## I Valence Electrons

Valence electrons occupy the outermost shell or highest energy level of an atom while core electrons are those occupying the innermost shell or lowest energy levels. This difference greatly influences the role of the two types of electrons in a chemical reaction. A valence electron is the number of electrons in the outermost shell of an element. The first step is to get the periodic table of chemical elements. Start labeling each of the columns that are on the periodic table from number 1 to number 18. These are the groups of the periodic table.

Valence Electrons The electrons in the last orbit which also determines mainly the electrical properties of the elements are known as valence electrons. It is well known to us that the outermost shell of an atom processes maximum 8 number of electrons. So the maximum number of valence electrons of an atom cannot be more than 8. Valence electrons are the electrons located at the outermost shell of an atom. Why are these electrons special? Because when two atoms interact, the electrons in the outermost shells are the first.

### Electron Configuration

The electrons in an atom fill up its atomic orbitals according to the Aufbau Principle; 'Aufbau,' in German, means 'building up.' The Aufbau Principle, which incorporates the Pauli Exclusion Principle and Hund's Rule prescribes a few simple rules to determine the order in which electrons fill atomic orbitals:

1. Electrons always fill orbitals of lower energy first. 1s is filled before 2s, and 2s before 2p.
2. The Pauli Exclusion Principle states no two electrons within a particular atom can have identical quantum numbers. In function, this principle means that if two electrons occupy the same orbital, they must have opposite spin.
3. Hund's Rule states that when an electron joins an atom and has to choose between two or more orbitals of the same energy, the electron will prefer to enter an empty orbital rather than one already occupied. As more electrons are added to the atom, these electrons tend to half-fill orbitals of the same energy before pairing with existing electrons to fill orbitals.

### Valency and Valence Electrons

The outermost orbital shell of an atom is called its valence shell, and the electrons in the valence shell are valence electrons. Valence electrons are the highest energy electrons in an atom and are therefore the most reactive. While inner electrons (those not in the valence shell) typically don't participate in chemical bonding and reactions, valence electrons can be gained, lost, or shared to form chemical bonds. For this reason, elements with the same number of valence electrons tend to have similar chemical properties, since they tend to gain, lose, or share valence electrons in the same way. The Periodic Table was designed with this feature in mind. Each element has a number of valence electrons equal to its group number on the Periodic Table. This table illustrates a number of interesting, and complicating, features of electron configuration.

First, as electrons become higher in energy, a shift takes place. Up until now, we have said that as the principle quantum number, increases, so does the energy level of the orbital. And, as we stated above in the Aufbau principle, electrons fill lower energy orbitals before filling higher energy orbitals. However, the diagram above clearly shows that the 4s orbital is filled before the 3d orbital. In other words, once we get to principle quantum number 3, the highest subshells of the lower quantum numbers eclipse in energy the lowest subshells of higher quantum numbers: 3d is of higher energy than 4s.

Second, the above indicates a method of describing an element according to its electron configuration. As you move from left to right across the periodic table, the above diagram shows the order in which orbitals are filled. If we were the actually break down the above diagram into groups rather than the blocks we have, it would show how exactly how many electrons each element has. For example, the element of hydrogen, located in the uppermost left-hand corner of the periodic table, is described as 1s1, with the s describing which orbital contains electrons and the 1 describing how many electrons reside in that orbital. Lithium, which resides on the periodic table just below hydrogen, would be described as 1s22s1. The electron configurations of the first ten elements are shown below (note that the valence electrons are the electron in highest energy shell, not just the electrons in the highest energy subshell).

### The Octet Rule

Our discussion of valence electron configurations leads us to one of the cardinal tenets of chemical bonding, the octet rule. The octet rule states that atoms becomeespecially stable when their valence shells gain a full complement of valence electrons. For example, in above, Helium (He) and Neon (Ne) have outer valence shells that are completely filled, so neither has a tendency to gain or lose electrons. Therefore, Helium and Neon, two of the so-called Noble gases, exist in free atomic form and do not usually form chemical bonds with other atoms.

