CHEMISTRY COMMUNITY

Chem_Mod

Hi Bella,

Thank you for sharing.

I do put much effort into encouragement and organize extensive additional support for students in my classes.

More importantly, excellent to hear you did not give up!
:-)

A lesson I hope will stay with you for life.

Chem_Mod

This was helpful. Thank you.

Chem_Mod

This was helpful. Thank you.

Chem_Mod

This was helpful. Thank you.

Chem_Mod

This was helpful. Thank you.

Chem_Mod

This was helpful. Thank you.

Chem_Mod

This was helpful. Thank you.

Chem_Mod

This was helpful. Thank you.

Chem_Mod

This was helpful. Thank you.

Chem_Mod

This was helpful. Thank you.

Chem_Mod

Wavelength = h/momentum, here we see that wavelength is inversely proportional to momentum. So any change in momentum would affect the wavelength.

Chem_Mod

Rydberg Equation: 1/λ=R(1/n(1)^2−1/n(2)^2) You can change n(1) and n(2), which refer to different energy levels in the Hydrogen atom. For example, you can use n(1)= 1 and n(2)=2 to find the wavelength of light emitted when an electron drops from the n=2 to the n=1 energy level (or the wavelength of ...

Chem_Mod

The octet rule is violated in compounds with more than eight electrons assigned to their valence shell. These are called expanded valence shell molecules. Such compounds are formed only by central atoms in the third row of the periodic table and beyond that have empty d orbitals in their valence she...

Chem_Mod

Induced dipoles, like London forces, are not considered dipoles. They are short term, induced dipoles. They are important when dealing with shape, such as rod shape is more affected by induced dipoles than spherical shapes. Dipoles result from electronegative pulling and are present in polar molecul...

Chem_Mod

Unhybridized p orbitals allow for pi bonding, not empty hybridized orbitals. Take for example an sp2, you would have the 3 hybridized sp2 orbitals, and then remember you would still have a leftover p orbital (you had 4 total- 1 s and 3 p's), so that leftover p orbital can make the pi bond, resulting...

Chem_Mod

Salts that contain the conjugate base (anion) of a weak acid will raise the pH by removing protons from H2O thus generating OH- 's. Na+ doesn't react with the hydrolysis of water. Remember in lecture when Dr. Lavelle said if the tomato sauce tasted really acidic, adding table salt wouldn't do anythi...

Chem_Mod

Bronsted Acids-Bases are all about proton transfer, H+. Bronsted Acid donates a proton/H+. Bronsted Base accepts a proton/H+. Lewis is all about electron transfer. Lewis Acid is an electron pair acceptor. Tip: Lewis Acid initials, LA, can be said as (e)Lectron Acceptor to help you remember. Lewis ba...

Chem_Mod

A neutralization reaction is when an acid and base react with each other to form a salt and water. Think of an acid and base as two antagonistic things, one as acidic and one as basic, so when they react, they neutralize the acidity and basicity of each other, which results in water because the acid...

Chem_Mod

Because there are 6 ligands, 3 from the Na and 3 from the oxalate, it will have an octahedral shape.

Chem_Mod

When hydrates are added, they do not factor into the coordination number. There was an example during the review session where we needed to write the reaction that would occur with water upon the addition of the following compound: FeCl3. Cl- would not react with the water since it is a spectator io...

Chem_Mod

Cl- is a spectator ion. Spectator ions exist in the same form on both the reactant and product sides of a chemical reaction. They are present in solutions but don't take part in a solution's chemical reaction. The alkali metals of the first column of the periodic table and the halogen gases from the...

Chem_Mod

In hydrogen bonding, the hydrogen bond donor must have a hydrogen attached to a highly electronegative atom (N,O,F). The hydrogen bond acceptor has a lone pair of electrons on a small highly electronegative atom (N,O,F).

Chem_Mod

Yes, bond dipole moments occur whenever there is a separation of positive and negative charges due to the unequal attraction that the two atoms have for the bonded electrons. The atom with the larger electrongegativity will have more pull for the bonded electrons than will the atom with smaller elec...

Chem_Mod

A dipole induced dipole attraction is a weak attraction that results when a polar molecule induces a dipole in an atom or in a nonpolar molecule by disturbing the arrangements of electrons in the nonpolar species. Dipole-dipole forces are attractive forces between the positive end of one polar molec...

