Q: Which of the following correctly describes the relationship between atomic mass unit (u) and grams?

$\displaystyle 1\ \mathrm{u} = 1.6605 \times 10^{-24}\ \mathrm{g}$

Q: A sample contains 30.5 g of manganese (Mn). Given the molar mass of Mn is $54.938\ \mathrm{g/mol}$, how many Mn atoms are present in the sample?

$\displaystyle 3.34 \times 10^{23}$ atoms

Q: Which of the following is the correct calculation for the atomic weight of an element with two isotopes: isotope A (mass = 10 u, abundance = 80%) and isotope B (mass = 11 u, abundance = 20%)?

$\displaystyle (10\ \mathrm{u}) \times 0.8 + (11\ \mathrm{u}) \times 0.2 = 10.2\ \mathrm{u}$

Question 1

Which experiment provided the first evidence that atoms contain negatively charged particles, and what was the key observation?

Accepted Answer

J. Thomson's cathode-ray tube experiment; the beam was deflected by electric and magnetic fields.

Question 2

According to Rutherford's gold foil experiment, what conclusion can be drawn about the structure of the atom?

Accepted Answer

Atoms have a small, dense, positively charged nucleus surrounded by mostly empty space.

Question 3

Which subatomic particle is primarily responsible for the chemical properties of an element?

Accepted Answer

Electron

Question 4

The atomic number ($Z$) of an element is defined as:

Accepted Answer

The number of protons in the nucleus.

Question 5

An isotope of carbon has 6 protons and 7 neutrons. What is its nuclear symbol?

Accepted Answer

$\displaystyle {}^{13}_{6}\mathrm{C}$

Question 6

Why is the atomic weight of carbon listed as 12.011 u on the periodic table, even though no single carbon atom has this mass?

Accepted Answer

It is the average of the masses of all carbon atoms, weighted by their natural abundance.

Question 7

Which of the following correctly describes the relationship between atomic mass unit (u) and grams?

Accepted Answer

$\displaystyle 1\ \mathrm{u} = 1.6605 	imes 10^{-24}\ \mathrm{g}$

Question 8

A sample contains 30.5 g of manganese (Mn). Given the molar mass of Mn is $54.938\ \mathrm{g/mol}$, how many Mn atoms are present in the sample?

Accepted Answer

$\displaystyle 3.34 	imes 10^{23}$ atoms

Question 9

Which statement best explains why most alpha particles passed straight through the gold foil in Rutherford's experiment?

Accepted Answer

Gold atoms are mostly empty space, so most alpha particles do not encounter the nucleus.

Question 10

Which of the following is the correct calculation for the atomic weight of an element with two isotopes: isotope A (mass = 10 u, abundance = 80%) and isotope B (mass = 11 u, abundance = 20%)?

Accepted Answer

$\displaystyle (10\ \mathrm{u}) 	imes 0.8 + (11\ \mathrm{u}) 	imes 0.2 = 10.2\ \mathrm{u}$

Question 11

Which of the following best describes an isotope?

Accepted Answer

Atoms of the same element with different numbers of neutrons.

Question 12

If an atom has 17 protons, 18 neutrons, and 17 electrons, what is its mass number?

Accepted Answer

$\displaystyle 35$

Question 13

Which of the following statements about the nucleus of an atom is correct?

Accepted Answer

The nucleus contains protons and neutrons.

Question 14

A neutral atom of chlorine has an atomic number of 17 and an atomic weight of approximately 35.5. Which statement is true?

Accepted Answer

Chlorine exists as a mixture of isotopes with different numbers of neutrons.

Question 15

Which of the following best explains why the molar mass of an element (in g/mol) is numerically equal to its atomic weight (in u)?

Accepted Answer

Because 1 mole contains Avogadro's number of atoms, and 1 u is defined as 1/12 the mass of a carbon-12 atom.

Question 16

Which of the following is the correct nuclear symbol for an atom with 20 protons and 22 neutrons?

Accepted Answer

$\displaystyle {}^{42}_{20}\mathrm{Ca}$

Question 17

If you have 1 mole of helium atoms, what is the total mass in grams? (Given: molar mass of He = 4.0026 g/mol)

Accepted Answer

$\displaystyle 4.0026$ g

Question 18

Which of the following best describes the size relationship between the atom and its nucleus?

Accepted Answer

The nucleus is about 1/100,000 the diameter of the atom.

Question 19

Which of the following best explains why atoms are electrically neutral?

Accepted Answer

Because the number of protons equals the number of electrons.

Structure of Atoms: Subatomic Particles, Atomic Mass, and the Mole

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