CLASS 6 CHEMISTRY CHAPTER 2

Elements

• Pure substance made up of identical atoms.
• Cannot be broken down into simpler substances.
• Basic unit of matter.
• About 118 elements have been discovered.

Atomicity

• Number of atoms present in one molecule of the element.

The Periodic Table

• Elements are arranged in increasing order of their atomic number.

Atomic Number

• Number of protons or electrons in an atom of an element.

Atom

• Basic unit of an element.
• Contains a nucleus with protons and neutrons, surrounded by electrons.

Metallic Elements

• Have lustre, malleable, ductile, and good conductors of heat and electricity.
• Examples include potassium, sodium, zinc, and copper.

Non-Metallic Elements

• Lack lustre, not malleable or ductile, and poor conductors of heat and electricity.
• Examples include carbon, sulfur, and phosphorus.

Metalloids

• Elements with properties of both metals and non-metals.
• Example is boron.

Noble Gases

• Unreactive, inert elements present in trace amounts in air.
• Examples include helium, neon, and argon.

Symbol

• Short form or abbreviated name of an element.
• Used to distinguish one element from another.
• Example: symbol of sulfur is ‘S’.

Molecule

• Formed by the combination of atoms of the same or different elements.
• Smallest particle of a pure substance that can exist independently and retain its properties.
• Example: diatomic molecule of nitrogen ‘N₂’.

Compounds

• Pure substance made up of two or more different elements combined in a fixed proportion.
• Example: hydrogen and oxygen form the compound water (H₂O).

Characteristics of Compounds

• Elements are present in a definite proportion.
• Compounds have a definite set of properties, different from the elements within them.
• Elements within a compound cannot be separated by physical methods.

Chemical Formula

• Representation of a substance using symbols.
• Example: chemical formula of sodium chloride is ‘NaCl’.

Mixture

• Impure substance formed by combining two or more pure substances in any ratio.

Separation Techniques:

• Sieving: Separates large particles from smaller ones. (e.g. bran from wheat flour)
• Magnetic Separation: Separates magnetic particles from non-magnetic ones using a magnet. (e.g. iron from plastic)
• Sublimation: Used to separate sublimable (turn directly into vapor on heating) substances from non-sublimable ones. (e.g. ammonium chloride from a mixture of ammonium chloride & sodium chloride)
• Filtration: Separates insoluble solid particles from a liquid using a filter paper. (e.g. chalk from water)
• Sedimentation: Insoluble solid particles settle down by gravity in a liquid. (e.g. sand settles down in water)
• Evaporation: Liquid component evaporates from a mixture leaving behind the solid component. (e.g. salt from seawater)

Important Chemical Formulas

• Gases:

  • Hydrogen (H₂)
  • Nitrogen (N₂)
  • Oxygen (O₂)
  • Chlorine (Cl₂)
  • Hydrogen chloride (HCl)
  • Ammonia (NH₃)
  • Carbon monoxide (CO)
  • Carbon dioxide (CO₂)
  • Nitrous oxide (N₂O)
  • Dinitrogen oxide (N₂O)
  • Nitrogen dioxide (NO₂)
  • Sulfur dioxide (SO₂)
  • Nitrogen monoxide (NO)

• Acids:

  • Hydrochloric acid (HCl)
  • Nitric acid (HNO₃)
  • Sulphuric acid (H₂SO₄)
  • Carbonic acid (H₂CO₃)

• Bases:

  • Potassium hydroxide (KOH)
  • Sodium hydroxide (NaOH)
  • Calcium hydroxide (Ca(OH)₂)
  • Zinc hydroxide (Zn(OH)₂)

• Salts:

  • Potassium nitrate (KNO₃)
  • Zinc sulphate (ZnSO₄)
  • Calcium carbonate (CaCO₃)
  • Ammonium chloride (NH₄Cl)

• Metallic Oxides & Sulphides:

  • Zinc oxide (ZnO)
  • Calcium oxide (CaO)
  • Magnesium sulphide (MgS)
  • Calcium sulphide (CaS)

Chemical Equations:

• Shorthand representation of a chemical reaction.
• Reactants: Substances that participate in the reaction.
• Products: Substances formed as a result of the reaction.
• The arrow (→) indicates the direction of the reaction.
• [A] Indicates heat applied.

