Q: A sample contains $$75.77\%$$ $$^{35}\mathrm{Cl} ($$mass $$34.97$$ amu) and $$24.23\%$$ $$^{37}\mathrm{Cl} ($$mass $$36.97$$ amu). What is the atomic mass of chlorine?

$$(0.7577 \times 34.97) + (0.2423 \times 36.97) = 35.45$$ amu

Q: How many atoms are present in $$2.00$$ moles of carbon?

$$2.00 \times 6.022 \times 10$$^{23}$$ = 1.204 \times 10$$^{24}$$ atoms

Q: Calculate the number of moles of carbon in a $$0.0265 g $$sample of graphite. (Atomic mass of C = $$12.01 g/$$mol)

$$0.0265 \div 12.01 = 2.21 \times 10$$^{-3}$$ mol

Question 1

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

Accepted Answer

Thomson's cathode ray tube experiment

Question 2

A sample of water is decomposed into 16.0 g of oxygen and 2.0 g of hydrogen. Which law does this observation best illustrate?

Accepted Answer

Law of definite proportions

Question 3

Which of the following statements is NOT part of Dalton’s atomic theory?

Accepted Answer

Atoms can be subdivided into protons, neutrons, and electrons.

Question 4

Which of the following best describes the plum pudding model of the atom?

Accepted Answer

A sphere of positive charge with electrons embedded throughout

Question 5

Which subatomic particle was discovered by James Chadwick?

Accepted Answer

Neutron

Question 6

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

$$24 - 12 = 12$$ neutrons

Question 7

Which of the following ions has the same number of electrons as a neutral argon atom?

Accepted Answer

$$\mathrm{K}^+$$

Question 8

Which element is defined by having 17 protons in its nucleus?

Accepted Answer

Chlorine

Question 9

A sample contains $$75.77\%$$ $$^{35}\mathrm{Cl} ($$mass $$34.97$$ amu) and $$24.23\%$$ $$^{37}\mathrm{Cl} ($$mass $$36.97$$ amu). What is the atomic mass of chlorine?

Accepted Answer

$$(0.7577 	imes 34.97) + (0.2423 	imes 36.97) = 35.45$$ amu

Question 10

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

Accepted Answer

Group 8A (noble gases)

Question 11

Which property is characteristic of metals?

Accepted Answer

They are malleable and ductile.

Question 12

How many atoms are present in $$2.00$$ moles of carbon?

Accepted Answer

$$2.00 	imes 6.022 	imes 10$$^{23}$$ = 1.204 	imes 10$$^{24}$$ atoms

Question 13

Which of the following best explains why elements in the same group of the periodic table have similar chemical properties?

Accepted Answer

They have the same number of valence electrons.

Question 14

A sulfur ion has 16 protons and 18 electrons. What is its charge?

Accepted Answer

$$16 - 18 = -2$$, so the charge is $$2-$$

Question 15

Which of the following is a correct statement about isotopes?

Accepted Answer

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

Question 16

Which of the following elements is a metalloid and is widely used in the electronics industry due to its semiconducting properties?

Accepted Answer

Silicon

Question 17

Calculate the number of moles of carbon in a $$0.0265 g $$sample of graphite. (Atomic mass of C = $$12.01 g/$$mol)

Accepted Answer

$$0.0265 \div 12.01 = 2.21 	imes 10$$^{-3}$$ mol

Question 18

Which of the following best describes the law of multiple proportions?

Accepted Answer

When two elements form more than one compound, the masses of one element that combine with a fixed mass of the other are in ratios of small whole numbers.

Atoms and Elements: Foundations of Modern Atomic Theory

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