Chem_Mod

The octet rule is violated in compounds with more than eight electrons assigned to their valence shell. These are called expanded valence shell molecules. Such compounds are formed only by central atoms in the third row of the periodic table and beyond that have empty d orbitals in their valence she...

Chem_Mod

You are welcome!

Chem_Mod

There is a good homework problem that addresses your question in detail. Take a look at the answer.

Chem_Mod

A chelating ligand should bond more than once to the same metal atom. Therefore, it must be polydentate. However, a regular polydentate ligand does not have to ligate to the same metal and therefore, it is not neccessarily chelating.

Chem_Mod

Pi bonds are formed by the overlap of two unhybridized p orbitals. There will be a bond above and below the sigma bond. This pi bond is only stable in one orientation so there cannot be any free rotation. There can never be free rotation around a bond formed by parallel overlap. This is why pi bonds...

Chem_Mod

Yes, always the case. As I showed in class for the p-orbitals to overlap (in phase) they need to be in the same plane (side-by-side) to form a pi-bond. If the atoms rotate then p-orbitals are not in the same plane and therefore are not overlapping. Stop by Drop-In Sessions, or Review Sessions, or Of...

Chem_Mod

Some elements in period 3 and later periods can accomodate five or more electron pairs, as in PCl5. To account for the trigonal bipyramidal arrangement of five electron pairs, we use one d-orbital as well as all the valence s- and p- orbitals of the atom. The resulting five orbitals are called sp3d ...

Chem_Mod

It is a useful check to determine if structure is correct.

During my review session students asked about alternative structures and I used formal charge.

When I ask in an exam question to give FC or show it is the lowest energy structure then FC definitely needed.

Chem_Mod

90 degree interactions between lone pairs and bonding pairs should be avoided. If the lone pairs occupy the axial positions, there will be 6 of these. If the lone pairs occupy the equatorial positions, the number of these unfavorable interactions will be reduced to 4 (and though the lone pairs thems...

Chem_Mod

Spectator ions exist in the same form on both the reactant and product sides of a chemical reaction. They are present in solutions but don't take part in a solution's chemical reaction. The alkali metals of the first column of the periodic table and the halogen gases from the second to last column o...

Chem_Mod

In general, adding more oxygen atoms to the central atom in an oxyacid helps to distribute the negative charge of the conjugate base over a greater number of atoms. If a proton is less strongly attached to any one of the oxygens, then you get a stronger acid. As the number of oxygens increases as yo...

Chem_Mod

You determine if a compound has ionic or covalent bonds by examining the electronegativity differences between atoms. You will not need to do calculations for electronegativity. If the electronegativity difference between two atoms is greater than 2, then an ionic bond will form (ex. salts like NaCl...

Chem_Mod

Good morning,

Here is an attached pdf of my worksheet for the final. We will go through this and then I will answer any remaining question any of you may have. :)

Chem_Mod

The order should be the same for species in the same row that tend to gain electrons: as you move to the right, the ion becomes smaller because of the increase in number of protons. However, if you are referring to species that lose electrons to form cations, this is because they lose all the electr...

Chem_Mod

The Roman numeral indicates the oxidation state of the metal, in this case 4. As you can see, it equals out to 0 because the metal is +4, and you have a total of 4 Chlorines of -4, thus resulting in the neutral compound.

Chem_Mod

Look at where the species outside of the brackets occurs on the periodic table. In this case, though you have omitted the brackets in your question, K3 should be outside of the brackets. K3 appears in period 1 and thus you know it tends to lose an electron to form K+. Therefore, K is the cation and ...

Chem_Mod

Determine the magnitude of the H-C-H bond angle by finding the molecular shape of the molecule. For example, CH4 is tetrahedral so the H-C-H bond angles are all 109.5 degrees. Do this for each molecule in the question, then order from smallest to largest bond angle.

Chem_Mod

S2- and P3- have the same number of electrons. However, S has a greater number of protons than P. This means the electrons held by S experience a greater attractive force to the nucleus of the S ion than the electrons held by P, making it harder to distort the electron cloud away from S2-. Thus P3- ...

Chem_Mod

You want to look at the strength of the intermolecular forces that the molecule can form. This is because boiling requires the intermolecular attractions between molecules to be broken. Thus, stronger intermolecular forces require more energy and therefore higher temperatures to be broken. Hydrogen ...

Chem_Mod

I think you are asking about the oxidation state of the metal cation in the coordinate compound. The overall charge of this compound is 0 or neutral, so we know that whatever charges each of the species inside the coordination sphere contains cancels out overall. We have Pt coordinated to four ligan...