Examples of Chemical Equations:

• Zinc and Sulphur:
  • Word Equation: Zinc + Sulphur → Zinc sulfide
• Sodium Hydroxide and Hydrochloric Acid:
  • Word Equation: Sodium hydroxide + Hydrochloric acid → Sodium chloride + Water
• Zinc and Sulphuric Acid:
  • Word Equation: Zinc + Sulphuric acid → Zinc sulphate + Hydrogen
  • Molecular Equation: Zn + H₂SO₄ (dil.) → ZnSO₄ + H₂ (g)

Elements

• An element is a pure substance made up of identical atoms
• It cannot be broken down into simpler substances
• There are about 118 elements discovered
• Scientists needed to arrange elements systematically, leading to the creation of the Periodic Table
• Atomicity refers to the number of atoms in a molecule of an element

The Periodic Table

• Elements are arranged in increasing order of their atomic number
• The atomic number represents the number of protons or electrons in an atom

Atom

• The basic unit of an element
• Contains a nucleus with protons (positively charged) and neutrons (neutral)
• Orbits surrounding the nucleus contain electrons (negatively charged)

Metallic Elements

• Examples: potassium, sodium, zinc, copper
• Characterized by luster, malleability (can be beaten into sheets), ductility (can be drawn into wires), and good conductivity of heat and electricity

Non-Metallic Elements

• Examples: carbon, sulfur, phosphorus
• Lack luster, are non-malleable and non-ductile, and are poor or non-conductors of heat and electricity

Metalloids

• Elements exhibiting properties of both metals and non-metals
• Example: boron

Noble Gases

• Unreactive, inert elements
• Present in traces in the air
• Examples: helium, neon, argon

Symbol

• A short form or abbreviated name of an element
• Distinguishes one element from another
• Example: the symbol for sulfur is "S"

Molecule

• Formed by combining atoms of the same element or different elements
• The smallest particle of a pure substance that can exist independently and retain its physical and chemical properties
• Example: diatomic molecule of nitrogen "N₂"

Compounds

• Pure substances made up of two or more different elements combined in a fixed proportion
• Example: hydrogen and oxygen combine to form water (H₂O)
• The elements in a compound are present in a definite proportion (e.g., 2 atoms of hydrogen combine with 1 atom of oxygen to form 1 molecule of water).
• Compounds possess a unique set of properties distinct from the properties of the individual elements they contain.
• Elements in a compound cannot be separated by physical methods (e.g., iron cannot be separated from iron sulfide (FeS) using a magnet).

Chemical Formula

• A representation of a substance (element or compound) using symbols
• Example: the chemical formula for sodium chloride is "NaCl"

Mixture

• An impure substance formed by combining two or more pure substances in any ratio
• Components of the mixture can be separated using various physical methods

Separation Techniques

• Sieving: Separating large particles from smaller ones (e.g., bran from wheat flour)
• Magnetic Separation: Separating magnetic particles from non-magnetic particles using a magnet (e.g., iron from plastic)
• Sublimation: Separation of sublimable substances from non-sublimable substances by heating the mixture (e.g., ammonium chloride from a mixture of ammonium chloride and sodium chloride).
• Filtration: Separating insoluble solid particles from a solid-liquid mixture using filter paper (e.g., chalk from water)
• Sedimentation: Settling down of insoluble solid particles in a solid-liquid mixture due to gravity (e.g., sand settles down in water)
• Evaporation: Removing a liquid from a mixture by vaporizing it, leaving behind the solid component (e.g., evaporating sea water to obtain salt)

Chemical Formulas of Important Compounds

• Gases:
  • H₂ (Hydrogen)
  • N₂ (Nitrogen)
  • O₂ (Oxygen)
  • Cl₂ (Chlorine)
  • HCl (Hydrogen chloride)
  • NH₃ (Ammonia)
  • CO (Carbon monoxide)
  • CO₂ (Carbon dioxide)
  • NO (Nitrous oxide)
  • N₂O (Dinitrogen oxide)
  • NO₂ (Nitrogen dioxide)
  • SO₂ (Sulfur dioxide)
  • CO (Carbon monoxide)
  • NO (Nitrogen monoxide [nitric oxide])
• Acids:
  • HCl (Hydrochloric acid)
  • HNO₃ (Nitric acid)
  • H₂SO₄ (Sulfuric acid)
  • H₂CO₃ (Carbonic acid)
• Bases:
  • KOH (Potassium hydroxide)
  • NaOH (Sodium hydroxide)
  • Ca(OH)₂ (Calcium hydroxide)
  • Zn(OH)₂ (Zinc hydroxide)
• Salts:
  • KNO₃ (Potassium nitrate)
  • ZnSO₄ (Zinc sulfate)
  • CaCO₃ (Calcium carbonate)
  • NH₄Cl (Ammonium chloride)
• Metallic Oxides & Sulfides:
  • ZnO (Zinc oxide)
  • CaO (Calcium oxide)
  • MgS (Magnesium sulfide)
  • CaS (Calcium sulfide)

