Atomic Foundations of Matter

Law of Conservation of Mass

• Definition: Is law ke according, mass can neither be created nor destroyed in a chemical reaction. Matlab, total mass of reactants hamesha total mass of products ke equal hota hai.
• Proposer: Antoine Lavoisier ne 1789 mein ye law diya tha, isliye unhe 'Father of Modern Chemistry' bhi kehte hain.
• Application: Ye law har chemical reaction par apply hota hai, chahe reaction open system mein ho ya closed system mein.
• Example: Agar 4.0 g Calcium Carbonate (CaCO₃) 2.92 g Hydrochloric Acid (HCl) se react karta hai, aur products mein 1.76 g Carbon Dioxide (CO₂), 0.72 g Water (H₂O), aur 4.44 g Calcium Chloride (CaCl₂) bante hain, toh:
• Reactants ka total mass: 4.0 g + 2.92 g = 6.92 g
• Products ka total mass: 1.76 g + 0.72 g + 4.44 g = 6.92 g
• Mass of reactants = Mass of products, toh law obey ho raha hai.

• Experimental Verification:
• Activity 9.2 (Set-up 1 - Open System): Agar baking soda aur vinegar ko open flask mein react karaya jaye, toh CO₂ gas escape ho jaati hai, aur final mass initial mass se kam aata hai. Isse lagta hai ki law violate ho raha hai, but actually gas escape ho gayi.
• Activity 9.2 (Set-up 2 - Closed System): Agar reaction ko balloon laga kar closed system mein kiya jaye, toh CO₂ gas balloon mein collect ho jaati hai, aur initial aur final mass same aata hai. Isse law verify hota hai.

• Important Note: Physical changes mein bhi mass conserve rehta hai. Jaise, salt ko water mein dissolve karne par total mass same rehta hai, ya paper ko tear karne par bhi uska total mass change nahi hota.

Law of Constant Proportions (Law of Definite Proportions / Proust's Law)

• Definition: Ek chemical compound mein elements hamesha fixed ratio by mass mein combine karte hain, chahe compound kisi bhi source se mila ho ya kaise bhi banaya gaya ho.
• Proposer: Joseph Proust ne ye law diya tha.
• Example: Water (H₂O):
• Water, chahe river se ho, borewell se ho ya ocean se, usme Hydrogen aur Oxygen ka mass ratio hamesha 1:8 hi hota hai.
• Agar 9 g water ko decompose karein, toh hamesha 1 g Hydrogen aur 8 g Oxygen hi milenge.
• Example: Copper Carbonate: Proust ne show kiya ki Copper Carbonate mein Copper, Carbon aur Oxygen ka proportion by mass hamesha same rehta hai, irrespective of its preparation method.
• Key Idea: Ye law batata hai ki compounds ki composition fixed hoti hai, unlike mixtures jinki composition variable ho sakti hai.

• Numerical Example: Sodium chloride (NaCl) mein Sodium (Na) aur Chlorine (Cl) ka mass ratio 23:35.5 hai. Agar 46 g Sodium react karta hai, toh kitna Chlorine chahiye?
• Ratio: Na : Cl = 23 : 35.5
• Agar Na = 23 g, toh Cl = 35.5 g
• Agar Na = 46 g (jo ki 23 g ka double hai), toh Cl = 35.5 g * 2 = 71 g Chlorine chahiye.

Dalton's Atomic Theory

• Basis: Ye theory Law of Conservation of Mass aur Law of Constant Proportions ko explain karti hai.
• Proposer: John Dalton ne 1808 mein ye theory di thi, jo matter ki study mein ek turning point thi.
• Main Idea: Dalton ne propose kiya ki chemical reactions mein atoms indivisible hote hain aur sirf rearrange hote hain, na ki create ya destroy hote hain.

• Postulates (Fundamental Assumptions):

1. All matter is made up of very tiny particles called atoms, jo chemical reactions mein participate karte hain.
2. Atoms indivisible particles hain, jinhe chemical reaction mein na toh create kiya ja sakta hai aur na hi destroy.
3. Ek given element ke atoms mass aur chemical properties mein identical hote hain.
4. Different elements ke atoms ke mass aur chemical properties different hote hain.
5. Atoms simple whole number ratio mein combine karke compounds banate hain.
6. Ek given compound mein atoms ka relative number aur kinds constant hote hain.

