Final answer:
Sodium (Na) needs to lose one electron to form a Na+ cation. Strontium (Sr) needs to lose two electrons to form a Sr2+ cation. Sulfur (S) needs to gain two electrons to form a S2- anion, and Astatine (At) needs to gain one electron to form an At- anion.
Step-by-step explanation:
To identify the number of electrons each atom needs to gain or lose to have a stable outer electron configuration, we will refer to their position on the periodic table and their electron configurations. Here are the details for each element:
- Sodium (Na): Sodium has one valence electron in its outermost shell (3s1). To achieve a noble gas configuration, Na needs to lose one electron and will form a cation with a charge of +1.
- Strontium (Sr): Strontium has two valence electrons in the outermost shell. Sr needs to lose two electrons to achieve a stable electron configuration, forming a cation with a charge of +2.
- Sulfur (S): Sulfur has six valence electrons (3s23p4). It needs to gain two electrons to achieve a stable electron configuration, forming an anion with a charge of -2.
- Astatine (At): As a halogen, astatine has seven valence electrons and needs to gain one electron to have a stable outer electron configuration, forming an anion with a charge of -1.