9th Class Chapter 3 Chemistry Long Questions

The unit of atomic radius picometers equal to 10 -¹² meters. When we move from left to right in a period, although atomic number increases, yet the size of atomic number, yet the size of atoms decreases gradually increase of effective nuclear charge which increase due to the addition of protons . This force pulls down or contracts the outermost shell towards the nucleas.

The size of atoms on their radiusincrease from top to bottom in a group. It is because a new shell of electrons is added up in the successive period, which decreases the effective nuclear charge.

The trend of atomic size of transition elements has slight variationwhen we consider this series in a period. The atomic size of the elements firstreduces or atom contracts and then there is increase in it when we move from left to right in 4th period.

The unit of inoizationenergy is Kilojoules per mole (kJ/mol).

In a period the value of ionization energy increases . It is because the size of atoms resucesand valence electron are held strongly by the electrostatic force of nucleus

In the group more and more shells lie between the valence shell and the nucleusof the atom , these shells reduces the electrons present in the outermost shell

The trend of electronegativityis same as of the ionization energy and electron affinity. It increases in a period because higher 7_effshortensdistance from the nucleas of the shared pair of electrons.

This enhance the power to attract the shared pair of electron.

It gradullydecrease down in a group because size of the atom increases . Thus attraction for the shared pair of electrons weakens.

2- A group contains main elements and B group contains transition elements

3- Metalloids are located to the boundary between metals and nonmetals

4- The period that contains only H and He has the number 1.

In periodic table group 1 consist of hydrogen, Lithium, Sodium, Potassium, rubidium, cesium and francium. Although elements of a group do not have continuoslyincreasing atomic number, yet they have similar electronic configuration in their valence shell . This is the reason elements of a group are called a family The group 1 and 2 and 13 to 17 contains the normal elements `d' sub-shells is in the process of completion.

The horizontal rows of elements in the periodic table are called period. The elements in a period have continuously increasing atomic number i.e. continuously changing electronic configuration along a period. As a result properties of elements in a periods are continuously changing. The number of valence electrons decides the position of an element in a period. For example, elements which have 1 electron in their valance shell occupies the left most position in the respective periods , such as alkali metals. Similarly, the elements having 8 electrons in their valences shells such as Nobel gases always occupy the right most position in the respective periods.

The vertical columns in the periodic table called groups. These groups are numbered from left ot right as 1 to 18. the element in a group don not have continuously increasing atomic numbers. Rather the atomic numbers of elements in a group increase with irregular gaps. But the elements of a group have similar electronic configuration i.e. same number of electrons are present in their Valence shells . For example, the first group elements have only 1 electron in their valence shells . Similarly group 2 elements have 2 electrons in their valence shells. it is the reason due to which elements of a group have similar chemical properties.

Definition: properties of elements are period function of their atomic numbers.

Definition: on the basis of completion of particular sub-shell , all the elements with similar sub-shell electronic configuration are preferred as a block of element

Types of periods:

Explanation: group 1 consist of hydrogen , lithium, sodium, potassium, rubidium, cesium and francium. Although elements of a group don not ace continuously increasing atomic number, yet they have similar electronic configuration i their valence shells. that is the reason elements of a group are also called a family. For example, all the group 1 elements have one electron in their valence shells, they are given the family name of alkali metals.

The group 1 and 2 and 13 to 17 contain the normal elements. In the normal elements, all the inner shells are completely filled with electrons, only the outer most shells are incomplete. For example, group 17 elements (halogens) have 7 electrons in their valence ( outermost) shell. The group 3 to 12 are called transition elements. In these elements d subshell is in the process of completion.

Definition: half of the distance between nuclei of the two bonded atoms is referred as atomic radius.

Units: the atomic radius of atoms is measured in pm.

Explanation with example: the distance between nuclei of two carbon atoms in its elemental form is 154 pm. Its means its half 77 pm is the radius of carbon atom

Explanation: the amount of energy needed to remove successive electrons present in an atom increase.

First ionization energy: if there is only 1 electron in the valence shell, the energy required to remove it will be called first ionization energy.

Explanation: affinity means attraction. Therefore, electron affinity means tendency of an atom to accept an electron to form an anion. For example , the electron affinity of fluorine is -328 KJmol^-1 i.e. one mole atom of fluorine released 328Kj of energy to form one mole of fluoride ions.

Explanation: it is an important property especially when covalent type of bonding of elements is under consideration.