Chemistry Section 1 (Altius MCAT Prep)

Q1. Draw and describe the Bohr model of an atom: include the relative size of the components, the charges on each species and their relative mass. Describe the aspects of the Bohr model still believed to be accurate and those that have been updated and/or replaced by modern quantum mechanics and atomic orbital theory

. The original Bohr model was that of a small, positively charged nucleus surrounded by very small negatively-charged electrons that orbit the nucleus in defined planetary-like orbits. This is the figure most students probably associate with an atom after basic high school or introductory college chemistry: A small round nucleus containing protons and neutrons, surrounded by electron orbitals (more correctly, "shells") of increasing size (the shells resembling the rings of a target). Students may have been taught that two electrons fit in the first shell, followed by eight in the next shell and in each shell thereafter until all electrons for that atom are assigned [Note: We've had many students confuse orbitals and shells because of this 2 + 8 + 8 "target" drawing of an atom. Clarify that one "shell" with 8 electrons would actually be two sub-shells, an s and a p, with two electrons in the s and 6 electrons in the p. The total is the same, but there would be an energy difference between s and p electrons—which is kind of misrepresented by the "target" drawing because it appears all 8 electrons are equidistant from the nucleus and of equal energy]. As a general concept for the MCAT students could almost, but not quite, get by with these concepts. Focus them 1) on the size of the components. A nucleus is made of protons and neutrons held together by the residual strong force (i.e., the residual force left over from the strong nuclear force that binds quarks together to form individual nucleons. Quarks are definitely beyond the scope of the MCAT but they have mentioned the strong nuclear force on rare occasion). Protons are positively charged, neutrons are neutral, and they are approximately the same size and mass. Electrons are much, much, much smaller—roughly 1/2000 of the mass of a proton. Because electrons are so small, the electron cloud is mostly, well, mostly nothing. A good approximation of relative size would be to explain that if a student sat in the middle of their dorm room and put a pencil dot on a piece of paper, that dot could approximate the size of the nucleus and the size of the electron cloud would fill the entire room. This might approximate the "average" atom. There is obviously a huge variance in size between hydrogen and francium. Emphasize that because of how small electrons are compared to the size of the electron cloud, atoms are mostly empty space. You might want to mention/discuss the Rutherford gold foil experiment to emphasize that atoms are mostly empty space. The Bohr model is often drawn when discussing energy levels. Electrons can and do jump from one level to another if they receive the exact quantum of necessary energy and will release a photon equal in energy to the difference between two energy levels when they "relax" back to a lower energy level. Adjustments and adaptations made to the Bohr model include the dualnature of electrons—namely that they show both wave-like and particle-like nature similar to light. Second, electrons do NOT orbit the nucleus in circular planetary-like patterns resembling the rings of a target. Briefly remind students of the s, p, d and f orbitals and their unique shapes. Clarify that these are not actual boundaries but mathematical wave functions that predict the probability of where an electron could be at any given instant. We would expect the electron to be somewhere within that orbital (as defined by that shape) even though the orbital itself has no physical boundaries. Instead of thinking of electrons as being added to an atom in the 2 + 8 + 8 . . . pattern, explain orbital filling corresponds to modern electron configuration diagrams—specifically to the number of electrons that can be held in an s, p, d and f orbital: 2, 6, 10 and 14. These numbers also match perfectly with the periodicity seen in the periodic table.

Q29. Predict the effects of doing each of the following to a reaction at equilibrium: 1) Adding/ Removing Reactants 2)Adding/removing Products 3)Increasing/Decreasing Pressure 4)Increasing or Decreasing Temperature

1) Adding reactants will shift the reaction to the right; Removing reactants will shift the reaction to the left; 2) Adding products will shift the reaction to the left; Removing products will shift the reaction to the right; 3) Increasing pressure will shift the reaction toward the side with fewer moles of gas; Decreasing pressure will shift the reaction toward the side with more moles of gas; 4) Increasing temperature will actually CHANGE the Keq and will shift the reaction. IF the reaction is exothermic increasing temperature will shift the reaction to the left and the Keq will decrease. If the reaction is endothermic increasing temperature will shift the reaction to the right and Keq will increase. The effect of decreasing temperature will have the exact opposite impact described for each type of reaction.

What element in its ground state will have the same electron configuration as a chloride ion? (Cl 1-)

1s2 2s2 2p6 3s2 3p6 (same as Ar & same as Ca 2+)

What is the electron configuration of calcium in calcium sulfate? (Ca 2+)

1s2 2s2 2p6 3s2 3p6 (same as Ar & same as chloride ion)

Which orbital is higher in energy, a 4p or a 5s? What about a 3d and a 4s?

