Q: A naturally occurring element has two isotopes: 70% of isotope X with a mass of 10 amu and 30% of isotope Y with a mass of 12 amu. What is the atomic mass of the element?

$$0.70 \times 10 + 0.30 \times 12 = 7 + 3.6 = 10.6$$ amu

Question 1

Which of the following statements correctly describes the location and charge of subatomic particles in an atom?

Accepted Answer

Protons and neutrons are found in the nucleus; protons are positively charged, neutrons are neutral, and electrons are negatively charged and found outside the nucleus.

Question 2

An atom of magnesium has an atomic number of 12 and a mass number of 25. How many neutrons does it have?

Accepted Answer

$$25 - 12 = 13$$ neutrons

Question 3

Which element is a metalloid, is located along the zigzag line of the periodic table, and is commonly used in computer chips?

Accepted Answer

Silicon (Si)

Question 4

Which group on the periodic table contains the noble gases?

Accepted Answer

Group 8A (18)

Question 5

A naturally occurring element has two isotopes: 70% of isotope X with a mass of 10 amu and 30% of isotope Y with a mass of 12 amu. What is the atomic mass of the element?

Accepted Answer

$$0.70 	imes 10 + 0.30 	imes 12 = 7 + 3.6 = 10.6$$ amu

Question 6

Which of the following electron configurations represents a neutral atom of phosphorus (atomic number 15)?

Accepted Answer

$$1s^2$$\ $$2s^2$$\ $$2p^6$$\ $$3s^2$$\ $$3p^3$$

Question 7

Which of the following best explains why the atomic radius increases as you move down a group in the periodic table?

Accepted Answer

Electrons are added to higher energy levels, increasing the distance from the nucleus.

Question 8

Which of the following elements is most likely to have the highest ionization energy?

Accepted Answer

Neon (Ne)

Question 9

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

Accepted Answer

$$131 - 53 = 78$$ neutrons

Question 10

Which of the following statements about electromagnetic radiation is correct?

Accepted Answer

Short-wavelength radiation has high frequency and high energy.

Question 11

Which of the following is the correct abbreviated electron configuration for calcium (atomic number 20)?

Accepted Answer

$$[Ar]\ 4s^2$

Question 12

Which of the following elements is a nonmetal and is found in Group 7A (17)?

Accepted Answer

Chlorine (Cl)

Question 13

Which of the following best describes the trend in metallic character across a period from left to right?

Accepted Answer

Metallic character decreases from left to right across a period.

Question 14

A neutral atom of sulfur has 16 electrons. What is its electron configuration?

Accepted Answer

$$1s^2$$\ $$2s^2$$\ $$2p^6$$\ $$3s^2$$\ $$3p^4$$

Question 15

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 16

Which of the following best explains why elements in the same group have similar chemical properties?

Accepted Answer

They have the same number of valence electrons.

Question 17

Which of the following is the correct Lewis symbol for a neutral atom of nitrogen?

Accepted Answer

The symbol N with five dots around it, representing five valence electrons.

Question 18

Which of the following statements about orbitals is correct?

Accepted Answer

Each orbital can hold a maximum of two electrons with opposite spins.

Question 19

A patient receives a dose of a radioactive isotope with a mass number of 99 and 43 protons. What is the element and how many neutrons does it have?

Accepted Answer

Technetium (Tc); $$99 - 43 = 56$$ neutrons

Question 20

Which of the following best describes what happens when an electron in an atom absorbs energy?

Accepted Answer

It moves to a higher energy level.

Atoms and Elements: Structure, Properties, and Periodic Trends

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