Q: How many atoms are present in 3.5 moles of helium? ($$1\ \text{mol} = 6.022 \times 10$$^{23}$$ atoms)

$$2.11 \times 10$$^{24}$$ atoms

Q: A copper penny weighs 3.10 g. How many copper atoms does it contain? (Molar mass of Cu = 63.55 g/mol, $$1\ \text{mol} = 6.022 \times 10$$^{23}$$ atoms)

$$2.94 \times 10$$^{22}$$ atoms

Q: Which of the following is the correct formula for calculating the number of moles from a given mass and molar mass?

$$\text{moles} = \frac{\text{mass (g)}}{\text{molar mass (g/mol)}}$$

Question 1

Which law is best demonstrated by the experiment shown in the second image, where the total mass before and after a chemical reaction remains unchanged?

Accepted Answer

Law of Conservation of Mass

Question 2

Which scientist is credited with the discovery of the electron using cathode ray tube experiments, as depicted in the images provided?

Accepted Answer

J.J. Thomson

Question 3

According to Dalton’s Atomic Theory, which statement is NOT considered valid based on modern atomic understanding?

Accepted Answer

Atoms of a given element are identical in mass and properties.

Question 4

A neutral atom of potassium (K) has an atomic number of 19. How many electrons does it have?

Accepted Answer

19

Question 5

Which of the following best describes the difference between isotopes of the same element?

Accepted Answer

They have different numbers of neutrons.

Question 6

Calculate the atomic mass of an element with two isotopes: 70% abundance of isotope A (mass = 10 amu) and 30% abundance of isotope B (mass = 12 amu). Use the formula $$	ext{Atomic Mass} = \sum (	ext{isotope mass}) 	imes (	ext{fractional abundance}).$$

Accepted Answer

$$10.6\ 	ext{amu}$$

Question 7

Which experiment led to the conclusion that the atom is mostly empty space with a small, dense, positively charged nucleus?

Accepted Answer

Rutherford’s Gold Foil Experiment

Question 8

A sample contains $$3.01 	imes 10$$^{23}$$ atoms of calcium. How many moles of calcium are present? (1$$\ 	ext{mol} = 6.022 	imes $$10^{23}$$ atoms)

Accepted Answer

$$0.500\ 	ext{mol}$$

Question 9

Which of the following elements is a metalloid, based on its position in the periodic table?

Accepted Answer

Silicon (Si)

Question 10

Which group of elements is characterized by being colorless, monatomic gases that are chemically inert?

Accepted Answer

Noble gases

Question 11

A neutral atom of sulfur has an atomic number of 16 and a mass number of 32. How many neutrons does it have?

Accepted Answer

16

Question 12

Which of the following statements about ions is correct?

Accepted Answer

Cations are positively charged ions.

Question 13

Which property is NOT characteristic of metals?

Accepted Answer

Brittle and dull

Question 14

How many atoms are present in 3.5 moles of helium? ($$1\ 	ext{mol} = 6.022 	imes 10$$^{23}$$ atoms)

Accepted Answer

$$2.11 	imes 10$$^{24}$$ atoms

Question 15

Which of the following best explains why isotopes of the same element have nearly identical chemical properties?

Accepted Answer

They have the same number of protons and electrons.

Question 16

A copper penny weighs 3.10 g. How many copper atoms does it contain? (Molar mass of Cu = 63.55 g/mol, $$1\ 	ext{mol} = 6.022 	imes 10$$^{23}$$ atoms)

Accepted Answer

$$2.94 	imes 10$$^{22}$$ atoms

Question 17

Which of the following is the correct formula for calculating the number of moles from a given mass and molar mass?

Accepted Answer

$$	ext{moles} = \frac{	ext{mass (g)}}{	ext{molar mass (g/mol)}}$$

Question 18

Which scientist’s experiment provided evidence that the charge of the electron is quantized and always a multiple of $$-1.6 	imes 10$$^{-19}$$ C?

Accepted Answer

Robert Millikan

Question 19

Which group on the periodic table contains elements that react violently with water and are soft, dull metals?

Accepted Answer

Alkali metals (Group 1A)

Question 20

Which of the following is a correct statement about the periodic table?

Accepted Answer

Elements in the same group have similar chemical properties.

Chapter 2: Atoms, Ions, and Elements: Foundations of Modern Atomic Theory

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