5 s orbital has higher energy. 3 d orbital has higher energy. The order of increasing energy for orbitals within a given principal energy level is s < p < d < f < ... This trend results from the fact that s orbitals have a greater electron density near the nucleus than p orbitals, and p orbitals have greater electron density near the nucleus than d orbitals. In a many-electron atom, the energies of the orbitals increase as follows 1s < 2s < 2p < 3s < 3p < 4s < 3d < 4p < 5s ... Note also that the higher principal energy levels (n values) have more subshells, and as these split in energy some of these subshells can actually be lower in energy than subshells from a lower principal energy level. Thus the energy of a 4s orbital is very close to the energy of a 3d orbital in a many-electron atom. In potassium and calcium atoms the energy of the 4s orbital is less than the energy of the 3d orbital.

Reactions What is a decomposition reaction?

A decomposition reaction is the opposite of a synthesis reaction - a complex molecule breaks down to make simpler ones. These reactions come in the general form: AB ---> A + B

State whether the following will increase or decrease as you go across a period or down a group of the periodic table: electron affinity, electronegativity, ionization energy, atomic radius and metallic character.

Atomic Radius: DOWN a Group: Atomic radius INCREASES as you go DOWN a Group because each successive Period (row) has an additional occupied energy level. If you visualize the not 100% accurate but still useful Bohr model of the atom, you can think of it this way: each time you drop down a row, you add a "ring." ACROSS a Period: Atomic radius DECREASES as you go ACROSS a Period because the net nuclear charge increases (Huh?). Remember, it's the protons (+) in the nucleus that pull on or attract the electrons in the orbitals. Across a Period you are adding more and more protons pulling on electrons occupying the same orbitals. The overall effect is more pulling power in the same basic space. This draws the electrons in closer, making the overall atomic radius smaller at the right side of a Period. Ionization Energy: DOWN a Group: Ionization energy DECREASES as you go DOWN a Group because the farther the valence electrons are from the nucleus (pulling power of the protons) the less energy it costs another atom to steal them. ACROSS a Period: Ionization energy INCREASES as you go ACROSS a Period because atoms are getting ever closer to that magic "octet" rule for stability via the Noble Gas configuration. In plain speak - your frequent buyer punch card gets one step closer to the freebie each time you move closer to the right of the Periodic Table so you guard those punches more carefully. The atomic radius is getting smaller, too, so those protons do a great job of holding on tighter. Electron Affinity: DOWN a Group: Electron Affinity DECREASES (a tiny bit) as you go DOWN a Group because elements become slightly less attractive toward electrons. Father from the pull of those protons, remember? ACROSS a Period: Electron Affinity INCREASES as you go ACROSS a Period because generally speaking (and remember, exclude the Noble Gases here) elements toward the right of the Periodic Table give off a great deal of energy when they gaining electrons to become more stable. Electronegativity: DOWN a Group: Electronegativity DECREASES as you go DOWN a Group because the valence electrons are increasingly farther away from the attraction of the protons in the nucleus. Less pull, less "desire" to grab other electrons. ACROSS a Period: Electronegativity INCREASES as you go ACROSS a Period because the number of protons (+ charges) in the nucleus increases. More protons in the nucleus means electrons are more strongly attracted to the nucleus. Chemical Reactivity: METALS DOWN a Group: In METALS reactivity INCREASES as you go DOWN a Group because the farther down a Group of metals you go, the easier it is for electrons to be given or taken away, resulting in higher reactivity. ACROSS a Period: In METALS reactivity DECREASES as you go ACROSS a Period because though they still want to give away valence electrons they have more of them to get rid of, which requires more energy. Not as easy to blow off a little steam! NON-METALS UP a Group: In NON-METALS reactivity INCREASES as you go UP a Group because the higher up and to the right atoms are, the higher the electronegativity, resulting in a more vigorous exchange of electrons. Fluorine? A greedy, impatient beast when it comes to electron exchange manners. ACROSS a Period: In NON-METALS reactivity INCREASES as you go ACROSS a Period because (notice how trends repeat?) the closer you get to fulling your s- and p- orbitals the more motivated you are to do so.

Why do bonds form? Is energy required or released when a bond is formed?

