Electronegativity is the power of an atom to attract electrons in a bond towards itself. This helps chemists predict if a bond is polar, non-polar, or ionic. Many factors influence electronegativity, and there are patterns in the periodic table that can help us understand it better. In this article, we’ll explore electronegativity, its factors, trends, and how it relates to bonding. We’ll also discuss bond polarisation and the electronegativity formula. So, let's dive in! Don't worry, we'll make it simple and easy to understand for anyone between the ages of 16-24.

Which factors affect electronegativity?

Let's look at a few factors which impact electronegativity.

Atomic radius

The atomic radius is the distance between the outer electrons in the outermost shell and the nucleus. The closer the electrons are to the nucleus, the stronger the attraction between them. As a result, if the atomic radius decreases, the attraction and electronegativity increase. On the other hand, if the distance between the electrons and the nucleus increases, the attraction gets weaker, and the electronegativity decreases.

Nuclear charge

The nuclear charge is the number of protons in the nucleus. The protons are positively charged, while electrons are negatively charged. Therefore, an increased number of protons in the nucleus results in a stronger attraction between the positively charged nucleus and negatively charged outer electrons. However, it's important to note that nuclear charge is not the same as an element or compound having a charge.

Shielding

The electronegativity of an atom generally increases as you move across a period from left to right. This is because the number of protons in the nucleus increases, causing a stronger attraction between the nucleus and outer electrons. As a result, atoms become more electronegative as you move across a period.

On the other hand, as you move down a group in the periodic table, the electronegativity generally decreases. This is because the number of subshells and inner shells increases, causing the outer electrons to be shielded from the attraction of the nucleus. As a result, atoms become less electronegative as you move down a group.

Electronegativity down a group

As you move down a group in the periodic table, electronegativity decreases due to the increase in the number of subshells and inner shells. This results in an increase in atomic radius, which is the distance between the nucleus and the outermost electrons. The addition of more shells of electrons causes the atom to become larger, which weakens the force of attraction between the nucleus and the outermost electrons. As a result, the electronegativity decreases.

Electronegativity across a period

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The Pauling scale is a numeric scale of electronegativities that can be used to predict the percentage ionic or covalent character of a chemical bond. The Pauling scale ranges from 0 to 4. Halogens are the most electronegative elements in the Periodic Table, with fluorine being the most electronegative element of all, with a value of 4.0. The elements that are least electronegative have a value of approximately 0.7; these are caesium and francium. Single covalent bonds can be formed by the sharing of a pair of electrons between two atoms. Examples of molecules made up of a single element are diatomic gases, and molecules such as H2, Cl2, and O2. Molecules made up of a single element contain bonds that are purely covalent. In these molecules, the difference in electronegativity is zero since both atoms have the same electronegativity value and, therefore, the sharing of electron density is equal between the two atoms. This means that the attraction towards the bonding pair of electrons is equal, resulting in a non-polar covalent bond.

However, when atoms with different electronegativities form a molecule, the sharing of electron density is not equally distributed between the atoms. This results in the formation of a polar covalent bond. In this case, the more electronegative atom (the atom with the higher value in the Pauling scale) attracts the bonding pair of electrons towards itself. Due to this, partial charges appear on the molecule, since the more electronegative atom gains a partial negative charge, while the less electronegative atom gains a partial positive charge.

An ionic bond is formed when one atom completely transfers its electrons to another atom which gains the electrons. This occurs when there is a large enough difference between electronegativity values of the two atoms in a molecule; the least electronegative atom transfers its electron(s) to the more electronegative atom. The atom which loses its electron(s) becomes a cation which is a positively charged species, whilst the atom which gains the electron(s) becomes an anion, which is a negatively charged species. Compounds such as magnesium oxide (MgO), sodium chloride (NaCl), and calcium fluoride (CaF2) are examples of this.

Usually, if the difference in electronegativity is greater than 2.0, the bond is likely to be ionic. If the difference is less than 0.5 then the bond will be a non-polar covalent bond. If there is an electronegativity difference between 0.5 and 1.9, then the bond will be a polar covalent bond.

Let's have a look at some examples. Take LiF:The electronegativity difference for this is 4.0 - 1.0 = 3.0, therefore this represents an ionic bond. HF: The electronegativity difference for this is 4.0 - 2.1 = 1.9, therefore this represents a polar covalent bond.CBr: The electronegativity difference for this is 2.8 - 2.5 = 0.3, therefore this represents a non-polar covalent bond.

Electronegativity formula

The electronegativity difference between two atoms can help determine the polarity of the bond they form. If the two atoms have similar electronegativities, the bond will be non-polar, and the electrons will be evenly shared between the two atoms. However, if the two atoms have different electronegativities, the bonding electrons will be attracted towards the more electronegative atom, resulting in a partial charge on each atom and a polar bond. The larger the electronegativity difference, the more polar the bond will be. This shift in electron density creates a dipole, which is a difference in charge distribution between the two atoms.

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Great summary! To add to that, electronegativity is an important concept in chemistry as it helps to explain how atoms bond with each other and form molecules. It is also used to predict the nature of chemical bonds, whether they are covalent or ionic. Understanding electronegativity can help us better understand the behavior of molecules and their reactions with other molecules.

Electronegativity

What is electronegativity?

Electronegativity is the power and ability of an atom to attract and pull a pair of electrons in a covalent bond towards itself.

Why does electronegativity increase across a period?

The nuclear charge increases because the number of protons in the nucleus increases. The atomic radius decreases as the distance between the nucleus and the outermost electron decreases. Shielding remains constant.

How does a large electronegativity difference affect molecular properties?

The larger the difference between the electronegativity of the elements forming the bond, the higher the chance of the bond being ionic.

What is the formula of electronegativity?

To calculate the polarity of a bond in a molecule, you have to subtract the smaller electronegativity from the larger one.  

What are some examples of electronegativity?

In a molecule such as hydrogen chloride, the chlorine atom drags the electrons towards itself slightly because it is the more electronegative atom and gains a partial negative charge, whereas hydrogen gains a partial positive charge.

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