14a scerri final

why is mendeleev most credited for discovering the periodic system?

he successfully predicted the existence of several elements

explain basis for placing helium in groups 2 and 18

-group 2: He has 2 es, & group 2 elements have 2 outer es

-group 18: He has a full outer shell like other noble gases & forms no compounds

how does Pauli principle explain why electrons don't collapse into the nucleus?

Pauli principle means that only 2 es can go into 1s, so no more es can enter 1s orbital

comment on importance of the threshold frequency for the development of quantum theory of light

threshold frequency implies threshold energy of h*v0. the minimum energy is interpreted as a quantum of light energy or a particle of light.

explain how Heisenberg uncertainty principle is related to the concept of indeterminism

predicting the future depends on knowing both position and momentum accurately. since this can't be known, the future is undetermined.

under what conditions do two waves produce destructive interference?

if the waves are in phase or if path length diff = n*wavelength

what's wrong with the lewis structure of the NO3- ion in the light of the experimental evidence on this ion which shows all bond lengths to be the same?

the lewis structure implies existence of double and single bonds

how can the lewis structure of NO3- ion be modified according to the quantum theory of bonding?

if all bonds btwn N and Os are pi bonds, they will all have the same length

how does the lewis theory define an acid and a base?

lewis acid is an electron pair acceptor; lewis base is an electron pair donor

explain how a sample of water can have a pH of 6 and still be neutral

neutral means [H+]=[OH-], which can occur at any pH value. pH=6 occurs if Kw=10^-12->[H+]=10^-6->pH=6

explain why the metal chromium has no color whereas compounds of nickel have colors

in the metal the 5d orbitals are degenerate->no transition possible->no color. if ligands are present, all d orbitals are repelled, but 2 of them more than the other 3. this gap allows for transition

what can you deduce about the ligands in a transition metal compound that absorbs light in the orange region of the visible light spectrum?

blue is absorbed. blue means high energy, therefore high field ligands.

explain the nature of the bonding btwn the ligands and the metal ion in [Fe(Cn)3(H2O)3] and how the metal ion is able to accept six lone pairs of electrons

dative covalent bonds. ligands donate lone pairs; metal accepts 6 lone pairs. Fe3+ is 3d6

how is CFSE diagram connected w the CFSE of transition metal compounds?

the longer the CFSE as in d3 and d8, the longer the departure from the expected values (full circles)

why is HI a stronger acid than HF?

the bond strength of HF is greater than that of HI

explain: Bohr's model of the atom was ad hoc whereas schrodinger's represented an improvement.

for Bohr, quantization is just assumed, whereas Schrodinger derived quantization and quantum numbers to explain orbitals.

explain: rutherford's model of atom couldn't explain a couple of features about atoms that Bohr's could.

rutherford's model had electrons orbiting the nucleus randomly and couldn't explain why the electrons didn't collapse into the nucleus, while Bohr's model showed stable energy levels and explained atomic spectra

give a quantum mechanical explanation for why periods 2 and 3 contain 8 elements, whereas periods 6 and 7 contain 32 of them.

periods 2 & 3 contain 8 elements bc there are 3 p orbitals and 1 s orbital (4 total) that can hold 8 electrons. periods 6 & 7 contain 32 bc 1 s orbital, 3 p orbitals, 5 d orbitals, and 7 f orbitals (16 total) can hold up to 32 electrons.

explain 3 significant ways the Bronsted-Lowry theory and the Arrhenius theory differ in their definition of acids and bases.

1. Ar theory is only applicable for acids/bases in water but BL theory is for any polar substance

2. Ar theory states that acids form H+, but BL theory states that acids donate a proton.

3. Bases form OH- in the Ar theory but accept protons in the BL theory.

how is a buffer solution made and why does it act to resist changes in pH?

a buffer solution is made from a weak acid & its conjugate base. it acts to resist changes in pH bc adding a little H+ or OH- will either react w the undissociated weak acid or excess conjugate base and not change the concentration significantly.

explain why the bond angles in CH4, NH3, and OH2 become progressively smaller

CH4 has no lone pairs; NH3 has a lone pair of electrons that push the H atoms closer together. OH2 has 2 lone pairs, which repel more and further push the H atoms together.

is it necessary for a molecule to have an AXn structure in order for it to have a net dipole?

No, a molecule can have other structures and still have a net dipole. HCLO doesn't have AXn structure, but it has a dipole.

once the energy of the electron is known, so is its exact position (T/F)

false

explain an important medical application for EDTA

it's used to bind to toxic heavy metals that enter the system and allow these heavy metals like lead to pass through the body relatively harmlessly.

what are the two main characteristics of chemical equilibrium?

