Question

5 identify the element based on the information below: located in period 4, has 3 valence electrons.

Explanation:

Step1: Recall electron - configuration rules

Elements in period 4 start filling the 4s orbital first, then 3d, and then 4p. For an element with 3 valence electrons in period 4, the first two valence electrons fill the 4s orbital ($4s^{2}$), and the third one fills the 3d orbital ($3d^{1}$). The electron - configuration of the element is $[Ar]4s^{2}3d^{1}$.

Step2: Identify the element from the electron - configuration

The atomic number of the element can be determined from its electron - configuration. Argon ($Ar$) has an atomic number of 18. Adding 2 electrons from the 4s orbital and 1 electron from the 3d orbital, we get an atomic number of 18 + 2+1=21.

Answer:

Scandium (Sc)