Atoms are with out feelings and don't "want" to form bonds. They only do so in situations where the resulting bond is a lower energy state than was the unbonded form (or than the previous bonds they were engaged in with other atoms). As a result, forming bonds always releases energy. This is a major point of confusion for students. ATP is often the molecule that exacerbates this confusion. The transition from ATP to ADP does release energy, but only because the forming of the new bonds in ADP releases more energy than was required to break the bonds in ATP—NOT because breaking the bonds in ATP released energy.

A certain metal is known to have a work function of 500J. If a photon of 500J strikes the surface of the metal, what will be the result?

Because the energy of the photon exactly equals the work function nothing will happen. Theoretically, it is as if the electron is now "freed" from its attraction to the nucleus but cannot move because it lacks any excess energy to transfer into KE.

Energy Levels & Photon-Light Emission What happens when energy is added? Released?

Because they are quanitized, you cannot cause an electron to move up one energy level until you add an amount of energy just greater than the difference in energy between the two energy levels. If an excess energy is added, but not enough of cause the electron to jump two energy levels, the electron will only jump one level and the excess energy will be released. If an electron drops one energy level, energy is released as a photon or as electromagnetic radiation. The energy released will be exactly equal to the difference in the two energy levels. Valence electrons cannot move up any further, but can be ejected.

Q36. What do catalysts change? What do they NOT change?

Catalysts change the rate of the reaction by offering an alternate route for the reaction with a lower energy transition state and therefore a lower energy of activation. [It may not be technically true to say that catalysts "lower the activation energy" simply because the "normal" uncatalyzed reaction will still be going on for some other molecules not interacting with the catalyst. Those molecules could react via the higher energy transition state and activation energy—and therefore for those specific molecules the Ea was not lowered. However, for the MCAT you can assume that if a catalyst is present all of the molecules will react via the catalyst and therefore it would be safe to say that the catalyst lowered the energy of activation. This is not to say this little caveat may not come up on the MCAT, but if it did it would be part of a passage, not required native background knowledge.] It is more important to focus on what catalysts do NOT change. They do NOT change the equilibrium, Keq, enthalpy change, entropy change, Gibbs free energy, or any other thermodynamic properties. The MCAT uses this question type heavily and students are often tricked into accepting a false concept such as: "adding a catalyst will increase percent yield."

Explain ionic vs covalent bonds

Covalent bonds are usually formed between two non-metals and involve sharing of electrons within the bond. This sharing need not be equal, and is in fact usually not due to differences in electronegativity. Electrons are only rarely shared equally in a covalent bond. For this to occur the two atoms involved must have identical electronegativities. Ionic bonds are usually formed a between a metal and a non-metal and are due to an electrostatic attraction. They can be conceptualized in two ways. First, you can visualize the two species as previously formed ions. For example, Na+ and Cl-. It is fairly obvious that these two species will be strongly attracted to one another by an electrostatic force. Alternatively, you can also visualize it as if the two atoms came together in their ground states (not as ions) and the more electronegative atom (Cl- in this case) pulled one electron completely away from sodium. This would result in essentially the same result, a sodium cation and a chloride anion.

E=hf what are the variables and in which equation would you manipulate it in?

E is the energy of a photon, h =Planck's constant and f=frequency. KE= E-Φ

Derive an equation that would allow you to calculate the Energy of a photon knowing only velocity and wavelength

E=hf f=velocity/wavelength E= hv/λ or (Plancks)(velocity)/(wavelength) Solve v = fλ for f to get: f = v/λ. Substitute this for frequency in the above equation to get E = hv/λ, often written as E = hc/λ.

Definition of Energy Levels.

Energy levels are the differences in energy among the various electrons in an atom. THEY ARE QUANITIZED!- look like stair steps, not ramp- you can be in energy level 1 or 2, but never between

How does each of the following affect equilibrium: addition of a catalyst, increased temperature, lowering the activation energy, stabilizing the transition state, addition of reactants/ products?

Equilibrium constants aren't changed if you add (or change) a catalyst. The only thing that changes an equilibrium constant is a change of temperature. Equilibrium constants are changed if you change the temperature of the system. Kc or Kp are constant at constant temperature, but they vary as the temperature changesThis is typical of what happens with any equilibrium where the forward reaction is exothermic. Increasing the temperature decreases the value of the equilibrium constant. Where the forward reaction is endothermic, increasing the temperature increases the value of the equilibrium constant. Equilibrium constants aren't changed if you change the concentrations of things present in the equilibrium. The only thing that changes an equilibrium constant is a change of temperature. The position of equilibrium is changed if you change the concentration of something present in the mixture. According to Le Chatelier's Principle, the position of equilibrium moves in such a way as to tend to undo the change that you have made. Suppose you have an equilibrium established between four substances A, B, C and D. According to Le Chatelier's Principle, if you decrease the concentration of C, for example, the position of equilibrium will move to the right to increase the concentration again.