Chem_Mod

Here is the answer key for the practice final we went over today. We hope the review session today was helpful. Study hard and good luck!
-Kate, Riya, Michelle

Chem_Mod

Bronsted acids by definition can donate protons (ie release H+). Bronsted bases can accept protons (ie form a bond with H+). The conjugate base of an acid is the species that results when the acid donates its proton. For example, Cl- is the conjugate base of the acid HCl. Similarly, a conjugate acid...

Chem_Mod

Both answers are correct; water typically donates only 1 lone pair because donating both would give it a very positive formal charge which is highly unfavorable for such an electronegative atom, and because the positioning of the lone pairs prevents both from donating to the same molecule at the sam...

Chem_Mod

@Katie, yes having a dipole moment would increase the boiling point of a compound compared to a compound that is nonpolar. This is because the dipole moment allows the molecule to have dipole-dipole intermolecular attractions, which are stronger and therefore require more energy/higher temperature t...

Chem_Mod

Polarizability describes a how much an atom could be polarized and distorted. Polarizability is the ability of an atom to be polarized.

Polarizing power, which is descriptive of cations, is the power that cation has to polarize a different atom.

Chem_Mod

Polydentate means that a ligand binds with a metal from multiple places. It "bites" from multiple locations. See below which I copy and pasted from my earlier post on chelating and polydentate. Structure is very important when it comes to chelating and polydentate material. For example, be...

Chem_Mod

A solvent is the substance that the other molecules (the solutes) are dissolved in. Chemical reactions commonly occur between compounds dissolved in a solvent. Water for example is a commonly used solvent, so common that we gave substances dissolved in water their own unique chemical state: aqueous ...

Chem_Mod

If the oxygen atoms were to donate their lone pairs to H+, this would result in O atoms with positive formal charge (three bonds and 2 lone pair electrons for a valence of 5, 6-5= +1). Oxygen is more electronegative than nitrogen (which also gained a positive formal charge upon accepting the protons...

Chem_Mod

If it accepted an electron pair, then it was a Lewis acid. Whatever subshell the transfer occurred in, the definition remains true.

Chem_Mod

Often when you see a lone pair, it can act as a Lewis base. Some atoms with lone pairs are better Lewis bases than others (depends on electronegativity, etc). A negatively charged species with a lone pair(s) or an N with a lone pair are usually good indicators of a Lewis base

Chem_Mod

No, electrons do not attract each other as they are the same charge. Pi bonds occur when electrons are shared through side-by-side orbital overlap rather than by end-to-end orbital overlap, which results in sigma bonding instead.

Chem_Mod

The concept of acids and bases is all about the donation of proton(acid) and the acceptance of the proton(base). Or from the Lewis acid base perspective, the donating and accepting of electron pairs. For applying this to other chemical topics, many homework problems include Lewis dot structures beca...

Chem_Mod

Week 5 worksheet key:

Chem 14A(corrected) KEY Wk 5 WS.docx: (38.9 KiB) Downloaded 17 times

Chem_Mod

Here is the worksheet for Monday's final review session (7/29):

Week 6 - Chemistry 14A.docx: (10.83 KiB) Downloaded 87 times

Chem_Mod

Ways to help identify if it is an acid or base include charge, because that will promote if the electron pair will be accepted or donated. Another way to tell is of the acid has a Hydrogen that it could donate, and for bases they would typically have a hydroxide OH-. There are some common substances...

Chem_Mod

First, the understanding of indicators is applied more in 14BL. Indicators are used to find the equivalence point in titrations, which are experimentally found. Also, because pretty much the only thing about weak acids and bases that we cover in 14A is they do not fully dissociate, and because we co...

Chem_Mod

pH value is determined by the concentration of Hydrogen. Different substances, like strong acids, weak acids, and amphoteric will all have their own general dissociation value, Ka, but it is how much present that will determine pH. The behavior of an amphoteric substance which determines if it acts ...

Chem_Mod

It is a good general assumption for cations as acids and anions as bases, since depending on the charge would promote either the accepting or donating of electron pairs. Also, we do not cover the f block and heavy d metals as their is little biological application, so I don't believe that would be t...

Chem_Mod

In this case for 6A9d, it does not affect, as the ammonia is just the solvent. The key here is to just see the proton transfer from NH4+ making it the acid to NH2- making it the base. If it helps visualize the reaction, this reaction is the similar to H3O+ + OH- ----> H20.