Chemical Reactions and Equations

• Chemical Equation: A concise representation of a chemical change.
• Reactants: Substances that participate in the chemical reaction.
• Products: Substances that are formed as a result of the chemical reaction.
• Arrow (→): Indicates the direction of the reaction.
• Heat (Δ or A): Represents heat being applied to initiate the reaction.
• Example:
  • Word Equation: Sodium hydroxide + Hydrochloric acid → Sodium chloride + Water
  • Molecular Equation: NaOH + HCl → NaCl + H₂O
• Simple Reaction: Zinc (Zn) + Dilute Sulfuric acid (H₂SO₄) → Zinc Sulfate (ZnSO₄) + Hydrogen (H₂)

Elements

• Pure substances made up of identical atoms.
• Cannot be broken down into simpler substances.
• Basic unit of matter.
• Approximately 118 elements have been discovered.
• Arranged in the periodic table in increasing order of atomic number.

Periodic Table

• A table where elements are arranged in increasing order of atomic number.
• Atomic number of an element represents the number of protons or electrons in its atom.

Atom

• The basic unit of an element.
• Contains a nucleus with protons (positively charged) and neutrons (neutral).
• Orbits around the nucleus contain negatively charged particles called electrons.

Metallic Elements

• Examples: potassium, sodium, zinc, copper.
• Possess luster, malleability (can be beaten into sheets), ductility (can be drawn into wires), and are good conductors of heat and electricity.

Non-metallic Elements

• Examples: carbon, sulfur, phosphorus.
• Lack luster, are non-malleable, non-ductile, and are poor or non-conductors of heat and electricity.

Metalloids

• Elements exhibiting properties of both metals and non-metals.
• Example: boron.

Noble Gases

• Unreactive, inert elements found in trace amounts in the air.
• Examples: helium, neon, argon.

Symbol

• A short form representation of an element, distinguishing one element from another.
• Example: the symbol for sulfur is ‘S’.

Molecule

• Formed when atoms of the same or different elements combine.
• The smallest particle of a pure substance that can exist independently, retaining the substance's physical and chemical properties.
• Example: diatomic molecule of nitrogen, ‘N₂’.

Compounds

• Pure substances made up of two or more different elements combined in a fixed proportion.
• Example: water (H₂O) formed from hydrogen and oxygen.

Characteristics of Compounds

• Elements in a compound are present in a definite proportion.
• Compounds have a distinct set of properties different from their constituent elements.
• Elements in a compound cannot be separated by physical methods.

Chemical Formula

• Represents a substance (element or compound) using symbols.
• Example: the chemical formula of sodium chloride is ‘NaCl’.

Mixture

• An impure substance formed by combining two or more pure substances in any ratio.
• Components can be separated by physical methods.

Separation Techniques

• Sieving: Separates large-sized particles from smaller ones. (Example: bran from wheat flour)
• Magnetic Separation: Separates magnetic particles from non-magnetic particles using a magnet. (Example: iron from plastic)
• Sublimation: Separates sublimable substances from non-sublimable ones by heating the mixture. (Example: ammonium chloride from a mixture of ammonium chloride and sodium chloride)
• Filtration: Separates insoluble solid particles from a solid-liquid mixture using a filter paper or filtration apparatus. (Example: chalk from water)
• Sedimentation: Allows insoluble solid particles to settle down in a solid-liquid mixture by gravity. (Example: sand settles down in water)
• Evaporation: Evaporates the liquid in a mixture leaving behind the solid component. (Example: evaporation of seawater leaves behind salt)

Chemical Formulas of Important Compounds

• Gases: H₂ (Hydrogen), N₂ (Nitrogen), O₂ (Oxygen), Cl₂ (Chlorine), HCl (Hydrogen chloride), NH₃ (Ammonia), CO (Carbon monoxide), CO₂ (Carbon dioxide), NO (Nitrous oxide), N₂O (Dinitrogen oxide), NO₂ (Nitrogen dioxide), SO₂ (Sulfur dioxide)
• Acids: HCl (Hydrochloric acid), HNO₃ (Nitric acid), H₂SO₄ (Sulfuric acid), H₂CO₃ (Carbonic acid)
• Bases: KOH (Potassium hydroxide), NaOH (Sodium hydroxide), Ca (OH)₂ (Calcium hydroxide), Zn (OH)₂ (Zinc hydroxide)
• Salts: KNO₃ (Potassium nitrate), ZnSO₄ (Zinc sulphate), CaCO₃ (Calcium carbonate), NH₄Cl (Ammonium chloride)
• Metallic Oxides & Sulfides: ZnO (Zinc oxide), CaO (Calcium oxide), MgS (Magnesium sulphide), CaS (Calcium sulphide)

Chemical Equations

• Representing a chemical reaction: A chemical equation is a shorthand form representing the result of a chemical change.
• Components of a chemical equation:
  • Reactants: Substances that participate in the chemical reaction.
  • Products: Substances formed as a result of the chemical reaction.
  • Arrow (→): Indicates the direction of the reaction.
  • [A]: Indicates heat is applied.

