Q: Which of the following is the correct formula for calculating the atomic mass of an element with two isotopes using their masses and relative abundances (as fractions)?

$$\text{Atomic mass} = (A_1$ \times f_1$) + (A_2$ \times f_2$)$$

Question 1

Which of the following statements best describes John Dalton’s atomic theory as it relates to chemical reactions?

Accepted Answer

Atoms only change the way they are bound together with other atoms during chemical reactions.

Question 2

A neutral atom of $$^{23}_{11}\mathrm{Na}$$ contains how many protons, neutrons, and electrons?

Accepted Answer

11 protons, 12 neutrons, 11 electrons

Question 3

Which experiment led to the discovery that atoms have a small, dense nucleus?

Accepted Answer

Rutherford’s gold foil experiment

Question 4

Which of the following is a property of metals as described in the periodic table?

Accepted Answer

They are malleable and ductile.

Question 5

How many electrons are present in the $$\mathrm{O}^{2-}$$ ion?

Accepted Answer

10

Question 6

Which of the following best explains why chlorine is found in nature as $$\mathrm{Cl}^-$$ ions in salt deposits?

Accepted Answer

Chlorine is a halogen and tends to gain one electron to achieve a stable electron configuration.

Question 7

Which of the following statements about isotopes is correct?

Accepted Answer

Isotopes of an element have the same chemical properties but different physical properties.

Question 8

A sample of chlorine contains two isotopes: $$^{35}\mathrm{Cl} ($$mass = 34.97 amu, abundance = 75.77%) and $$^{37}\mathrm{Cl} ($$mass = 36.97 amu, abundance = 24.23%). What is the atomic mass of chlorine? (Round to two decimal places)

Accepted Answer

$$35.45\ \mathrm{amu}$$

Question 9

Which group of elements is known for being chemically inert and stable?

Accepted Answer

Noble gases

Question 10

A main-group metal forms a cation by:

Accepted Answer

Losing electrons to achieve the same number of electrons as the nearest noble gas.

Question 11

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

Accepted Answer

When elements are arranged in order of increasing atomic mass, certain sets of properties recur periodically.

Question 12

Which of the following ions has the same number of electrons as a neutral atom of neon ($$\mathrm{Ne}$$)?

Accepted Answer

$$\mathrm{Na}^+$$

Question 13

An isotope of argon has a mass number of 40 and an atomic number of 18. How many neutrons does it contain?

Accepted Answer

22

Question 14

Which of the following best explains why silicon is widely used in the electronics industry?

Accepted Answer

Silicon is a metalloid and exhibits properties of both metals and nonmetals, making it a good semiconductor.

Question 15

Which of the following is the correct formula for calculating the atomic mass of an element with two isotopes using their masses and relative abundances (as fractions)?

Accepted Answer

$$	ext{Atomic mass} = (A_1$ 	imes f_1$) + (A_2$ 	imes f_2$)$$

Question 16

Which of the following elements is most likely to form a $$2+$$ ion?

Accepted Answer

Magnesium ($$\mathrm{Mg})$$

Question 17

A naturally occurring element has two isotopes: one with a mass of $$68.9255\ \mathrm{amu}$$ and abundance $$60.11\%$$, and another with a mass of $$70.9247\ \mathrm{amu}. $$What is the atomic mass of the element?

Accepted Answer

$$69.72\ \mathrm{amu}$$

Question 18

Which of the following statements about the modern periodic table is correct?

Accepted Answer

Elements are arranged in order of increasing atomic number.

Question 19

Which of the following best describes a chalcogen?

Accepted Answer

A reactive nonmetal commonly found in metal ores as oxides and sulfides.

Atoms and Elements: Foundations of Modern Chemistry

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