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

$\text{Atomic mass} = (\text{mass of isotope 1} \times \text{fractional abundance 1}) + (\text{mass of isotope 2} \times \text{fractional abundance 2})$

Question 1

Which experiment provided the evidence that atoms have a small, dense, positively charged nucleus?

Accepted Answer

Rutherford's gold foil experiment

Question 2

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 3

Which of the following statements about isotopes is correct?

Accepted Answer

Isotopes of an element have different numbers of neutrons.

Question 4

A sample contains $3.5$ moles of helium. How many helium atoms are present in the sample?

Accepted Answer

$2.11 	imes 10^{24}$ atoms

Question 5

Which law states that the total mass of substances present does not change during a chemical reaction?

Accepted Answer

Law of Conservation of Mass

Question 6

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

Accepted Answer

Elements in the same group have similar chemical properties.

Question 7

A chlorine atom has an atomic number of $17$ and a mass number of $35$. How many protons, neutrons, and electrons does a neutral chlorine atom have?

Accepted Answer

$17$ protons, $18$ neutrons, $17$ electrons

Question 8

Which of the following is a property of metals?

Accepted Answer

Malleable and good conductors of electricity

Question 9

Calculate the atomic mass of an element with two isotopes: $X$-10 (mass $10.012$ amu, abundance $19.91\%$) and $X$-11 (mass $11.009$ amu, abundance $80.09\%$).

Accepted Answer

$10.81$ amu

Question 10

Which of the following statements about ions is correct?

Accepted Answer

A cation is formed when an atom loses electrons.

Question 11

Which of the following is a metalloid?

Accepted Answer

Silicon

Question 12

How many moles of calcium are present in $3.01 	imes 10^{23}$ atoms of calcium?

Accepted Answer

$0.500$ mol

Question 13

Which of the following is NOT a postulate of Dalton's atomic theory that is still considered valid today?

Accepted Answer

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

Question 14

A neutral atom of potassium has an atomic number of $19$ and a mass number of $39$. What is the number of electrons in this atom?

Accepted Answer

$19$

Question 15

Which group on the periodic table contains elements that are all colorless, monatomic gases at room temperature?

Accepted Answer

Noble gases

Question 16

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 17

Which of the following elements is a transition metal?

Accepted Answer

Tungsten

Question 18

If a neutral atom of copper ($Cu$) loses two electrons, what is the resulting ion's charge and number of electrons?

Accepted Answer

$+2$ charge, $27$ electrons

Question 19

Which of the following best describes the difference between atomic mass and molar mass?

Accepted Answer

Atomic mass is the mass of one atom in amu; molar mass is the mass of one mole in grams.

Question 20

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

Accepted Answer

$	ext{Atomic mass} = (	ext{mass of isotope 1} 	imes 	ext{fractional abundance 1}) + (	ext{mass of isotope 2} 	imes 	ext{fractional abundance 2})$

Atoms, Ions, and Elements: Foundations of Atomic Theory and the Periodic Table

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