Examples of Chemical Equations

• Simple reaction between zinc and sulfur:
  • Word equation: Zinc + Sulfur → Zinc sulfide
  • Molecular equation: Zn + S [A] → ZnS
• Simple reaction between sodium hydroxide and dilute hydrochloric acid:
  • Word equation: Sodium hydroxide + Hydrochloric acid → Sodium chloride + Water
  • Molecular equation: NaOH + HCl [dil.] → NaCl + H₂O
• Simple reaction between zinc and dilute sulfuric acid:
  • Word equation: Zinc + Sulfuric acid → Zinc sulfate + Hydrogen
  • Molecular equation: Zn + H₂SO₄ [dil.] → ZnSO₄ + H₂ [g]

Elements

• A pure substance made up of identical atoms.
• Cannot be broken down into simpler substances.
• The basic unit of matter.
• Around 118 elements discovered to date.
• Arranged in a table known as the Periodic Table.
• Atomicity refers to the number of atoms in a molecule of an element.
• Elements are arranged in the Periodic Table by increasing atomic number.

Atomic Number

• Represents the number of protons or electrons in an atom of an element.
• Protons and electrons are equal in number.
• For example, Hydrogen has one electron and an atomic number of 1, placing it first in the table.

Atom

• The basic unit of an element.
• May not exist independently.
• Contains a nucleus with positively charged protons and neutral neutrons.
• Orbits surrounding the nucleus are home to negatively charged electrons.

Metallic Elements

• Possess luster, meaning they are shiny.
• Malleable, capable of being beaten into sheets.
• Ductile, capable of being drawn into wires.
• Good conductors of heat and electricity.
• Examples include Potassium, Sodium, Zinc, and Copper.

Non-metallic Elements

• Lack luster.
• Non-malleable and non-ductile.
• Poor conductors or non-conductors of heat and electricity.
• Examples include Carbon, Sulfur, and Phosphorus.

Metalloids

• Exhibit properties of both metals and non-metals.
• Example: Boron

Noble Gases

• Unreactive and inert elements found in traces in the air.
• Examples include Helium, Neon, and Argon.

Symbol

• A short form or abbreviation representing an element, distinguishing it from others.
• For example, the symbol for sulfur is 'S.'

Molecule

• Formed when atoms of the same or different elements combine.
• Smallest particle of a pure substance that can exist independently while retaining its properties.
• For example, a diatomic molecule of nitrogen 'N₂.'

Compounds

• A pure substance made up of two or more different elements combined in a fixed proportion.
• For example, hydrogen and oxygen combine to form water (H₂O).

Characteristics of Compounds

• Elements in a compound are present in a definite proportion.
• For example, two hydrogen atoms combine with one oxygen atom to form one molecule of water.
• Compounds have a specific set of properties different from the elements they contain.
• Elements in a compound cannot be separated by physical means.
• For example, iron cannot be separated from iron sulfide using a magnet.

Chemical Formula

• Represents a substance, whether an element or compound, using symbols.
• For example, the chemical formula for sodium chloride is 'NaCl'.

Mixture

• An impure substance formed by combining two or more pure substances in any ratio.

Separation Techniques

• Sieving: Separates large particles from smaller ones. (e.g., bran from wheat flour).
• Magnetic Separation: Separates magnetic particles from non-magnetic ones using a magnet. (e.g., iron from plastic).
• Sublimation: Separates sublimable substances from non-sublimable ones by heating the mixture. (e.g., ammonium chloride from a mixture of ammonium chloride and sodium chloride).
• Filtration: Separates insoluble solid particles from a solid-liquid mixture using a filter paper or other apparatus. (e.g., chalk from water).
• Sedimentation: Insoluble solid particles settle down by gravity in a solid-liquid mixture. (e.g., sand settles down in water).
• Evaporation: The process of evaporating a liquid from a mixture, leaving behind the solid component. (e.g., evaporation of seawater leaves behind salt).

Important Chemical Formulae (Examples)

Gases

• H₂ (Hydrogen)
• N₂ (Nitrogen)
• O₂ (Oxygen)
• Cl₂ (Chlorine)
• HCl (Hydrogen chloride)
• NH₃ (Ammonia)
• CO (Carbon monoxide)
• CO₂ (Carbon dioxide)
• NO (Nitrous oxide)
• N₂O (Dinitrogen oxide)
• NO₂ (Nitrogen dioxide)
• SO₂ (Sulfur dioxide)

Acids

• Derived from plants (e.g., citric acid from oranges) or minerals (e.g., hydrochloric acid [HCl] from sodium chloride).
• Typically sour in taste.

