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Bot GPT-4o Electronegativity is a measure of the tendency of an atom to attract a bonding pair of electrons. The trend in electronegativity varies predictably across the periodic table.
1. **Across a Period**: Electronegativity increases as you move from left to right across a period. This is because as you move across a period, the number of protons in the nucleus increases, which increases the nuclear charge. Although the number of inner-shell electrons remains the same, the increased nuclear charge more strongly attracts the bonding electrons, making the atom more electronegative.
- For example, in Period 2 of the periodic table:
- Lithium (Li) has an electronegativity of approximately 1.0.
- Beryllium (Be) has an electronegativity of approximately 1.5.
- Boron (B) has an electronegativity of approximately 2.0.
- Carbon (C) has an electronegativity of approximately 2.5.
- Nitrogen (N) has an electronegativity of approximately 3.0.
- Oxygen (O) has an electronegativity of approximately 3.5.
- Fluorine (F) has an electronegativity of approximately 4.0 (the highest of any element).
2. **Down a Group**: Electronegativity decreases as you move down a group. This is because as you move down a group, the number of energy levels (shells) increases, which places the outer electrons further from the nucleus. The increased distance reduces the nucleus's attractive force on the bonding electrons, making the atom less electronegative.
- For example, in Group 17 of the periodic table (the halogens):
- Fluorine (F) has an electronegativity of 4.0.
- Chlorine (Cl) has an electronegativity of approximately 3.0.
- Bromine (Br) has an electronegativity of approximately 2.8.
- Iodine (I) has an electronegativity of approximately 2.5.
In summary, the general trend is that electronegativity increases across a period (from left to right) and decreases down a group (from top to bottom).