CHEMISTRY COMMUNITY

SophiaBarden 2E

We primarily look at water when observing Hydrogen bonds. In the gas phase, molecules are in constant motion. Each gas molecule moves independently of the others, therefore, there are no hydrogen bonds forming. In liquids, the molecules slide past each other freely but move in relation to one anothe...

SophiaBarden 2E

There are a couple rules when dealing with equilibrium constants and combining equations. When you are adding two equations together, then you multiple the Ks together. When youre substracting one reaction from another, then you divide respectively. But remember when youre manipulating on equation t...

SophiaBarden 2E

I think in general when calculating equilibrium compositions, you solve for K using the reaction as they have it written out for you. For #4 you just need to calculate Kp as [Pproduct]/[Preactants] using the ICE chart and use x to add up the total pressure

SophiaBarden 2E

I assume the time that it takes for a reaction to reach equilibrium really depends on how much you perturb the system. So if you had a little vs a lot of reactant then it would take varying amounts of time to reach Equilibrium.

SophiaBarden 2E

K is the equilibrium constant, basically meaning the ratio of products to reactants. Now whenever something in the reaction is changed, the amounts of each thing will shift in a way that creates the same ratio as before(reaction will work to go back to K). So if the products in a reaction were sudde...

SophiaBarden 2E

Lavelle mentioned that we currently dont have the tools to solve this type of problem, but that we will be able to in the future units! I think understanding the trends is important right now and having a good understanding of that will prepare us for when we are presented with a more concrete probl...

SophiaBarden 2E

K, the equilibrium constant, is the ratio of products to reactants. Applying the Le Chateliers principle to a system that under goes a pressure change, that reaction will adjust to minimize the effects of said change. This means while the change in pressure does cause a change in concentration, the ...

SophiaBarden 2E

So try an remember that bond angels depend on the structure of the molecule. Think of using the VSEPR notation to help you out! linear, AX2 (180), trigonal planar AX3 (120), tetrahedral AX4 (109.5), octahedral AX6(90, 120, 180) So now when we have molecules with lone pairs, say a molecule like a Ang...

SophiaBarden 2E

Many atoms that have access to the d orbital can have expanded octets. In general, we probably wont see any outside of the normal ones like P, Si, Cl, S, but basically any element beyond the third principle level is able to form expanded octets!

SophiaBarden 2E

When we have ions bonded to a bracketed [] compound, the we take the charge of the full compound into consideration, not just the charge of the metal. For b, c calculate the charge of the compound (sulfato with a 2- and Cobalt with a 3+) which is an overall charge of +1, and we add subsequent Chlori...

SophiaBarden 2E

So in most of these examples, the cation/anions connected to the acid/base are going to dissociate when placed in water! lone anions/cations are called specators, because they don't affect the pH of a solution (Na can neither steal or donate a H atom). For the first example, i honestly have no idea ...

SophiaBarden 2E

For the bases, Sr(OH)2 and KOH, we can tell the Sr(OH)2 would be a stronger base because it contributes two OH- to a solution, compared to one by KOH.
NH3 is normally a very weak base.
For the acids HbrO and HclO4, the HClO4 is a strong acid with a much higher pH than the HbrO.
hope this helps!

SophiaBarden 2E

Im kind of confused on the relationship that pKa has in terms of pH. I know it is for weak acids, but what kind of calculaions might I need to be aware of?

SophiaBarden 2E

Lavelle said we should be able to recognize the ligand names and nomenclature. Iron involve in coordination compounds are always Ferrate, but in normal compounds, they are normally just iron.

SophiaBarden 2E

So I am trying to study for the final and complete the textbook problems but they are... not showing up? I will have some part of the question and then it will give options like a) b) c) but they arent completely blank. I've tried different browsers/ restarting / and have had this problem since yest...

SophiaBarden 2E

Yes! You will need a periodic table in front of you as well! There are two general rules when it comes to measuring acidity of a compound: 1 - Longer bonds are weaker bonds, so the longer/weaker a bond is between the Hydrogen and other atom, the stronger the acidity! (This is because the strong acid...

SophiaBarden 2E

In anyone else having trouble accessing the lectures on CCLE? I haven't been able to watch Friday's lecture since I started trying to this morning and I was hoping it would be fixed by now.... Also would like to note that the UCLA VPN/ reloading / restarting didn't help me at all so must be a CCLE i...