• Significance: Dalton ke postulates ne modern understanding of atoms aur unke behavior ka base banaya.
• Example: Hydrogen aur Oxygen atoms combine karke water banate hain, but atoms khud destroy ya change nahi hote. Magnesium air mein burn karke Magnesium Oxide banata hai, jisme Magnesium aur Oxygen atoms combine hote hain.

• Limitations (Modern Context):
• Atoms indivisible nahi hote, unke andar subatomic particles (electrons, protons, neutrons) hote hain.
• Ek hi element ke atoms ka mass different ho sakta hai (Isotopes).
• Different elements ke atoms ka mass same ho sakta hai (Isobars).
• Atoms simple whole number ratio ke alawa complex ratios mein bhi combine kar sakte hain (e.g., organic compounds).
• Atomic reactions (nuclear reactions) mein atoms ko create ya destroy kiya ja sakta hai.

Atoms Combine Kyun Karte Hain?

• Stability: Atoms combine karte hain taaki stable electronic configuration achieve kar sakein, jaisa ki noble gases ke paas hota hai (octet rule ya duplet rule for H, He).
• Octet Rule: Valence shell mein 8 electrons hone chahiye.
• Duplet Rule: K-shell mein 2 electrons hone chahiye (Hydrogen, Helium).
• Energy Reduction: Jab atoms combine karte hain, toh system ki total energy individual atoms ki energies ke sum se kam ho jaati hai, jisse resultant arrangement zyada stable ho jaata hai.
• Chemical Bond: Wo force jo atoms ko ek saath hold karta hai, use chemical bond kehte hain.
• Ways of Combining:

1. Sharing of electrons: Atoms apne valence electrons ko share karte hain.
2. Transfer of electrons: Ek atom electrons lose karta hai aur doosra gain karta hai.

• Molecules: Atoms combine karke molecules banate hain. Molecule ek electrically neutral entity hoti hai jisme ek se zyada atoms hote hain, aur ye independently exist kar sakti hai aur substance ki saari properties show karti hai.
• Elemental Molecules: Same element ke atoms combine karte hain (e.g., H₂, O₂, Cl₂).
• Compound Molecules: Different elements ke atoms combine karte hain (e.g., HCl, H₂O).

Covalent Bond (Sharing of Electrons)

• Definition: Jab atoms electrons ko share karke stable electronic configuration achieve karte hain, toh unke beech jo bond banta hai use covalent bond kehte hain.
• Types of Covalent Bonds:
• Single Bond: Jab do atoms ek-ek electron share karte hain (total 2 shared electrons). Represented by a single line (—).
• Example: H₂ molecule: Har H atom ke paas 1 electron hota hai. Stable hone ke liye 2 chahiye (duplet). Dono H atoms ek-ek electron share karte hain, banata hai H—H.
• Example: Cl₂ molecule: Har Cl atom ke paas 7 valence electrons hote hain. Stable hone ke liye 8 chahiye (octet). Dono Cl atoms ek-ek electron share karte hain, banata hai Cl—Cl.
• Example: HCl molecule: H ke paas 1 electron, Cl ke paas 7 valence electrons. Dono ko 1-1 electron chahiye. H aur Cl ek-ek electron share karte hain, banata hai H—Cl.
• Double Bond: Jab do atoms do-do electrons share karte hain (total 4 shared electrons). Represented by two lines (=).
• Example: O₂ molecule: Har O atom ke paas 6 valence electrons hote hain. Stable hone ke liye 8 chahiye. Dono O atoms do-do electrons share karte hain, banata hai O=O.
• Triple Bond: Jab do atoms teen-teen electrons share karte hain (total 6 shared electrons). Represented by three lines (≡).
• Example: N₂ molecule: Har N atom ke paas 5 valence electrons hote hain. Stable hone ke liye 8 chahiye. Dono N atoms teen-teen electrons share karte hain, banata hai N≡N.
• Formation of Water (H₂O):
• Oxygen ko 2 electrons chahiye, aur har Hydrogen ko 1 electron chahiye.
• Ek Oxygen atom do Hydrogen atoms ke saath ek-ek electron share karta hai, jisse O ka octet aur dono H ka duplet complete ho jaata hai.
• Structure: H—O—H.
• Covalent Compounds: Wo compounds jo covalent bonds se bante hain, unhe covalent compounds kehte hain.

