Substance and it's Nature | General Awareness for SSC CGL PDF Download

Introduction

Matter is the fundamental substance that makes up the universe. Everything we see, touch, and experience is composed of matter. Understanding the nature of matter is crucial for students preparing for competitive exams like IIT-JEE, as it forms the basis of numerous concepts in chemistry and physics. This article aims to provide a comprehensive and detailed explanation of matter and its nature, presented in a student-friendly manner.

Definition and Classification of Matter

What is Matter?

Matter is defined as anything that has mass and occupies space. It is composed of particles such as atoms and molecules, which are the building blocks of all physical substances. The study of matter involves exploring its properties, behavior, and interactions under various conditions.

States of Matter

Matter exists in three primary states: solid, liquid, and gas. Each state has distinct characteristics based on the arrangement and movement of particles.

Solid State:

• Particles are closely packed in a fixed, orderly arrangement.
• Solids have a definite shape and volume.
• The intermolecular forces are strong, resulting in limited particle movement.
• Examples: Ice, iron, wood.

Liquid State:

• Particles are closely packed but not in a fixed arrangement.
• Liquids have a definite volume but take the shape of their container.
• The intermolecular forces are weaker than in solids, allowing particles to move freely.
• Examples: Water, oil, alcohol.

Gaseous State:

• Particles are far apart and move freely.
• Gases have neither a definite shape nor volume; they expand to fill their container.
• The intermolecular forces are very weak, resulting in high particle movement.
• Examples: Oxygen, nitrogen, carbon dioxide.

Other States of Matter

In addition to the primary states, matter can also exist in other forms under extreme conditions:

Plasma:

• A high-energy state where atoms are ionized (electrons are separated from nuclei).
• Common in stars, including the sun, and certain laboratory conditions.
• Examples: Lightning, neon signs.

Bose-Einstein Condensate (BEC):

• A state of matter formed at temperatures close to absolute zero.
• Particles occupy the same space and quantum state, acting as a single quantum entity.
• Examples: Superfluid helium.

Properties of Matter

Matter possesses a variety of properties that can be categorized into physical and chemical properties.

Physical Properties

Physical properties are characteristics that can be observed or measured without changing the composition of the substance. These include:

Mass and Volume:

• Mass is the amount of matter in a substance, measured in kilograms or grams.
• Volume is the amount of space occupied by the substance, measured in liters or cubic meters.

Density:

• Density is the mass per unit volume of a substance.
• Formula: Density (ρ) = Mass (m) / Volume (V).

Melting and Boiling Points:

• The melting point is the temperature at which a solid turns into a liquid.
• The boiling point is the temperature at which a liquid turns into a gas.

Solubility:

• Solubility is the ability of a substance to dissolve in a solvent.
• It varies with temperature and pressure.

Conductivity:

• Electrical conductivity is the ability of a substance to conduct electricity.
• Thermal conductivity is the ability to conduct heat.

Chemical Properties

Chemical properties describe a substance’s ability to undergo chemical changes and form new substances. These include:

Reactivity:

• Reactivity refers to how readily a substance undergoes chemical reactions.
• Highly reactive substances, like sodium, react quickly with other materials.

Combustion:

• Combustion is the process of burning in the presence of oxygen, producing heat and light.
• Examples: Burning of wood, gasoline.

Oxidation:

• Oxidation is the reaction of a substance with oxygen.
• Examples: Rusting of iron, tarnishing of silver.

Acidity and Basicity:

• Acidity is the tendency of a substance to donate hydrogen ions (H+).
• Basicity is the tendency to donate hydroxide ions (OH-).
• Measured using the pH scale.

The Atomic Theory

Historical Development

The concept of matter has evolved over centuries, with significant contributions from various scientists:

Democritus (460-370 BC):

• Proposed that matter is composed of indivisible particles called “atomos”.

John Dalton (1766-1844):

• Developed the modern atomic theory.
• Stated that atoms are the smallest units of matter and cannot be created or destroyed.

J.J. Thomson (1856-1940):

• Discovered the electron using the cathode ray experiment.
• Proposed the “plum pudding” model, where electrons are embedded in a positively charged sphere.

Ernest Rutherford (1871-1937):

• Conducted the gold foil experiment.
• Proposed the nuclear model of the atom, with a dense, positively charged nucleus surrounded by electrons.

Niels Bohr (1885-1962):

• Introduced the Bohr model, where electrons orbit the nucleus in fixed energy levels.

Erwin Schrödinger (1887-1961) and Werner Heisenberg (1901-1976):

• Developed quantum mechanics.
• Introduced the concept of electron probability clouds and the uncertainty principle.

Modern Atomic Theory

The modern atomic theory states that:

• Atoms are the basic units of matter, consisting of a nucleus (protons and neutrons) and electrons.
• Electrons occupy orbitals around the nucleus, defined by quantum numbers.
• Atoms of the same element have the same number of protons but can have different numbers of neutrons (isotopes).
• Chemical reactions involve the rearrangement of electrons, not changes in the nucleus.