Chem_Mod

Reading this question, it appears they are just using these molecules and ions just as tools to help teach the concept of Lewis acid and bases. The book probably picked these as they are fairly complex lewis structures that also test your knowledge of expanded octet and formal charge. Even though it...

Chem_Mod

The reason there is not 2 double bonds to both oxygens is because then the sulfur would have a formal charge of -1 while both oxygens would be 0. There is only one double bond so that the sulfur has a formal charge of 0 and then the oxygen, which is more electronegative, receives the negative charge...

Chem_Mod

Remember that hybridizing hybridizes the different s p d orbitals. How many total orbitals would there be in an s and p? 4, 1 s and 3 p. In an sp3- which has 4 hybridized orbitals- all 4 ( 1 from s and 3 from p) become hybridized to sp3 orbitals. For sp2, which has 3 hybridized orbitals, to make the...

Chem_Mod

NH3 is amphiprotic because if put in water, it can donate a proton and become NH2- and the water becomes H3O+. OR, it could accept a proton and become NH4+ and water becomes hydroxide OH-. Typically an amphiprotic would have at least a Hydrogen to begin with so that it could donate it or it could ac...

Chem_Mod

The Iodine does not participate in any of the transfer of the proton, only the part of NH4+ to NH3. The iodine only serves to make it a salt so it can be easily added to the water solution, it serves a spectator role.

Chem_Mod

Yes, everything after the midterm will be on the Final. Knowing the difference between shape and geometry is important as it shows the relationship of the lone pairs and bonds.

Chem_Mod

If you are referring to increase and decrease of the bond angles like 109.5* and 120*, then it is determined by the structure. So sp3 is tetrahedral, so it has the same angle of 109.5* as the regular tetrahedrals. Same with the sp2 having a structure of trigonal planar and 120* bond angles.

Chem_Mod

Sigma bonds can rotate. Pi bonds can not rotate because they arise from the unhybridized p orbitals, and because of their shape they must be in the same orientation, thus restricting a rotational ability or else the bond will be broken.

Chem_Mod

Edta is an example of a polydentate ligand, specifically a hexadentate ligand. The edta molecule can "bite" from 6 different locations at once, if you can see from the image. https://www.bing.com/images/search?view=detailV2&id=14F6AC00CFA138F3E8CC24C5B0A388F1CF9FB392&thid=OIP.mCERt...

Chem_Mod

If you are referring to the dark solid wedge which shows in 3D the bond is coming towards you, and the dashed wedge showing the bond is going further from you, then do not worry about drawing any 3D structures as it is unnecessary. If we examine a trigonal bipyramidal structure from a birds eye view...

Chem_Mod

The Bronsted acids and bases are the reactants, which are the original molecules that do the accepting or donating of protons. The conjugates are the products. The acid corresponds with a conjugate base, while a base corresponds with a conjugate acid. See how the water was the base and becomes hydro...

Chem_Mod

Consider (a) [Fe(CN)6]^4-.The first thing you want to do is identify the ligands and the transition metal atom. In this case, the ligand is CN- (it is a negatively charged ligand) and the metal is Fe (oxidation state will be found in the following steps). Now we know that there are 6 CN- so their ch...

Chem_Mod

Sodium Hydroxide is a strong base. The Arrhenius definition (which is not a major focus of this class) describes a base as a substance that dissociates in water to form hydroxide ion (OH-). "Salts with a base" just refers to salts which are formed by the reaction of a weak acid and a stron...

Chem_Mod

Here are the Week 5 Worksheet Answers

Chem_Mod

Answers for this last week. And you always find my one typo! Sorry, 1b was meant to just be CH3F, not CH2F.

Chem_Mod

Polydentate ligands range in the number of atoms used to bond to a central metal atom or ion. For example, EDTA is a hexadentate ligand (polydentate ligand) that has six donor atoms with electron pairs that can be used to bond to a central metal atom or ion. Bidentate ligands will have two donor ato...

Chem_Mod

EDTA is a hexadentate ligand that can form very stable complexes (usually octahedral structures) with most of the transition metals.The sodium salt of EDTA can be found in many commercial products. See the link below for more information about it:
https://www.chem.purdue.edu/gchelp/cchem/polys.html

Chem_Mod

No, you will not be given a table of common ligands for the final. You will be given a periodic table and a constants/equations sheet. Therefore, be sure to familiarize yourself with some of the common ligands Dr. Lavelle went over in lecture.

