Unit 2/3 Test Electrons & Periodic Table

What is the electron configuration of a neutral carbon atom?

Answer explanation

A neutral carbon atom has 6 electrons. The electron configuration is 1s² 2s² 2p², which accounts for all 6 electrons. The other options either have too many or too few electrons for a neutral carbon atom.

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DOK Level 1: Recall

Which of the following elements has the smallest atomic radius?

• Lithium (Li)

• Beryllium (Be)

• Boron (B)

• Carbon (C)

Answer explanation

Carbon (C) has the smallest atomic radius among the given elements due to its higher nuclear charge and greater effective nuclear attraction on its electrons, leading to a more compact atomic structure compared to Lithium, Beryllium, and Boron.

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DOK Level 1: Recall

Describe the trend in atomic radius as you move down a group in the periodic table.

• It decreases

• It increases

• It remains constant

• It fluctuates

Answer explanation

As you move down a group in the periodic table, additional electron shells are added, which increases the distance between the nucleus and the outermost electrons. This results in an increase in atomic radius.

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DOK Level 2: Skill/Concept

Which of the following elements is most electronegative?

• Hydrogen (H)

• Carbon (C)

• Nitrogen (N)

• Oxygen (O)

Answer explanation

Oxygen (O) is the most electronegative element among the choices, with an electronegativity value of 3.44 on the Pauling scale, compared to hydrogen (2.20), carbon (2.55), and nitrogen (3.04).

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DOK Level 1: Recall

Explain why ionization energy generally increases across a period from left to right.

• Increased nuclear charge attracts electrons more strongly

• Decreased nuclear charge allows electrons to spread out

• Additional electron shells are added

• Electrons are lost, reducing size

Answer explanation

Ionization energy increases across a period because the nuclear charge increases, attracting electrons more strongly. This makes it harder to remove an electron, thus requiring more energy.

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DOK Level 2: Skill/Concept

Predict the electron configuration of a chlorine atom

Answer explanation

Chlorine has 17 electrons. The correct electron configuration is 1s² 2s² 2p⁶ 3s² 3p⁵, indicating it has 5 electrons in the 3p subshell, which is characteristic of chlorine.

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DOK Level 2: Skill/Concept

Which of the following statements best explains why electronegativity decreases down a group?

• Electrons are added to the same energy level

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

• Nuclear charge decreases

• Electrons are removed from the outer shell

Answer explanation

Electronegativity decreases down a group because electrons are added to higher energy levels, which increases their distance from the nucleus. This greater distance reduces the nucleus's ability to attract bonding electrons.

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DOK Level 3: Strategic Thinking

What is the general trend of ionization energy as you move down a group in the periodic table?

• It increases

• It decreases

• It remains constant

• It fluctuates

Answer explanation

As you move down a group in the periodic table, the ionization energy generally decreases. This is due to the increased distance of the outer electrons from the nucleus and increased electron shielding, making them easier to remove.

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DOK Level 1: Recall

• Bromine (Br)

• Krypton (Kr)

• Selenium (Se)

• Arsenic (As)

Answer explanation

The electron configuration [Ar] 4s^2 3d^{10} 4p^5 corresponds to the element with atomic number 35, which is Bromine (Br). The configuration indicates it has 5 electrons in the 4p subshell, characteristic of Bromine.

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DOK Level 1: Recall

How does the electron configuration of noble gases differ from that of other elements?

• Noble gases have completely filled valence shells

• Noble gases have partially filled d subshells

• Noble gases have no s subshells

• Noble gases have filled f subshells

Answer explanation

Noble gases have completely filled valence shells, which makes them stable and unreactive. This is in contrast to other elements, which often have partially filled shells and are more likely to react to achieve stability.

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DOK Level 2: Skill/Concept