CHEMISTRY COMMUNITY

Brian Kwak 1D

Lewis acids accept a pair of electrons and Lewis bases donate a pair of electrons. So an example would be BF3 and NH3. Where NH3 can form a bond with BF3 by donating its electron pair to boron. In this example BF3 is a Lewis acid and NH3 is a Lewis acid.

Brian Kwak 1D

Greek prefixes are used to designate the number of each type of ligand in the complex ion, e.g. di-, tri- and tetra-. If the ligand already contains a Greek prefix (e.g. ethylenediamine) or if it is polydentate ligands (ie. can attach at more than one binding site) the prefixes bis-, tris-, tetrakis...

Brian Kwak 1D

No we won’t have to know how many rotations but it is an important concept in my opinion because if a question asks how many places a ligand can bind you would have to draw the molecule out and then see how many lone pairs it has to donate to figure out if it’s monodentate, bidentate and etc.

Brian Kwak 1D

Ligands are ions or neutral molecules that bond to a central metal atom or ion. Ligands act as Lewis bases (electron pair donors), and the central atom acts as a Lewis acid (electron pair acceptor). Ligands have at least one donor atom with an electron pair used to form covalent bonds with the centr...

Brian Kwak 1D

A coordination complex is the product of a Lewis acid-base reaction in which neutral molecules or anions (called ligands) bond to a central metal atom (or ion) by coordinate covalent bonds. The coordination sphere of a coordination compound or complex consists of the central metal atom/ion plus its ...

Brian Kwak 1D

AX3E2. From this we can see that the central atom has 5 areas of electron density so the shape is trigonal bipyramidal. Now when it comes to naming the shape only the molecules connected to it count towards its name and we can see that only 3 molecules are attached. Now for a trigonal bipyramidal wh...

Brian Kwak 1D

Prioritize the valence electron/octet guideline and then the charges. For charges you want the lowest charges possible and the separation of charges.

Brian Kwak 1D

I don’t know if this will help you remember the definition but the prefix intra means within,inside, on the inside and the prefix inter means between. So using that logic intermolecular forces would be forces between molecules and intramolecular forces would mean forces inside the molecule like cova...

Brian Kwak 1D

The highest energy level electron would be lost first. For elements in the 4th row it’s important to note that the 4s is a higher energy level than 3d so if the configuration only has 3d and 4s orbitals then 4s would be lost first.

Brian Kwak 1D

dipole moment would be calculated by the electronegativity difference between the atoms then you use that to figure out the intermolecular force. The dipole moment cancels in CO2 due to the shape. N2 has no dipole moment because there is no electronegativity difference. So the only forces would Lond...

Brian Kwak 1D

Yes we will be given the molecular formula unless it’s a question that wants us to find it like in test 1. The reason the textbook doesn’t write it out is because you have access to the book and can look it up in the book( or that is what I am assuming).

Brian Kwak 1D

I am not going to repeat what hanna said, but to answer your question about hydrogen bonds. Hydrogen bonds only occur with N, O, F that is attached to a hydrogen and it is a type of dipole dipole interaction.

Brian Kwak 1D

I would also like to note that if they don’t directly give you the energy of the photon, but give you frequency or wavelength then you will have to use the equations c=λν and E=hν to find the energy of the photon then plug it into the equation E(Photon) = Work function/threshold energy - Kinetic ene...

Brian Kwak 1D

So the ground state for the neutral copper is [Ar] 3d^(10) 4s^(1) and remember that if it is an ion like Cu+ you would have to remove the highest charged electron because it is easier to remove than a lower charge and in the configuration the highest in energy is 4s so it will be the easiest to remo...

Brian Kwak 1D

If the question asks you to find the configuration of an ion you would have to first find the configuration of the neutral atom and then account for the charge of that ion. For example if it is a - charge you add an electron and if its + you remove an electron.

Brian Kwak 1D

For the purposes of this course you only need to know Cu and Cr, but all the elements in those rows show the same pattern because it is more stable for the elements to be either have all the d orbital filled with electrons or half filled.

Brian Kwak 1D

Mn would have 7 valence electrons. If you look at the configuration which is [Ar] 3d^5 4s^2. You can see that there is 7 electrons which could possibly be used to bond and since its in the 4th period. Since argon is a Nobel gas the electrons in those states/orbitals will not bond because it is alrea...

Brian Kwak 1D

It depends on the question if they ask for the ‘full ground state’ then you cant use the short hand, but if they don’t then you could write it as [Ar] to represent that it lost the 2 electrons from the +2 charge. If the question states you can use the abbreviation then yes, if not then no.