Write the balanced reactions for the combustion of Ethane

Ethane: 2C2H6 + 7O2 → 6H2O + 4CO2

What is the electron configuration of Fe2+

Fe2+: 1s2 2s2 2p6 3s2 3p6 3d6

What is the electron configuration of Fe3+

Fe3+: 1s2 2s2 2p6 3s2 3p6 3d5

What is the electron configuration of Fe

Fe: 1s2 2s2 2p6 3s2 3p6 4s2 3d6

Acids

Follow the "ate- ic -- ite-ous" convention. If the ion name ends in "-ate", replace the ending with "-ous" as in: Nitrite --> Nitric Acid. If the ion name ends in "ite" , replace that ending with "ous" as in: Nitrite --> Nitrous Acid. If the parent is a single ion rather than a polyatomic ion, replace the "ide" ending with "-ic" and add "Hydro-" as a prefix, as in: Iodide --> Hydroiodic Acid.

Q34. For a reaction with two reactants, A and B, a graph of ln[A] vs. time is linear. How many of the following statements are true? 1) Reactant A must be first order, 2) Reactant B co uld be first order, 3) Reactant B cannot be impacting rate, 4) Reactant B must be in excess.

Getting a positive result (i.e., a line for one of the graphs) gives us much more information. Because the graph of ln[A] is linear we know that statement 1 is true, reactant A is indeed first order. We also know, however, that no other reactants are impacting rate. Statement 2 is NOT known. Reactant B could be first order; however, if it is first order then we know it MUST be in excess because only reactant A is impacting rate. Reactant B could also not be first order. It could be zero order and not impacting rate at all—an alternative explanation for why only reactant A is impacting rate. Statement 3 is known for this exact moment and set of conditions. Reactant B cannot be impacting the rate; if it were, the graph of ln[A] would not have been linear. Statement 4 is NOT known but could be true. We know that reactant B is not impacting rate, but that could be either because it is in excess or because it is zero order.

The Work Function- Explain.

If you bombard certain metals w/ energy, you can cause the ejection of an electron from their outermost shell (valence). The amount of energy required to do this is called the "work function" and is usually given the variable Φ. Not the same as ionization energy- Ionization energies are measure for lone atoms in gaseous states. The work function refers specifically to valence electrons being ejected from the surface of a solid metal. If you add less energy than the work function, the electron won't be ejected. If you add more energy, the excess energy is transferred into the kinetic energy of the ejected electron.

Q31. How will increasing each of the following affect reaction rate: reactants, products, catalyst, energy of activation, energy of the transition state, energy of the reactants, and temperature?

Increasing the concentration of the reactants will increase the rate of the reaction as long as the reactant in question is in the rate law; increasing the concentration of products has no effect on reaction rate [Note: This might be a good place to emphasize that kinetics is usually studied only for the very, very early stages of a reaction - the initial rate method - when all reactants and catalysts are available in excess]; increasing the concentration of a catalyst will increase rate; increasing the energy of activation or the energy of the transition state (which would increase the energy of activation) decreases rate at constant temperature; increasing the energy of the reactants would make them closer to the energy of activation and would therefore increase rate; increasing the temperature will increase the average KE of the reactants and therefore increase rate; [Note: Increasing the concentration of a catalyst can produce diminishing returns. Having more catalyst, for example, increases the likelihood that the reactants and the catalyst will interact. However, if you had 1,000 times more catalyst molecules than you have reactant molecules, adding more catalyst at that point would have little effect on the rate - a graph of rate vs. concentration of a catalyst approaches a horizontal asymptote.]

Which two elements in the periodic table, if united in a bond, would create a bond w/ max possible ionic character?

Ionic character is due to a difference in electronegativity between the two atoms in a bond. So, a C-C bond, for example, would have zero ionic character. Theoretically, the greatest possible ionic character would exist in francium fluoride. However, francium is extremely unstable with a half-life of around 20 minutes. It also happens to be among the rarest of all elements, so it is unlikely that francium-fluoride has ever been formed.

What is an isotope?

Isotopes are atoms with the same number of protons , but differing numbers of neutrons . Isotopes are different forms of a single element . Examples: Carbon 12 and Carbon 14 are both isotopes of carbon , one with 6 neutrons and one with 8

Equation that relates work function. What are the variables?

