Question

The elements in the ________ period of the periodic table have a core-electron configuration that is the same as the electron configuration of neon. A) first

B) second
C) third
D) fourth
E) fifth

Answer 1

The elements in the second period of the periodic table have a core-electron configuration that is the same as the electron configuration of neon.

Step-by-step explanation:

The elements in the second period of the periodic table have a core-electron configuration that is the same as the electron configuration of neon.

Sodium, element number 11, is the first element in the third period of the periodic table. Its electron configuration is 1s²2s²2p63s¹. The first ten electrons of the sodium atom are the inner-shell electrons and the configuration of just those ten electrons is exactly the same as the configuration of the element neon (Z = 10).

This provides the basis for a shorthand notation for electron configurations called the noble gas configuration. The elements that are found in the last column of the periodic table are an important group of elements called the noble gases. They are helium, neon, argon, krypton, xenon, and radon. A noble gas configuration of an atom consists of the elemental symbol of the last noble gas prior to that atom, followed by the configuration of the remaining electrons. So for sodium, we make the substitution of [Ne] for the 1s²2s²2p6 part of the configuration. Sodium's noble gas configuration becomes [Ne] 3s¹.

Answer 2

The elements in the second period of the periodic table have the same core-electron configuration as the element neon, represented by the electron configuration 1s²2s²2p⁶.

Step-by-step explanation:

The elements in the second period of the periodic table have a core-electron configuration that is the same as the electron configuration of neon.

To determine which period of the periodic table shares the same core electron configuration as neon, one has to look at the arrangement of the electrons within the elements. The electron configuration of neon, which is in the second period, ends with the configuration 1s²2s²2p⁶. This electron configuration indicates that neon has a full 2s and 2p sublevel, making its electron configuration representative of the second period. This is highlighted by elements such as sodium (Na), with an electron configuration of 1s²2s²2p⁶3s¹, where the first ten electrons (1s²2s²2p⁶) represent the core electrons that match neon's electron configuration.

Sodium is the first element in the third period, but its core (or inner-shell) electrons up to 1s²2s²2p⁶ are the same as those of the noble gas neon, from the second period. Therefore, the answer to the question is option B) second. This is known as the noble gas configuration, where the core electron configuration matches that of the closest noble gas of a lower atomic number, in this case, neon (Ne).