Chem_Mod

A neutralization reaction is when an acid and base react to form water and a salt and involves the combination of H+ ions and OH- ions to generate water. The neutralization of a strong acid and a strong base will result in a pH of 7 and a water and salt. However, the neutralization of a strong acid ...

Chem_Mod

A neutralization reaction is when an acid and base react to form water and a salt. HCN (aq) could react with CaO to form Ca(CN)2. However, it will not result in the formation of water. HCN (aq) + CaO --> Ca(CN)2 + OH- A reaction with HCN (aq) and Ca(OH)2 results in the formation of water and a salt....

Chem_Mod

The fundamentals section was for the beginning of the course to provide a refresher of high school level chemistry. However, such as the acid base section is good prep for the acid base chapter.

Chem_Mod

Week 5 worksheet:

Chem 14A Summer 19 Wk 5 WS.docx: (7.57 KiB) Downloaded 21 times

Chem_Mod

A chelate is a chemical compound composed of a metal ion and a chelating agent. A chelating agent is a substance whose molecules can form several bonds to a single metal ion. In other words, a chelating agent is a multidentate ligand. An example of a simple chelating agent is ethylenediamine. See th...

Chem_Mod

The Bronsted-Lowry definition of acids and bases focuses on the transfer of protons. A Bronsted acid is a proton donor and a Bronsted base is a proton acceptor. When identifying compounds as Bronsted acids or bases, we must take into account the solvent that we are dissolving the compound in. When N...

Chem_Mod

Structure is very important when it comes to chelating and polydentate material. For example, because of the structure, a bidentate ligand can have 2 interactions per molecule. Look at these two links, both of oxalate with iron, and see how because of the structure of oxalate, it is binding to the i...

Chem_Mod

Remember what the basis of what hybridization is, it is hybridizing the subshells to create an orientation suitable for bonding. So the subshells, such as s or p, are hybridized and become for example and sp^3. However, the actual energy level (or shell) doesn't change, so that first 2 in C 2sp^2 re...

Chem_Mod

A possibility of why there can be a linear shape with lone pairs is if you consider a molecule with 5 regions of electron density around the central atom, such as trigonal bipyramidal, see saw, and T. You can go even further and have all 3 of the equatorial regions be lone pairs, thus resulting in t...

Chem_Mod

The structure of CH2Cl2 is tetrahedral. All the non-central atoms will be approximately 109.5 degrees away from each other. Lewis structures show a 2D image but the real 3D image is a tetrahedral so no matter where you draw the chlorine atoms, they will technically always be next to each other. As l...

Chem_Mod

Questions on the final will be similar to the homework. However, it is still highly recommended to study the concepts covered in lecture and discussion sections.

Chem_Mod

Dipole moment measures the extent of net charge separation in a molecule. Bond dipole moment is used to determine molecular polarity. Valence electrons contribute to the electron arrangement about the central atom but only bonded atoms are considered in the identification of the shape. Lone pairs di...

Chem_Mod

This week I cover coordination compounds (Monday) and acids and bases (Wednesday) in class.
Therefore do some of both of these sections to hand in HW Thursday in discussion section.

Don't forget to thank TAs and UAs for all their effort and assistance.

Chem_Mod

Here is the Week 5 Worksheet.

Chem_Mod

If the complex ion is an anion, the name of the metal ends with the suffix -ate. For example, Co in a complex anion is called cobaltate and Pt is called platinate. For some metals, Latin names are used in the complex anions. For example, Fe is called ferrate (not ironate).

Chem_Mod

AX3E2 is not linear. It is T-shaped. An example of this VSEPR type is ClF3. It has three fluorine atoms and one Cl atom as the central atom. It has two lone pairs and has three bonds. The three fluorine atoms are arranged around the central Cl atom to form a T-shaped molecule.

Chem_Mod

dsp3 and sp3d are both correct.

Chem_Mod

Charge distribution refers to which parts of the molecule have more or less electron density than other parts. For example, H2 has a symmetric charge distribution (the charge is distributed equally throughout the whole molecule) because the bonded atoms have the exact same electronegativity so there...

Chem_Mod

Yes, polarity depends on shape in general, and whether a molecule is cis or trans changes its shape. Cis and trans is not a key topic in this class, but if you wish to learn more about it, try using the index of your textbook to find pages where it is mentioned :)

Search found 17203 matches