Question

in the modern periodic table how do the following properties change on moving from top to bottom and left to right in a period? 1 valency. 2 atomic size. 3 ionization​

Answer 1

Answer:

On moving from left to right across a period, the atomic radius decreases. With increase in atomic number, the nuclear charge increases but the number of shells in the atoms of all the elements in a period remains the same. ... On moving from left to right across a period, ionisation potential increases.

Explanation:

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Answer 2

Answer:

$(\ 1\ )$  From top to bottom in the periodic table, the valency remains the same, and from left to right in a periodic table, the valency increases and then decreases·

$(\ 2\ )$  From top to bottom in a periodic table, the atomic size is increasing, and from left to right, the atomic radius is decreasing·

$(\ 3\ )$  From top to bottom in a periodic table, the ionization enthalpy decreases, and from left to right in a periodic table, the ionization enthalpy gets increased·

Explanation:

$(\ 1\ )$ Valency

The valency is defined as "the number of electrons needed or lost by an atom to complete its octet"·

From top to bottom in a periodic table, the valency remains the same· Because all elements belong to the same group· So all of them have the same electronic configuration· For example if we take the oxygen family, all elements in the group will have the same  $ns^2\ np^4$ electronic configuration· All elements needs $2\ e^-$ to attain a stable electronic state· So their valency is $2$·

So from top to bottom in the periodic table, the valency remains the same·

From left to right in a periodic table, the valency increases and then decreases· The valency is increasing $1$ to $4$  from the group $1$ to $14$ and then decreasing $3$ to $0$ from the group $15$ to $18.$

$(\ 2\ )$  Atomic Size

It is defined as ''the measure of distance from the nucleus to the outermost shell"·

From top to bottom in a periodic table, the atomic size is increasing· From top to bottom, the electrons are added to an extra shell· So the distance from the nucleus to the outermost shell increases· Effectively, the atomic size also increases·

From left to right in a periodic table, the atomic radius is decreasing· As the atomic number increases from left to right, the electrons are added to the same shell· So the distance from the nucleus to the outermost shell decreases, which effectively decreases the atomic radius of the elements·

$(\ 3\ )$ Ionization Enthalpy

Ionization enthalpy is defined as "the energy required to remove the most loosely bounded electrons from an isolated gaseous state"·

From top to bottom in a periodic table, the ionization enthalpy decreases· Because from top to bottom, the atomic size is increasing· So the effective nuclear charge that experienced by the outermost electron decreases· So it requires only less energy to remove an electron from its shell· So the ionization enthalpy decreases from top to bottom in a group·

From left to right in a periodic table, the ionization enthalpy gets increased· Because here, as the atomic number increases from left to right, the electrons are added to the same shell· So the distance from the nucleus to the outermost shell decreases, which effectively decreases the atomic radius and increases the nuclear charge· The electrons are more towards the nucleus of the atom· So it is difficult to remove an electron from its outermost shell· Hence, the ionization energy is increases from left to right in a period·