CHEM 1150 Final Exam Study Guide

Consider the question: Is there an attractive force between a pencil and the earth?

Is this a scientific question?

I. Yes

II. No

Because

III. It can be tested and answered through observations and experiments

IV. The answer is already known and we find it online

V. There is no way to design an experiment to answer this question

I and III

Which of the following properties ascribed to atoms by Dalton do we still consider valid?

I. Elements are composed of small indivisible, indestructible particles called atoms

II. All atoms of an element are identical and have the same mass and properties

III. Atoms of a given element are different from atoms of other elements

IV. Compounds are formed by combinations of atoms of two or more elements

III and IV

Electrons are negatively charged. Which experiment provided evidence to support this claim? What is the specific evidence used to support this claim?

Experiment:

I. The gold foil experiment

II. The cathode ray tube experiment

Evidence:

III. Most of the positively charged alpha particles shot at a thin gold foil passed straight through

IV. A small fraction of the positively charged alpha particles shot at a thin gold foil were deflected

V. The beam of particles emitted from the cathode bent toward the positively charged plate

VI. The beam of particles emitted from the cathode behaved the same no matter what type of metal the cathode was made of

II and V

Which of the following contain(s) atoms?

Heat

Light

Energy

Dust

All of the above

Dust

4

4

The diagram below shows alpha particles being fired at a piece of gold foil. Where will the majority of the alpha particles be detected (point I, II, or III) and why?

Because:

IV. Alpha particles bounce off the nuclei within the gold atoms, because the nuclei are much more massive than the alpha particles

V. The alpha particles are repelled when they come close to the nuclei, because both are positively charged

VI. The alpha particles go straight through the atom, because it is mostly empty space

Refer to Exam 1 question 6 for imagery

III and VI

Thomson's cathode ray tube experiment proved false what part of Dalton's atomic theory?

All atoms are indivisible and indestructible

How would the strength of the electrostatic force change if the distance between charged objects decreased?

The electrostatic force would become stronger

Consider the following statement: A nitrogen molecule is made of the same type of atoms

Is this statement true or false and why?

I. True

II. False

Because:

III. An element is made of one type of atom. Nitrogen is an element that exists as a diatomic molecule

IV. Nitrogen is a compound that exists as diatomic molecules. Compounds are made of different types of atoms

V. Nitrogen is an element, and therefore must exist as separate atoms not molecules

I and III

Why does the potential energy increase as two xenon atoms move extremely close together?

Because the repulsive force, between the overlapping electron clouds, is dominant

Bromine (Br2) melts at 266 K and boils at 332 K. Which of the following is the best representation of bromine at 300 K?

(Picture the BeSocratic HW where we would draw atoms/molecules in solid, liquid, and gaseous states. Then choose the best diagram option)

See Exam 1 question 11 for A, B, C, and D

C

The diagram to the right is for two subatomic particles.

What does the curve show?

I. The potential energy decreases as the objects get closer together

II. The potential energy increases as the object get closer together

Which of the two subatomic particles could this curve represent?

III. Two neutrons

IV. Two electrons

V. One proton and one electron

I and V

Which statement best describes the forces that exist between helium atoms in the solid state?

The partial positive end of one atom's instantaneous dipole attracts the partial negative end of the neighboring atom's induced dipole

When a covalent bond is formed between two nitrogen atoms:

I. Energy is absorbed

II. Energy is released

III. A molecule is formed

IV. The nitrogen changes from the gaseous and liquid state

II and III

The London dispersion forces between two neon atoms compared to the LDF's between two argon atoms where both systems are the most stable is:

I. The same

II. Stronger

III. Weaker

Because

IV. They are both noble gases

V. Neon has a smaller electron cloud, therefore there will be a smaller separation of charge resulting in a weaker force

VI. Neon has a smaller electron cloud, therefore there will be a larger separation of charge resulting in a stronger force

III and V

Is the following statement true or false?

When chlorine freezes, LDF's are formed

This statement is

I. True

II. False

Because

III. When a substance freezes, covalent bonds are formed

IV. There are LDFs in both the solid state and the liquid state, but more in the solid state

V. There are LDFs in the solid state but not the liquid state

I and IV

Which do you predict to have the higher boiling point, di-fluorine (F2) or neon (Ne) and why?

Please Note: The radii of an individual fluorine (F) atom and neon (Ne) atom are pretty similar

F2 because the LDFs between fluorine molecules are stronger, requiring more energy to overcome

Use the potential energy curve in question 18 (Exam 1) to explain the change in kinetic energy as two atoms move from Z to Y.

The kinetic energy increases because the atoms are attracted to each other and are speeding up

6

6

Select the evidence and reasoning that supports the claim that light is a wave.

