Periodic Trends

Electronegativity (EN)

Electronegativity is a measure of an atom's ability to attract shared electrons in a chemical bond. It is a fundamental concept in organic chemistry, as it influences molecular polarity, reactivity, and the nature of chemical bonds.

• Trend Across a Period: Electronegativity increases from left to right across a period in the periodic table.

• Trend Down a Group: Electronegativity decreases as you move down a group.

• Most Electronegative Element: Fluorine (F) is the most electronegative element.

• Least Electronegative Elements: Alkali metals (e.g., Lithium, Sodium) have the lowest electronegativity values.

Example: In a C–F bond, fluorine attracts the shared electrons more strongly than carbon, making the bond highly polar.

Atomic Size (Atomic Radius)

Atomic size (or atomic radius) refers to the distance from the nucleus to the outermost electron shell of an atom. This property affects how atoms interact and bond with each other.

• Trend Across a Period: Atomic size decreases from left to right across a period due to increasing nuclear charge, which pulls electrons closer to the nucleus.

• Trend Down a Group: Atomic size increases as you move down a group because additional electron shells are added, making the atom larger.

• Smallest Atoms: Helium (He) and other noble gases at the top right have the smallest atomic radii.

• Largest Atoms: Alkali metals at the bottom left (e.g., Cesium, Francium) have the largest atomic radii.

Example: Sodium (Na) is larger than chlorine (Cl) in the same period, but both are smaller than potassium (K), which is in the period below.

Summary Table: Periodic Trends

Additional info: These trends are essential for understanding reactivity, bond polarity, and the behavior of organic molecules in various chemical reactions.