KE= E-Φ E is the amount of energy added and KE is the kinetic energy of the ejected electron.

Q30. Provide conceptual definitions for, and clarify the difference between kinetics and thermodynamics

Kinetics is about the reaction rate; how fast are things working out? Thermodynamics is about the potential reactivity; to decide whether it would work out or not Kinetics: rate, catalysts, enzymes, energy of activation, reaction order, and transition state Thermodynamics: Keq, Q, entropy, enthalpy, Gibbs free energy, "favorability", "spontaneity" Only thing that repeats is the temperature Kinetics is the study of reaction rate. In other words, how quickly the reaction proceeds. This is usually measured in terms of how fast the reactants disappear by tracking changes in the concentration of the reactants as a function of time (i.e., Molarity/second ; M/s). By contrast, the thermodynamics of a reaction reflect the potential reactivity (for example, given infinite reaction time) and includes all measurements of energy flow and relative stability. Thermodynamics produces the quantities ∆H, ∆G, ∆S, Keq and so forth. Conceptually, students should think of rate as depending on how fast the reactant molecules are moving (how much KE they have) and the relative height of the Energy of Activation "hill" that they must surmount in order to turn into products. The reactant molecules must also collide with the right orientation to one another. At any given time molecules in the mixture of reactants will have a varietyofdifferentenergies.Somewillhaveenoughtoreactwhileotherswillnot. Because temperature is a measure of the average KE of the molecules, increasing t emperature will cause a greater fraction of the molecules to have sufficient energy to overcome the barrier and therefore more of them will react. It is fairly straightforward to imagine that if only a tiny fraction of the reactants have enough energy to g et over the hill, a very long time must pass before all of the reactants—just a few at a time—make it over the hill. By contrast, if the average energy of the reactants is very close to the energy of activation, then a greater percentage of them will exceed that threshold and it will take far less time for most of the reactant molecules to make it over the hill. Further, if the reactants have more KE (higher temperature) they will be moving more quickly and collide more often, increasing the probability that two reactants will strike one another with the correct orientation needed to react. A simple, but effective conceptual approach to thermodynamics is to think of it as differences in energy across a reaction. If the bond energies of the reactants are lowe r than the bond energies of the products, then the products are by definition more stable. We would expect therefore, that as the molecules transform from a less stable state to a more stable state there would be a release of energy (i.e., an exothermic process). If the reverse is true we would expect that energy would be required (i.e., endothermic) to drive the molecules from a more stable state (higher BE) to a less stable state (lower BE). Entropy works in a similar way, but it is a measure of randomness or disorder and has the units of energy/temperature (J/K). It requires energy to create order. Conversely, there is an energy release associated with going from a more ordered state to a less ordered state. Gibbs free energy combines these concepts and represents the total free, available energy either produced or required by a reaction as a function of BOTH changes in the bond energies (∆H) and changes in the entropy state (∆S). Those are good conceptual starting points for both kinetics and thermodynamics. A key take home message in preparing for the MCAT, however, is that you must differentiate between the two without confusion. It is IMPERATIVE that students understand that the rate of a reaction is independent of its thermodynamic properties. For example, there are many examples of highly exothermic reactions with very large Keq, that proceed very slowly. Similarly, just because one reaction proceeds to equilibrium more quickly than another does not allow us to intuit anything about the relative stabilities of reactants vs. products for the two reactions. As we say in the notes for this lesson, help your students create a "Wall of Separation" between kinetics and thermodynamics. Things they should associate with thermodynamics include: Keq, Q, entropy, enthalpy, Gibbs free energy, "favorability," "spontaneity," "differences in energy between products vs. reactants," and yield. Things they should associate with kinetics include: rate, catalysts, enzymes, energy of activation, reaction order, and transition state. Temperature is the IMPORTANT exception because it traverses the "wall of separation" and impacts both thermodynamics and kinetics. Increased temperature increases the rate of the reaction. Increased temperature can either increase or decrease the Keq depending on whether the reaction is exothermic or endothermic (we'll discuss this in more detail later). Drill into your students' heads that "temperature is the only thing that changes Keq."

Larger atoms don't form pi bonds. Why?

Larger atoms form weaker pi bonds because of a decrease in the overlap of the p-orbitals.

When you disrupt the equilibrium, creating a "shift" according to the Le Chatelier's principle what happens to Keq? Does it change?