Elements, Compounds, and Mixtures

Elements

An element is a pure substance consisting of only one type of atom. Elements cannot be broken down into simpler substances by chemical means. They are classified based on their properties:

Metals:

• Good conductors of heat and electricity.
• Malleable, ductile, and have a shiny appearance.
• Examples: Gold, silver, copper.

Non-metals:

• Poor conductors of heat and electricity.
• Brittle and lack metallic luster.
• Examples: Oxygen, sulfur, carbon.

Metalloids:

• Have properties intermediate between metals and non-metals.
• Examples: Silicon, germanium.

Compounds

A compound is a substance formed when two or more elements chemically combine in a fixed ratio. Compounds have different properties from the elements that form them. Examples include water (H₂O), carbon dioxide (CO₂), and sodium chloride (NaCl).

Mixtures

A mixture is a combination of two or more substances that retain their individual properties. Mixtures can be homogeneous or heterogeneous:

Homogeneous Mixtures:

• Uniform composition throughout.
• Also called solutions.
• Examples: Saltwater, air.

Heterogeneous Mixtures:

• Non-uniform composition.
• Different components can be observed.
• Examples: Sand and iron filings, oil and water.

Atomic and Molecular Structure

Atomic Structure

Atoms consist of a nucleus containing protons and neutrons, surrounded by electrons in various energy levels or orbitals.

Nucleus:

• Contains protons (positively charged) and neutrons (neutral).
• Accounts for most of the atom’s mass.

Electrons:

• Negatively charged particles.
• Occupy orbitals arranged in shells around the nucleus.

Molecular Structure

Molecules are formed when atoms bond together. The type and arrangement of these bonds determine the molecule’s properties.

Covalent Bonds:

• Formed by the sharing of electrons between atoms.
• Examples: H₂, O₂, H₂O.

Ionic Bonds:

• Formed by the transfer of electrons from one atom to another, resulting in positively and negatively charged ions.
• Examples: NaCl, MgO.

Metallic Bonds:

• Formed between metal atoms, where electrons are free to move throughout the structure.
• Examples: Copper, iron.

The Periodic Table

Development of the Periodic Table

The periodic table organizes elements based on their atomic number, electron configuration, and recurring chemical properties. It was developed through contributions from scientists like:

Dmitri Mendeleev (1834-1907):

• Created the first periodic table, arranging elements by atomic mass.
• Predicted the existence of undiscovered elements.

Henry Moseley (1887-1915):

• Arranged elements by atomic number, leading to the modern periodic table.

Structure of the Periodic Table

The periodic table is divided into periods (rows) and groups (columns):

Periods:

• Horizontal rows numbered 1 to 7.
• Elements in the same period have the same number of electron shells.

Groups:

• Vertical columns numbered 1 to 18.
• Elements in the same group have similar chemical properties due to the same number of valence electrons.

Periodic Trends

The periodic table exhibits trends in various properties of elements:

Atomic Radius:

• Decreases across a period (left to right) due to increasing nuclear charge.
• Increases down a group due to the addition of electron shells.

Ionization Energy:

• Increases across a period due to higher nuclear charge.
• Decreases down a group due to increased distance from the nucleus.

Electronegativity:

• Increases across a period as atoms more strongly attract electrons.
• Decreases down a group as atoms have a weaker pull on electrons.

Metallic and Non-metallic Character:

• Metallic character decreases across a period and increases down a group.
• Non-metallic character shows the opposite trend.

Chemical Reactions and Equations

Types of Chemical Reactions

Chemical reactions involve the rearrangement of atoms to form new substances. Major types include:

Combination Reactions:

• Two or more substances combine to form a single product.
• A + B → AB.

Decomposition Reactions:

• A single compound breaks down into two or more products.
• AB → A + B.

Displacement Reactions:

• An element displaces another in a compound.
• A + BC → AC + B.

Double Displacement Reactions:

• Exchange of ions between two compounds.
• AB + CD → AD + CB.

Combustion Reactions:

• A substance reacts with oxygen, producing heat and light.
• Hydrocarbon + O₂ → CO₂ + H₂O.

Balancing Chemical Equations

Balancing chemical equations ensures the conservation of mass. Each side of the equation must have the same number of atoms of each element. Steps include:

1. Write the unbalanced equation.
2. Count the number of atoms of each element on both sides.
3. Use coefficients to balance the atoms.
4. Check that all atoms are balanced and adjust if necessary.

Stoichiometry

Stoichiometry involves calculations based on balanced chemical equations. It includes:

Mole Concept:

• A mole is 6.022 × 10²³ particles of a substance.
• Molar mass is the mass of one mole of a substance.

Calculations:

• Use the balanced equation to determine the mole ratio of reactants and products.
• Convert moles to grams or liters as required.

Conclusion

Understanding the nature of matter is essential for mastering chemistry. This comprehensive overview covers the definition, classification, properties, atomic theory, periodic table, and chemical reactions, providing a solid foundation for students preparing for competitive exams like IIT-JEE. Through studying these concepts, students can develop a deeper appreciation for the complexity and beauty of the material world.