Question

what element has the electron configuration 1s²2s²2p⁶3s²3p²?
nitrogen
silicon
selenium
silver
question 12
2.5 pts
atomic size generally
decreases as you move from left to right across a period.
decreases as you move from top to bottom within a group.
increases as you move from left to right across a period.
remains constant within a period.

Explanation:

First Question:

Step1: Calculate the total number of electrons

For the electron configuration \(1s^{2}2s^{2}2p^{6}3s^{2}3p^{2}\), sum the exponents: \(2 + 2+6 + 2+2=14\). The number of electrons in a neutral atom is equal to the atomic number.

Step2: Identify the element

The element with atomic number \(14\) is silicon (\(Si\)). Nitrogen (\(N\)) has atomic number \(7\), selenium (\(Se\)) has atomic number \(34\), and silver (\(Ag\)) has atomic number \(47\).

Second Question:

Step1: Recall the trend of atomic size

• Across a period (left - to - right): As the atomic number increases, the number of protons in the nucleus increases. The electrons are added to the same principal energy level. The increased nuclear charge pulls the electrons closer, so atomic size decreases.
• Down a group (top - to - bottom): New energy levels are added, so the atomic size increases.

Answer:

First Question: silicon
Second Question: decreases as you move from left to right across a period.