I believe it is a Covalent Bond because 1st off, Calcium sulfide is made up of 2 elements, Calcium (Na) and Sulfer (S). Both elements want to obtain 8 electrons to become balanced (An octet) so therefore, these electrons are shared between these 2 elements.
It posed a contradiction to Quantum Theory
The reaction is:
C₂H₄ + 3O₂ → 2CO₂ + 2H₂O; ΔH = 1410 kJ
When we reverse this reaction, the sign of the enthalpy change, ΔH, will be changed. The enthalpy change for the reversed reaction would be 1,410 kJ.
Next, we must also multiply the reaction by 2, so the final enthalpy change for the reverse reaction will be:
ΔH = 2,820 kJ
4.98 x 10^3 would be 4980.
The atoms on the outermost level are called electrons.