Structure Unit Review answers PDF

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Sch4 Sch4U: U: Structure and PPrroperties TTest est R Re eview A. Short Answer and Problems 1.

For each of the following molecules: a) draw the Lewis structure;

AsHCl4,

TeI51-

PCl3,

b) complete the chart:

Molecule

Hybrid Orbitals

Shape

Polar/Non-Polar MOLECULE

SiH4

sp3

tetrahedral

Non-Polar

AsHCl4 PCl3 TeI51-

2. Create an energy level diagram for the phosphorus atom in the most stable configuration and provide a brief definition for Hund’s Rule, the Aufbau Principle, and the Pauli-Exclusion principle.

Hund’s Rule: electrons are spread horizontally before pairing. Unpaired electrons in the same orbital block have the same spin. Aufbau: Lower energy orbitals are filled with electrons before higher energy orbitals Pauli-Exclusion Principle: electrons in the same orbital have opposite spins.

3. Create a short-form electron configuration for:

a) Bi atom

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b) Ag+ ion

4.

Scientist Thomson

De Broglie

Empirical Evidence Cathode rays are deflected from negative charge and have a mass approximately 2000 times less than hydrogen A single electron is able to move through 2 slits and create an interference pattern

Atomic spectra is a unique characteristic of all elements. Schrödinger While circular orbits work for hydrogen, the correlation does not apply to other elements.

Advancement of Atomic Theory Atoms contain subatomic particles that are negatively charged and are free to move

Electrons (and all other particles) with motion create waves of momentum that allow them to travel through both slits Electron orbits can take a variety of pathways around the atom. Solutions to Schrodinger’s equations results in s, p, d and f orbitals

5. Determine the molar mass of a solute based on the following experimental data: Freezing Point Freezing Point Mass of Solvent: Mass of Solute: of Pure Solvent: of Mixture: 78.000g

3.600g

68.2oC

63.9oC

Kf of solvent 19.61 K.Kg/mol

B. Communication 1. By detailing the problem with Rutherford’s atomic model, explain the reasons for Bohr’s ideas about electron structure in an atom. Because electrons are negatively charged particles, the law of electrostatic attraction suggests that the electrons should be drawn into the positively charged nucleus. There is nothing in the Rutherford model to prevent this. Bohr proposed that quantum theory should result in a set of natural “barriers” that would prevent electrons from occupying specific regions around the atom thus preventing the electrons from being pulled into the nucleus.

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2. Compare and contrast the expected and actual observations of the Gold Foil Experiment. For each observation, provide a rationale for the expectation based on Thomson’s Model and rationale for the actual observation based on Rutherford’s Model. Because Thomson’s model is neutral, positively charged alpha particles should pass straight through. Most particles did pass straight through, but some were occasionally deflected at various angles. Rutherford proposed that the positive charge of the atom was concentrated into a very small space in the middle of the atom (called the nucleus) while the electrons were spread diffusely outside like water in a cloud.

3. Summarize the 4 observations of the electron double slit experiment and briefly relate the contributions of de Broglie and Heisenberg to rationalize these observations. #1) An electron beam travels through 2 slits and creates an interference pattern similar to wave transmission. #2) A single electron travels through 2 slits and also creates an interference pattern: de Broglie proposed the concept of a matter wave (the momentum of the electron causes it to move with wave-like characteristics). #3) If the electron is observed before it reaches the screen, the interference pattern changes to a particle pattern (2 bands). #4) Even if the electrons are routed away from the same screen, they still create an interference pattern that is reduced to a particle pattern when observed. Heisenberg suggested that the act of observing the electron fundamentally changed the momentum of the electron. This is known as the uncertainty principle. 4. Draw a diagram showing the orbitals and the bond type (pi or sigma) of all the bonds in the molecule C2H4. As part of your answer use orbital diagrams showing how electrons in carbon are promoted from ground state to achieve the hybrid orbitals necessary for the observed bonding arrangement of C2H4. Since each carbon atom requires only 3 steric points, sp2 hybrid orbitals are created for the overall bonding structure (with sigma bonds). This leaves 1 unhybridized p-orbital on each carbon atom available for a pi bond.

5. Explain why the structure of CH3F can be used to explain why it has a higher boiling point than CF4. Both molecules are symmetrical tetrahedral molecules. As such, even through CF4 contains polar bonds, it is a non-polar molecule because the resultant sum of all 4 polar bonds is zero (the symmetry cancels out the polarity). CH3F only has one polar bond leaving it with an overall build up of negative charge in the area of the fluorine atom. The dipole-dipole force between the polar CH3F is stronger than the London dispersion force between the CF4 resulting in a higher boiling point.

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C. Multiple Choice 1. A central atom with 3 pairs of electrons in sigma bonds and 3 lone pairs of electrons would have what hybridization?

a. sp

b. sp2

c. sp3d

d. sp3d2

e. sp3

2. Which element could have it’s last electron in the following quantum state:

a. iron

n=4; L= 0; ml = 0; ms = - ½ b. uranium c. calcium d. sulfur

e. bromine

3. Which element has the electron configuration 1s22s22p63s23p64s23d6? a. iron b. aluminum c. ruthenium d. silicon 4. Which of the following solids are typically considered the “hardest” a. Ionic crystals c. covalent network e. none of the above b. Molecular crystals d. metallic 5. Which of the following compounds would have the lowest boiling point?

a. H2

b. CF4

c. CH4

d. CH2F2

e. CH3F

6. A substance is a brittle crystal that does not conducts electricity when dissolved in water. The substance must be: a. metallic crystal c. covalent crystal e. frozen gas b. ionic crystal d. molecular crystal 7. Which of the following quantum numbers correctly indicates a p orbital

a. ms = -1/2

b. L=1,

c. L = 3

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d. ml = 5

e. n=3...