Q: What is the maximum number of electrons that can occupy the $$n=3$$ principal energy level?

$$2n^2 = 2$$ \times $$3^2 = 18$ electrons

Q: A chlorine atom has two naturally occurring isotopes: $$^{35}\mathrm{Cl} (75.77$$%) and $$^{37}\mathrm{Cl} (24.23$$%). What is the atomic mass of chlorine?

$$0.7577 \times 35.0 + 0.2423 \times 37.0 = 35.5$$ amu

Question 1

Which statement best describes the difference between isotopes of the same element?

Accepted Answer

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

Question 2

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

Accepted Answer

$$31 - 15 = 16$$ neutrons

Question 3

Which experiment provided evidence for the existence of the atomic nucleus?

Accepted Answer

Rutherford's gold foil experiment

Question 4

What is the charge and relative mass of a neutron?

Accepted Answer

Charge: $$0$$, Mass: $$1.009$$ amu

Question 5

Which of the following ions is isoelectronic with neon ($$Z=10$$)?

Accepted Answer

$$\mathrm{Na^+}$$

Question 6

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

Accepted Answer

Atomic number: $$17$$, Mass number: $$35$$

Question 7

Which statement about the periodic law is correct?

Accepted Answer

The physical and chemical properties of elements are periodic functions of their atomic numbers.

Question 8

Which element is most likely to form a cation by losing one electron to achieve a noble gas configuration?

Accepted Answer

Sodium ($$\mathrm{Na})$$

Question 9

What is the maximum number of electrons that can occupy the $$n=3$$ principal energy level?

Accepted Answer

$$2n^2 = 2$$ 	imes $$3^2 = 18$ electrons

Question 10

Which of the following best explains why atomic size increases down a group in the periodic table?

Accepted Answer

The valence shell is higher in energy and farther from the nucleus.

Question 11

Which principle states that electrons fill the lowest-energy orbital available first?

Accepted Answer

Aufbau Principle

Question 12

What is the electron configuration of a neutral magnesium atom ($$Z=12$$)?

Accepted Answer

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

Question 13

Which of the following ions is smaller than its parent atom?

Accepted Answer

$$\mathrm{Na^+}$$

Question 14

Which sublevel contains five orbitals and can hold a maximum of ten electrons?

Accepted Answer

d sublevel

Question 15

Which of the following best describes the shape of a p orbital?

Accepted Answer

Dumbbell-shaped

Question 16

Which element has the highest ionization energy among the following?

Accepted Answer

Neon ($$\mathrm{Ne})$$

Question 17

What is the shorthand electron configuration for potassium ($$Z=19$$)?

Accepted Answer

$$[Ar]4s^1$

Question 18

Which of the following statements about metals is correct?

Accepted Answer

Metals tend to lose electrons and have high thermal and electrical conductivity.

Question 19

Which rule states that each orbital in a subshell is half-filled before any orbital is completely filled?

Accepted Answer

Hund's Rule

Question 20

A chlorine atom has two naturally occurring isotopes: $$^{35}\mathrm{Cl} (75.77$$%) and $$^{37}\mathrm{Cl} (24.23$$%). What is the atomic mass of chlorine?

Accepted Answer

$$0.7577 	imes 35.0 + 0.2423 	imes 37.0 = 35.5$$ amu

The Structure of the Atom and the Periodic Table: Study Notes

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