Unit 1: Atomic Structure & Properties
Chemistry · Unit 1 · Paper 3

Atomic Structure & Properties unit test

A test on this unit alone, marked as a percentage and a letter grade — for the test your class is actually sitting, rather than for May. Answer everything, then submit once: seeing the answer to question 3 before attempting question 4 makes the final percentage meaningless.

Paper 1Paper 2Paper 3
Each paper is built from this unit’s 21 terms and is the same for everyone, so a teacher can assign “Unit 1, Paper 3” and every student sits the identical test. Multiple choice is marked objectively; the written sections you mark yourself against the model answer and rubric.
Suggested time 31 min 28 points0/17 attempted
1

Average atomic mass

2

Photon energy

3

Shielding

4

Electronegativity

5

Molar mass

6

Isotopes

7

Ionic radius

8

Why the first ionization energy of oxygen is below nitrogen

9

Mole and Avogadro's number

10

Empirical vs molecular formula

11

Percent composition

12

Valence electrons

Short answer 1. Define or explain: Absorption and emission spectra

3 pts

Short answer 2. Define or explain: Mass spectrometry

3 pts

Short answer 3. Define or explain: Effective nuclear charge (Zeff)

3 pts

Short answer 4. Define or explain: Ionization energy trend

3 pts

Free response

4 pts

A student performs a spectrophotometry experiment with V2+(aq) solutions and produces a calibration curve by measuring the absorbance of several solutions of known concentration. FIGURE 1 — Absorbance against concentration (M). The plotted points lie on a straight line through the origin: Concentration (M) 0.000 0.020 0.040 0.050 0.070 0.090 Absorbance 0.00 0.08 0.16 0.20 0.28 0.36 FIGURE 2 — a particle diagram, inside a circle, of the V2+ ions in a solution whose absorbance is 0.32. It contains 8 V2+ ions. Water molecules are omitted for clarity. FIGURE 3 — an empty circle of the same size, representing the same volume. The student then measures the absorbance of a different V2+(aq) solution of unknown molarity, but the absorbance is higher than 0.36, the upper limit of the graph. The student transfers 3.00 mL of this solution to a 25.0 mL volumetric flask, dilutes to the mark with distilled water, and measures the absorbance of the diluted solution.

(a) The released exam asks the student to draw, in the circle in Figure 3, the correct number of V2+ ions to represent the concentration of a solution with an absorbance of 0.08. State that number and show the reasoning that gives it.

(b)(i) The absorbance of the diluted solution is 0.22. Determine the molarity of V2+(aq) in the diluted solution.

(b)(ii) Determine the molarity of V2+(aq) in the original, undiluted solution.

(c) The concentration of V2+(aq) calculated in part (b)(ii) is lower than the actual concentration of the undiluted solution. The student claims that the calculated concentration is too low because during the dilution step, the final level of the solution was higher than the mark on the volumetric flask. Do you agree or disagree? Justify your answer.