Le Châtelier's principle states that if the system is changed in a way that increases the concentration of one of the reacting species, it must favor the reaction in which that species is consumed. In other words, if there is an increase in products, the reaction quotient, Qc, is increased, making it greater than the equilibrium constant, Kc.

Q32.Draw an energy coordinate diagram for both an endothermic and an exothermic reaction. Draw an energy coordinate diagram for a two-step reaction with a fast step and a slow step. For all, label products, reactants, ∆H, energy of activation (Ea), and transition state(s).

Look for the following as you examine your student's drawings. 1) For an endothermic reaction the vertical placement of products on the graph should be HIGHER than the placement of reactants and for an exothermic reaction the placement of the reactants on the graph should be higher. For a reaction with a fast and slow step there should be two hills representing two transition states. The higher of the two hills would represent the SLOW step and the lower of the two hills would represent the FAST step. Here is an example of a properly labeled diagram (Step 1 is fast, Step 2 is slow):

Metals form ______, but non-metals form ______?

Metals form cations, but non-metals form anions. Metals tend to give up electrons and form cations. Non- metals tend to accept electrons and form anions.

Write the balanced reactions for the combustion of methane.

Methane: CH4 + 2O2 → 2H2O + CO2

What is the electron configuration of Mg2+

Mg2+: 1s2 2s2 2p6

What is the electron configuration of Na+

Na+: 1s2 2s2 2p6

How do you name Ionic Compounds?

Name the cation first and then the anion. (calcium sulfate is CaSO4 not SO4Ca)- duh

How do you name a binary compound?

Name the element furthest down and to the left on the periodic table first (most metallic?); use poly prefixes as necessary ( Nitrogen Trioxide, Carbon Monoxide, Sulfur Dioxide, etc). Some have common names such as ammonia and water.

Identify the following referring to the periodic table: period, group/family, alkali metals, alkaline earth metals, transition metals, lanthanides, actinides, halogens, noble gases, s-block, p-block, d-block and f-block.

Period: Are arranged horizontally across the periodic table (rows 1-7). These elements have the same valence shell. Group/family: Are arranged vertically down the periodic table (columns or group, 1- 18 or 1-8 A,B). These elements have the same number electrons in the outer most shells, the valence shell. Alkali metals: The alkali metals, found in group 1 of the periodic table (formerly known as group IA), are very reactive metals that do not occur freely in nature. These metals have only one electron in their outer shell. Therefore, they are ready to lose that one electron in ionic bonding with other elements. As with all metals, the alkali metals are malleable, ductile, and are good conductors of heat and electricity. The alkali metals are softer than most other metals. Cesium and francium are the most reactive elements in this group. Alkali metals can explode if they are exposed to water. The Alkali Metals are: Lithium, Sodium, Potassium, Rubidium, Cesium, and Francium. Alkaline earth metals: The alkaline earth elements are metallic elements found in the second group of the periodic table. All alkaline earth elements have an oxidation number of +2, making them very reactive. Because of their reactivity, the alkaline metals are not found free in nature. The Alkaline Earth Metals are: Beryllium, Magnesium, Calcium, Strontium, Barium, and Radium. Transition metals: The 38 elements in groups 3 through 12 of the periodic table are called "transition metals". As with all metals, the transition elements are both ductile and malleable, and conduct electricity and heat. The interesting thing about transition metals is that their valence electrons, or the electrons they use to combine with other elements, are present in more than one shell. This is the reason why they often exhibit several common oxidation states. There are three noteworthy elements in the transition metals family. These elements are iron, cobalt, and nickel, and they are the only elements known to produce a magnetic field. Lanthanides and actinides: The lanthanides and actinides form a group that appears almost disconnected from the rest of the periodic table. This is the f block of elements, known as the inner transition series. This is due to the proper numerical position between Groups 2 and 3 of the transition metals. Halogens: The halogens are five non-metallic elements found in group 17 of the periodic table. The term "halogen" means "salt-former" and compounds containing halogens are called "salts". All halogens have 7 electrons in their outer shells, giving them an oxidation number of -1. The halogens exist, at room temperature, in all three states of matter: Solid- Iodine,Astatine Liquid- Bromine Gas- Fluorine, Chlorine The Halogens are: Fluorine Chlorine Bromine Iodine Astatine Noble gases: The six noble gases are found in group 18 of the periodic table. These elements were considered to be inert gases until the 1960's, because their oxidation number of 0 prevents the noble gases from forming compounds readily. All noble gases have the maximum number of electrons possible in their outer shell (2 for Helium, 8 for all others), making them stable. Helium, Neon, Argon, Krypton, Xenon, and Radon. s-block: First two groups of the periodic table -- alkali metals and alkaline earths p-block: Last six element groups of the periodic table, excluding helium. The p-block elements include all of the nonmetals except for hydrogen and helium, the semimetals, and the post-transition metals. d-block: Transition metals of element groups 3-12. f-block: Inner transition elements, usually the lanthanide and actinide series, including lanthanum and actinium.