1. the concentration of both the reactants and products are constant

2. the forward rate of the reaction equals the backwards rate

suppose you wanted to make a buffer solution using C2H5OOH, propanoic acid. what do you need to add?

the propanoic acid's conjugate base (C2H5COO-) is needed w a common ion

comment on the typical concentrations that should be used in order to resist changes of pH and explain.

the higher the concentrations of both the acid and its conjugate base, the better to resist changes in pH bc then more buffer is created for increasing strong [H+] or [OH-] that could then be neutralized by the high concentration of buffers

explain qualitatively how the addition of H+ ions would leave the pH of the buffered solution essentially unchanged

the added H+ ions would react w the base, CH3COO- to neutralize the increase in H+ concentration, resulting in little change in pH value

how do the molecular orbital and valence bond/hybridization approaches complement each other?

MO theory accounts for stabilization and magnetism while VB/H can't, although VB/H can account for rationalizing structure

why, according to quantum mechanics, does an orbiting electron not lose energy and crash into the nucleus?

according to QM, the orbiting electron is a quantized wave, bound in certain energy levels, so that they jump from level to level and don't lose energy

the term dynamic equilibrium means

that reactants and products are continuously interconverting, though their concentrations remain the same; the reaction rate of the forward reaction is equal to that of the backwards reaction

explain how the simple estimate of the effective nuclear charge of atoms varies across the third period starting at sodium and anding at argon

Zeff=Z-inner electrons, so the Zeff increases across the 3rd period bc the inner electrons remains the same while the # of protons (= atomic # Z) increases.

how can Zeff be used to explain the trend in atomic radius across the same period?

Zeff describes the effective nuclear charge of an atom, so across a period (left to right), the # of protons increases, pulling electrons closer to the nucleus, thus decreasing atomic radius

explain why the typical transition metals have no color whereas compounds that these metals form w a # of ligands have color.

metal coordination complexes have color due to the removal of degenerate orbital levels bc some of the orbitals experience electrical repulsion w the ligands. transition metals do not experience repulsion as they don't have multiple ligands

why do compounds of zinc and cadmium have no colors even if they are bonded to a # of ligands?

since all the orbitals are filled (d10), electrons won't transfer orbitals, thus no color is emitted

consider the compound [Mn(NH3)6]^2+. explain the nature of the bonding btwn ligands and metal ion.

the ligands form dative bonds w the metal in which they denote both of their electrons to bond

what type of info about molecules do the molecular orbital and valence bond/hybridization approaches respectively provide?

MO helps describe stability and magnetic behavior of a molecule, while VB/H rationalizes its structure/shape

explain why CH3OOH is a weaker acid than CH2ClCOOH

due to the Cl in CH2ClOOH, its strong bond polarity attracts (pulls) the electrons of the end hydrogen, thus weakening the bond on H, making it easier to break/ionize, whereas CH3OOH does not, making it a weaker acid

explain what Kw means and how it causes the pH of water to be 7 at 298K.

Kw is the equilibrium constant of water, which is 10^-14 at 25 degrees C. [H+]=[OH-] at 25 C for water, so Kw=[H+]^2 -> 10^-14 = [H+]^2, so pH=7, or -log(H+)=7, since Kw=[H+][OH-].

how many orbitals total can occur in the 4th shell of any atom?

16 (n^2)

explain what causes the color in transition metal compounds

color is caused by the removal of degeneracy in the d orbital, causing molecules to absorb light of certain frequency. the degeneracy is removed by the presence of ligands.

predict the color observed when [Co(CN)6]^3- gives an electronic transition in the visible range.

yellow; CN->high field->ligand absorbs high energy light (violet)->emits complement (yellow)

in what sense does quantum mechanics imply that "a particle is not a particle"?

a particle is also a wave, w a certain frequency and wavelength

in what sense does quantum mechanics imply that "an orbital is not an orbit"?

orbitals are clouds of probability of the presence of an electron. electrons do not orbit, they are also waves.

in what sense does quantum mechanics imply that "spin is not spin"?

electrons do not spin, they have diff magnetic "spin" while occupying the same orbital

what experiment directly supports de Broglie's hypothesis of the wave nature of matter?

electron diffraction by a crystal

Why are resonance structures important?

Resonance structures are a better depiction of a Lewis dot structure because they clearly show bonding in molecules.

As water is heated, pH decreases. This means that:

a) the water is no longer neutral

b) [H+] > [OH-]

c) [OH-] > [H+]

d) a and b are correct

e) none of these

none of these

explain the term diamagnetic and give an example of a diamagnetic molecule

a diamagnetic molecule is a diatomic molecule that has all of its electrons paired. ex: N2

what's wrong about the statement "in an exothermic reaction heat is given out. It follows that if the temperature of the reaction is increased, the reaction will proceed more effectively from left to right or in the exothermic direction in order to remove the added heat"?

the reaction should proceed from right to left to remove added heat through an endothermic process.