Ca + Br2 --> CaBr2

its synthesis and the reason the reaction happens is stable electron configuration but i don't understand why.

Synthesis because it's two elements combining to form a single product. Stable electron configuration because

Ca has two electrons as the metal (solid). It wants to give those two electrons up and if it does, then the last shell has 8 electrons in it (it is 1s2 2s2 2p6 3s2 3p6 4s2 as the metal. Losing the 2 4s electrons leaves it with 8 in the 3rd shell.) Bromine, as the element, has 7 electrons in its outside shell. It wants to gain 1 electron to make 8. So 1 Ca atom combines with 2 Br atoms, giving 1 electron to each Br, to make CaBr2. The Ca is now a +2 ion and the 2 Br atoms are Br^- ion. This is a typical ionic bond.

okay but doesnt this happen in a lot of the synthesis ones then?

The reaction between calcium (Ca) and bromine (Br2) is a synthesis reaction, also known as a combination reaction. In this reaction, calcium and bromine combine to form calcium bromide (CaBr2).

The reason behind this reaction happening lies in the concept of achieving a stable electron configuration. Atoms naturally tend to form chemical bonds with other atoms in order to attain a more stable electron configuration, usually by gaining, losing, or sharing electrons.

Calcium is in Group 2 of the periodic table and has two valence electrons in its outermost energy level (2s2). By losing these two electrons, calcium can achieve the stable electron configuration of the previous noble gas, argon (Ar), which has a completely filled outermost energy level (3s2 3p6).

On the other hand, bromine is in Group 17 and has seven valence electrons in its outermost energy level (4s2 4p5). By gaining one electron from calcium, bromine can achieve the stable electron configuration of the next noble gas, krypton (Kr), which also has a completely filled outermost energy level (4s2 4p6).

When calcium reacts with bromine, calcium loses two electrons to become Ca2+ (calcium cation), and bromine gains one electron to become Br- (bromide anion). The oppositely charged ions attract each other, resulting in the formation of the ionic compound calcium bromide (CaBr2), which consists of calcium cations and bromide anions held together by electrostatic forces.

Overall, the reaction between calcium and bromine happens because both elements can achieve a more stable electron configuration by forming calcium bromide through the transfer of electrons.