Sentence Starter:

According to the formula, when the charge size increases, the electrostatic attraction force  .

Step 2: Effect of Distance

If you move the positive and negative charges further apart (increase Distance), what happens to the force?

Sentence Starter:

According to the formula, when the distance between charges increases, the attraction force  .

Unit 3: Chemical Forces Page 2 of 3 (Tier 2)

Unit 3 Assessment: Tiered Exam Tier 3: Challenger

Coulomb's Law Calculations

Part 5

Proportional Scaling of Forces

Apply mathematical proportional reasoning to Coulomb's Law. Solve the scenarios and explain your reasoning clearly in the workspaces provided.

Scenario A: Doubling Charge

Imagine an ionic bond between Sodium (Na+) and Chlorine (Cl-) has an attractive force of F1. If you replace Sodium with Magnesium (Mg2+), you have doubled one of the charges. What is the new force in terms of F1?

New Force is 2 × F1

New Force is 1/2 × F1

Show or explain your reasoning mathematically:

Scenario B: Doubling Distance

Two ions are spaced at a distance of r with attractive force F1. If you double the distance to 2r, what is the new force in terms of F1?

New Force is 1/4 × F1

New Force is 1/2 × F1

Show or explain your reasoning mathematically:

Unit 3: Chemical Forces Page 3 of 3 (Tier 3)

Part 2: Model Identification

• Model A: Element (atoms are separate, identical and pure)
• Model B: Compound (atoms are bonded into distinct molecules)

Part 3: Periodic Table Structure

• Question 1 (Row): Period
• Question 2 (Column): Group
• Question 3 (Left side): Metal

Part 4: Short-Answer with Supports (Sentence completion guide)

Question 1: Elements in the same column have similar reactivity levels because they have the same number of valence (outer) electrons.

Question 2: A homogeneous mixture looks uniform and identical throughout (like saltwater), while a heterogeneous mixture has clearly visible, separated parts (like a salad or oil and water).

Assessment Suite Teacher Guide Page 2 of 3

Teacher Resource Guide Answer Keys & Rubrics

Chemical Forces Tiered Exam Key

Key 3

Chemical Forces Tiered Exam (Pages 1, 2, & 3)

Tier 1: Foundation Level (Page 1)

• Question 1 (loses electrons): Cation (+)
• Question 2 (gains electrons): Anion (-)
• Pair 1 (+ vs -): Attract (pull together)
• Pair 2 (+ vs +): Repel (push apart)

Tier 2: Core Level (Page 2)

• Sodium final charge: +1 (since it lost 1 electron)
• Chlorine final charge: -1 (since it gained 1 electron)
• Step 1: Charge Size: increases
• Step 2: Distance: decreases (as distance increases, attractive force falls)

Tier 3: Challenger Level (Page 3)

Scenario A (Doubling Charge): New Force is 2 × F1. Since electrostatic force is directly proportional to the product of charges, doubling one charge doubles the attractive force.

Scenario B (Doubling Distance): New Force is 1/4 × F1. According to the inverse-square law, doubling distance (d to 2d) reduces force by a factor of 4 (22 = 4).

Assessment Suite Teacher Guide Page 3 of 3