CHEMISTRY COMMUNITY

KaitlynBali_4B

Let's take this reaction for example: NaOH (aq) + HCl (aq) --> NaCl (aq) + H20 (l). This is a neutralization reaction. The Lewis acid is the H+ from HCl because, after dissociating from HCl, it accepts the lone pair of electrons from the oxygen atom on the OH- (that dissociates from NaOH) in order t...

KaitlynBali_4B

According to the Arrhenius definition, it will be obvious whether or not the compound is an acid or a base according to its formula: acids will have an H in its formula and will add H+ to water, and bases will have OH in its formula and will be able to add OH- to water. If the compound is not an obv...

KaitlynBali_4B

So does this increase acidity strength or decrease it? An acid is a relatively strong acid if its resulting anion is stable. An anion with resonance is stable, and so its acid can be considered to be a strong acid relative to other acids. However, it does not mean that the acid is necessarily a &qu...

KaitlynBali_4B

Katherine Brenner 3H wrote:What lecture did we go over this for fall 2019 quarter?

My notes on this topic are from the December 4th lecture.

KaitlynBali_4B

To add on, here are some of the strong bases that I have in my notes from the lecture and from review sessions: Li2O, Na2O, NaOH, KOH, CaO, Ca(OH)2, and Mg(OH)2.

KaitlynBali_4B

The metal cations will have a positive charge that the partial negative charge of the oxygen atom in a water molecule will be attracted to. Because the metal cation is acting as an electron pair acceptor in this situation (by accepting an electron pair from an oxygen atom), it is considered to be an...

KaitlynBali_4B

It is important to note that not all reactions between an acid and a base form a salt and water. Ruby explained that this is what occurs in neutralization reactions. In a reaction between ammonium and water, ammonium is the acid and water is the base. A salt is not formed in this reaction, and it is...

KaitlynBali_4B

Although carboxylic acids are considered to be weak acids, it is also important to remember that the acid can become stronger if the groups attached to the carboxyl group have high electronegativities. However, they will not necessarily be a strong as a strong acids like HCl.

KaitlynBali_4B

The book explains that more electronegative atoms in the conjugate bases of acids is what allows for electron delocalization, essentially the spread of the negative charge of the base, in the anion. This electron delocalization is what allows for the anions to be stable. The book discusses this on p...

KaitlynBali_4B

I also found Figure 6A.6 in the book on page 448 to be extremely helpful. One thing that I found important was that an Arrhenius acid or base is a compound that supplies the H+ or OH-, not the H+ or OH- itself. However, the definition of a Lewis acid would define an H+ by itself as an acid because i...

KaitlynBali_4B

I just wanted to clarify that the book defines amphoteric compounds as compounds that react with both acids and bases, not necessarily as compounds that can act as both acids and bases. That is why aluminum oxide can be classified as amphoteric but not amphiprotic (because aluminum oxide does not ha...

KaitlynBali_4B

It is also important to recognize whether or not the complex has already formed an ionic compound. If the complex has already formed a compound, it may seem like no charge is present. Take note of the charge of the cation or anion that is a part of that compound in addition to its complex. Multiply ...

KaitlynBali_4B

To determine how many bonds a ligand can form, pay attention to number of lone pair electrons it has. For example, diethylenetriamine has three nitrogen atoms each with a lone pair of electrons. This ligand can form three bonds.

KaitlynBali_4B

The book says that if the symbol of the metal has a name that is Latin in origin, then the stem of the Latin name is used in naming.

KaitlynBali_4B

Chelates can form when more than one ligand binds to a metal atom and forms a ring of atoms. If one ligand has more than one atom that can bind to a metal atom, the appropriate chelate ring can form. However, the ligands one these isomers are amines. Amines only have one lone pair of electrons on th...

KaitlynBali_4B

Ligands that form chelates can essentially "extract" metals from certain systems and solutions. That is why they are important in biological systems. Chelates work by binding to metal atoms at more than one point.

