$$ (35 \times 0.7577) + (37 \times 0.2423) = 35.48 $$

Charge: +1, Mass: $$1.67 \times 10$$^{-24}$$ g

$$ (12 \times 0.9889) + (13 \times 0.0111) + (14 \times 0.0001) = 12.011 $$

Question 1

Which of the following statements best describes the main finding of Rutherford’s gold foil experiment?

Accepted Answer

Most of the atom is empty space with a small, dense, positively charged nucleus.

Question 2

A neutral atom of an element has 15 protons and 16 neutrons. What is the correct nuclear symbol for this atom?

Accepted Answer

$$ ^{31}_{15}\mathrm{P} $$

Question 3

Which experiment led to the discovery of the electron, and what apparatus was used?

Accepted Answer

Thomson’s cathode ray tube experiment using a cathode ray tube

Question 4

If an element has 78 electrons and 117 neutrons, what is its atomic number?

Accepted Answer

78

Question 5

Which of the following best defines an isotope?

Accepted Answer

Atoms with the same number of protons but different numbers of neutrons.

Question 6

Calculate the atomic mass of chlorine given two isotopes: one with mass number 35 (75.77% abundance) and one with mass number 37 (24.23% abundance).

Accepted Answer

$$ (35 	imes 0.7577) + (37 	imes 0.2423) = 35.48 $$

Question 7

Which subatomic particle has the smallest mass?

Accepted Answer

Electron

Question 8

A neutral atom has an atomic number of 34 and a mass number of 78. How many neutrons does it have?

Accepted Answer

44

Question 9

Which of the following statements about Dalton’s atomic theory is NOT correct according to modern understanding?

Accepted Answer

Atoms of the same element are identical.

Question 10

What is the charge and approximate mass of a proton?

Accepted Answer

Charge: +1, Mass: $$1.67 	imes 10$$^{-24}$$ g

Question 11

Which model of the atom first proposed that electrons are embedded in a positively charged sphere?

Accepted Answer

Thomson’s plum pudding model

Question 12

If an atom has 91 protons and 140 neutrons, what is its mass number?

Accepted Answer

231

Question 13

Which of the following best explains why the atomic mass of carbon is not a whole number?

Accepted Answer

It is the weighted average of all naturally occurring isotopes.

Question 14

What is the definition of one atomic mass unit (amu)?

Accepted Answer

One-twelfth the mass of a carbon-12 atom.

Question 15

Which of the following is a correct statement about isotopes of hydrogen?

Accepted Answer

They have the same number of protons but different numbers of neutrons.

Question 16

A sample contains 98.89% $$^{12}\mathrm{C}$$, 1.11% $$^{13}\mathrm{C}$$, and 0.01% $$^{14}\mathrm{C}. $$What is the atomic mass of carbon?

Accepted Answer

$$ (12 	imes 0.9889) + (13 	imes 0.0111) + (14 	imes 0.0001) = 12.011 $$

Question 17

Which of the following is NOT a conclusion from Rutherford’s gold foil experiment?

Accepted Answer

Electrons are embedded in a positive sphere.

Question 18

Which of the following is the correct calculation for the number of neutrons in an atom with mass number 78 and atomic number 34?

Accepted Answer

$$ 78 - 34 = 44 $$

Question 19

Which scientist determined the mass of the electron and what was the value he found?

Accepted Answer

Robert Millikan; $$9.11 	imes 10$$^{-28}$$ g

Question 20

Which of the following best describes the location of electrons in the modern atomic model?

Accepted Answer

In the electron cloud surrounding the nucleus

Atomic Structure & Periodicity: Foundations and Calculations

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