Chem 107 Exam 2 Study Guide – Biochemistry Concepts and Practice

Q1. What is Coulomb’s law? What are its general rules about strengths of attraction?

Background

Topic: Atomic Structure and Electrostatic Forces

This question tests your understanding of Coulomb’s law, which describes the force between charged particles, and how it applies to atomic and molecular interactions.

Key Terms and Formulas:

• Coulomb’s law: $F = k \frac{q_1 q_2}{r^2}$

• $F$ = force between charges

• $k$ = Coulomb’s constant

• $q_1, q_2$ = magnitudes of the charges

• $r$ = distance between the charges

Step-by-Step Guidance

1. Recall that Coulomb’s law describes the force between two charged particles. The force increases with greater charge and decreases as the distance between charges increases.

2. Think about how this law applies to atoms: electrons and protons are charged, and their attractions/repulsions can be explained using this law.

3. Consider the implications for atomic structure: the closer an electron is to the nucleus, the stronger the attraction due to the smaller $r$ value.

4. Review the general rules: greater charge means stronger attraction, and shorter distance means stronger attraction.

Try solving on your own before revealing the answer!

Final Answer:

Coulomb’s law states that the force between two charges is directly proportional to the product of their charges and inversely proportional to the square of the distance between them. Stronger attractions occur with higher charges and shorter distances.

Q2. Does Coulomb’s law explain what holds the protons so close together in the nucleus of an atom? Explain your reasoning.

Background

Topic: Atomic Structure – Nuclear Forces

This question tests your understanding of the forces within the atomic nucleus and whether Coulomb’s law is responsible for holding protons together.

Key Terms:

• Coulomb’s law (electrostatic force)

• Strong nuclear force

• Protons (positively charged particles)

Step-by-Step Guidance

1. Recall that protons are positively charged and, according to Coulomb’s law, should repel each other.

2. Think about the actual situation in the nucleus: protons are packed closely together.

3. Consider what other force might be responsible for holding them together, since Coulomb’s law predicts repulsion.

4. Identify the strong nuclear force as the force that overcomes the repulsion between protons at very short distances.

Try solving on your own before revealing the answer!

Final Answer:

No, Coulomb’s law does not explain what holds protons together in the nucleus. The strong nuclear force is responsible for binding protons and neutrons together, overcoming the repulsive electrostatic force between protons.

Q3. Which attraction is the strongest: (a) The valence electron to the nucleus on a sodium (Na) atom (b) The valence electron to the nucleus on a chlorine (Cl) atom (c) The valence electron to the nucleus on a silicon (Si) atom? Use what you know about Coulomb’s law to explain the reasoning for your choice.

Background

Topic: Atomic Structure – Effective Nuclear Charge

This question tests your ability to use Coulomb’s law and concepts like effective nuclear charge to compare the strength of attraction between valence electrons and the nucleus in different atoms.

Key Terms:

• Valence electron

• Effective nuclear charge ($Z_{eff}$)

• Coulomb’s law

Step-by-Step Guidance

1. Recall that the strength of attraction depends on the nuclear charge and the distance of the valence electron from the nucleus.

2. Compare the atomic numbers and electron configurations of Na, Cl, and Si.

3. Consider the effective nuclear charge for each atom, which is higher for elements with more protons and fewer shielding electrons.

4. Use Coulomb’s law to reason which atom’s valence electron experiences the strongest attraction to the nucleus.

Try solving on your own before revealing the answer!

Final Answer:

The valence electron in chlorine (Cl) experiences the strongest attraction to the nucleus, due to its higher effective nuclear charge and smaller atomic radius compared to sodium (Na) and silicon (Si).

Q4. Use Coulomb’s law to predict which electron would be easier to pull off the fluorine atom: a valence electron or a core electron. Then explain your reasoning.

Background

Topic: Atomic Structure – Ionization Energy

This question tests your understanding of the difference between valence and core electrons, and how Coulomb’s law relates to ionization energy.

Key Terms:

• Valence electron

• Core electron

• Ionization energy

• Coulomb’s law

Step-by-Step Guidance

1. Recall that valence electrons are farther from the nucleus than core electrons.

2. According to Coulomb’s law, the force of attraction decreases as the distance from the nucleus increases.

3. Consider the shielding effect: core electrons are more tightly bound due to less shielding.

4. Predict which electron would require less energy to remove based on these factors.

Try solving on your own before revealing the answer!

Final Answer:

It would be easier to pull off a valence electron from fluorine, because valence electrons are farther from the nucleus and experience less attraction compared to core electrons.

Q5. Use what you know about Shell Models and Coulomb’s law to explain why fluorine (F) is much more reactive than iodine (I).

Background

Topic: Periodic Trends – Reactivity

This question tests your understanding of how atomic structure and Coulomb’s law influence the reactivity of elements, especially halogens.

Key Terms:

• Shell model

• Reactivity

• Coulomb’s law

• Halogens

Step-by-Step Guidance

1. Recall that fluorine and iodine are both halogens, but fluorine is higher up in the periodic table.

2. Fluorine’s valence electrons are closer to the nucleus, so the attraction is stronger according to Coulomb’s law.

3. Stronger attraction means fluorine can more easily gain electrons, making it more reactive.

4. Iodine’s valence electrons are farther from the nucleus, so the attraction is weaker and it is less reactive.

Try solving on your own before revealing the answer!

Final Answer:

Fluorine is much more reactive than iodine because its valence electrons are closer to the nucleus and experience a stronger attraction, making it easier for fluorine to gain electrons.

Q6. What is the octet rule?

Background

Topic: Chemical Bonding – Octet Rule

This question tests your understanding of the octet rule, which is fundamental to predicting how atoms bond and form compounds.

Key Terms:

• Octet rule

• Valence electrons

• Stable electron configuration

Step-by-Step Guidance

1. Recall that atoms tend to gain, lose, or share electrons to achieve a full set of eight valence electrons.

2. Think about how this rule applies to main group elements.

3. Consider exceptions to the rule, such as hydrogen and helium.

Try solving on your own before revealing the answer!

Final Answer:

The octet rule states that atoms tend to form bonds in order to have eight electrons in their valence shell, achieving a stable electron configuration similar to noble gases.

Q7. Sodium (Na) and chlorine (Cl) atoms react to make table salt (NaCl). When this reaction occurs, determine which atom loses electrons and which atom gains electrons, and how many electrons each atom loses/gains.

Background

Topic: Ionic Bonding

This question tests your understanding of electron transfer during the formation of ionic compounds, specifically NaCl.

Key Terms:

• Ionic bond

• Electron transfer

• Cation (Na+), anion (Cl-)

Step-by-Step Guidance

1. Recall that sodium is a metal and chlorine is a nonmetal.

2. Metals tend to lose electrons to achieve a stable configuration, while nonmetals tend to gain electrons.

3. Determine how many electrons are transferred in the formation of NaCl.

4. Identify which atom becomes a cation and which becomes an anion.

Try solving on your own before revealing the answer!

Final Answer:

Sodium (Na) loses one electron and becomes a cation (Na+), while chlorine (Cl) gains one electron and becomes an anion (Cl-). One electron is transferred from Na to Cl.