Evidence

I. When light shines on a piece of metal, electrons are ejected

II. When light shines through a double slit, a pattern of bright and dark lines appear

III. When light shines on a sample of atoms, some of the light is absorbed

Reasoning

IV. Different waves of light are absorbed by the electrons in atoms depending on which element is present

V. Waves of light interfere constructively when they arrive in-phase and destructively when they arrive out-of-phase

VI. Waves of light transfer their energy to electrons, overcoming the electrostatic attraction within the nucleus

II and V

Hydrogen produces emission lines (colored lines on the spectrum) with the following wavelengths: 410 nm, 434 nm, 486 nm, and 656 nm. Where would you expect to see the absorption lines (dark lines) for hydrogen on its absorption spectrum and why?

(This is question 2 from Exam 2 that was voided, although, the answer I put was found on a separate quizlet so I am choosing to believe it is correct...BUT proceed with caution lol)

The absorption lines for hydrogen would appear at exactly the same wavelengths, because the energies of the photons emitted and absorbed by hydrogen are the same.

The energies of four photons of light are listed below. Which photon has the longest wavelength?

E = h(c/wavelength)

E = 1 x 10^-12 J

E = 8 x 10^-16 J

E = 5 x 10^-18 J

E = 2 x 10^-19 J

E = 2 x 10^-19 J

5

5

What is the evidence that supports the claim that light is a particle?

When light shines on metal there is a threshold frequency, below which no electrons are ejected from a metal

An MRI (magnetic resonance imaging) machine operates at a frequency of 30 kilohertz (kHz), what wavelength radiation does this correspond to?

(This is just a memorization question of the wavelength diagrams within our chapter slides PowerPoint)

1 x 10^4 m

The diagram to the right represents energy transitions for an electron in an atom. which arrow corresponds to the absorption of yellow light (as opposed to violet light)?

See exam 2 question 7

D

Why must we consider the wave properties of an electron, but not the wave properties of macroscopic objects (such as humans)?

The wavelength of the electron is similar in size to the atom and affects its properties whereas the wavelength of the macroscopic object is much smaller than the object and does not affect its properties

Write the electron configuration for fluorine (F) and the electron configuration for chlorine (Cl). What is different about the valence electrons in these two atoms?

I. There are different numbers of valence electrons

II. The valence electrons have different energies

III. The valence electrons are in different orbitals (s, p, d, f)

IV. The valence electrons are in different size orbitals

II and IV

What is the electron configuration of Mg+?

1s2 2s2 2p6 3s1

Reminder: cations are (+) and removes an electron. The configuration for Mg is 1s2 2s2 2p6 3s2 so the 3s2 becomes 3s1

Consider K+ and Cl-. Which do you predict is larger and why?

Cl- is larger because fewer protons are attracting the same number of electrons as in K+

Use the data table for the first eight ionization energies of a particular element shown below to predict and explain which element you would expect to show this trend in successive ionization energies.

I. Fluorine

II. Oxygen

Because

III. Core electrons are more strongly attracted to the nucleus than valence electrons

IV. Valence electrons release more energy when they are removed from the atom

See Exam 2 question 12 for data table

None

1

1

Atomic radius __________ from left to right across a row on the Periodic Table.

I. Increases

II. Decreases

Because

III. The number of electrons increases

IV. The mass increases

V. The relative attraction between the protons and the other electrons increases

II and V

How many core and valence electrons does one atom of iodine (I) have?

46 core and 7 valence -- Iodine is in Group 7 (# of valence) and Atomic #53 so 53-7 is 46 core electrons. This is how to solve for elements in Groups 1-8

The potential energy curve to the right is for two H-atoms undergoing nuclear fusion. As indicated by the region inside the dashed oval, as the nuclei move very close to each other, the potential energy decreases. Why does it decrease?

I. The dominant force between the nuclei is attractive

II. The dominant force between the nuclei is repulsive

III. The attractive and repulsive forces are balanced

Because

IV. Nuclei are positively charged and interact through the electrostatic force

V. The strong nuclear force acts on nuclei over very short distances

See Exam 2 question 16 for diagram

I and V

Nuclear reactions can release large amounts of energy because ...

Part of the mass of the reactants is converted into energy

The lines in the emission spectrum of hydrogen result from ...

Energy given off in the form of visible light when an electron moves from a higher energy state to a lower energy state

According to the Heisenberg uncertainty principle, it is impossible to know precisely both the position and the _______ of an electron.

Momentum

The atomic radius of main-group elements in the periodic table generally increases down a group because ...

The principal quantum number of valence electrons increases

To the right is a complete molecular orbital diagram for a diatomic molecule. The electrons are shown in the atomic orbitals and in the molecular orbitals. how many bonds exist between the atoms in this diatomic molecule?

See Exam 3 question 1

2 bonds

Carbon can exist in many forms known as allotropes. Two such allotropes are diamond and graphite (graphene). Unlike diamond, graphite conducts electricity this is because ...

In graphite, there are unhybridized P-orbitals that extend over the entire sheet forming a delocalized pi bonding network where electrons are free to move.

(Note: freely moving electrons = conductor of electricity)

What is the best explanation for why metals are ductile?

