Question

exam 2: periodicity & electron configuration/em spectrum
which elements do not have the same number of valence electrons?
○ na and cs
○ ar and he
○ n and o
○ b and c are both correct answers.

Explanation:

Step1: Determine valence - electrons of Na and Cs

Na (sodium) is in Group 1, has 1 valence electron. Cs (cesium) is also in Group 1, has 1 valence electron.

Step2: Determine valence - electrons of Ar and He

Ar (argon) is a noble gas in Group 18, has 8 valence electrons. He (helium) is a noble gas in Group 18, but has 2 valence electrons.

Step3: Determine valence - electrons of N and O

N (nitrogen) is in Group 15, has 5 valence electrons. O (oxygen) is in Group 16, has 6 valence electrons.

Step4: Analyze the options

Options b (Ar and He) and c (N and O) have elements with different numbers of valence electrons.

Answer:

D. b and c are both correct answers.