Which requires the most oxygen to combust, propane, propanol or propanoic acid?

Propane (C3H8) = 3 points for carbon Propanol (C3H8O) = 2.5 points ( 3 - 0.5 = 2.5). 3 points for carbon and 0.5 for oxygen. Propanoic acid (C3H6O2) = 2 points ( 3 - 1 = 2). 3 points for carbon and 1 point for oxygen because we have two oxygens so (0.5 + 0.5 = 1). Propane will require the most oxygen to combust. Add 1.0 for each carbon and subtract 0.5 for each oxygen. The species with the lowest total will require the least oxygen and the one with the highest total will require the most. This is not however, the actual number of moles required. The only way to determine the exact moles of oxygen required is to write out and balance the combustion reaction. REMEMBER that water is never combustible.

Write the balanced reactions for the combustion of propanol.

Propanol: 2C3H8O + 9O2 → 8H2O + 6CO2.

How do you name monatomic ions?

Replace the last syllable with "ide" (sulfide ion, hydride ion, chloride ion)

What is the expected condosity of 3M LiCl?

Sodium is more metallic than lithium, so we would expect an NaCl solution to conduct electricity better than an equimolar LiCl solution. This means the NaCl solution would need to be less concentrated in order to conduct equally as well. This predicts a condosity of something less than 3.0 for a 3.0M LiCl.

What is the bond length?

The distance between the nuclei of the atoms forming the bond

What is the difference in empirical & molecular formulas?

The empirical formula is the simplest formula for a compound. A molecular formula is the same as or a multiple of the empirical formula, and is based on the actual number of atoms of each type in the compound.

Heisenberg Uncertainty Principles

The more precisely one property is measured, the less precisely the other can be controlled, determined, or known. It implies that it is impossible to simultaneously measure the present position while also determining the future motion of a particle, or of any system small enough to require quantum mechanical treatment.

Q33. For a reaction with two reactants, A and B, a graph of 1/[A] vs. time is non-linear.Which of the following is known? 1) The reaction cannot be second order in A and independent of B, 2) Reactant B must be involved in the rate law, 3) Reactant B cannot be in excess.

The observation that a graph of 1/[A] is non-linear is somewhat inconclusive. The graph could have been non-linear because both reactants are impacting the rate (violating the rule that these graphs will only be linear if only one reactant species is impacting rate). However, it could also be non-linear if reactant A is the only reactant impacting rate, but reactant A is not second order. For example, suppose that reactant A is actually first order; the graph of 1/[A] would not be linear, but the graph of ln[A] would be. Statement 1 is the best choice because if reactant A was second order and reactant B did not impact rate, we would expect a linear plot. Statement 2 is NOT known. Reactant B could be in the rate law and that is why the graph is not linear; however, it is equally plausible that reactant B is NOT in the rate law and the graph of 1/[A] is not linear because A is first order, not second order. Statement 3 is NOT known either. As we have already explained, the graph could be linear either way. If reactant B is in excess then the graph could be non-linear because reactant A is actually first order, not second order. If reactant B is not in excess (and is in the rate law) then the graph could be non-linear because both A and B are impacting rate.

What is the percent mass of carbon in glucose? what is the percent mass of hydrogen in water?

The total MW of glucose is 180g. The weight of the six carbon atoms in glucose is 72g. Therefore, (72/180) x 100 = 40%. The total mass of water is 18g. The mass of the two hydrogen atoms is 2g. Therefore, (2/18) x 100 = 11%.

Q38. Why can you usually ignore the rate law for the uncatalyzed reaction?

The uncatalyzed reaction usually proceeds at a rate that is much slower than the catalyzed reaction. Therefore, the products from the reaction will be almost exclusively result from the catalyzed pathway. We can ignore the parallel uncatalyzed reaction because even though we know it is occurring simultaneously, its contribution to the progress of the reaction is negligible.

Q37. What is the difference between an enzyme and a catalyst? Are all catalysts enzymes? Are all enzymes catalysts?

