FBISE 9th Class Chemistry Chapter 4 Structure of Molecules Short Questions Answers

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Class/Subject: 9th Class Chemistry

Chapter Name: Structure of Molecules

Board: Federal  Board

Helpful For:

  • Federal Boards 9th Class Chemistry Annual Examination
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FBISE 9th Class Chemistry Chapter 4 Structure of Molecules Short Questions Answers

What is meant by the Octet rule?

The tendency of atoms to acquire eight electron configurations in their valence shells, when bonding is called the octet rule.

What is meant by the Duplet rule?

The tendency of some atoms to acquire two electrons configurations in their valence shells, when bonding is called the duplet rule.

Define Chemical bond?

The chemical force which keeps the atoms together is commonly described as a chemical bond.

How is an ionic bond formed?

Ionic bonds are formed between two atoms when one atom loses electrons and the other atom gains these electrons. The force of attraction that binds oppositely charged ions is called ionic bonds.

What are the characteristics of the ionic bond?

i. The atom which loses its electrons becomes a positively charged ion, called a cation. The atom which gains these electrons becomes a negatively charged ion called an anion.
ii. These two oppositely charged ions are then held together by the electrostatic forces of attraction to form an ionic bond.
iii. Those compounds in which the constituent ions are held together by ionic bonds are called ionic compounds.
iv. Ionic bond is produced between an element having low ionization energy and others having high electron affinity.
v. The elements of groups 1 and 2 form ionic compounds when reacting with elements of groups 16, 17.

What is a Covalent bond?

A Covalent bond is formed by the mutual sharing of electrons between two atoms is called a Covalent bond.

What is a non-polar covalent bond?

When two identical atoms share electron pairs, both the atoms exert the same force on the shared electron pairs. Such a covalent bond is called a nonpolar covalent bond.

What is a polar covalent bond?

The covalent bond formed between two unlike atoms which differ in their electronegativity is said to be a polar covalent bond.

Define dipole-dipole interactions?

The slightly negative end of a polar molecule is weakly attracted to the slightly positive end of another molecule. Such attracting forces are called dipole-dipole interactions.

Define hydrogen bonding?

The interaction of highly electron-deficient hydrogen and lone pair on a nearby highly electronegative atom such as N, O, or F is called a hydrogen bond. This phenomenon is called hydrogen bonding.

Why noble gases are non-reactive?

The noble gases do have 2 or 8 electrons in their valence shells. It means that all the noble gases have their valence shell filled. Their atoms do not have vacant space in their valence shell to accommodate extra electrons. Therefore, noble gases do not gain, lose or share electrons. That is why they are non-reactive, in ordinary conditions.

What is the mode of reaction of an atom concerning their group?

The mode of reaction of an atom depends upon its number of valence shell electrons. E.g. group I has only 1 electron in its valence shell and group 17 has 7 electrons in its valence shell.

What is meant by a single covalent bond?

When one electron is contributed by each bonded atom, one bond pair is formed and it forms a single covalent bond. It is represented by (-). A few examples of molecules with single covalent bonds are hydrogen, chlorine, hydrochloric acid, methane, etc.

What is meant by a triple covalent bond? Give example.

When each bonded atom contributes three electrons, three bond pairs are involved in bond formation. This type is called a triple covalent bond. It is represented by (≡). A few examples of molecules with triple covalent bonds are nitrogen, ethyne, etc.

What is meant by bond pair?

The electrons that pair up to form a chemical bond are called bond pair electrons.

What is meant by lone pair?

A non-bonded electron pair available on an atom is termed a lone pair of electrons.

Describe Lewis's structure diagram.

The electronic configuration of the valence shells of atoms is shown in small ‘dots’ or ‘crosses’ around the symbol of the element. Each dot or cross represents an electron. This is a standard method of Lewis to describe the electronic configuration of the valence shell of an atom. It is called the Lewis structure diagram.

Define coordinate covalent bond?

A type of covalent bond in which the bond pair of electrons is donated by one bonded atom is only called a coordinate covalent bond.

What is meant by an electronegative atom?

The will attract the bond pair of electrons more strongly than the other one during polar covalent bond formation. This atom will be called a more electronegative atom as compared to the other bonded atom. For example, in HCl molecules, Cl is a more electronegative atom as compared to H atom.

What is meant by a metallic bond?

A bond formed between metal atoms (positively charged ions) due to mobile or free electrons are called a metallic bond.

What is meant by intermolecular forces?

A weak force of attraction formed between two molecules is called intermolecular forces.

What is meant by Van der Waals forces?

All intermolecular forces, which are collectively called Van der Waals forces, are electrical. The result from the attractions of opposite charges may be temporary or permanent.

Why does ice float on the surface of the water?

At 0°C ice has a lesser density (0.0917 g/cm3), than water (0.100 g/cm3), due to which ice floats on the surface of the water.

Write any two properties of ionic compounds?

i. They are made up of positively and negatively charged ions.
ii. They are consist of ions, not molecules.

What is meant by malleability and ductility?

Malleability is the property by which a metal can be drawn into sheets, while ductility is the property by which a metal can be drawn into wires.

Why the covalent compounds of bigger size molecules have high melting points?

Bigger molecules with three-dimensional bonding form covalent crystals which are very stable and hard due to which they have high melting and boiling points.

Why ionic compounds are easily soluble in water?

Water has a high dielectric constant that weakens the attraction between the ions of ionic compounds due to which they are easily soluble in water.

What do you mean by dipole-induced forces?

The positive end of the polar molecule attracts the mobile electrons of the nearby non-polar molecule. In this way, polarity is introduced in the non-polar molecule and both become dipoles. These forces are called dipole-induced forces.

Why is the BF3 electron-deficient?

Boron has the electronic configuration is 1s2 2s2 2p1. This means that it needs five more electrons to be stabilized. In BF3 it shares three electrons, each with one fluorine atom, and thus attains six electrons in it its valence shell. It still retains the tendency to gain two more electrons and therefore remains electron deficient.

What type of elements tend sharing of electrons?

The elements with electronegativity values less than 1.7 show a tendency of sharing electrons between them.

How an atom can accommodate eight electrons in its valence shell?

An atom can accommodate eight electrons in its valence shell in three ways.
i. By giving valence shell electrons (if they are less than four) to other atoms.
ii. By gaining electrons from other atoms (if the valence shell has five or more electrons in it).
iii. By sharing valence electrons with other atoms.

Is there a need for more adhesives?

Yes, there is a need for more adhesive. The adhesive action of points and dyes is developed due to hydrogen bonding.

What is the importance of glues and adhesives in our society?

An adhesive or stick on in a material, usually in a liquid or semi-liquid state, that adheres or bonds items together. Adhesives come from either natural or synthetic sources. The types of material that can be bonded are very fast but they are especially useful for bonding thin materials. Adhesives cure (harden) by either evaporating a solvent or by chemical reactions that occur between two or more constituents.

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