Chapter 4 Exam Review

Which group of elements in the periodic table is characterized by an especially stable electron arrangement?

• 8B

• 8A

• 2A

• 2B

Answer explanation

The group 8A, also known as the noble gases, has a full valence shell, making their electron arrangement especially stable. This stability is why they are less reactive compared to other elements.

Tags

NGSS.HS-PS1-1

The structural difference between a sodium atom and a sodium ion is that the sodium ion has

• one more proton than the sodium atom

• more proton and one less electron than the sodium atom

• one less electron than the sodium atom

• one less proton than the sodium atom

Answer explanation

A sodium ion (Na+) has lost one electron compared to a neutral sodium atom (Na). This results in the ion having the same number of protons (11) but one less electron, making the correct choice 'one less electron than the sodium atom'.

Which of the following are isoelectronic?

• Kr and Cl⁻

• S²⁻ and Ar

• Al³⁺ and Ar

• Ne and Ar

Answer explanation

S²⁻ has 18 electrons (16 from S + 2 from gaining 2 electrons), while Ar also has 18 electrons. Therefore, S²⁻ and Ar are isoelectronic, sharing the same electron configuration. Other pairs do not match in electron count.

Tags

NGSS.HS-PS1-1

Which of the following cations is isoelectronic with S²⁻?

• Ca²⁺

• Na⁺

• Rb⁺

• Mg²⁺

Answer explanation

S²⁻ has 18 electrons (same as Ar). Ca²⁺ also has 18 electrons (loses 2 from Ca). Na⁺ (11), Rb⁺ (37), and Mg²⁺ (12) do not match. Thus, Ca²⁺ is isoelectronic with S²⁻.

Tags

NGSS.HS-PS1-1

How many dots surround B in the Lewis dot symbol for boron?

• 2

• 5

• 9

• 3

Answer explanation

In the Lewis dot symbol for boron, which has an atomic number of 5, there are 3 valence electrons. Therefore, there are 3 dots surrounding the element B, making the correct answer 3.

How many dots surround Br in the Lewis dot symbol for Br⁻?

• 9

• 7

• 8

• 1

Answer explanation

Bromine (Br) has 7 valence electrons. In the Br− ion, it gains an extra electron, totaling 8. The Lewis dot symbol for Br− shows 8 dots surrounding it, representing these valence electrons.

Which of the following Lewis dot symbols is incorrect?

• 
• 
• 
• 

Tags

NGSS.HS-PS1-1

NGSS.HS-PS1-2

Which of the following Lewis dot symbols is incorrect ?

• 
• 
• 
• 

Tags

NGSS.HS-PS1-1

NGSS.HS-PS1-2

A potassium ion and an argon atom have the same

• properties

• electron configuration

• net charge

• nuclear charge

Answer explanation

A potassium ion (K+) and an argon atom (Ar) both have the same electron configuration of 1s² 2s² 2p⁶, which corresponds to the noble gas configuration. This is why they share the same electron configuration.

Tags

NGSS.HS-PS1-1

How many dots are shown on the Lewis symbol for chloride ion, and what is the ion’s charge?

• six dots, positive charge

• eight dots, negative charge

• five dots, no charge

• seven dots, negative charge

Answer explanation

The Lewis symbol for the chloride ion (Cl-) shows eight dots, representing its eight valence electrons after gaining one electron. The ion has a negative charge due to this gain, making the correct answer 'eight dots, negative charge'.