Chemistry Periodic Trends

Electron Gain Enthalpy

• Electron gain enthalpy generally becomes more negative across a period as we move from left to right.
• Electron gain enthalpy becomes less negative down a group.
• Chlorine has the most negative electron gain enthalpy, while phosphorus has the least negative electron gain enthalpy.

Electronegativity

• Electronegativity is a qualitative measure of an atom's ability to attract shared electrons to itself in a chemical compound.
• Electronegativity is not a measurable quantity, but numerical scales have been developed, such as the Pauling scale, Mulliken-Jaffe scale, and Allred-Rochow scale.
• The Pauling scale is the most widely used, with a value of 4.0 assigned to fluorine.

Classification of Elements and Periodicity in Properties

The Main Group Elements

• The main group elements include Group 0 elements: He, Ne, Ar, Kr, Xe, and Rn.

Electronegativity

• Electronegativity is the ability of an atom to attract electrons, and its value varies depending on the element to which it is bound.
• Electronegativity is not a measurable quantity, but it helps predict the nature of the force that holds atoms together.

Trends in Electronegativity

• Electronegativity generally increases across a period from left to right (e.g., from lithium to fluorine).
• Electronegativity decreases down a group (e.g., from fluorine to astatine).
• Electronegativity can be related to atomic radii, which decrease across each period and increase down each group.
• As atomic radius decreases, the attraction between outer electrons and the nucleus increases, resulting in increased electronegativity.

Electronegativity Values

• Table 3.8(a) shows electronegativity values on the Pauling scale across periods.
• Table 3.8(b) shows electronegativity values on the Pauling scale down a family.
• Electronegativity values decrease with increasing atomic radii down a group.

Relationship between Electronegativity and Atomic Radius

• The trend in electronegativity is similar to that of ionization enthalpy.
• Non-metallic elements have a strong tendency to exhibit non-metallic properties.

Explore the trends of electron gain enthalpy and electronegativity across periods and groups in the periodic table.