KaitlynBali_4B

For the exercises in this chapter, you are usually only determining the shape around one central atom only. After choosing a central atom to focus on, you would look at the bonds stemming from that one central atom only (and ignore the other bonds branching off the other central atom that it is bond...

KaitlynBali_4B

I feel that it is best to memorize the bond angles. However, I have been noticing a trend: when there are three atoms in one plane, the angle tends to be 120 degrees between the bonds, and when there are four atoms in one plane, the angles tend to be 90 degrees between the bonds. The "unique&qu...

KaitlynBali_4B

Simple molecules will usually have a predictable and stable shape. Since molecules tend to usually have one stable structure, I think that molecules, when they are stable, will only have one shape.

KaitlynBali_4B

Dipoles usually cancel when the dipole moment of two atoms are facing the opposite direction.

KaitlynBali_4B

To add onto this, the number of atoms bonded to the central atom will almost always be the best indication of the molecular shape. The book even states that when naming the molecular shape, only the positions of the atoms are considered. For example, if there are three atoms bonded to the central at...

KaitlynBali_4B

Hydrogen bonding is a type of dipole - dipole interaction. It is the strongest type of intermolecular interaction. They are not stronger than covalent bonds. While hydrogen bonds will break with a certain amount of energy (such as the amount of energy it takes for water molecules to break their hydr...

KaitlynBali_4B

In part B, if a molecule has higher vapor pressure, it is because its molecular bonds were easier to break and that is why it evaporated faster. You are correct in your understanding that the hydrogen bonds in the water molecular are strong: this is why it has a lower vapor pressure (its intermolecu...

KaitlynBali_4B

Fluorine is more electronegative, but that only means that it will have a stronger hold on the electrons in its own bond between its central carbon atom than the other molecule will have. This question is asking about intermolecular forces: the attraction between molecules, not the atoms. The argume...

KaitlynBali_4B

- ion-dipole interaction: between an ion and a polar molecule - dipole - dipole interaction: a polar molecule's charge creates a dipole moment in a another molecule (creating an intermolecular bond in the process) - London dispersion: bond between two molecules create by the ceaseless flickering of ...

KaitlynBali_4B

This homework problem asks to explain the difference between the boiling points of AsF3 (which has a boiling point of 63 degrees Celsius) and AsF6 (which has a boiling point of -53 degrees Celsius). They answer key explains that based off the Lewis structures of the molecules, the first one is more ...

KaitlynBali_4B

Just to add on, a coordinate covalent bond looks like a single bond between two atoms. The two electrons are shared between the two atoms in that bond, but those two electrons actually just come from one of the atoms.

KaitlynBali_4B

Why is boron stable with only six valence electrons in a molecule?

KaitlynBali_4B

The book also points out that there is an exception to this hydrogen rule for borane compounds (in these compounds, hydrogen atoms aren't always the terminal atoms).

KaitlynBali_4B

The reason why you want the formal charges of each atom to be close to zero as possible is because it indicates very little rearrangement of electrons around the atoms in the molecule when compared to the arrangement of the electrons in the atoms in their free state. This is an indication of stabili...

KaitlynBali_4B

Yes, the example in the book also shows that the most stable structure is S = C = N. Nitrogen does have a -1 formal charge in this structure, and carbon and sulfur both have formal charges of 0. This example is on page 85 in the book. In the structure C = N = S, the formal charges are -2 for C, +1 f...

KaitlynBali_4B

The book explains a molecule with resonance does not flicker between different structures and is rather a blend between the different resonance structures. The bonds between every nitrogen and oxygen atom in a nitrate ion have properties that are in between the properties of double and single bonds....

KaitlynBali_4B

Resonance is term used to describe a molecule that has a blend of structures that results from delocalized electrons. I am drawing the conclusion that if electrons in a molecule are delocalized, the molecule is immediately described to have resonance.

KaitlynBali_4B

To add on, an ionic solid is not held together by the bonds between specific pairs of ions (like how covalent bonds are bonds between two atoms). All of the anions and cations react with one another to form a solid. The book describes it as a "global interaction" between all of the cations...

