Q: A sample of magnesium consists of 79% $^{24}\mathrm{Mg}$ (mass = 23.99 u), 10% $^{25}\mathrm{Mg}$ (mass = 24.99 u), and 11% $^{26}\mathrm{Mg}$ (mass = 25.98 u). What is the atomic mass of magnesium? (Round to two decimal places.)

$(0.79 \times 23.99) + (0.10 \times 24.99) + (0.11 \times 25.98) = 24.31$ u

Q: A certain element has two naturally occurring isotopes: $^{10}\mathrm{B}$ (19.9%, mass = 10.01 u) and $^{11}\mathrm{B}$ (80.1%, mass = 11.01 u). What is the atomic mass of boron?

$(0.199 \times 10.01) + (0.801 \times 11.01) = 10.81$ u

Q: A sample contains 100 atoms of $^{35}\mathrm{Cl}$ and 75 atoms of $^{37}\mathrm{Cl}$. What is the average atomic mass of chlorine in this sample? ($^{35}\mathrm{Cl}$: 34.97 u, $^{37}\mathrm{Cl}$: 36.97 u)

$\frac{(100 \times 34.97) + (75 \times 36.97)}{175} = 35.83$ u

Question 1

Which of the following correctly matches the element name with its symbol?

Accepted Answer

Potassium: $\mathrm{K}$

Question 2

An atom has an atomic number of 17 and a mass number of 35. How many neutrons does it contain?

Accepted Answer

$35 - 17 = 18$ neutrons

Question 3

Which of the following elements is a metalloid?

Accepted Answer

Silicon ($\mathrm{Si}$)

Question 4

Given the isotope $^{13}\mathrm{C}$, what is the number of protons, neutrons, and electrons in a neutral atom?

Accepted Answer

6 protons, 7 neutrons, 6 electrons

Question 5

Which statement about subatomic particles is correct?

Accepted Answer

Protons are positively charged and located in the nucleus.

Question 6

A sample of magnesium consists of 79% $^{24}\mathrm{Mg}$ (mass = 23.99 u), 10% $^{25}\mathrm{Mg}$ (mass = 24.99 u), and 11% $^{26}\mathrm{Mg}$ (mass = 25.98 u). What is the atomic mass of magnesium? (Round to two decimal places.)

Accepted Answer

$(0.79 	imes 23.99) + (0.10 	imes 24.99) + (0.11 	imes 25.98) = 24.31$ u

Question 7

Which element is located in period 3, group 2 of the periodic table?

Accepted Answer

Magnesium ($\mathrm{Mg}$)

Question 8

A neutral atom of phosphorus has an atomic number of 15 and a mass number of 31. How many electrons does it have?

Accepted Answer

15 electrons

Question 9

Which of the following best describes the location of electrons in an atom?

Accepted Answer

Electrons are found in regions outside the nucleus called energy levels or shells.

Question 10

Which of the following elements is a nonmetal?

Accepted Answer

Sulfur ($\mathrm{S}$)

Question 11

A hospital uses a radioactive isotope of iodine, $^{131}\mathrm{I}$, for thyroid imaging. If $^{131}\mathrm{I}$ has an atomic number of 53, how many neutrons does it have?

Accepted Answer

$131 - 53 = 78$ neutrons

Question 12

Which of the following statements about isotopes is correct?

Accepted Answer

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

Question 13

Which element is in group 17 and is a nonmetal?

Accepted Answer

Chlorine ($\mathrm{Cl}$)

Question 14

A certain element has two naturally occurring isotopes: $^{10}\mathrm{B}$ (19.9%, mass = 10.01 u) and $^{11}\mathrm{B}$ (80.1%, mass = 11.01 u). What is the atomic mass of boron?

Accepted Answer

$(0.199 	imes 10.01) + (0.801 	imes 11.01) = 10.81$ u

Question 15

Which of the following best describes the charge and location of a neutron?

Accepted Answer

Neutrons are neutral and located in the nucleus.

Question 16

A neutral atom of calcium has an atomic number of 20 and a mass number of 40. If it loses two electrons to form an ion, what is the charge of the resulting ion?

Accepted Answer

$+2$

Question 17

Which of the following elements is most likely to be a good conductor of electricity?

Accepted Answer

Copper ($\mathrm{Cu}$)

Question 18

Which of the following is the correct symbol for the element with atomic number 6?

Accepted Answer

$\mathrm{C}$

Question 19

A sample contains 100 atoms of $^{35}\mathrm{Cl}$ and 75 atoms of $^{37}\mathrm{Cl}$. What is the average atomic mass of chlorine in this sample? ($^{35}\mathrm{Cl}$: 34.97 u, $^{37}\mathrm{Cl}$: 36.97 u)

Accepted Answer

$\frac{(100 	imes 34.97) + (75 	imes 36.97)}{175} = 35.83$ u

Question 20

Which of the following statements is true regarding the periodic table?

Accepted Answer

Elements in the same group have similar chemical properties.

Atoms and Elements: Structure, Classification, and Atomic Mass

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