Examples of Acids

• HCl (Hydrochloric acid)
• HNO₃ (Nitric acid)
• H₂SO₄ (Sulfuric acid)
• H₂CO₃ (Carbonic acid)

Bases

• Typically hydroxides (or oxides) of metals.
• Bitter in taste.
• Example: Sodium hydroxide (NaOH), which is the hydroxide of the metal Sodium (Na).

Examples of Bases

• KOH (Potassium hydroxide)
• NaOH (Sodium hydroxide)
• Ca(OH)₂ (Calcium hydroxide)
• Zn(OH)₂ (Zinc hydroxide)

Salts

• Chemicals formed by the reaction of a base with an acid, producing salt and water.
• Example: Potassium nitrate (KNO₃)

Examples of Salts

• KNO₃ (Potassium nitrate)
• ZnSO₄ (Zinc sulphate)
• CaCO₃ (Calcium carbonate)
• NH₄Cl (Ammonium chloride)

Metallic Oxides and Sulfides

• ZnO (Zinc oxide)
• CaO (Calcium oxide)
• MgS (Magnesium sulfide)
• CaS (Calcium sulfide)

Chemical Equations

• A shorthand representation of the results of a chemical change.

Representing a Chemical Equation

• Reactants: Substances that participate in the chemical reaction.
• Products: Substances formed as a result of the chemical reaction.
• → (arrow): Indicates the direction of the reaction.
• Δ: Indicates heat - meaning reactants are heated to produce the product.

Examples of Chemical Equations

• Reaction: Zinc (metal) and sulfur (non-metal) react on heating.

• Reactants: Zinc and sulfur

• Product: Zinc sulfide

• Chemical Equation: Zn + S → ZnS + Δ

• Reaction: Sodium hydroxide (NaOH) and dilute hydrochloric acid (HCl) react.

• Word Equation: Sodium hydroxide + Hydrochloric acid → Sodium chloride + Water

• Chemical Equation: NaOH + HCl → NaCl + H₂O

• Reaction: Zinc (Zn) and dilute sulfuric acid (H₂SO₄) react.

• Word Equation: Zinc + Sulfuric acid → Zinc sulfate + Hydrogen

• Chemical Equation: Zn + H₂SO₄ (dil.) → ZnSO₄ + H₂ (g)

Elements

• Pure substances made up of identical atoms
• Cannot be broken down into simpler substances
• Basic unit of matter
• About 118 elements discovered
• Arranged in a periodic table in increasing order of atomic number
• Atomic number is the number of protons or electrons in an atom
• Atomicity refers to the number of atoms in a molecule of an element

Periodic Table

• Elements are arranged in increasing order of their atomic number

Atom

• The basic unit of an element
• Consists of a nucleus containing protons and neutrons, surrounded by orbiting electrons

Metallic Elements

• Examples: potassium, sodium, zinc, copper
• Have luster, malleable, ductile, and are good conductors of heat and electricity

Non-metallic Elements

• Examples: carbon, sulfur, phosphorus
• Lack luster, not malleable or ductile, and are poor conductors of heat and electricity

Metalloids

• Elements that exhibit properties of both metals and nonmetals
• Example: boron

Noble Gases

• Unreactive, inert elements found in trace amounts in air
• Examples: helium, neon, argon

Symbol

• A short form or abbreviated name of an element
• Distinguishes one element from another
• Example: the symbol for sulfur is S

Molecule

• Formed by the combination of atoms of the same or different elements
• Smallest particle of a pure substance that can normally exist independently and retain its properties
• Example: diatomic molecule of nitrogen - N₂

Compounds

• Pure substances made up of two or more different elements combined in a fixed proportion
• Example: water (H₂O) formed from hydrogen and oxygen

Characteristics of Compounds

• Elements present in a definite proportion
• Compound has unique properties different from its constituent elements
• Elements cannot be separated by physical methods

Chemical Formula

• Represents a substance (element or compound) using symbols
• Example: chemical formula of sodium chloride is NaCl

Mixture

• An impure substance formed by combination of two or more pure substances in any ratio

Methods of Separation

• Sieving: separating large particles from smaller ones (e.g., bran from wheat flour)
• Magnetic separation: separating magnetic particles from non-magnetic particles using a magnet (e.g., iron from plastic)
• Sublimation: separating sublimable substances from non-sublimable substances by heating (e.g., ammonium chloride from a mixture of ammonium chloride and sodium chloride)
• Filtration: separating insoluble solid particles from a liquid using a filter paper (e.g., chalk from water)
• Sedimentation: allowing insoluble solid particles to settle down in a liquid by gravity (e.g., sand settling in water)
• Evaporation: removing a liquid from a mixture by evaporation, leaving behind the solid component (e.g., evaporating seawater to obtain salt)