Most elements, however, do not have a full outer shell and are too unstable to exist as free atoms. Instead they seek to fill their outer electron shells by forming chemical bonds with other atoms and thereby attain Noble Gas configuration. An element will tend to take the shortest path to achieving Noble Gas configuration, whether that means gaining or losing one electron. For example, sodium (Na), which has a single electron in its outer 3s orbital, can lose that electron to attain the electron configuration of neon. Chlorine, with seven valence electrons, can gain one electron to attain the configuration of argon. When two different elements have the same electron configuration, they are called isoelectronic.

### Diamagnetism and Paramagnetism

The electron configuration of an atom also has consequences on its behavior in relation to magnetic fields. Such behavior is dependent on the number of electrons an atom has that are spin paired. Remember that Hund's Rule and the Pauli Exclusion Principle combine to dictate that an atom's orbitals will all half-fill before beginning to completely fill, and that when they completely fill with two electrons, those two electrons will have opposite spins.

An atom with all of its orbitals filled, and therefore all of its electrons paired with an electron of opposite spin, will be very little affected by magnetic fields. Such atoms are called diagmetic. Conversely, paramagnetic atoms do not have all of their electrons spin-paired and are affected by magnetic fields. Postbox in wall panels. There are degrees of paramagnetism, since an atom might have one unpaired electron, or it might have four.

### Copper I Valence Electrons

#### Explanation:

Iodine, $' I '$, is located in period 5, group 17 of the periodic table, and has an atomic number equal to $53$.

That means that a neutral iodine atom will have a total of $53$ electrons surrounding its nucleus.

Now, out of these $53$ electrons, some are considered core electrons and some areconsidered valence electrons.

${n}_{'} \to t a l ' = {n}_{'} c \mathmr{and} e ' + {n}_{'} v a \le n c e '$

But how would you distinguish between the two types of electrons?

To do that, you need to look at the electron configuration of iodine, which looks like this

$' I : ' 1 {s}^{2} 2 {s}^{2} 2 {p}^{6} 3 {s}^{2} 3 {p}^{6} 3 {d}^{10} 4 {s}^{2} 4 {p}^{6} 5 {s}^{2} 4 {d}^{10} 5 {p}^{5}$

You know that the valence electrons are defined as being the electrons located on the highest energy level of that atom, which is given by the principal quantum number, $n$, for main group elements.

Notice that, in iodine's case, the highest energy level is $n = 5$. You have two subshells occupied with electrons on this energy level, $5 {s}^{2}$ and $5 {p}^{5}$.

This means that iodine has a total of

${\underbrace{2 {e}^{-}}}_{\textcolor{b l u e}{' \mathfrak{o} m 5 s \subset s h e l l '}} + {\overbrace{5 {e}^{-}}}^{\textcolor{red}{' \mathfrak{o} m 5 p \subset s h e l l '}} = ' 7 v a \le n c e ' {e}^{-}$

The rest of the electrons will thus be core electrons.

${n}_{'} c \mathmr{and} e ' = {n}_{'} \to t a l ' - {n}_{'} v a \le n c e '$

${n}_{'} c \mathmr{and} e ' = 53 - 7 = \textcolor{g r e e n}{' 46 c \mathmr{and} e ' {e}^{-}}$

Therefore, a neutral iodine atom has $46$ core electrons and $7$valence electrons.

### I Valence Electron Calculator

Iodine has $7$valence electrons and $46$ core electrons for a total of $53$, the atomic number.

### I Element Valence Electrons

Iodine is in the group 17 elements, known as halogens, and all of them have $7$valence electrons.

A valence electron is capable of bonding with valence electrons of another atom to complete the octet of electrons each atom needs in its outer shell.

The core electrons are not available for bonding with other elements

When more than one atom bonds with others, a molecule is formed. The completed molecule will not have an electron charge associated with it.