Atoms and Elements

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Physical Chemistry › Atoms and Elements

Questions 1 - 10
1

In an atom or molecule, why can't two electrons have the same four electronic quantum numbers?

The Pauli Exclusion Principle

Heisenberg Uncertainty Principle

Harmonic Reaction Orders

Kinetic energy operator

The first law of thermodynamics

Explanation

The Pauli Exclusion Principle explains various phenomena such as the structure of atoms and how different atoms combine to share electrons. When you have two electrons that are located in the same orbital, the quantum numbers n, l and ml are the same. However, ms will be different. Two electrons cannot have the same four electronic quantum numbers because no more than two electrons may occupy an orbital, and if they do, the spin of one must cancel the spin of the other so their spins will have a zero net spin angular momentum.

2

What is the complete ground state electron configuration for the magnesium atom?

1s22s22p63s2

1s22s23s2

1s42p63s2

1s22s22p23s2

1s22s22p63s6

Explanation

Magnesium has an atomic number of 12, so the total number of electrons in its configuration should add up to twelve. The maximum number of electrons in the s subshell is two. Of all the answer choices, only 1s22s22p63s 2 fits the criteria. The sum of the exponent values is 12, matching the atomic number of magnesium, and the number of electrons in the s and p subshells matches the maximum amount possible.

3

Which of the following represents the alkaline earth metal with the greatest atomic number?

Explanation

Alkaline earth metals are group II elements; among them, radium has the largest atomic number.

4

Which of the following trends decreases as you move from left to right on the periodic table?

Atomic radius

Electronegativity

Electron affinity

Ionization energy

Explanation

Although it may seem counterintuitive, atomic radius does decrease from left to right on the periodic table. The reason for this is because the added positive charge in the nucleus causes the elctrons to be pulled more strongly towards the center, which decreases the atomic radius.

5

In an atom or molecule, why can't two electrons have the same four electronic quantum numbers?

The Pauli Exclusion Principle

Heisenberg Uncertainty Principle

Harmonic Reaction Orders

Kinetic energy operator

The first law of thermodynamics

Explanation

The Pauli Exclusion Principle explains various phenomena such as the structure of atoms and how different atoms combine to share electrons. When you have two electrons that are located in the same orbital, the quantum numbers n, l and ml are the same. However, ms will be different. Two electrons cannot have the same four electronic quantum numbers because no more than two electrons may occupy an orbital, and if they do, the spin of one must cancel the spin of the other so their spins will have a zero net spin angular momentum.

6

What is the complete ground state electron configuration for the magnesium atom?

1s22s22p63s2

1s22s23s2

1s42p63s2

1s22s22p23s2

1s22s22p63s6

Explanation

Magnesium has an atomic number of 12, so the total number of electrons in its configuration should add up to twelve. The maximum number of electrons in the s subshell is two. Of all the answer choices, only 1s22s22p63s 2 fits the criteria. The sum of the exponent values is 12, matching the atomic number of magnesium, and the number of electrons in the s and p subshells matches the maximum amount possible.

7

Which of the following represents the alkaline earth metal with the greatest atomic number?

Explanation

Alkaline earth metals are group II elements; among them, radium has the largest atomic number.

8

Which of the following are true regarding and orbitals?

I. Both and orbitals can contain a maximum of two electrons

II. In a given shell, orbitals are more numerous because they are spherical in shape

III. orbitals have lower energy than orbitals within the same shell

I and III

I only

III only

I and II

Explanation

Orbitals are regions in an electron shell where electrons might be located. There are several types of orbitals such as , and . Most elements found on the periodic table contain electrons within one of these orbitals. A characteristic of an orbital is that it can only contain two electrons maximum. A shell might contain multiple orbitals; however, each orbital can only contain two electrons. Each orbital has a unique shape that corresponds to the electron density (the possible location of an electron at a given point in time). The orbital has a spherical shape whereas the orbital has a dumbbell shape. As mentioned, a shell can contain multiple types of orbitals. A shell can typically contain one orbital, three orbitals, five orbitals, and seven orbitals. Remember that the shape of the orbital has no bearing on the amount of orbitals in a shell. An orbital is higher in energy if it is found farther away from the nucleus. The orbitals in order of increasing energy is as follows . Therefore, an orbital has lower energy than a orbital in the same shell.

9

Which of the following trends decreases as you move from left to right on the periodic table?

Atomic radius

Electronegativity

Electron affinity

Ionization energy

Explanation

Although it may seem counterintuitive, atomic radius does decrease from left to right on the periodic table. The reason for this is because the added positive charge in the nucleus causes the elctrons to be pulled more strongly towards the center, which decreases the atomic radius.

10

Which of the following are true regarding and orbitals?

I. Both and orbitals can contain a maximum of two electrons

II. In a given shell, orbitals are more numerous because they are spherical in shape

III. orbitals have lower energy than orbitals within the same shell

I and III

I only

III only

I and II

Explanation

Orbitals are regions in an electron shell where electrons might be located. There are several types of orbitals such as , and . Most elements found on the periodic table contain electrons within one of these orbitals. A characteristic of an orbital is that it can only contain two electrons maximum. A shell might contain multiple orbitals; however, each orbital can only contain two electrons. Each orbital has a unique shape that corresponds to the electron density (the possible location of an electron at a given point in time). The orbital has a spherical shape whereas the orbital has a dumbbell shape. As mentioned, a shell can contain multiple types of orbitals. A shell can typically contain one orbital, three orbitals, five orbitals, and seven orbitals. Remember that the shape of the orbital has no bearing on the amount of orbitals in a shell. An orbital is higher in energy if it is found farther away from the nucleus. The orbitals in order of increasing energy is as follows . Therefore, an orbital has lower energy than a orbital in the same shell.

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