Important Chemical Formulas

• Gases: H₂, N₂, O₂, Cl₂, HCl, NH₃, CO, CO₂, NO, N₂O, NO₂, SO₂
• Acids: HCl (hydrochloric acid), HNO₃ (nitric acid), H₂SO₄ (sulfuric acid), H₂CO₃ (carbonic acid)
• Bases: KOH (potassium hydroxide), NaOH (sodium hydroxide), Ca(OH)₂ (calcium hydroxide), Zn(OH)₂ (zinc hydroxide)
• Salts: KNO₃ (potassium nitrate), ZnSO₄ (zinc sulphate), CaCO₃ (calcium carbonate), NH₄Cl (ammonium chloride)
• Metallic Oxides & Sulphides: ZnO (zinc oxide), CaO (calcium oxide), MgS (magnesium sulphide), CaS (calcium sulphide)

Chemical Equations

• Shorthand representation of a chemical change
• Reactants are substances that undergo change
• Products are substances formed as a result of the change
• Arrow indicates the direction of the reaction
• [A] indicates heat
• Example: Zn + S [A] → ZnS (zinc reacts with sulfur when heated to form zinc sulfide)

Elements

• Elements are pure substances made up of identical atoms.
• Elements cannot be broken down into simpler substances.
• About 118 elements have been discovered.
• The need to arrange elements systematically led to the creation of the periodic table.
• Atomic number represents the number of protons or electrons in an element.
• Elements with the same atomic number are considered the same element.
• The atomic number determines the element's position on the periodic table.

The Periodic Table

• Elements are arranged in increasing order of their atomic number.
• The periodic table helps organize and understand the properties of elements.

Atom

• Atoms are the basic unit of an element.
• Atoms are divisible into a nucleus and surrounding orbits.
• The nucleus contains protons (positively charged) and neutrons (neutral).
• Electrons (negatively charged) orbit the nucleus.

Types of Elements

• Metallic elements like potassium, sodium, zinc, and copper have lustre, are malleable, ductile, and good conductors.
• Non-metallic elements like carbon, sulfur, and phosphorus lack lustre, are non-malleable and non-ductile, and are poor conductors.
• Metalloids like Boron exhibit properties of both metals and non-metals.
• Noble gases are inert, unreactive elements found in air. Examples include helium, neon, and argon.

Symbols

• Symbols are abbreviated names that distinguish one element from another.
• For example, the symbol for sulfur is 'S'.

Molecule

• A molecule is formed by the combination of atoms of the same or different elements.
• It's the smallest independently existing particle of a substance.
• A diatomic molecule of nitrogen is represented by 'N₂'.

Compounds

• Compounds are pure substances made of two or more different elements combined in fixed proportions.
• For example, hydrogen and oxygen combine to form water (H₂O).

Characteristics of Compounds

• Elements in a compound are present in a definite proportion.
• Compounds have a specific set of properties distinct from their constituent elements.
• Elements within a compound cannot be separated by physical methods.

Chemical Formula

• A chemical formula represents a substance using symbols.
• For example, the chemical formula for sodium chloride is 'NaCl'.

Mixtures

• Mixtures are impure substances formed by combining two or more pure substances in any ratio.

Separation Techniques

• Sieving: Separating large particles from smaller ones.
• Magnetic separation: Separating magnetic particles from non-magnetic particles.
• Sublimation: Separating sublimable substances from non-sublimable substances by heating the mixture.
• Filtration: Separating insoluble solid particles from a solid-liquid mixture.
• Sedimentation: Settling down of insoluble solid particles in a solid-liquid mixture.
• Evaporation: Evaporating the liquid in a mixture to leave behind the solid component.

Important Chemical Formulas

• Gases: H₂ (hydrogen), N₂ (nitrogen), O₂ (oxygen), Cl₂ (chlorine), HCl (hydrogen chloride), NH₃ (ammonia), CO (carbon monoxide), CO₂ (carbon dioxide), NO (nitrous oxide), N₂O (dinitrogen oxide), NO₂ (nitrogen dioxide), SO₂ (sulfur dioxide).
• Acids: HCl (hydrochloric acid), HNO₃ (nitric acid), H₂SO₄ (sulfuric acid), H₂CO₃ (carbonic acid).
• Bases: KOH (potassium hydroxide), NaOH (sodium hydroxide), Ca(OH)₂ (calcium hydroxide), Zn(OH)₂ (zinc hydroxide).
• Salts: KNO₃ (potassium nitrate), ZnSO₄ (zinc sulphate), CaCO₃ (calcium carbonate), NH₄Cl (ammonium chloride).
• Metallic Oxides & Sulphides: ZnO (zinc oxide), CaO (calcium oxide), MgS (magnesium sulphide), and CaS (calcium sulfide).

