Q: Which of the following is the correct formula for calculating the average atomic mass of an element with two isotopes?

$$\text{Average atomic mass} = (\text{fraction of isotope 1}) \times (\text{mass of isotope 1}) + (\text{fraction of isotope 2}) \times (\text{mass of isotope 2})$$

Q: If you have a 12.01 g sample of carbon, how many atoms of carbon does it contain?

$$6.022 \times 10$$^{23}$$ atoms

Question 1

Which experiment provided the first direct evidence for the existence of the atomic nucleus?

Accepted Answer

Rutherford's gold foil experiment

Question 2

According to Dalton's atomic theory, which statement is correct?

Accepted Answer

Atoms combine in simple whole-number ratios to form compounds.

Question 3

A sample of carbon monoxide contains 1.33 g of oxygen per 1 g of carbon, while carbon dioxide contains 2.67 g of oxygen per 1 g of carbon. What law does this observation illustrate?

Accepted Answer

Law of Multiple Proportions

Question 4

Which of the following best describes the result of Rutherford's gold foil experiment?

Accepted Answer

Most alpha particles passed straight through, but some were deflected at large angles.

Question 5

Which of the following statements about isotopes is TRUE?

Accepted Answer

Isotopes of an element have different numbers of neutrons.

Question 6

Which group in the periodic table contains elements that are highly unreactive and exist as gases at room temperature?

Accepted Answer

Noble gases

Question 7

A neutral atom of magnesium has an atomic number of 12 and a mass number of 24. How many neutrons does it contain?

Accepted Answer

$$12$$

Question 8

Which of the following is a property of metals?

Accepted Answer

They are malleable and ductile.

Question 9

Which element is a metalloid and is commonly used in the electronics industry due to its semiconducting properties?

Accepted Answer

Silicon

Question 10

What is the charge and relative mass of a proton?

Accepted Answer

Charge: $$+1$$, Mass: approximately equal to a neutron

Question 11

Which of the following best explains why most of the mass of an atom is concentrated in the nucleus?

Accepted Answer

The nucleus contains protons and neutrons, which are much heavier than electrons.

Question 12

A sample contains $$3.01 	imes 10$$^{23}$$ atoms of sodium. How many moles of sodium are present in the sample?

Accepted Answer

$$0.50$$ mol

Question 13

Which of the following is the correct formula for calculating the average atomic mass of an element with two isotopes?

Accepted Answer

$$	ext{Average atomic mass} = (	ext{fraction of isotope 1}) 	imes (	ext{mass of isotope 1}) + (	ext{fraction of isotope 2}) 	imes (	ext{mass of isotope 2})$$

Question 14

Which of the following statements about the cathode ray tube experiment is correct?

Accepted Answer

It showed that cathode rays are composed of negatively charged particles.

Question 15

A main-group nonmetal typically forms an anion with the same number of electrons as which of the following?

Accepted Answer

The nearest noble gas

Question 16

If you have a 12.01 g sample of carbon, how many atoms of carbon does it contain?

Accepted Answer

$$6.022 	imes 10$$^{23}$$ atoms

Question 17

Which of the following is a correct conversion factor for converting from moles of atoms to number of atoms?

Accepted Answer

$$1 	ext{ mol atoms} = 6.022 	imes 10$$^{23}$$ 	ext{ atoms}$$

Question 18

Which of the following elements is a halogen?

Accepted Answer

Chlorine

Question 19

A student weighs out 4.00 g of helium. How many moles of helium does this represent? (Molar mass of He = 4.00 g/mol)

Accepted Answer

$$1.00$$ mol

Question 20

Which of the following best describes the difference between a period and a group in the periodic table?

Accepted Answer

A period is a horizontal row; a group is a vertical column.

Atoms and Elements: Foundations of Atomic Theory and Structure

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