.

BryantChung_4B

Resonance hybrid is how a molecule actually appears, when all the possible resonance structures are blended together.

BryantChung_4B

Yes, like the above student said, the numbers should add up to the charge of the actual molecule, showing that it is indeed the most favorable model.

BryantChung_4B

The textbook includes formal charge numbers just to show which resonance structures would be more favorable, but it isn't required unless asked.

BryantChung_4B

The position of double bonds can change between resonance structures, because the electrons are not in a specific place but rather scattered around the atom. This is why they are called "delocalized."

BryantChung_4B

Yes, it might be confusing because 3d comes before it and d is higher energy, but you can just think of the highest shell (n = ...) as the outer layer to take electrons from.

BryantChung_4B

Fluorine only has electrons in the n=2 shell, meaning there are no higher layers to "shield" the positive charge from attracting electrons. It also has the highest number of protons in its period, making the nucleus attract electrons very strongly.

BryantChung_4B

Yes, but if you are referring to the electronegativity difference between two atoms, you can just know that ionic bonds happen when the electronegativity difference is greater than 1.6.

BryantChung_4B

Kennedi3K wrote:Is this the same for ionization energy?

Yes, if electronegativity increases, the nucleus attracts electrons more strongly, meaning the electrons are also harder to remove.

BryantChung_4B

I don't know any mnemonics, but I can try to help. If we're just talking about electron affinity, ionization energy, and atomic radius, you can just remember one: that atomic radius increases as you go to the left and downwards. The other 2 trends are just the opposite (IE and electron affinity incr...

BryantChung_4B

Px, Py, Pz just refers to the orientation of the P orbital, the subscript x, y, z, means that the orbital is positioned along whichever axis.

BryantChung_4B

I'm not sure how to tell if an electron is in up or down spin state, but just know the spin quantum number (m_s) can only be -1/2 or +1/2, meaning down spin and up spin respectively.

BryantChung_4B

Yes, the quantum numbers tell you things like which subshell and orbital, using this information you can know the electron configuration.

BryantChung_4B

It would increase. Simply increasing the intensity (or number) of photons will not eject more electrons, but increasing the frequency will.

BryantChung_4B

Basically looking at something is just processing visible light. Generally we know that visible light wavelengths range from about 400 to 700 nm, so 600 nm would be suitable for reading.

BryantChung_4B

As the others have stated, the difference between solution and dilution is almost like creation and modifying. Dilution is simply using a concentrated solution to create a less concentrated one.

BryantChung_4B

Thank you for ur PSA!

BryantChung_4B

You're given one thing: the molar mass of M(OH)2. We can subtract molar mass of (OH)2 from this to find the mass of M, the unknown metal. Next, the sulfide is simply the molecule after (OH)2 is replaced by a sulfur ion, becoming MS. You can just add the known mass of M to the mass of sulfur to find ...

BryantChung_4B

I'm not completely sure, but there can be times where a constant is given like the speed of light c (3 x 10^8). In that case, you would not have to take into account that the constant only has 1 sig fig, it is just given to complete calculations.

BryantChung_4B

I just wrote mine with pencil, as it wasn't really specified :)

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