What is the formula for the ionic compound formed by calcium and sulfur? a) Cas b) Cas c) Cas d) Cass e) Cas. ________________________________________________________________________________________________________________________________________________
The correct answer and explanation is:
The correct answer is CaS.
Explanation :
Ionic compounds are formed when a metal reacts with a non-metal, transferring electrons to achieve a stable electron configuration (usually a full outer shell). Calcium (Ca) is a metal in Group 2 of the periodic table, known as the alkaline earth metals. It has two valence electrons in its outermost shell. To become stable, calcium loses these two electrons, forming a positively charged ion (Ca2+Ca^{2+}).
Sulfur (S), on the other hand, is a non-metal in Group 16 (the chalcogens). It has six valence electrons in its outer shell and needs two additional electrons to achieve a full outer shell. When sulfur gains two electrons, it becomes a negatively charged ion (S2−S^{2-}).
To form an ionic compound, the total positive charge must equal the total negative charge, resulting in a neutral compound. Since calcium forms Ca2+Ca^{2+} and sulfur forms S2−S^{2-}, they combine in a 1:1 ratio to balance the charges. This gives the formula CaS.
In this compound:
- Ca2+Ca^{2+}: Calcium ion contributes +2 charge.
- S2−S^{2-}: Sulfide ion contributes -2 charge.
These ions are held together by strong electrostatic forces of attraction, known as ionic bonds. The resulting compound, calcium sulfide (CaSCaS), is electrically neutral because the charges cancel each other out.
Calcium sulfide is a crystalline solid with high melting and boiling points, typical of ionic compounds. It is also brittle and dissolves in water to release its constituent ions. These properties arise from the strong ionic bonds between the calcium and sulfide ions.
In summary, the correct formula for the ionic compound formed by calcium and sulfur is CaS, which is determined by their charges and the principle of charge neutrality in ionic compounds.