Brian Kwak 1D

This would be a multi step problem. First to use the equations E=hν and C=λν , if they gave you the frequency of the photon. Then once you have that information you could solve for the work function if they provided you with the kinetic energy of the ejected electron. Then you could use all the know...

Brian Kwak 1D

Depends on the know information you have. If you know the kinetic energy of an electron then you could use 1/2mv^2 or if you know the momentum of the electron then you could use p=mv. Also the units for momentum would be kg.m.s^-1.

Brian Kwak 1D

You can try http://gen.lib.rus.ec/
Library genesis might have the pdf version or not I’m not too sure. Also you can download the pdf version of your books if your taking other classes at UCLA. It’s definitely a useful resource.

Brian Kwak 1D

For the exams will the states always be given or would we have to extrapolate that information?

Brian Kwak 1D

When the energy of light(photon) is equal to the work function(threshold energy). For me it’s easier to think of it in terms of the law of conservation of energy and the equation: energy of light(photon) = threshold energy(work function) + kinetic energy of electron(excess energy in the form of kine...

Brian Kwak 1D

Like everyone stated before you would use both the equations C=λv and E=hv. It’s important to note that the equation with speed of light is only applicable to problems dealing with light. You can then reconfigure the equations to solve for the variable you are looking for.

Brian Kwak 1D

Other than the metal becoming a cation are there any other structural changes in the metal? Like would the electron orbital be closer to the nucleus because of the loss of the electron?

Brian Kwak 1D

Density is the ratio of mass to volume, mass/volume(either in liters or meters cubed). DENSITY is a physical property of matter, as each element and compound has a unique density associated with it. Density defined in a qualitative manner as the measure of the relative "heaviness" of objec...

Brian Kwak 1D

0 kelvin is the lowest possible temperature. Absolute zero is defined as 0 kelvin, which is the lowest possible temperature. Also it may be easier to remember that kelvin is a absolute Temperature scale so absolute 0 logically would mean 0 K.

Brian Kwak 1D

Atomic mass is related to a single element while molar mass is the total mass of the compound. So you would need to sum the atomic masses of the compound(molecular formula) to get the molar mass of the compound. It’s important to note that atomic mass and molar mass is g/mol.

Brian Kwak 1D

As previously stated the molecular formula can not be solved without knowing what the molar mass is. If you have the molar mass then you can divide the molar mass by the molar mass of the empirical formula, if you calculated the empirical formula. Now if you have the molar mass of the molecule and t...

Brian Kwak 1D

For the examples you provided Professor lavelle does not expect us to know the molecular formula, but for common things like diatomic molecules and water and carbon dioxide we may need to know what they are.

Brian Kwak 1D

It is because of the concept of conservation of mass which states that in an isolated system mass can not be created nor destroyed by chemical reactions or physical transformations. Since the chemical reaction can not destroy or create mass the number of elements from the reactants must equal the nu...

Brian Kwak 1D

He will be posting the working sheet which is already up. Just need to search up Pork Ramen and also he will not be posting the answer key.

Brian Kwak 1D

Thank you for posting this! It was helpful with my studying!

Brian Kwak 1D

Thank you Lyndon for the help this quarter!

Brian Kwak 1D

Also wanted to note that the rate laws on the constants and equation sheet will not be labeled which order it is for. So I would recommend getting familiar with the different formulas for zero, first and second order formulas and how to use them. As Saman has sated it may be helpful to know how to d...

Brian Kwak 1D

A reaction which is not first-order reaction naturally but made first order by increasing or decreasing the concentration of one or the other reactant is known as Pseudo first order reaction. In pseudo-first order reactions, we are basically isolating a reactant by increasing the concentration of th...

Brian Kwak 1D

I use an iPad Pro with notability for hand written notes as well as recording the lectures. After the lecture I take some time to review the notes and periodically try to retrieve the information that he covered in lecture and concepts throughout the week to refresh my memory and using my notes as a...

Brian Kwak 1D

Review sessions information is now posted on his website. Started today and there are review sessions until the Saturday before the exam.

Brian Kwak 1D

The rate laws will be given but will not be labeled which order it is. I recommend familiarizing yourself with the derivative and integrTed rate laws so you can recognize which is for which order of reaction.

Brian Kwak 1D

The overall reaction would be the sum of all the exponents in the rate law for that reaction.

Brian Kwak 1D

A reaction mechanism is the step by step sequence of elementary reactions by which overall chemical change occurs. A chemical mechanism is a theoretical conjecture that tries to describe in detail what takes place at each stage of an overall chemical reaction.