The word catalyst is a more general term for any substance that increases the rate of a reaction without being altered or consumed during the process. An enzyme is one type of biological catalyst. Enzymes are long protein chains folded into complex tertiary structures that feature an active site that is unusually specific to the reactants and/or transition state of the reaction it catalyzes. The order of amino acids in the protein and the folding of the protein are such that the active site has a very specific contour and layout—with complementary shapes and electrostatic regions that stabilize the transition state of the reaction and thereby lower the energy of activation. It could be said that all enzymes are catalysts, but there are many catalysts that are not enzymes. In fact, the catalysts you will encounter in general chemistry are almost always inorganic compounds or solid metals. Some texts define "catalyst" as being inorganic molecules that catalyze reactions, and enzymes as being organic molecules that catalyze reactions. However, because an enzyme is still "catalyzing" a reaction, we think the use of the term "catalyst" as a more categorical term makes the most sense.

Reactions What is a single displacement reaction?

This is when one element trades places with another element in a compound. These reactions come in the general form of: A + BC ---> AC + B

What is a double displacement rxn or metathesis rxn?

This is when the anions and cations of two different molecules switch places, forming two entirely different compounds. These reactions are in the general form: AB + CD ---> AD + CB

Q35. Describe how you could use the rate order graphs to determine the order of each reactant in a multi-reactant reaction experimentally in the lab: What would you need to measure? What would you do with the data?

To determine the order of each reactant experimentally you would only need to ensure that all other reactants were in excess and measure the concentration of the limiting reactant as a function of time. You would then use the measured concentration of the reactant in question in each of the types of graphs. If all other reactants are in excess, one of these graphs should be linear. You may be tempted to think that you wouldn't get a positive result if the reactant you were testing was NOT impacting rate. However, that would produce a line for [A] vs. time (i.e., the reaction would zero order in that species). Remember that zero order reactants are not included in the rate law!

Continue the street/apartment/room analogy used above to explain how many rooms there are in an s, p , d and f subshell.

Using the analogy provided, an orbital equates to a room and each room has two beds to be occupied by a maximum of two persons/electrons. There is only one room in an s subshell (studio apartment) and it can hold two electrons. There are three bedrooms in a p subshell and each bedroom can hold two electrons for a total of six. There are five bedrooms in a d subshell and each bedroom can hold two electrons for a total of ten. There are seven bedrooms in an f subshell and each bedroom can hold two electrons for a total of fourteen. Much like teenagers, electrons do NOT like to share rooms. Therefore, they will always fill empty orbitals first and only pair up inside the same orbital once it becomes necessary

Cations are smaller than their neutral counterpart and anions are larger than their neutral counterpart, why? Explain the difference in size between anions, cations, and neutral atoms.

When an element loses electrons and becomes a cation with net positive charge, the full nuclear charge remains in force and can attract the remaining electrons more effectively simply because there are fewer electrons and thus less electron-electron repulsion. Cations are smaller than their neutral counterparts just for this reason. For anions, however, adding electrons increases electron electron repulsion without a compensating increase in attraction to the nucleus. Anions are larger than their neutral counterparts as a result, and the increasing electron-electron repulsion makes it (a) difficult to stick a second extra electron onto a singly charged anion in the first place (the anion repels the second extra electron) and (b) unlikely that more than maybe two extra electrons will ever be stable when bound to any neutral atom.

How do you name compounds with transition metals?

When written in words, compounds that include transition elements must have a roman numeral showing the oxidation state of the metal (ex. iron (II) sulfate vs. iron (III) sulfate).

Predict the effect of doing each of the following to a reaction at equilibrium: adding/removing reactants, adding/removing products, increasing/decreasing pressure, increasing/decreasing temperature.

adding reactants ---> right adding products ---> left Increase pressure --> side with less moles Decrease pressure --> side with more moles Volume- Opposite of Pressure Exothermic (treat heat as a product) Endothermic (treat heat as a reactant)

What does it mean to shift the equilibrium?

all it means is to change the proportions of the various substances present in the equilibrium mixture (more blue squares) Recall that K is a "snapshot" of equilibrium that tells us where it is located and what it looks like. As far as the MCAT is concerned, temperature is the ONLY thing that changes K. (NOTE: Don't confuse what we said about shifting K with LeChatelier's principle. Le Chatelier's principle DOES NOT deal with moving K. It just says that K will ALWAYS be the same place and if you cause a disturbance that makes the ratio of products to reactants no longer equal to K, the reaction will proceed in whatever direction gets it back to K).