In their typical state, atoms are electrically neutral because they contain an equal number of protons and electrons, balancing out their charges. However, atoms can undergo a transformation where they gain or lose electrons, leading to the formation of charged particles known as ions.
The Neutral Bromine Atom
To understand the bromide ion, it is first helpful to consider the neutral bromine atom.
Every atom is defined by its atomic number, which represents the precise count of protons within its nucleus. This atomic number is a unique identifier for each element and can be found on the periodic table.
For bromine, the atomic number is 35. In a neutral bromine atom, the number of electrons orbiting the nucleus is exactly equal to the number of protons in the nucleus. Since bromine has an atomic number of 35, a neutral bromine atom therefore contains 35 protons and 35 electrons.
Understanding Ions
Ions are charged particles. This charge arises when an atom gains or loses one or more electrons, disrupting the balance between its protons and electrons. Atoms typically form ions to achieve a more stable electron configuration, often by filling their outermost electron shell.
There are two main types of ions: cations and anions. Cations are atoms that have lost electrons, resulting in a net positive charge because they then have more protons than electrons.
Conversely, anions are atoms that have gained electrons, leading to a net negative charge due to an excess of electrons compared to protons. The specific charge of an ion is indicated by a superscript next to its chemical symbol, with a minus sign signifying a gained electron and a positive sign indicating a lost electron.
Calculating Electrons in the Bromide Ion (Br-)
The bromide ion, represented as Br-, is an example of an anion. The superscript minus sign indicates that the bromine atom has gained one electron. The formation of an ion involves only the gain or loss of electrons; the number of protons within the atom’s nucleus remains constant.
Starting with a neutral bromine atom, which has 35 electrons, the formation of a bromide ion means that this atom has acquired an additional electron.
Therefore, to determine the total number of electrons in a bromide ion, one simply adds the gained electron to the original number of electrons in the neutral atom. This calculation results in 35 electrons plus 1 additional electron, totaling 36 electrons in a bromide ion.