Periodic Table - Metallic to Non-Metallic Character

This section explains how the metallic character of elements changes across a period in the periodic table. We will discuss the trends in atomic radius, ionization energy, and electronegativity that contribute to this change.

Metallic Character and its Definition

Metallic character refers to an element's ability to lose electrons and form positive ions (cations). Elements with high metallic character are typically good conductors of heat and electricity, are malleable (can be hammered into sheets), and ductile (can be drawn into wires).

Trend Across a Period

Generally, the metallic character of elements decreases as you move from left to right across a period in the periodic table.

Atomic Radius

As you move across a period, the number of protons in the nucleus increases. This leads to a stronger effective nuclear charge experienced by the electrons. The increased effective nuclear charge pulls the electrons closer to the nucleus, resulting in a decrease in atomic radius.

Property	Trend Across a Period
Atomic Radius	Decreases
Ionization Energy	Increases
Electronegativity	Increases

Ionization Energy

Ionization energy is the energy required to remove an electron from an atom. As the effective nuclear charge increases across a period, the electrons are held more tightly. Therefore, it requires more energy to remove an electron, resulting in an increase in ionization energy.

Electronegativity

Electronegativity is the ability of an atom to attract electrons in a chemical bond. Across a period, the increasing effective nuclear charge leads to a stronger attraction for electrons. Consequently, electronegativity increases from left to right.

Metallic to Non-Metallic Transition

1. Left side of a period: Elements tend to be metals. They have low ionization energies, low electronegativities, and are good conductors of electricity.
2. Right side of a period: Elements tend to be non-metals. They have high ionization energies, high electronegativities, and are poor conductors of electricity.
3. Metals in the middle of a period: Exhibit intermediate properties.

Exceptions to the Trend

There are some exceptions to the general trend. For example, group 2 elements (alkaline earth metals) have higher ionization energies than group 1 elements (alkali metals) despite being in the same period. This is due to the increased effective nuclear charge in group 2.

Summary

The metallic character of elements decreases across a period due to the increasing effective nuclear charge, which leads to a decrease in atomic radius, an increase in ionization energy, and an increase in electronegativity. This results in a transition from metallic properties on the left of the period to non-metallic properties on the right.