Question

explain how metallic character decreases across a period and increases down a group?

Answer 1

Mettalic character decreases along a period. Metallic character is defined by the ability of atoms to loss electron to attain noble gas state but along a period the tendency of atoms to gain electron increases thus mettalic character decreases
Now along a group tendency of atoms to loss electron increases and thus mettalic character increases

Answer 2

Metallic Character is the tendency of an element to lose electrons and form +vely charged cations.

Down a Group:

-metallic character increases because

• of an increase in the number of shells
• therefore, the distance between the nucleus and valance shell is increased
• so, the forces of attraction between protons in the nucleus and the valance electrons decreases
• effective nuclear charge decreases
• Therefore, it is easier to lose electrons.

For example, in Group-1,

$\begin{array}{||c|c||} \cline{1-2} \bold{Element} & \bold{Electronic \; Configuration} \\ \cline{1-2} Li & 2,1 \\ \cline{1-2} Na & 2,8,1 \\ \cline{1-2} K & 2,8,8,1 \\ \cline{1-2} \end{array}$

Considering these three elements, Potassium is the most metallic and Lithium is the least reactive.

Across a Period:

-metallic character decreases because

• the number of both protons and electrons increases.
• hence, the forces of attraction between them also increases.
• the effective nuclear charge increases.
• Therefore, it is difficult to lose electrons.

For example,

In Period-3

$\begin{array}{|c||c|c|c|c|} \cline{1-5} \bold{Element:} & Na & Mg & S & Cl \\ \cline{1-5} \bold{No. \; of \; p^+} & 11 & 12 & 16 & 17 \\ \cline{1-5} \bold{No. \; of \; e^-} & 11 & 12 & 16 & 17 \\ \cline{1-5} \end{array}$

Here, Sodium is the most metallic and chlorine is the least metallic.