Electronegativity of an element can be defined as the ability of an atom to attract the shared pair electrons in a covalent compound towards itself. In this complete transfer of electron from one atom to another atom does not take place, only limited movement of electron towards the more electronegative atom happens whereas in electron gain enthalpy the electron is completely absorbed by one of the atoms in a chemical bonding. In the case of electronegativity, partial negative charge (δ–) is created on the atom which attracts the electron towards itself and a partial positive charge(δ+) is created in the atom from which the electron is little far away.
Electronegativity depends on the following factors:
- Atomic size
- Nuclear charge
- Cationic charge
- Neighbouring atom
- Atomic size: The atomic radius of an atom is inversely proportional to the electronegativity of an atom. Smaller the size of an atom, higher will be the Electronegativity. If an atom is smaller in size, then the effective nuclear charge of an atom will be more towards the outermost shell and the electrons will be attracted towards the atom. So when in a periodic table the electronegativity increases while moving left to right in a period as atomic radius decreases. Whereas while moving down the group electronegativity decreases. Fluorine is the most electronegative element.
- Nuclear charge: If the nuclear charge of an atom is more then it will more strongly attract the electrons of outermost orbit (there are more positive charge to attract some negative charge). So, higher the nuclear charge more will be the electronegativity of the respective atom.
- Cationic charge: The third factor on which electronegativity depends on is the cationic charge. The atom which will have cationic charge will be short with the number of electrons. So they want to gain electrons; hence, it will pull electrons to remove its positive charge. The size of the cationic charge will also be small. Thus, the atom with the cationic charge will be more electronegative.
- Neighbouring atom: The electronegativity of an element also depends upon the adjacent atom. For example: Take two compounds CH3I and CF3 In CH3I, carbon is more electronegative than hydrogen; hence, it will pull electrons from hydrogen and Iodine is more electronegative than carbon so it pulls electrons from it. But in the case of CH3F, Fluorine atom is more electronegative than carbon, so fluorine pulls electrons density towards itself and now carbon is partially positive. In spite of the fact that iodine is more electronegative than carbon, carbon pulls electrons from iodine towards itself as it needs more electron than iodine. Thus, electronegativity of CF3I is greater than CH3I.
We have about 118 elements, which is a huge number to remember the electronegativity of each element. For that we can study the series shown below that will help in memorizing the electronegativity of elements. Nitrogen and chlorine have almost similar electronegative value. Fluorine is the most electronegative element and metals are the least electronegative element.
In several books, we find formulas like Pauling scale of electronegativity and Mulliken scale of electronegativity to find the electronegativity of an element, but it is least important as we are never asked to find the exact value of electronegativity of any compound. Halogens are the elements which have the highest electronegativity and alkali metals with least electronegativity.
Metallic and non-metallic character: Metals are the one which lose electron easily whereas non-metals are the one which gain electron easily. For example: Out of sodium, magnesium and aluminium, sodium will lose one electron easily as it has only electron to lose to obtain noble gas configuration whereas magnesium and aluminium have 2 & 3 electrons respectively.
Metallic character decreases while non-metallic character increases on moving left to right in a period.
Chemical reactivity: Elements in the extreme left of the periodic table reacts with the elements in the extreme right of the periodic table very easily. This is due to the low ionization enthalpy of extreme left side elements and high electron gain enthalpy of extreme right side elements.
This was just a brief layout about the trends of various properties in the periodic table. To know more about various properties of elements and their trend in periodic table watch the video.