KaitlynBali_4B

To add on, nonmetals have ionization energies that are too high and would make it really hard to remove electrons to encourage ionic bonding. This is a reason why nonmetals engage in covalent bonding instead (electron sharing in between atoms).

KaitlynBali_4B

I also read in the book that the size of the atom is another main factor that determines whether or not an atom can expand its valence shell or not. A potassium atom is capable of having five chlorine atoms bond to it, but a nitrogen atom is much smaller in size and cannot form this many bonds.

KaitlynBali_4B

One thing that I find interesting to note is that the discovery of these magnetic spins was a result of Schrodinger's realization that hydrogen's observed spectral lines did not have the frequencies that he predicted they would have. Two scientists later discovered this magnetic spin property, and r...

KaitlynBali_4B

One other thing to note is that as you go down a group, the number of protons in an atom also increases. Repulsion from the positive nuclei in ionic compounds also slightly contributes to larger ionic radii.

KaitlynBali_4B

I agree. Furthermore, an understanding of electron shielding and ionization energies will make it easier to remember that ionization energies decrease down a group and increase across a period. Ionization energies decrease down a group because the number of protons in an element increases as you go ...

KaitlynBali_4B

Just to add on, the less attracted an electron is to the nucleus is, the greater chance it has to form bonds such as ionic bonds. Elements with high ionization energies have electrons that require more energy to be removed (ionization energy is essentially a measure of how difficult it is to remove ...

KaitlynBali_4B

After the 4s state/orbital is occupied and electrons enter the 3d state, the 3d state would be lower in energy than the 4s state. This occurs for multi electron atoms after the atomic number 20 (Calcium). For Scandium (z=21), you would put 3d1 before 4s2 because the 4s state is higher in energy tha...

KaitlynBali_4B

I am also having trouble understanding the concept of quantum numbers. Could someone clarify Professor's explanation of classical wave mechanics using his example of water molecules being poured from a bucket?

KaitlynBali_4B

An increase in intensity only leads to an increase in the number of electrons that are ejected, not an increase in the kinetic energy of the electrons. This is the photoelectric effect. An increase in the kinetic energy would occur with an increase in intensity if light behaved like a wave in the wa...

KaitlynBali_4B

To add on to these comments, I would like to mention that black bodies absorb a wide range of wavelengths (unlike individual atoms) because the atoms and electrons in black bodies act collectively.

KaitlynBali_4B

Yes, and electron affinities are highest towards the right of the periodic table. To add on, a positive electron affinity means that that energy is released when an electron is added onto an atom. When energy must be used to add an electron onto an atom, that means that there is negative electron af...

KaitlynBali_4B

First you would solve for the frequency by rearranging and using this formula: c = λv. Then you would use the Rydberg equation (it is on page 7 of our book). Here is a link to the Rydberg Equation too: https://calistry.org/calculate/rydbergEquation (I had a difficult time typing the equation here).

KaitlynBali_4B

What is the purpose of an empirical formula? Is it ever used for anything aside from being the foundation of a molecular formula?

KaitlynBali_4B

Yes, I agree with Sion Hwang 4D 's solution. To clarify, the M is referring to an element on the periodic table. The element is solved to be Calcium, a metal in group two on the periodic table. Knowing that Sulfur has a -2 charge was not necessary to solve this problem (although knowing this would h...

KaitlynBali_4B

Molarity is the concentration of moles in a solution. Knowing the molarity of a solution is essential when you create dilutions and conduct reactions with aqueous solutions.

KaitlynBali_4B

Making this connection helped me with one of the homework problems: 6.022*10^23 formula units = 1 mol of an ionic compound

KaitlynBali_4B

Usually scientific notation is used to make it easier to write extremely large or extremely small numbers without having to write out every single digit. It is okay to not write out 0.0014 in scientific notation. However, it is preferred that you write it in scientific notation for it to be more con...

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