Kaplan MCAT General Chemistry Review

A few years before Dmitri Mendeleev published the first rendition of the modern periodic table, the English chemist John Newlands suggested the concept of periodicity when he arranged all of the then-known elements by increasing atomic weights and found that every eighth element exhibited similar properties. He dubbed his principle the “Law of Octaves” and created a chart in which the elements would be organized into groups of seven. In this chart (below), the eighth element would appear immediately to the right of the previous element that shares its properties:

Newlands’ discovery was initially dismissed as a coincidence. Soon afterward, Mendeleev created a more elaborate table that was eventually refined into the version that is common today. This table also arranged the elements by molecular weight, but refuted the idea of octaves. It was capable of accommodating the s-block (groups 1A and 2A), the p-block (groups 3A to 8A), the d-block (transition metals), and the f-block (lanthanoids and actinoids). In anticipation of the discovery of more elements, Mendeleev left several empty spaces in the table; for instance, he predicted the discovery of two elements with mass between 65 and 75 amu and a third element with mass between 40 and 50 amu.

30. Several of the atomic mass calculations were inaccurate during the time that periodicity was first discovered. Which of the following pairs of elements were NOT arranged correctly by mass on Newlands’s table?

A. Gold and platinum

B. Manganese and iron

C. Yttrium and indium

D. Tantalum and tungsten

31. Which of the following most strongly discredits the accuracy of the law of octaves?

A. The discovery of all of the naturally occurring elements in the s-block and the p-block.

B. The discovery of most of the naturally occurring elements in the d-block and the f-block.

C. J. J. Thomson’s discovery of the electron.

D. Ernest Rutherford’s discovery of the nucleus.

32. Mendeleev’s table was modified several times after its initial publication. Which of the following findings did NOT require modification of the existing entries in the table?

I. A unique element is characterized by a specific number of protons.

II. Electrons are arranged in orbitals and energy levels.

III. The atomic mass of gallium is approximately 70 amu.

A. II only

B. III only

C. II and III only

D. I, II, and III

33. Assuming that all known elements at the time were accounted for in Newlands table of elements, which of the following had NOT been discovered when Newlands published his table?

A. f-block elements

B. Halogens

C. Metalloids

D. Noble gases

34. Mendeleev predicted the existence of an element with atomic mass of 44. If his prediction were correct, which of the following properties would it exhibit?

A. Its atomic radius would be larger than calcium’s atomic radius.

B. Its ionic radius would be larger than calcium’s atomic radius.

C. It would lose an electron less readily than calcium would.

D. It would accept an electron less readily than calcium would.

35. What element on Newlands’ table had the largest atomic radius?

A. Uranium

B. Cesium

C. Bismuth

D. Osmium

36. Which of the following, if true, would MOST strengthen the claim that Newlands should be credited as the inventor of the modern periodic table?

A. Although most scientists dismissed Newlands’ theory, it was widely accepted within his home country of England.

B. Mendeleev approved of Newlands’ work upon reading about it a few years after he formulated his own periodic table.

C. Mendeleev created his version of the periodic table in an attempt to refute Newlands’ theory.

D. Newlands created a refined version of his system that was similar to Mendeleev’s table, but failed to publish it before Mendeleev.

PASSAGE V (QUESTIONS 37–44)

A student inserts a sliding divider into a simple cylinder to perform a series of three experiments with an unknown gas. The gas exhibits ideal behavior. Before each experiment, the divider is reset so that V₁ = V₂ and the contents are at STP. The total volume of the cylinder is 2 L. The student’s cylinder apparatus is illustrated below:

Experiment 1

The student increases the temperature of the gas in V₁ to 45°C while keeping the temperature of V₂ constant.

Experiment 2

The student uses mechanical force to move the central divider in the cylinder such that 3 V₁ = V₂. The temperature of the gas and the cylinder remains constant throughout this experiment.

Experiment 3

The student releases half of the molar contents of V₂, and does not change the molar contents of V₁.

While these experiments are being performed in near-ideal conditions (can be assumed to be ideal), an equation was derived in 1873 by Johannes van der Waals to account for the nonideal behavior of gases:

37. In Experiment 1, what is the final volume of 1 mol of gas in V₁?

A. 164R L

B. 318R L

C. 358R L

D. 403R L