What is electronegativity?
What is electronegativity?
Electronegativity is the tendency of atoms to attract a shared pair of electrons towards themselves in a covalent bond formed between it and another atom.
or,
The capacity of an element to attract more shared electrons between two elements during the formation of a covalent bond it is called its electronegativity.
or,
When two atoms of a molecule are bonded covalently, the ability of an atom that is bonded to another atom or atoms to attract electrons to itself is called electronegativity.
Electronegativity Chart
How do we find electronegativity?
There are two main ways to find electronegativity:
Electronegativity Chart: This is the most common and easiest way. You can find a periodic table that also lists the electronegativity values for each element. These charts are available in many chemistry textbooks and online resources. The Pauling electronegativity scale is the most commonly used system.
Periodic Table Trends: While not an exact calculation, you can estimate the relative electronegativity of elements by looking at their position on the periodic table. Electronegativity generally:
- Increases as you move from left to right across a period.
- Decreases as you move from top to bottom down a group.
This means the most electronegative elements are found in the top right corner of the table (fluorine being the most), and the least electronegative elements are found in the bottom left (francium being the least).
How to find the electronegativity of an element?
There are two main ways to find the electronegativity of an element:
- Using a periodic table: Many periodic tables will list the electronegativity values for each element alongside other properties like atomic number and atomic mass. These values are typically based on the Pauling electronegativity scale, which is the most common one used.
- Using an electronegativity chart: Similar to a periodic table with electronegativity values, you can find dedicated electronegativity charts that only focus on this property. These charts might offer a clearer view of the trends and might be easier to use for finding specific elements.
Why does electronegativity increase across a period?
Electronegativity increases across a period of the periodic table from left to right due to two main factors:
- Increasing Effective Nuclear Charge: As you move across a period, the number of protons in the nucleus increases. This means there's a greater positive charge attracting the electrons. However, the number of electron shells stays the same. This effectively increases the pull on the outermost electrons by the nucleus, making them harder to share with other atoms.
- Decreasing Atomic Radius: Another factor is the size of the atom. Across a period, the atomic radius tends to decrease. This means the outermost electrons are closer to the positively charged nucleus, experiencing a stronger attraction and increasing electronegativity.
In essence, both a stronger pull from the nucleus and a closer distance to it make it harder for an atom to share electrons, which is what defines higher electronegativity.
Why does electronegativity decrease down a group?
Electronegativity weakens as you move down a group in the periodic table because of increasing atomic size. There are two key factors at play here:
- Distance from the nucleus: As you go down a group, the number of electron shells increases. This means the valence electrons (the outermost electrons involved in bonding) are further away from the positively charged nucleus. The weaker the attraction between the nucleus and the electrons, the less tightly the atom holds onto its electrons and the weaker its electronegativity.
- Shielding effect: Inner electrons partially shield the outermost valence electrons from the full attractive force of the nucleus. This shielding effect becomes more prominent down a group as there are more inner shells. So, even though the nuclear charge increases slightly down a group (due to more protons), the shielding effect weakens the net attraction on the valence electrons, leading to lower electronegativity.
In essence, the increasing distance and shielding effect weaken the grip an atom has on its electrons, making it less electronegative as you move down a group.
Which element has the highest electronegativity?
The element with the highest electronegativity on the periodic table is fluorine (F). It has an electronegativity value of 4.0, which is the highest possible value on the most common electronegativity scale developed by Linus Pauling. This means fluorine has the strongest attraction for electrons in a chemical bond compared to all other elements.
How is electronegativity related to covalent bonding?
Electronegativity plays a key role in determining the character of covalent bonds. Here's the breakdown:
- Electronegativity: This is a measure of an atom's ability to attract electrons towards itself in a chemical bond. The higher the electronegativity, the stronger the attraction.
- Covalent Bonding: Covalent bonds form when atoms share electrons. In a pure covalent bond, the electrons are shared equally between the atoms.
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