Q: What is the average atomic mass of an element with two isotopes: 70% $$^{35}Cl ($$mass = 34.97 u) and 30% $$^{37}Cl ($$mass = 36.97 u)?

$$(0.70 \times 34.97) + (0.30 \times 36.97) = 35.57\ \text{u}$$

Q: Which equation correctly represents the calculation of percent abundance for isotope A, given average atomic mass $$M_{avg}$$, mass of isotope A $$m_A$$, and mass of isotope B $$m_B$$?

$$\text{Percent abundance of A} = \frac{M_{avg} - m_B}{m_A - m_B} \times 100\%$$

Question 1

Which of the following best describes the difference between accuracy and precision in scientific measurements?

Accepted Answer

Accuracy refers to how close measurements are to the true value, while precision refers to how close measurements are to each other.

Question 2

A student measures the mass of a sample as 12.340 g. How many significant figures are in this measurement?

Accepted Answer

$$5$$

Question 3

Which of the following is the correct scientific notation for the number 0.0004560?

Accepted Answer

$$4.560 	imes 10$$^{-4}$$

Question 4

Which subatomic particle determines the identity of an element?

Accepted Answer

Proton

Question 5

What is the average atomic mass of an element with two isotopes: 70% $$^{35}Cl ($$mass = 34.97 u) and 30% $$^{37}Cl ($$mass = 36.97 u)?

Accepted Answer

$$(0.70 	imes 34.97) + (0.30 	imes 36.97) = 35.57\ 	ext{u}$$

Question 6

Which group on the Periodic Table contains the noble gases?

Accepted Answer

Group 18

Question 7

Which of the following best explains why atomic radius increases down a group?

Accepted Answer

Additional energy levels are added, increasing the distance between the nucleus and valence electrons.

Question 8

Which of the following elements is a diatomic molecule in its natural state?

Accepted Answer

Oxygen

Question 9

What is the charge of the stable ion formed by magnesium?

Accepted Answer

$$+2$$

Question 10

Which of the following best describes the concept of shielding (screening) in atoms?

Accepted Answer

The reduction in effective nuclear charge on valence electrons due to inner electrons.

Question 11

Which equation correctly represents the calculation of percent abundance for isotope A, given average atomic mass $$M_{avg}$$, mass of isotope A $$m_A$$, and mass of isotope B $$m_B$$?

Accepted Answer

$$	ext{Percent abundance of A} = \frac{M_{avg} - m_B}{m_A - m_B} 	imes 100\%$$

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 of the following best describes the trend in ionization energy across a period from left to right?

Accepted Answer

Ionization energy increases due to increased effective nuclear charge.

Question 14

Which property is defined as the energy change when an electron is added to a neutral atom in the gas phase?

Accepted Answer

Electron affinity

Question 15

Which of the following best explains why cations are smaller than their neutral atoms?

Accepted Answer

Cations have more protons than electrons, resulting in a stronger attraction to the nucleus.

Question 16

Which of the following is a correct representation of the isotope carbon-14?

Accepted Answer

$$^{14}_{6}	ext{C}$$

Question 17

Which of the following elements is a metalloid?

Accepted Answer

Silicon

Question 18

Which of the following best describes the trend in electronegativity down a group?

Accepted Answer

Electronegativity decreases due to increased atomic radius and shielding.

Question 19

Which of the following is the correct order of increasing atomic radius for the elements Na, Mg, and Al?

Accepted Answer

Al \u003c Mg \u003c Na

Question 20

A radioisotope is best described as:

Accepted Answer

An isotope with an unstable nucleus that undergoes radioactive decay.

Matter, Chemical Trends, and Chemical Bonding: Study Guide

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