Ionic Bond (Electron Transfer)

• Definition: Jab electrons ka complete transfer hota hai ek atom se doosre atom tak, jisse ions bante hain aur unke beech electrostatic force of attraction develop hota hai, use ionic bond kehte hain.
• Formation of Ions:
• Cation: Jab ek atom electron lose karta hai, toh us par positive charge aata hai aur wo cation ban jaata hai (e.g., Na → Na⁺ + e⁻).
• Generally, metals (jinme 1, 2, ya 3 valence electrons hote hain) electrons lose karke cations banate hain.
• Anion: Jab ek atom electron gain karta hai, toh us par negative charge aata hai aur wo anion ban jaata hai (e.g., Cl + e⁻ → Cl⁻).
• Generally, non-metals (jinme 5, 6, ya 7 valence electrons hote hain) electrons gain karke anions banate hain.
• Example: Sodium Chloride (NaCl):
• Sodium (Na): Atomic number 11 (Electronic configuration: 2, 8, 1). Iske paas 1 valence electron hai. Ye 1 electron lose karke stable octet (2, 8) achieve karta hai aur Na⁺ cation banata hai.
• Chlorine (Cl): Atomic number 17 (Electronic configuration: 2, 8, 7). Iske paas 7 valence electrons hain. Ye 1 electron gain karke stable octet (2, 8, 8) achieve karta hai aur Cl⁻ anion banata hai.
• Bond Formation: Na⁺ aur Cl⁻ ions ke beech strong electrostatic force of attraction hota hai, jo unhe ek saath hold karta hai, jisse ionic bond banta hai.
• Ionic Compounds: Wo compounds jo ionic bonds se bante hain, unhe ionic compounds kehte hain.
• Ye single molecules ke roop mein exist nahi karte, balki 3-D crystal lattice banate hain jisme ions regularly arranged hote hain.
• Example: NaCl crystal mein, har Na⁺ ion 6 Cl⁻ ions se ghira hota hai, aur har Cl⁻ ion 6 Na⁺ ions se ghira hota hai.
• Polyatomic Ions: Kuch ions ek se zyada atoms ke combination se bante hain aur un par net charge hota hai (e.g., SO₄²⁻ (Sulfate), CO₃²⁻ (Carbonate), NH₄⁺ (Ammonium)).

Naming Covalent Compounds

• Prefix System: Atoms ki sankhya (number) batane ke liye prefixes use karte hain.
• Prefixes: mono- (1), di- (2), tri- (3), tetra- (4), penta- (5), hexa- (6), etc.
• Rules:

1. First Element: Regular name rehta hai. Agar ek hi atom hai toh 'mono-' omit kar dete hain.
2. Second Element: Naam '-ide' par end hota hai.
3. Vowel Dropping: Agar prefix 'o' ya 'a' par end ho raha hai aur element ka naam vowel se start ho raha hai, toh prefix ka last vowel drop kar dete hain (e.g., monoxide, not monooxide).

• Examples:
• CO: Carbon monoxide (not monocarbon monoxide)
• CO₂: Carbon dioxide (not monocarbon dioxide)
• CS₂: Carbon disulfide (do Sulfur atoms)
• PCl₃: Phosphorus trichloride (teen Chlorine atoms)
• SF₆: Sulfur hexafluoride (chhe Fluorine atoms)
• N₂O₄: Dinitrogen tetroxide (not dinitrogen tetraoxide)
• N₂O₅: Dinitrogen pentoxide
• Exception for Hydrogen: Agar Hydrogen first element hai, toh koi prefix nahi lagate (e.g., H₂S is Hydrogen sulfide, not dihydrogen sulfide).
• Common Names: Kuch compounds ke common names hote hain jo IUPAC names se zyada use hote hain (e.g., H₂O is Water, NH₃ is Ammonia).

