How Many Valence Electrons Does Bromine (Br) Have? [Valency of Bromine]

Bromine, a chemical element with the symbol Br and atomic number 35, is a very reactive gas so that does not occur in free states but exists as halide salts or table salts. At standard temperature and pressure, it is found as a liquid like mercury.

You are here to know valence electrons of bromine atom, aren’t you? Don’t worry along with bromine valence electrons we will explain its valency also. But before that let’s have some basic ideas about what these two terms are:

Difference Between Valence Electrons and Valency

Valence electrons are the total number of electrons present in the outermost shell of an atom (i.e. in outermost orbital). The valence electrons for a neutral atom are always definite, it cannot be varied (more or less) in any condition for a particular atom and may or may not be equal to its valency.

Valency is defined as the total number of electrons an atom can lose, gain, or share at the time of bond formation to get a stable electronic configuration i.e. to complete an octet. The valency of an atom can be variable in different compounds or chemical reactions due to the different bonding circumstances. Most of the time valency varies/changes due to change in oxidation and reduction states.

Bromine (Br) Valence Electrons

There are four simple steps to find out the valence electrons for bromine atom which are:

Step 1: Find the Atomic Number

To find out the atomic number of bromine, we can use the periodic table. With the help of the periodic table, we can easily see that the atomic number of bromine is 35. As its atomic number is 35, it has 35 protons, and for neutral bromine, the number of protons is always equal to the number of electrons i.e. has 35 electrons in its nucleus.

Step 2: Write Electron Configuration

Electron configuration is the arrangement of electrons on the orbitals. The bromine atom has a total of 35 electrons so, we have to put 35 electrons in orbitals. The electrons will be placed in different orbitals according to the energy level: [1s, 2s, 2p, 3s, 3p, 4s, 3d, 4p, 5s, 4d, 5p, 6s, 4f, 5d, 6p, 7s, 5f]. Now,

Bromine electron configuration Br (35) = 1s²2s²2p⁶3s²3p⁶3d¹⁰4s²4p⁵(complete configuration).

= [Ar] 4s² 3d¹⁰ 4p⁵(condensed configuration).

Step 3: Determine Valence Shell

As we know, the valence shell of an atom can be found from the highest number of principle quantum numbers are expressed in the term of n, and in [Ar] 4s² 3d¹⁰ 4p⁵, the highest value of n is 4 so that the valence shell of bromine is 4s² 3d¹⁰ 4p⁵.

Step 4: Find Valence Electrons

The total number of electrons present in the valence shell of an atom are called valence electrons, and there are a total of seven electrons present in the valence shell of bromine (4s² 3d¹⁰ 4p⁵). Thus, bromine has seven valence electrons.

Valency of Bromine (Br)

There are many different ways to find out the valency of an atom which reflects the ability of an atom to bond with other atoms. Valence describes how easily an atom or a free radical can combine with other chemical species. The valency of an atom is determined based on the number of electrons lost, gained, or shared with another atom at the time of bond formation.

An atom is said to be stable when its outermost shells have eight electrons (except H & He). If the total number of electrons in outermost shells is between one to four, the atom has positive valency and if electrons are between four to eight, the valency is calculated by subtracting from eight and valency will be zero. Atoms having four outermost electrons possess both positive and negative valency, and atoms having eight outermost electrons, valency will be zero (i.e. noble gases).

Elements like bromine can reach the stable state (nearest inert gas configuration: Ar) by getting one electron. So that the valency of bromine is 1.

Mathematically, the electronic configuration of bromine is 2, 8, 18, 7. And as we know, if electrons in the outermost shell exceed from 4, it should be subtracted from 8. So,

Electron Configuration of bromine (Br) = 2, 8, 18, 7

We can see the outermost shell of bromine has 7 electrons so, have to subtract it from 8.

8 – 7 = 1

That’s why valency of bromine is 1.

Note: In general, bromine has a stable oxidation state of -1 most of the time but it can differ in some compounds with values 0 (Br2), +1 (NaBrO), +3 (NaBrO2), +4 (BrO3), +5 (NaBrO3), +7 (NaBrO4). Do not confuse with -1 or something else (+1, +3, +4, etc.) with a positive or negative sign, it is just an oxidation number that can vary from compound to compound. But its valency is always 1 in any case.  

In another sense, a bromine atom can form a maximum of one covalent bond in a chemical bonding (For example: HBr, CH3Br, CaBr2, etc.), and that what valency is, the maximum ability to form bonds with atoms at the time of chemical bonding.

We can also find the valency of bromine with the help of the periodic table. As bromine belongs to group 17 (17A or VIIA) along with fluorine (F), chlorine (Cl), iodine (I), and astatine (At). These group elements are also called halogens. All these elements have valency one.