Question

Moving towards right in Modern Periodic Table:

• A. Atomic radius and metallic nature increases
• B. Atomic radius and metallic nature decreases
• C. Atomic radius decreases and metallic nature increases
• D. Atomic radius increases and metallic nature decreases

Hint:

Across a period (left to right), atomic radius and metallic character both decrease, while electronegativity increases.

Answer 1

The Correct Option is B

In the modern periodic table, several important trends occur as we move from left to right across a period (row), primarily involving changes in atomic radius and metallic character. \medskip 1.
Decrease in Atomic Radius:

As we move across a period from left to right, the atomic number of each successive element increases by one. This means that each element has one more proton in its nucleus than the previous element.
The increase in the number of protons results in a higher
nuclear charge, which is the total positive charge exerted by the nucleus.
Although electrons are also added with each step, they enter the
same principal energy level (shell) across a period. Because these added electrons do not significantly increase electron shielding within the same shell, the increasing nuclear charge exerts a stronger electrostatic pull on the electrons.
This stronger attraction pulls the electrons closer to the nucleus, leading to a
gradual decrease in atomic radius from left to right.
For example, in Period 2, the atomic radius decreases from lithium (Li) to neon (Ne): \[ \mathrm{Li}>\mathrm{Be}>\mathrm{B}>\mathrm{C}>\mathrm{N}>\mathrm{O}>\mathrm{F}>\mathrm{Ne} \]
2.
Decrease in Metallic Nature:

Metals are generally found on the left side of the periodic table and tend to
lose electrons easily to form positive ions (cations).
Moving from left to right across a period, elements become less inclined to lose electrons. Instead, they tend to
gain or share electrons in chemical reactions.
This change corresponds to a gradual shift from metallic behavior to
non-metallic behavior.
The tendency to gain electrons and form negative ions (anions) increases across the period.
For example, sodium (Na) on the far left of Period 3 is a highly metallic element that readily loses one electron, whereas chlorine (Cl) near the right side is a non-metal that readily gains one electron.
This results in a
decrease in metallic character and a corresponding
increase in non-metallic character as we move from left to right.
3.
Underlying Cause and Effect:

These trends are fundamentally due to the
effective nuclear charge felt by the outermost electrons.
Because electrons added across the same period do not significantly shield each other from the increasing positive charge of the nucleus, the effective nuclear charge increases.
Consequently, electrons are held more tightly, resulting in smaller atomic sizes and a decreased tendency to lose electrons (which characterizes metals).
4.
Additional Trends:

Along with atomic radius and metallic character, other properties such as
ionization energy (energy required to remove an electron) and
electronegativity (tendency to attract electrons) also change across a period.
Ionization energy generally
increases across a period due to the stronger hold of the nucleus on electrons.
Electronegativity also
increases, reflecting the growing tendency of atoms to attract electrons in a bond.
\medskip In summary, across a period in the modern periodic table, the atomic radius decreases and metallic character diminishes from left to right. These changes are due to the increasing nuclear charge pulling electrons closer, thereby increasing the attraction between the nucleus and electrons and altering the chemical behavior of the elements.