Q: Which of the following is the correct formula for calculating the atomic weight of an element with multiple isotopes?

$$\text{Atomic Weight} = \sum [(\text{isotope mass}) \times (\text{fractional natural abundance})]$$

Question 1

Which of the following statements best describes the difference between a scientific law and a scientific theory?

Accepted Answer

A scientific law is a summary of observed behavior, while a scientific theory provides an explanation for why and how that behavior occurs.

Question 2

Which experiment provided the first direct evidence for the existence of electrons?

Accepted Answer

Thomson's cathode ray tube experiment

Question 3

According to Dalton’s atomic theory, which of the following is NOT correct?

Accepted Answer

Atoms can be divided into smaller particles that retain the properties of the element.

Question 4

A sample of carbon dioxide contains 2.67 g of oxygen for every 1.00 g of carbon. A sample of carbon monoxide contains 1.33 g of oxygen for every 1.00 g of carbon. Which law is illustrated by the ratio $$\frac{2.67}{1.33} = 2$$?

Accepted Answer

Law of multiple proportions

Question 5

Which of the following statements about isotopes is TRUE?

Accepted Answer

Isotopes of an element have the same number of protons but different numbers of neutrons.

Question 6

Which of the following best explains why most alpha particles passed straight through the gold foil in Rutherford’s experiment?

Accepted Answer

The gold atoms are mostly empty space.

Question 7

Which of the following is the correct formula for calculating the atomic weight of an element with multiple isotopes?

Accepted Answer

$$	ext{Atomic Weight} = \sum [(	ext{isotope mass}) 	imes (	ext{fractional natural abundance})]$$

Question 8

Which property is NOT characteristic of metals?

Accepted Answer

Tends to gain electrons in chemical reactions

Question 9

Which group of elements is most likely to form 1− ions?

Accepted Answer

Halogens

Question 10

A neutral atom of chlorine has an atomic number of 17 and a mass number of 35. How many protons, neutrons, and electrons does it contain?

Accepted Answer

17 protons, 18 neutrons, 17 electrons

Question 11

Which of the following elements is a metalloid and often used as a semiconductor in electronics?

Accepted Answer

Silicon

Question 12

Which of the following best describes the periodic law as discovered by Mendeleev?

Accepted Answer

Elements are arranged in order of increasing mass, and elements with similar properties recur at regular intervals.

Question 13

Which of the following is a diatomic molecule at room temperature?

Accepted Answer

Oxygen ($$O_2)$$

Question 14

A main-group element forms a cation with a charge equal to its group number. Which element forms a $$2+$$ ion?

Accepted Answer

Magnesium

Question 15

Which of the following statements about the structure of the atom is correct?

Accepted Answer

Most of the atom’s mass is concentrated in the nucleus.

Question 16

Which of the following is the empirical formula for hydrogen peroxide ($$H_2O_2$$)?

Accepted Answer

$$HO$$

Question 17

A sample contains 90.48% $$^{20}Ne$$, 0.27% $$^{21}Ne$$, and 9.25% $$^{22}Ne. $$Which isotope is most abundant?

Accepted Answer

$$^{20}Ne$$

Question 18

Which of the following best describes the difference between an empirical formula and a molecular formula?

Accepted Answer

An empirical formula shows the lowest whole-number ratio of atoms, while a molecular formula shows the actual number of atoms in a molecule.

Question 19

Which of the following is a property of noble gases?

Accepted Answer

They are mostly unreactive and exist as monatomic gases.

Question 20

Which of the following best explains why sodium reacts violently with water while magnesium reacts less vigorously?

Accepted Answer

Sodium is an alkali metal and loses one electron more easily than magnesium, which is an alkaline earth metal.

Atoms, Molecules, and the Foundations of Modern Chemistry

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