CHEMISTRY COMMUNITY

Kaitlyn Jang 1F

I find it helpful to separately write out all of the given values in a problem, and then write down the variable that I am trying to find. Then I pick an equation (or equations if it is multistep) to help me find that variable. I think it's easier to have some derivations of equations memorized too.

Kaitlyn Jang 1F

Light is absorbed when energy level increases (electron gets excited). Light is emitted when energy level decreases (electron goes back to ground state).

Kaitlyn Jang 1F

standard units for c are m/s

Kaitlyn Jang 1F

Hertz is just the unit for frequency. You can denote frequency using Hz or s^-1 because they are the same.

Kaitlyn Jang 1F

Velocity of light is the same as speed of light, c=3.00x10^8 m/s. Frequency varies and can be found through given wavelengths and/or energy in a problem.

Kaitlyn Jang 1F

Acids typically have a hydrogen since it donates protons (ex: HCl). Bases will have hydroxide (OH) in their formula for you to identify (ex: sodium hydroxide: NaOH).

Kaitlyn Jang 1F

There is no specific list but it’ll be helpful to remember the 7 most common acids.

Kaitlyn Jang 1F

By definition, bronsted acids donate protons and bronsted gases accept protons. When an acid and base react in an equation, the acid has a conjugate base that accepts its proton, and the base has a conjugate acid that forms when the base accepts the proton.

Kaitlyn Jang 1F

Bronsted acids donate protons, but Lewis acids accept electrons.

Kaitlyn Jang 1F

Are hydrogen bonds stronger than ion-dipole interactions?

Kaitlyn Jang 1F

Shape will not vary because resonance structures don't matter in determining shape

Kaitlyn Jang 1F

Check to see if the dipoles cancel out in molecules. It helps to draw out arrows to signify the dipoles of each atom to visually see if they cancel out or not to create a polar or nonpolar molecule.

Kaitlyn Jang 1F

Only if hybridization is also on the one page of notes he has left to teach us on Monday

Kaitlyn Jang 1F

You should know it since it was talked about in lecture, but besides that it helps you identify the different shapes of molecules with lone pairs.

Kaitlyn Jang 1F

I don't think we have to know exact values of electronegativity. However, the periodic table should tell us the polarity (or lack thereof) of molecules based on the trends of electronegativity.

Kaitlyn Jang 1F

C, N, O, and F must follow the octet rule at all times. Atoms can begin having expanded octets at period 3 or greater. Typical atoms with expanded octets include sulfur, phosphorus, and silicon (all of which are in period 3).

Kaitlyn Jang 1F

The primary difference of these two types of bonds is that atoms in an ionic bond have a greater difference in electronegativity than the atoms in a covalent bond. Due to the complete oppositely charged atoms in an ionic bond, electrons are donated from one atom to the other. However, electrons in c...

Kaitlyn Jang 1F

Ionic bonds are stronger because the atoms have a greater difference in electronegativity than those in covalent bonds that form partial charges.

Kaitlyn Jang 1F

Ionization energy does increase going left to right across a periodic table. However, comparing the electronic configuration of nitrogen and oxygen, you can see that nitrogen ends at 2p3 and oxygen is 2p4. Half or fully filled orbitals are stable, and nitrogen's 2p orbital is filled halfway so it is...

Kaitlyn Jang 1F

Polarizability is the ability of an atom to form instantaneous dipoles. Thus, when an atom has a bigger atomic radius, it's polarizability increases because there are more electrons and the electrons are more dispersed.

Kaitlyn Jang 1F

Anions are larger because when adding electrons, electron-electron repulsion increases and create a larger atomic radius. Cations lose electrons from the valence shell which make them smaller in size.

Kaitlyn Jang 1F

Electron is excited and moves to the next orbital.

Kaitlyn Jang 1F

A polar molecule has polar bonds, meaning the electrons in a covalent bond is unequally shared due to one of the atoms being more strongly electronegative than the other. An example of this would be H2O, where oxygen is more electronegative than hydrogen. The unequal sharing creates dipoles, and oxy...

Kaitlyn Jang 1F

Also, many times ClO2 is associated with a negative charge, which means it would have a total of 20 electrons instead of 19.