Valence electrons act as a "sea of electrons" surrounding the nuclei and holding them

Compare the two molecular representations shown to the right.

These structures represent

I. The same molecules

II. Isomers

III. Different molecules that are not isomers

Because

IV. Free rotation around the bond between the two carbon atoms makes the structures the same

V. Rotation is not possible around a double bond without breaking it

VI. These structures have different numbers of carbon and hydrogen atoms

See Exam 3 question 4 for molecules

II and V

Which do you predict has the higher boiling point and why?

I. Br2

II. Ne

Because

III. When this substance boils, covalent bonds are overcome

IV. Covalent bonds are stronger than LDFs

V. The strength of the LDFs depends on the size of the molecule/atom (electron cloud)

I and V

Draw the lewis structure for sulfur dichloride, SCl2. How many lone pairs of electrons are on the sulfur atom?

2 lone pairs

(Note: practice lewis structures so if he gives another compound on the exam you feel comfortable in solving; there is a video on YouTube that is easy to understand I can link it if I need too)

Draw the lewis structure for a nitrogen molecule, N2 (N---N). When nitrogen melts, what interaction(s) are overcome?

London Dispersion Forces

For the structure to the right, what is the electron center geometry for the oxygen atom that the arrow is pointing to?

See Exam 3 question 8

None

Use the Lewis structure in Exam 3 question 8 to answer this question. What is the shape around the oxygen atom that the arrow is pointing to?

Bent

2

2

The lewis structure for Ethene (C2H4) is shown below. What is the hybridization and the shape around the carbon labelled with the arrow?

See Exam 3 question 11

sp2 hybridized and trigonal planar

The lewis structure for ethene (C2H4) is shown in Exam 3 question 11. Which statement below are true regarding ethene's pi bond?

I. The pi bond in ethene is made from the interaction between an unhybridized p orbital on each carbon atom

II. The pi bond in ethene is made from the direct orbital overlap between the sp2 hybrid orbitals on each carbon

III. Rotating around the pi bond in ethene requires energy to break the interaction

IV. There is no free rotation around the pi bond in ethene

I and III

Dipole-dipole interactions and LDFs are two types of intermolecular forces. For molecules of about the same size ...

Dipole-dipole interactions are the stronger force due to the presence of permanent dipoles

Remember: LDF < Dipole-Dipole < Covalent Bond < Hydrogen Bond

The lewis structure for difluoroborane (HBF2) is shown to the right. Is this a polar molecule?

I. Yes

II. No

III. Sometimes

Because

IV. The bond dipoles add together to create a molecular dipole

V. The bond dipoles cancel each other out when they are added together

VI. The bond dipoles may cancel each other out or create a molecular dipole depending on how the lewis structure is drawn

See Exam 3 question 14

None

Which element is more electronegative?

I. Oxygen

II. Nitrogen

Because

III. The valence electrons are further from the nucleus

IV. The valence electrons experience a higher effective nuclear charge

V. Oxygen has more electrons than nitrogen

I and IV

Three molecules of methanol (CH3OH) are shown below. Which of the labeled interactions are hydrogen bonding interactions?

See Exam 3 question 16 for molecules

IV -- the lone pairs are the give-away

What are the strongest intermolecular forces present in dimethyl ether (CH3OCH3) in the liquid state?

If needed refer to Exam 3 question 17 for lewis structure

Dipole-dipole interactions

True or False: NaBr has the lowest melting point of the following ionic compounds: NaBr, CaO, LiF, and MgO

I. True

II. False

Because

III. NaBr is least ionic

IV. NaBr is made of larger ions with smaller charges

V. NaBr is made of smaller ions with smaller charges

I and IV

What is the most likely formula for the compound formed between calcium and fluorine?

CaF2

If the same amount of thermal energy were transferred to equal masses of water, copper, granite, and ethanol, which substance would reach the highest temperature?

Water (4.18 J)

Copper (0.385 J)

Granite (0.79 J)

Ethanol (2.42 J)

Copper (0.385 J) because it has the lowest energy required to increase 1 degree C

What happens on the molecular level when thermal energy (heat) is added to increase the temperature of water form 10 C to 50 C?

The water molecules speed up, and collide with the thermometer, transferring energy to the thermometer. This energy causes the mercury atoms in the thermometer to vibrate more, and the liquid expands -- thus showing an increase in the temperature scale.

3

3

Which do you predict to have a higher boiling point and why?

I. CH3OH

II. CH3CH2CH2OH

Because

III. More hydrogen bonding interactions need to be overcome requiring more energy

IV. The LDFs are stronger because the molecule is larger, so more energy is required to overcome them

V. There are more covalent bonds to break, requiring more energy

II and IV

Which do you expect to have the highest melting point?

I. MgO

II. CaO

Because

III. The internuclear distance is smaller, therefore the force is stronger and requires more energy to overcome

IV. The charge is high; therefore, interactions are stronger and require more energy to overcome

I and III