In order to understand why Br has a negative charge, we need to look at its electronic configuration and the concept of ionization.
The element bromine (Br) belongs to Group 17 of the periodic table, also known as the halogens. It has an atomic number of 35, indicating that it has 35 electrons in its neutral state.
To determine the charge of an ion, we need to consider the number of electrons gained or lost by the atom. In the case of bromine, it tends to gain one electron to achieve a stable electron configuration.
The octet rule states that atoms tend to gain, lose, or share electrons to achieve a stable electron configuration with eight valence electrons. Bromine has seven valence electrons, so by gaining one more electron, it can complete its octet and achieve a stable configuration similar to its nearest noble gas, krypton.
When bromine gains an electron, it becomes a negatively charged ion called a bromide ion (Br-). The negative charge indicates that the ion has one more electron than protons, resulting in an overall negative charge of one.
The formation of bromide ions is essential in various chemical reactions and compounds. For example, in ionic compounds such as sodium bromide (NaBr), bromine gains an electron from sodium, which donates one electron to form a stable ionic bond.
It is important to note that the charge of an ion is not determined by the element itself, but rather by the gain or loss of electrons. In the case of bromine, it gains one electron to become negatively charged. Other elements in Group 17, such as fluorine, chlorine, and iodine, also tend to gain one electron and form negatively charged ions (fluoride, chloride, iodide, respectively).
Bromine becomes a negatively charged ion (Br-) by gaining one electron to achieve a stable electron configuration. This additional electron satisfies the octet rule, making the bromide ion more stable and allowing it to participate in various chemical reactions and compounds.