Brian Kwak 1D

As everyone stated before n represents the moles of electrons. To figure it out you could do the reduction and oxidation half-reactions for the reaction to calculate it. Balance the reactions so there are equal number of electrons for both the oxidation and reduction half reactions. I just want to n...

Brian Kwak 1D

I had a question about the cell diagram. If the anode or cathode has elements that do not go under a phase change we annotate it as Fe3+(aq),Fe2+(Aq)ΙPt(s) right? Also when there is no phase change and no metal we add a inert metal to the cell diagram right??

Brian Kwak 1D

When balancing half reactions first balance the Oxygens with H2O then depending on the type of solution it is you either add H+ to balance the hydrogens from H20 (in an acidic solution, usually the question will explicitly state it) or OH to balance the H from H20 (basic solution).

Brian Kwak 1D

It is a multi-step process where first you use q=nCΔt and rearrange the equation to solve for the specific heat because the specific heat is needed to solve for ΔS=nCln(T2/T1).

Brian Kwak 1D

If you are referring to the changes in entropy due to changes in temperature and volume then yes. Since entropy is a state function. You can add the entropy values due to changes in volume and temperature.

Brian Kwak 1D

Entropy is a STATE FUNCTION. So therefore entropy is path independant meaning that you only need the final and initial values to calculate the entropy.

Brian Kwak 1D

Thank you for the review session! I also thank you for posting these notes to help supplement my own notes and conceptual understanding of the material!

Brian Kwak 1D

I think the most important part for atm and bar is to be consistent with the units throughout the calculations so you don’t get points deducted. I would really pay attention to the wording of the problem if they give you atm then just use atm throughout your calculations. Consistency is important, t...

Brian Kwak 1D

Lyndon is a very busy man... he hasn’t made the worksheets yet but he will over the weekend from what he told me. I believe it will be named hotdog because Dr.lavelle made a joke about naming it that and ... maybe just maybe it will be named HOTDOG! But don’t quote me on that. Also the time is at 7p...

Brian Kwak 1D

I read the textbook but in a very organized way. Since there is a lot of information in the textbook which can sometimes make it confusing and hinders your comprehension. I use the outlines for each section and cater my reading to focus on the things that were on the outline. For example I would rea...

Brian Kwak 1D

Just asking for clarification but for an Adiabatic isolated system as dr.lavelle stated that there can be exchange or more specificly loss of internal energy as work correct? So compared to an isolated system where there is no exchange of matter or energy because there is no surroundings therefore m...

Brian Kwak 1D

Could anyone help me with these two terms. I know that a adiabatic isolated system is one with adiabatic boundaries where energy can leave as work and there is no exchange in matter or energy. An isolated system is one where there is no exchange of energy and matter. I am having difficulty understan...

Brian Kwak 1D

Methods one and three are more accurate than method 2. The reason is because for the bond enthalpy chart, it has the average values of the bond enthalpies and doesn’t take into consideration the reaction. Methods 1 and 3 should yield similar results that are more accurate than method 2. It really de...

Brian Kwak 1D

Two elements are liquid in their standard state: mercury and bromine. Eleven elements are gas in their standard state. All of the noble gases (He, Ne, Ar, Kr, Xe, Rn) as well the halogens flourine and chlorine. Hydrogen, oxygen and nitrogen are the others. All other elements are solid in their stand...

Brian Kwak 1D

Molecules in their standard state (most stable) have an standard enthalpy formation of zero. It is important to note “Standard” which refers to a specific pressure which is 1 atm and a specific heat which is 25 degrees celcius. If a molecule is in its most stable state at 1 atm and 25 degrees celciu...

Brian Kwak 1D

I also wanted to input that pH is also related to the concentration of Hydronium ions (H3O+). For example if you have a pH of 1 to convert that into concentration you would take the antilog of -1 (The reason you take the antilog is because pH=-log[H3O+] and we know that the ph is 1 so we solve for t...

Brian Kwak 1D

I posted a photo further specifying significant figures for logs. But as it states on dr Lavelles PDF of “More on Significant figures” how ever many significant figures in the number your calculating is how ever many significant figures you have after the calculation.

Brian Kwak 1D

Sorry could you specify what question it is? Also there is a solution manual errors pdf on Dr.Lavelles website (Chemistry Community). All solution manual errors would be on that pdf. If its not on there then you could always back track to see if there were any errors calculating.

Brian Kwak 1D

Thank You for the clarification! So, can I assume that if Professor Lavelle asks a question pertaining to finding Pressure, Temperature, Moles, or Volume to use the Ideal gas constant to calculate it, if I am given the other variables?