SophiaBarden 2E

Yes but actually calculating bond angles are beyond the scope of this class so most of the time, we just state that the angles are approximations

SophiaBarden 2E

Acids are primarily : nonmetal-oxides
Bases are primarily : metal-oxides
- simple molecules containing Nitrogen are normally basic
Amphoteric : Metalloid-oxides including (but not limited to) Be, Sb, Sn, Al, Ga, Pb
- H2O is also amphoteric

SophiaBarden 2E

When trying to find the charge of a metal in a complex that you are unfamiliar with, it is best to calculate the formal charge of each atom respectively. Then do the equation [overall charge] - [sum of all formal charges] = the oxidation number (charge) of the atom you need. For example, finding the...

SophiaBarden 2E

An en ligand is neutral and the edta ligand has a 4- charge. My TA mentioned that we should memorize these and the ones on the paper that Lavell posted on his website! He may provide teh charge but It is always better to be at least familiarized and more prepared for the final. [url]https://lavelle....

SophiaBarden 2E

Just a reminder for freshman as well, the first two years of a bio major are meant to "weed out" people. But don't let that get to you, especially if you have not finished the LS7 series!!!! It is definitely difficult and meant to basically introduce you to every possible biology concept u...

SophiaBarden 2E

Cyanido and cyano are actually the same. They both denote CN- Ligand bound to the transition metal. Lavelle mentioned in lecture that there is actually a new way of naming complexes and that either work (but i would stick to his way, which is cyano). Here is a link from the website that Lavelle ment...

SophiaBarden 2E

In order to find the number that comes after a metal when naming compounds, you must first understand that it is the oxidation number! This basically means the charge on the metal atom, in most cases, they will provide the complex charge and you must calculate the formal charges of all the atoms wit...

SophiaBarden 2E

This is a cool Chemistry tool that my friend showed me because I was having a hard time with the visualization of molecules and 3D structures. I just wanted to place it here to help people out with their studying and homework as we tackle the last weeks of Chem 14A!!! You can search or draw any mole...

SophiaBarden 2E

The most stable lewis structure is what you should use as a template for figuring out the shape/structure of a molecule. I have a hard time visualizing 3D models as well so I use this cool website that you can search any structure up and it provides you with a 3D model to interact with! This was hel...

SophiaBarden 2E

https://molview.org/?cid=962 I depend a lot on visualization and structures to understand molecules so I sometimes use this cool website. It lets you search any molecule and then displays the lewis structure and most importantly, the 3D model that you can interact with. This also helps with equator...

SophiaBarden 2E

Here is a helpful little way to remember, but I believe it is also realllyyyy important to understand why the hybridization occurs rather then memorize the numbers. https://d3i71xaburhd42.cloudfront.net/ac73a46dc482862c4baa12b73f648f3dd3fa5989/28-Table1-1.png The attachments ^ means the number of bo...

SophiaBarden 2E

This is a little look into organic chemistry, so when working with Carbon, it super important to remember that they tend to form ring structures! The Carbons joinn together in cyclic rings and the Hydrogens are bonded to each Carbon, but not involved in the ring structure!

SophiaBarden 2E

Structures must be resonant structures if the delocalized electrons are in equivalent positions across all structures. It is helpful to make sure that the number of bonding pairs and lone pairs of electrons are equal. The overall formal charge must be equal as well.

SophiaBarden 2E

So generally speaking, pi bonds are the second bonding pair in a double bond. When we encounter structures that have resonance (multiple structures with bonds in different but equivalent positions), then we see delocalized pi bonds. Think of them as an extra bonding pair of electrons that doesn't st...

SophiaBarden 2E

Localized electrons are electrons that are involved in bonding with other atoms. We encounter delocalized electrons when we are looking at molecules that have resonance structures. If the pair of electrons can be involved in bonds in different but equal positions, then they are delocalized

SophiaBarden 2E

The sapling provided some help on equatorial vs axial but I still do not understand how we might form a 3D structure of a molecule without knowing beforehand how many atoms are in each plane?

SophiaBarden 2E

Considering we had class on the school holiday, its a safe bet to except a lecture!! Im sure TA's will send ou8t a email if your discussion is on thursday or friday so keep an eye out for that!