Chemical Equations

• Chemical Equations are a shorthand representation of chemical changes.
• Reactants: Substances that participate in the chemical reaction.
• Products: Substances formed as a result of the reaction.
• Arrow (→): Indicates the direction of the reaction.
• [A]: Indicates heat.

Example of a Chemical Equation

• Reaction: Zinc (Zn) reacts with dilute sulfuric acid (H₂SO₄)
• Word Equation: Zinc + Sulphuric acid → Zinc sulphate + Hydrogen
• Molecular Equation: Zn + H₂SO₄ [dil.] → ZnSO₄ + H₂ [g]

Elements

• An element is a pure substance made up of identical atoms.
• Elements cannot be broken down into simpler substances.
• There are about 118 known elements.
• The elements are arranged in a periodic table in order of increasing atomic number.
• The atomic number of an element is the number of protons or electrons in an atom of that element.
• Atomicity indicates the number of atoms present in a molecule of an element.
• Metallic elements have luster, are malleable, ductile, and good conductors of heat and electricity.
• Non-metallic elements lack luster, are not malleable or ductile, and are poor conductors of heat and electricity.
• Metalloids possess properties of both metals and non-metals.
• Noble gases are unreactive inert elements found in trace amounts in air.

Compounds

• Compounds are pure substances formed by the combination of two or more different elements in a fixed proportion.
• Elements in a compound are present in a definite proportion, meaning they always combine in the same ratio.
• Compounds have a definite set of properties that differ from the properties of the individual elements they are composed of.
• Elements in a compound cannot be separated by physical means.
• Chemical formulas represent substances using symbols.

Mixtures

• Mixtures are impure substances formed by combining two or more pure substances in any ratio.
• Mixtures can be separated by physical means.
• Common separation techniques include sieving, magnetic separation, sublimation, filtration, sedimentation, and evaporation.

Important Chemical Formulas

• Gases:
  • H₂: Hydrogen
  • N₂: Nitrogen
  • O₂: Oxygen
  • Cl₂: Chlorine
  • HCl: Hydrogen chloride
  • NH₃: Ammonia
  • CO: Carbon monoxide
  • CO₂: Carbon dioxide
  • NO: Nitrous oxide
  • N₂O: Dinitrogen oxide
  • NO₂: Nitrogen dioxide
  • SO₂: Sulphur dioxide
• Acids: (Derived from plants or minerals)
  • HCl: Hydrochloric acid
  • HNO₃: Nitric acid
  • H₂SO₄: Sulphuric acid
  • H₂CO₃: Carbonic acid
• Bases: (Hydroxides or oxides of metals)
  • KOH: Potassium hydroxide
  • NaOH: Sodium hydroxide
  • Ca(OH)₂: Calcium hydroxide
  • Zn(OH)₂: Zinc hydroxide
• Salts: (Formed by the reaction of a base with an acid)
  • KNO₃: Potassium nitrate
  • ZnSO₄: Zinc sulphate
  • CaCO₃: Calcium carbonate
  • NH₄Cl: Ammonium chloride
• Metallic Oxides and Sulphides:
  • ZnO: Zinc oxide
  • CaO: Calcium oxide
  • MgS: Magnesium sulphide
  • CaS: Calcium sulphide

Representing Chemical Reactions

• Chemical equations are a shorthand way to represent the results of a chemical change.
• A chemical equation includes reactants (substances that take part in the reaction) and products (substances formed as a result of the reaction).
• The arrow in a chemical equation indicates the direction of the reaction.
• The symbol "[→]" represents heat, indicating that the reactants are heated to produce the products.

Examples of Chemical Reactions

• Example 1: Zinc and Sulfur
  • Word equation: Zinc + Sulfur → Zinc sulphide
• Example 2: Sodium Hydroxide and Hydrochloric Acid
  • Word equation: Sodium hydroxide + Hydrochloric acid → Sodium chloride + Water
• Example 3: Zinc and Dilute Sulphuric Acid
  • Word equation: Zinc + Sulphuric acid → Zinc sulphate + Hydrogen
  • Molecular equation: Zn + H₂SO₄ [dil.] → ZnSO₄ + H₂ [g]

Elements

• Pure substance made of identical atoms
• Cannot be broken down into simpler substances
• Basic unit of matter
• 118 elements discovered to date
• Arranged in the periodic table