Brian Kwak 1D

We multiple it because we want to find the K(constant) for the given equation: 2BrCl(g) + H2(g) =(this is suppose to be the forward and reverse reaction) Br2(g) + 2 HCl(g). If you derive the Equilibrium constant for this equation it gives you: ([HCl]^2 [Br]^2)\([Brcl]^2 [H2]) If you add the equation...

Brian Kwak 1D

I am confused of when to use the Combined Gas Law. I know that if I am give moles and other information that I can calculate for Pressure, Temperature, or Volume, but when would I have to use the Combined Gas Law? If they change the variable and ask a question where the volume and temperature change...

Brian Kwak 1D

If I am not mistaken it is because when you multiple K1 and K2 (the equilibrium constant equation for both of the given chemical reactions) you the equilibrium constant for the given equation after you do the algebra and cancel out the Cl2. It makes more sense when you write out the Equilibrium cons...

Brian Kwak 1D

I don’t think we have to since it wasn’t really covered in lecture from what i remember, but i would remember the how to calculate pH and pOh which is -log[H] and -log[OH].

Brian Kwak 1D

What exactly do we need to know from this section for the final exam?

Brian Kwak 1D

Also wanted to stated that the trend also applies to electronegativity as well.
Decreases down a column and increases acreage the row.

Brian Kwak 1D

Answering with slightly less than 109.5 is what Lavelle probably expects. From speaking with friends that took this course previously that would suffice for an answer.

Brian Kwak 1D

Single > double > triple bonds. My thought process is that since double and triple bonds have pi bonds, which are overlap/side-to-side orbital interactions the bonds have to be closer than a single.

Brian Kwak 1D

AX2, AXE, AXE2, and AX2E3 are the only linear structures.

Brian Kwak 1D

Thank you guys for posting this. Missed some lectures due to a concussion and you guys just saved my life.

Brian Kwak 1D

Sorry I cant find the midterms from last year would the person that found it be so kind enough to elaborate so use laymen can find it to practice?

Brian Kwak 1D

No cheat sheets sorry. I asked people that previously took this course and nope there will not be any cheet sheets or open notes allowed. The periodic table and list of constants and equations will be given unless things have changed like the last 2-3 quarters.

Brian Kwak 1D

Its completely free response.

Brian Kwak 1D

I would recommend using a systematic approach to these kinds of problems. Just write the equation that you need to use to find the answer and if you don’t have all relevant information for that equation them most likely you would have to use another equation like de Broglie to get that information a...

Brian Kwak 1D

Thanks for clarifying!

Brian Kwak 1D

I don’t think knowing the possible resonance structures would be important. Working through some of the practice exams I got didn’t see any questions where they asked to draw all resonance structures or asking how many possible ones there are. So far I have been drawing the most stable Lewis structu...

Brian Kwak 1D

Thank you for the clarification.

Brian Kwak 1D

Thank you for these explanations. Y’all are my heroes.

Brian Kwak 1D

From my limited understanding Protons are what you should be mainly concerned about because the protons are what gives a positive charge for the electrons to be attracted to. Therefor the more protons the higher the positive charge and therefor electrons will be closer to the nucleus.

Brian Kwak 1D

As stated before the Formula is used only to find the Kinetic energy but if you don’t have all the requested information I’m pretty sure you can also use de Broglie equation to help you find that portion. Since the equation is KE= 1/2 MV^2 and you don’t have velocity you can use de Broglie’s equatio...

Brian Kwak 1D

I just had a question. For Ionic and Covalent bonds would it be specifically one or would it be more accurate to say its one a spectrum? For example a Bond would have more ionic properties than covalent?

Brian Kwak 1D

From what my TA said there will be a few common ions that we will have to remember. Didn’t really specify which ones so I understand your pain. Just to be safe though I am remembering all the common ions that Lavelle posted on his site. But I think as long as you know the suffix and prefixes for ion...

Brian Kwak 1D

thank you!

Brian Kwak 1D

Will the formulas and constants always be given on the exams? I’m asking because for test 1 will we always be given them? Or will we have to memorize them as we go like for the midterms and finals?

Brian Kwak 1D

Thank you for the advice its very helpful since I will be taking the mcat sometime next year.

Brian Kwak 1D

No its not part of our grade. Looking at the syllabus it says nothing about the audio visual assignments. I believe its there to help the students that are rusty with chem topics before taking this like such as myself ...

Brian Kwak 1D

Does anyone know if the step up program covers material that the professor covere that week or if they also help with previous weeks materials if we are still struggling even after the practice questions/homework??

Brian Kwak 1D

Yes the molecular and empirical formulas can be the same. Just remember to calculate the molar mass of said compound. Since the empirical formula is the ratio of atoms in relation to the element with the lowest moles.

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