Naming Ionic Compounds

• Rules:

1. Cation First: Pehle cation ka naam likhte hain, phir anion ka.
2. Anion Ending: Simple anions ke naam '-ide' par end hote hain (e.g., Chloride, Oxide, Sulfide).
3. Polyatomic Ions: Polyatomic ions ke naam generally '-ide' par end nahi hote (e.g., Sulfate, Carbonate, Hydroxide, Ammonium).

• Formation: Typically metals (cations) aur non-metals (anions) ke combination se bante hain.
• Examples:
• NaCl: Sodium chloride
• CaO: Calcium oxide
• MgS: Magnesium sulfide
• FeCl₃: Iron(III) chloride or Ferric chloride (Roman numeral charge batata hai)
• Cu₂O: Copper(I) oxide or Cuprous oxide
• NH₄Cl: Ammonium chloride (Ammonium ek polyatomic cation hai)

Chemical Formulae Kaise Likhein?

• Chemical formulae likhne ke liye criss-cross method ek easy tareeka hai, jisme valencies ya charges ko cross-over karte hain.

Covalent Compounds ki Formulae

• Steps:

1. Symbols Likho: Constituent elements ke symbols likho.
2. Valencies Likho: Har element ki valency uske symbol ke neeche likho (Table 9.1 refer kar sakte ho).
3. Criss-Cross Karo: Valencies ko cross-over karke subscripts banao.
4. Simplify Karo: Agar valency 1 hai toh use nahi likhte. Agar subscripts mein koi common factor hai toh divide karke simplest ratio mein likhte hain.

• Examples:
• Hydrogen Chloride (HCl):
• Symbols: H, Cl
• Valency: 1, 1
• Formula: HCl (1 nahi likhte)
• Hydrogen Sulfide (H₂S):
• Symbols: H, S
• Valency: 1, 2
• Formula: H₂S
• Carbon Tetrachloride (CCl₄):
• Symbols: C, Cl
• Valency: 4, 1
• Formula: CCl₄

Ionic Compounds ki Formulae

• Steps:

1. Cation Phir Anion: Pehle cation ka symbol, phir anion ka symbol likho.
2. Charges Likho: Symbols ke neeche unke charges (sirf numbers, sign nahi) likho.
3. Criss-Cross Karo: Charges ko cross-over karke subscripts banao.
4. Simplify Karo: Agar subscripts mein common factor hai toh divide karke simplest whole number ratio mein likho.
5. Polyatomic Ions: Agar ek se zyada polyatomic ion hain, toh unhe brackets ( ) mein rakhte hain aur subscript bahar likhte hain.

• Examples:
• Calcium Chloride (CaCl₂):
• Symbol: Ca, Cl
• Charge: 2+, 1-
• Formula: CaCl₂
• Aluminium Oxide (Al₂O₃):
• Symbol: Al, O
• Charge: 3+, 2-
• Formula: Al₂O₃
• Magnesium Oxide (MgO):
• Symbol: Mg, O
• Charge: 2+, 2-
• Formula: Mg₂O₂ ko simplify karke MgO
• Magnesium Hydroxide (Mg(OH)₂):
• Symbol: Mg, OH
• Charge: 2+, 1-
• Formula: Mg(OH)₂ (OH ko bracket mein kyunki ye polyatomic ion hai aur 2 units hain)
• Calcium Carbonate (CaCO₃):
• Symbol: Ca, CO₃
• Charge: 2+, 2-
• Formula: Ca₂(CO₃)₂ ko simplify karke CaCO₃
• Aluminium Sulfate (Al₂(SO₄)₃):
• Symbol: Al, SO₄
• Charge: 3+, 2-
• Formula: Al₂(SO₄)₃