Kaitlyn Jang 1F

If there is a negative charge, then you add however many more electrons are shown in the number of the charge. Conversely, if there is a positive charge then you subtract however many number of electrons that the charge shows.

Kaitlyn Jang 1F

Remembering them will help you write out electron configurations using the periodic table.

Kaitlyn Jang 1F

All of these types of radii share the same periodic trends, however atomic radii is just specifically referring to the half distance between two atoms while covalent radii is for 2 atoms covalently bonded, and ionic is for 2 atoms with an ionic bond.

Kaitlyn Jang 1F

I think you should know that on the periodic table, ionization energy increases going left to right across a period because atomic radius decreases, so electrons are more closely attracted to the nucleus. Going down a group, ionization energy decreases because valence electrons are shielded further ...

Kaitlyn Jang 1F

I don't think we have to know exact bond lengths, but it may be helpful to keep in mind that single bonds are longer than double bonds which are longer than triple bonds (triple bond length<double bond length<single bond length, so triple bonds are shortest).

Kaitlyn Jang 1F

Electronegativity is the tendency of an atom to to attract electrons to itself, and it increases as you move left to right across a periodic table and decreases down a group. Electron affinity is mainly referring to the amount of energy released when an electron is added to an atom. Its periodic tre...

Kaitlyn Jang 1F

You can look up a periodic table that is color coded orbital, and use that to guide you through the configurations. Typically, the elements in the first 2 groups are s orbitals, 3-12 is d orbital, and 13-18 (excluding Helium witch is s-orbital) are p-orbitals. For example, to find the electron confi...

Kaitlyn Jang 1F

Hund's Rule states that electrons try to fill up orbitals separately and only pair when necessary because the like negative charges tend to repel. Think of it like this, if you have a sibling who was annoying you, you wouldn't share a room with them unless you absolutely had to; electrons are the sa...

Kaitlyn Jang 1F

You need to have mass to use the De Broglie Equation, however photons of light do not have mass.

Kaitlyn Jang 1F

Wavelength is measured in meters, however some questions give or ask for the wavelength in nanometers. In the case that it does give nanometers of wavelength, just make sure to convert it to meters (nm x 10^-9) so that you can get the correct answer since the speed of light also has a unit of m/s an...

Kaitlyn Jang 1F

Most constants (Rydberg's, Planck's, etc.), equations (c = λ ν, E = h ν, etc.) are given on the sheet. However, you can figure out (or memorize) derivations of some equations that are not given.

Kaitlyn Jang 1F

A particle with a De Broglie wavelength of less than 10^-15 m does not have very detectable wavelike particles.

Kaitlyn Jang 1F

When subtracting energy removed from energy of a photon, why is the resulting excess energy also equal to kinetic energy of the electron?

Kaitlyn Jang 1F

Is spectroscopy only valid to identify H-atoms or can it be used to identify other atoms as well?

Kaitlyn Jang 1F

Can you use electromagnetic radiation equations when using the Rydberg constant equation to find wavelength?

Kaitlyn Jang 1F

Why can molecular spectroscopy not be used to identify molecules?

Kaitlyn Jang 1F

The general rule is to round your final answer at the end to the same number of significant figures as the number with the least digits. Try not to round your answers before your final answer, though. Otherwise, your answer will not be as accurate as you want it to be.

Kaitlyn Jang 1F

The syllabus states that "only non-programmable, non-graphing calculators are allowed." Buy one and use it for the test.

Kaitlyn Jang 1F

You could write out the numbers before the final answer out at least 6 decimal places to get a more accurate final answer. Make sure you only round your answer to the correct number of sig figs at the end of the entire problem. If you round before, your answer will be farther off from from exact cal...

Kaitlyn Jang 1F

Can someone explain when we know to write answers in powers of 10 and when it's not necessary? Scientific notation is most typically used when the number of zeros in a number is too long to write out (usually starting around 3 or 4 decimal zeros before or after the first non-zero number). For exampl...

Kaitlyn Jang 1F

You would round up to to .457. When the digit before the number of sig figs you are rounding to is greater than 5, you round up. If the digit is less than 5, you round down.

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