Periodic Table

• Elements arranged in increasing order of their atomic number
• Atomic number is the number of protons or electrons in an atom
• Examples:
  • Hydrogen: one electron, atomic number 1
  • Helium: two electrons, atomic number 2

Atom

• Basic unit of an element
• Composed of:
  • Nucleus: contains protons (positively charged) and neutrons (neutral)
  • Orbits: contain electrons (negatively charged)

Metallic Elements

• Examples: Potassium, Sodium, Zinc, Copper
• Characteristics:
  • Lustrous
  • Malleable (can be beaten into sheets)
  • Ductile (can be drawn into wires)
  • Good conductors of heat and electricity

Non-metallic Elements

• Examples: Carbon, Sulfur, Phosphorus
• Characteristics:
  • Lack luster
  • Non-malleable
  • Non-ductile
  • Poor or non-conductors of heat and electricity

Metalloids

• Exhibit properties of both metals and non-metals
• Example: Boron

Noble Gases

• Unreactive, inert elements found in trace amounts in air
• Examples: Helium, Neon, Argon

Symbol

• Short form or abbreviated name of an element
• Distinguishes one element from another
• Example: Symbol for sulfur is 'S'

Molecule

• Formed by the combination of atoms of the same element or different elements
• Smallest particle of a pure substance that can normally exist independently and retain the substance's physical and chemical properties
• Example: Diatomic molecule of nitrogen 'N2'

Compounds

• Pure substance composed of two or more different elements (atoms) combined in a fixed proportion
• Example: Hydrogen and oxygen form the compound water (H2O)

Characteristics:

• Elements in a compound are present in a definite proportion.
• Compounds have a definite set of properties.
• Elements in a compound cannot be separated by physical methods.

Chemical Formula

• Represents a substance (element or compound) using symbols
• Example: Chemical formula of sodium chloride is 'NaCl'

Mixture

• Impure substance formed by combining two or more pure substances in any ratio

Separation Techniques

• Sieving: Separates large particles from smaller particles (e.g., bran from wheat flour)
• Magnetic Separation: Separates magnetic particles from non-magnetic particles (e.g., iron from plastic)
• Sublimation: Separates sublimable substance from a mixture by heating (e.g., ammonium chloride from a mixture of ammonium chloride and sodium chloride)
• Filtration: Separates insoluble solid particles from a solid-liquid mixture using filter paper (e.g., chalk from water)
• Sedimentation: Insoluble solid particles settle down in a solid-liquid mixture by gravity (e.g., sand settles in water)
• Evaporation: Liquid is evaporated from a mixture leaving behind the solid component (e.g., evaporation of seawater leaves behind salt)

Important Chemical Formulas

Gases

• H2: Hydrogen
• N2: Nitrogen
• O2: Oxygen
• Cl2: Chlorine
• HCl: Hydrogen chloride
• NH3: Ammonia
• CO: Carbon monoxide
• CO2: Carbon dioxide
• NO: Nitrous oxide
• N2O: Dinitrogen oxide
• NO2: Nitrogen dioxide
• SO2: Sulfur dioxide

Acids

• HCl: Hydrochloric acid
• HNO3: Nitric acid
• H2SO4: Sulphuric acid
• H2CO3: Carbonic acid

Bases

• KOH: Potassium hydroxide
• NaOH: Sodium hydroxide
• Ca(OH)2: Calcium hydroxide
• Zn(OH)2: Zinc hydroxide

Salts

• KNO3: Potassium nitrate
• ZnSO4: Zinc sulphate
• CaCO3: Calcium carbonate
• NH4Cl: Ammonium chloride

Metallic Oxides and Sulphides

• ZnO: Zinc oxide
• CaO: Calcium oxide
• MgS: Magnesium sulphide
• CaS: Calcium sulphide

Chemical Equations

• Shorthand form representing the result of a chemical change

Components of a Chemical Equation

• Reactants: Substances that participate in the chemical reaction.
• Products: Substances formed as a result of the chemical reaction.
• Arrow (→): Indicates the direction of the reaction.
• [A]: Indicates heat (e.g., Zinc and sulfur are heated to give zinc sulfide)

Examples of Chemical Equations

• Zinc and Sulfur reaction:
  • Word Equation: Zinc + Sulfur → Zinc sulphide
• Sodium hydroxide and hydrochloric acid reaction:
  • Word Equation: Sodium hydroxide + Dilute hydrochloric acid → Sodium chloride + Water
  • Molecular Equation: NaOH + HCl (dil.) → NaCl + H2O
• Zinc and dilute sulphuric acid reaction:
  • Word Equation: Zinc + Dilute sulphuric acid → Zinc sulphate + Hydrogen
  • Molecular Equation: Zn + H2SO4 (dil.) → ZnSO4 + H2 (g)