Ionic aur Covalent Compounds ki Properties ka Comparison

| Property | Ionic Compounds | Covalent Compounds | | :--------------------- | :----------------------------------------------- | :------------------------------------------------ | | Bonding | Electron transfer se bante hain | Electron sharing se bante hain | | Physical State | Generally solid (crystalline solids) | Solid, liquid, ya gas ho sakte hain | | Melting & Boiling Point | High (strong electrostatic forces) | Generally low (weak intermolecular forces) | | Solubility | Generally soluble in water, insoluble in organic solvents (kerosene, petrol) | Generally insoluble in water, soluble in organic solvents (kerosene, petrol) | | Electrical Conductivity | Solid state: Non-conductor (ions fixed) | Solid/Liquid/Gas: Non-conductor (no free ions/electrons) | | | Molten/Aqueous solution: Good conductor (free ions) | Aqueous solution: Generally non-conductor (except acids/bases that ionize) | | Structure | Crystal lattice (3-D repeating pattern of ions) | Discrete molecules |

• Explanation of Conductivity:
• Ionic Compounds: Solid state mein ions fixed positions par hote hain, move nahi kar sakte, isliye electricity conduct nahi karte. Molten state ya aqueous solution mein ions free ho jaate hain aur electricity conduct karte hain.
• Covalent Compounds: Inmein free ions ya free electrons nahi hote, isliye ye electricity conduct nahi karte, chahe solid ho, liquid ho ya gas. Kuch covalent compounds (jaise acids) water mein dissolve hone par ions banate hain aur tab conductivity show karte hain, but ye unki intrinsic property nahi hai.

• Examples:
• Ionic: Sodium chloride (NaCl), Copper sulfate (CuSO₄)
• Covalent: Camphor, Naphthalene, Sugar, Water (H₂O), Carbon dioxide (CO₂)

Molecular Mass (Covalent Compounds ke liye)

• Definition: Molecular mass ek molecule mein present sabhi atoms ke atomic masses ka sum hota hai.
• Unit: Iski unit atomic mass unit (u) hoti hai.
• Calculation Steps:

1. Compound ka chemical formula pata karo.
2. Har element ka atomic mass pata karo.
3. Formula mein har element ke atoms ki sankhya ko uske atomic mass se multiply karo.
4. Sabhi elements ke products ko add kar do.

• Example 1: Water (H₂O)
• Atomic mass: H = 1 u, O = 16 u
• Molecular mass of H₂O = (1 u × 2) + (16 u × 1) = 2 u + 16 u = 18 u
• Example 2: Carbon Dioxide (CO₂)
• Atomic mass: C = 12 u, O = 16 u
• Molecular mass of CO₂ = (12 u × 1) + (16 u × 2) = 12 u + 32 u = 44 u
• Example 3: Nitric Acid (HNO₃)
• Atomic mass: H = 1 u, N = 14 u, O = 16 u
• Molecular mass of HNO₃ = (1 u × 1) + (14 u × 1) + (16 u × 3) = 1 u + 14 u + 48 u = 63 u

Formula Unit Mass (Ionic Compounds ke liye)

• Definition: Ionic compounds molecules nahi banate, balki crystal lattice banate hain. Isliye, unke liye formula unit mass calculate karte hain, jo ki ek formula unit (simplest whole number ratio of ions) mein present sabhi atoms ke atomic masses ka sum hota hai.
• Unit: Iski unit bhi atomic mass unit (u) hoti hai.
• Calculation Steps: Same as molecular mass calculation.
• Example 1: Sodium Oxide (Na₂O)
• Atomic mass: Na = 23 u, O = 16 u
• Formula unit mass of Na₂O = (23 u × 2) + (16 u × 1) = 46 u + 16 u = 62 u
• Example 2: Calcium Nitrate (Ca(NO₃)₂)
• Atomic mass: Ca = 40 u, N = 14 u, O = 16 u
• Formula unit mass of Ca(NO₃)₂ = (40 u × 1) + {(14 u × 1) + (16 u × 3)} × 2
• Pehle NO₃ ka mass = 14 + (16*3) = 14 + 48 = 62 u
• Phir Ca(NO₃)₂ ka mass = 40 + (62 * 2) = 40 + 124 = 164 u
• Example 3: Potassium Chloride (KCl)
• Atomic mass: K = 39 u, Cl = 35.5 u
• Formula unit mass of KCl = (39 u × 1) + (35.5 u × 1) = 39 u + 35.5 u = 74.5 u

• Key Difference: Conceptually, molecular mass molecules ke liye hai aur formula unit mass ionic compounds ke liye, but calculation method same hai.