ACT science practice test 63

Directions: Each passage is followed by several questions. After reading a passage, choose the best answer to each question and fill in the corresponding oval on your answer document. You may refer to the passages as often as necessary.

You are NOT permitted to use a calculator on this test.

In 1922, Niels Bohr revised the atomic model to include a positively charged nucleus surrounded by negatively charged electrons that traveled in well-defined shells around the nucleus. The shells can be thought of as concentric circles around the nucleus. A neutral atom contains the same number of protons in the nucleus as electrons surrounding the nucleus. The inside shell can hold two electrons, and the second shell can hold eight electrons. An electrostatic attraction occurs between the positively charged protons in the nucleus and the negatively charged electrons. A representation of Bohr's shell model is shown in Figure 12.1.

Figure 12.1

Partial evidence for this atomic shell model comes from the study of ionization energies of different elements. Ionization energy is the amount of energy required to remove an electron from an atom or ion in the gaseous state. The first ionization energy removes the electron farthest from the nucleus and can be represented by the following formula:

where X represents a neutral atom.

The nth ionization energy removes additional electrons from an already charged ion. For example, the third ionization energy can be represented by the following formula:

The ionization energies in kJ/mol of the first 10 elements can be found in Table 12.1.

TABLE 12.1

1. How much energy does it take to remove the outermost electron from beryllium (Be)?

A. 900 kJ/mol
B. 1,757 kJ/mol
C. 14,849 kJ/mol
D. 21,007 kJ/mol

2. Which of the following statements regarding the ionization energy of the third proton of the elements listed is true?

A. There is a general and consistent increase as the elements get larger.
B. There is a general and consistent decrease as the elements get larger.
C. Increases are then followed by a decrease.
D. After an early dip, there is a general increase.

3. How much energy is required to remove an electron from nitrogen as shown in the following equation?

A. 1,402 kJ/mol
B. 2,856 kJ/mol
C. 4,578 kJ/mol
D. 7,475 kJ/mol

4. The first ionization energy of Element 2, hydrogen, is much larger than the first ionization energy for Element 3, lithium. Which statement best explains this trend?

A. Helium has only two electrons while lithium has three.
B. Helium is a very light element; therefore, it is very hard to remove its electrons.
C. Both of helium's electrons are the first shell, while one of lithium's electrons is found in the second shell.
D. Helium has two protons providing the positive electrostatic attraction, while lithium has three protons providing a larger attraction.

5. Which best explains why there is no seventh ionization energy listed for the element carbon?

A. It is hard to measure the energy required to remove carbon's seventh electron.
B. Carbon does not have seven electrons surrounding its nucleus.
C. The seventh ionization energy of carbon is equal to the first ionization energy of nitrogen, so it does not need to be listed.
D. The seventh, eighth, ninth, and tenth ionization energies of carbon are all equal to the sixth, so they do not need to be listed.

6. Figure 12.2 shows an electron being removed from the element oxygen. How much energy is associated with the image shown?

Figure 12.2

A. 1,314 kJ/mol
B. 3,388 kJ/mol
C. 71,330 kJ/mol
D. 84,078 kJ/mol

7. According to Table 12.1, how many electrons must the element nitrogen have in its outermost shell?

A. Two
B. Five
C. Seven
D. Eight

8. Referring to Table 12.1, what evidence supports the fact that each element has only two electrons in the first, innermost shell?

A. The first two ionization energies are always smaller than the rest.
B. The last two ionization energies are always significantly larger than the rest.
C. There is a significant jump between the second and third ionization energies for most elements.
D. The first two ionization energies of helium and lithium are both relatively small.

9. Which set of ionization energy (IE) data represents an atom that has one electron in its outermost electron shell?

First IE, Second IE, Third IE, Fourth IE

A. 300, 600, 1801, 2230
B. 700, 2892, 3019, 3299
C. 1121, 1398, 4456, 4876
D. 854, 1981, 2765, 3344

10. Helium and lithium are isoelectronic. This means their electron structure is identical. They both have two electrons in the first shell outside of the nucleus. Why does it take less energy to remove an electron from helium than it does to remove an electron from lithium?

A. Helium has two protons, but lithium has three.
B. Lithium has already had the outermost electron removed.
C. The first ionization energy of lithium is smaller than that of helium.
D. Lithium has a positive charge so removing electrons is more difficult.

11. How many kJ of energy would be required to remove all of the electrons from 1 mol of helium atoms?

A. 2,372 kJ
B. 5,250 kJ
C. 7,622 kJ
D. 10,500 kJ