SophiaBarden 2E

Viscosity and Surface tension are directly related to one another; increase viscosity then the surface tension increases. This is due to the intermolecular forces between molecules. Take a look at water! Water has surface tension that stems from hydrogen bonding between H20 molecules, this means tha...

SophiaBarden 2E

So we have only written our electron configurations in "ground state" for our atoms in this class, and i think it is a safe bet that we wont go beyond that. But you can write your hybrid orbitals in electron configurations when filling it out for hybrid molecules!

SophiaBarden 2E

The octet rule would only be "broken" if an atom has more than 8 valence electrons filling its outer orbital. You most make sure you calculate the total electrons involved in a molecule and make sure to calculate the formal charge of each atom. As with every chemistry rule, there are many ...

SophiaBarden 2E

You will always be provided with a Periodic table in which you can determine the charge difference between atoms. A higher charge difference between two atoms will mean the electrons in the covalent bond are not exactly equally shared. Using the Periodic table and charges from there, you should be a...

SophiaBarden 2E

Ionic bonds form between atoms with high electronegativity differences (a cation and anion), and is generally between metals and nonmetals. Covalent bonds generally form between two nonmetals, and the difference in electronegativity largely contributes to the ionic character of the covalent bond. In...

SophiaBarden 2E

Lavelle mentioned in his lectures that it will be important to remember the NAMES for bond angles of different structures (i.e. Linear, Trigonal Planar, Octohedral). Be able to recognize these patterns among molecules and look at the textbook example problems that lavelle assigns!

SophiaBarden 2E

The final date and time is on December 13th. from11:00am-1:30pm on a sunday! It is cumulative and my TA said it will reflect the two midterms so most likely multiple choice but plan for many more questions! It covers everything that we have learned and normally has homework/textbook problems on it s...

SophiaBarden 2E

Look at what blocks and element types each atom belongs too. A general rule to follow is that ionic bonds form between atoms with high electronegativity differences, and is almost exclusively between cations and anions. This generally means the bond is between a metal and nonmetal. On the other hand...

SophiaBarden 2E

Due to the lone pair on the Nitrogen, these elctrons have a much stronger repulsion to the bonded electrons between the Nitrogen and Oxygens. This stronger repulsion results in the angle you see in the structure, as the lone electron pair repels the Oxygens with a stronger force than they repel each...

SophiaBarden 2E

I believe it is due to the fact that rod shaped atoms have more surface area to interact with one another. The less distance and resulting more interaction between the two atoms creates a stronger dipole moment.

SophiaBarden 2E

Lavelle explained that Hydrogen bonding occurs in H2O but not H2S but I did not really understand why? H2S seems to fit the description of an H atom covalently bonded to an electronegative atom and close to the electronegative S in another H2S molecule would form a H bond (why does that not occur?)

SophiaBarden 2E

Lavelle is expanding on the previous knowledge that you learned in highschool, and this higher level chemistry often comes with many more exceptions! Oxygen often loans it's lone e- pair in something called coordinate covalent bonding (covered in the 11/04, Wednesday lecture). Hydrogen bonding can a...

SophiaBarden 2E

The oxidation number of an ion is synonymous with the charge on an ion. So Cl has an ionic charge of -1 and therefore an oxidation number of -1. Elements Cl, Br, and I have different oxidation numbers when bonded to F or O. In the case like ClF, the Cl oxidation number is +1 because F has a -1

SophiaBarden 2E

Here is a helpful graphic that is much easier to understand than my lengthy explanation!

SophiaBarden 2E

The protons and neutrons are clustered tightly in the center of an atom (the nucleus). Their masses contribute to most of the atom's atomic weight because electrons are much much smaller. However, electrons orbit the nucleus rather than cluster together. The bigger the nucleus (the more p+ and n), t...

SophiaBarden 2E

When dealing with molecules that have multiple potential structures (resonance structures), to find the most stable structure, you calculate the molecule formal charges. Choosing the molecule that has the smallest formal charge normally indicates which structure is most stable(and sometimes most oft...

SophiaBarden 2E

In lecture he denotes the arrow in dipole moments to point towards the atoms/molecule with the more negative charge. I believe that if you are able to discern the correct partial charges for atoms in a molecule, then that should be sufficient information for exams!

