Pakistan Competitive Exam

Part I Concepts and Terms Related to Constituents & Structure

1.Molecule:

The smallest unit of a chemical compound that retains the chemical properties of that compound.

2.Atom:

The basic unit of a chemical element, consisting of a nucleus containing protons and neutrons, with electrons orbiting around it.

3.Element:

A substance composed of atoms with the same atomic number; it cannot be broken down into simpler substances by chemical means.

4.Compound:

A substance composed of two or more elements chemically combined in a fixed ratio.

5.Chemical Bond:

The attractive force that holds atoms or ions together in a compound.

6.Ionic Bond:

A type of chemical bond that involves the transfer of electrons from one atom to another, resulting in the formation of ions.

7.Covalent Bond:

A type of chemical bond that involves the sharing of electron pairs between atoms.

8.Metallic Bond

: A type of chemical bond that occurs in metals, where electrons are delocalized and shared among all the atoms.

9.Crystal Structure:

The arrangement of atoms, ions, or molecules in a crystalline solid.

10.Polymorphism:

The ability of a solid material to exist in more than one form or crystal structure.

11.Amorphous:

A term used to describe materials that lack a definite, regular crystalline structure.

12.Hydrogen Bonding

: A type of weak bond that occurs between a hydrogen atom and an electronegative atom (such as oxygen, nitrogen, or fluorine) in another molecule.

13.Van der Waals Forces:

Weak intermolecular forces between atoms or molecules, including dipole-dipole interactions, London dispersion forces, and hydrogen bonding.

14. Cohesion

: The attraction between molecules of the same substance.

15. Adhesion

: The attraction between molecules of different substances.

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Part II Concepts and Terms Related to Constituents & Structure

1.Hydrophobic:

Repelling, tending not to combine with, or incapable of dissolving in water.

2.Hydrophilic:

Having an affinity for water; readily absorbing or dissolving in water.

3.Constituent:

A component or part of a whole; one of the elements composing a substance.

4.Lattice:

A regular, repeating arrangement of points in three-dimensional space, used to represent the structure of crystals.

5.Polymer:

A large molecule composed of repeating structural units, or monomers, connected by covalent chemical bonds.

6.Monomer:

A molecule that can react together with other monomers to form a larger polymer chain.

7.Isomer:

One of two or more compounds that have the same molecular formula but different structures or spatial arrangements.

8.Chirality:

A property of asymmetry important in various branches of science, describing the "handedness" of molecules and their mirror-image forms.

9.Macromolecule:

A very large molecule, such as a polymer, composed of many smaller structural units linked together.

10.Crystalline:

Having a regular, repeating arrangement of atoms, ions, or molecules in a solid.

11.Cellulose:

A complex carbohydrate that is the main structural component of plant cell walls.

12.Protein Structure:

The complex three-dimensional arrangement of atoms in a protein molecule, crucial for its function.

13.Carbohydrate

: A biomolecule consisting of carbon, hydrogen, and oxygen atoms, including sugars, starches, and cellulose.

14. Lipid:

A biomolecule that includes fats, oils, and other substances that are insoluble in water.

15. Nucleic Acid:

A complex biomolecule, such as DNA or RNA, that is involved in the storage, transmission, and expression of genetic information.

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The Famous Theory Related to Constituents & Structure

Law of Definite Proportions: Proposed by Joseph Proust, this law states that a given chemical compound always contains its component elements in fixed and definite proportions by mass.

Law of Multiple Proportions: Formulated by John Dalton, this law states that when two elements form more than one compound, the masses of one element that combine with a fixed mass of the other element are in ratios of small whole numbers.

Dalton's Atomic Theory: Proposed by John Dalton, the theory consists of several postulates: elements are composed of tiny, indivisible particles called atoms; atoms of the same element are identical, while those of different elements are different; atoms combine in simple, whole-number ratios to form compounds; and chemical reactions involve the combination, separation, or rearrangement of atoms.

Thomson's Plum Pudding Model: Proposed by J.J. Thomson, this model suggested that atoms are composed of a positively charged substance with negatively charged electrons embedded within it, much like plums embedded in a pudding.

Rutherford's Nuclear Model: Formulated by Ernest Rutherford, this model proposed that atoms have a small, dense, positively charged nucleus at their center, with electrons orbiting around it. This discovery was made through the famous gold foil experiment.

Bohr Model of the Atom: Introduced by Niels Bohr, this model refined Rutherford's nuclear model by incorporating the concept of quantized energy levels for electrons. It suggested that electrons move in specific orbits around the nucleus and can jump between these orbits by emitting or absorbing.

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Scientists and Their Discoveries related to Constituents & Structure

Law of Definite Proportions:

Proposed by Joseph Proust, this law states that a given chemical compound always contains its component elements in fixed and definite proportions by mass.

Law of Multiple Proportions:

Formulated by John Dalton, this law states that when two elements form more than one compound, the masses of one element that combine with a fixed mass of the other element are in ratios of small whole numbers.

Dalton's Atomic Theory:

Proposed by John Dalton, the theory consists of several postulates: elements are composed of tiny, indivisible particles called atoms; atoms of the same element are identical, while those of different elements are different; atoms combine in simple, whole-number ratios to form compounds; and chemical reactions involve the combination, separation, or rearrangement of atoms.

Thomson's Plum Pudding Model:

Proposed by J.J. Thomson, this model suggested that atoms are composed of a positively charged substance with negatively charged electrons embedded within it, much like plums embedded in a pudding.

utherford's Nuclear Model:

R Formulated by Ernest Rutherford, this model proposed that atoms have a small, dense, positively charged nucleus at their center, with electrons orbiting around it. This discovery was made through the famous gold foil experiment.

Bohr Model of the Atom

: Introduced by Niels Bohr, this model refined Rutherford's nuclear model by incorporating the concept of quantized energy levels for electrons. It suggested that electrons move in specific orbits around the nucleus and can jump between these orbits by emitting or absorbing energy.