Electron Configuration and Valence Electrons

What is the electron configuration of the element oxygen (O)?

• 1s² 2s² 2p⁶

• 1s² 2s² 2p⁴

• 1s² 2s¹ 2p⁶

• 1s² 2p⁴

Which of the following elements has 7 valence electrons?

• Nitrogen (N)

• Oxygen (O)

• Fluorine (F)

• Sodium (Na)

Which electron configuration corresponds to an atom of potassium (K)?

• 1s² 2s² 2p⁶ 3s² 3p⁶ 4s²

• 1s² 2s² 2p⁶ 3s² 3p⁶ 4s² 3d¹⁰

• 1s² 2s² 2p⁶ 3s² 3p⁶ 4s² 4p⁶

• 1s² 2s² 2p⁶ 3s² 3p⁶ 4s² 4p⁶ 5s¹

How many valence electrons are in an atom of chlorine (Cl)?

• 1

• 3

• 7

• 8

Which of the following best explains the periodic trend in the number of valence electrons across a period?

• The number of valence electrons increases as you move from left to right across a period.

• The number of valence electrons decreases as you move from left to right across a period.

• The number of valence electrons remains constant across a period.

• The number of valence electrons increases as you move down a group.