SophiaBarden 2E

Is a Hydrogen bond considered a coordinate covalent bond, or a distinct other type of bonding that occurs?

SophiaBarden 2E

I understand that some elements like Chlorine and Sulfur are able to expand their octets. Will we have to draw any Lewis dot structures with these expansions (what would the correct notation for that be), and how might we gauge whether an element will have an expanded octect??

SophiaBarden 2E

The LS7 series can be very time consuming but the most relevant information for tests is always presented in lectures! Launchpad is an online course that you must complete before each class, but for the most part, it is an information dump that you simply have to sort through by tuning into the most...

SophiaBarden 2E

My TA mentioned that the midterm would be a couple more questions but the total amount of points it is worth will be fairly close to midterm 1's points. Lavelle mentioned that the freebie question was likely a one time thing so I wouldn't expect something like that to show up on the second midterm.

SophiaBarden 2E

Third period elements (like Cl and P etc) have an n=3 and 5 d-orbitals. This makes it possible for a select number of elements to expand their octets. Normally the energy of empty 3d-orbitals is higher than 4s orbital, but the difference can be so small that d orbitals acquire more electrons to expa...

SophiaBarden 2E

I found that the textbook problems were super helpful!! They often get more complex than examples on sapling or in lecture so it really solidifies your understanding of the concepts. Also going to multiple Peer learning workshops is very helpful!

SophiaBarden 2E

I also found that we often have to use the same two equations ( c=λv, E=hν) and move them around in different ways (hence the E=hc/λ) in order to find the necessary components to a problem. I find it helpful to write out what each variable represents and the units because then you know what informat...

SophiaBarden 2E

Crash course chemistry is also a great place to find the basic information very clearly explained with plenty of examples. Plus, the information is portrayed in a fun and engaging way!

SophiaBarden 2E

Rewatching the lecture video from last Friday, i was trying to understand why we add/subtract the electrons from the charges when calculating the total valence electrons in each molecule. Where do those electrons come from and why do we count them in our structures.

SophiaBarden 2E

I ordered my textbook and access code on September 28 and then I got an email that it was shipped on Oct 8. My free trial just ended (great timing two days before midterm) and i still haven't received the access code. Is anyone experiencing similar problems/ have any idea what to do?

SophiaBarden 2E

In what context or problem are you talking about? remember the "normal energy" is the amount of energy/light being exerted onto a metal in cases like the photoelectric experiment. The work function is the amount of energy required to eject an electron from the surface of a substance. There...

SophiaBarden 2E

From friends that have taken Lavelle's classes before; The sig figs matter! Lavelle will give you options that give the same answer but with varying sigfigs to test your knowledge (and rounding ability for some reason lol). So make sure you use the exact values given on the constants and equations s...

SophiaBarden 2E

The homework textbook problems are awesome practice for the midterm!! Everyone that i know that has taken this class told me that homework problems always show up on the exams (and Lavelle mentioned it as well), and the exam problems follow the same format as many homework problems. Making sure you ...

SophiaBarden 2E

We only look at the ratios between the same element when looking at the ratio of Cu and CuBr2. So there is 1 Cu : 1 Cu

SophiaBarden 2E

In the audio visual lectures, Lavelle even rounded numbers as far as .2 off. I think a good rule of thumb though is anything more than .2 from a whole number should be further multiplied out to get the ratios.

SophiaBarden 2E

Given the structure of each molecule, you are also able to figure out the molecular formulas from them! A general rule of thumb is that each question that Lavelle gives should have all the information necessary to solve it (no google allowed during tests)! Each corner of the molecule will be a Carbo...

SophiaBarden 2E

Doing all the steps together (using parenthesis to separate and organize the problem) on a scientific calculator is ideal! And remember to not round your answers until the very end. You may find that with a phone calculator, it is much harder to keep track of complex equations, and often is not as a...

SophiaBarden 2E

In my discussion class, my TA said that 0.500g is only 1 significant figure. I am pretty sure it was 3 significant figures, but I just wanted to double check here. The Sig figs sheet on Lavelle's website states that trailing zeros with a decimal point are counted as significant. Take a look at that...

SophiaBarden 2E

Does Sapling homework normally take into account the sig figs? I had some problems submitting an answer with the correct rounding and took multiple tries.

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