Chapter 3 Atoms And Molecules 2024-2025 Notes PDF

Downloaded From: Telegram ID @ajinkyasolunke YouTube Channel: Ajinkya Solunke Instagram ID ajinkya_solunke CHAPTER 3. ATOMS AND MOLECULES  Created two important laws of...

Downloaded From: Telegram ID @ajinkyasolunke YouTube Channel: Ajinkya Solunke Instagram ID ajinkya_solunke CHAPTER 3. ATOMS AND MOLECULES  Created two important laws of (DETAILED NOTES) chemical combination. INTRODUCTION  Ancient Indian Philosophers: LAWS OF CHEMICAL COMBINATION  Maharishi Kanad (500 BC):  The following two laws of chemical combination were established after o Thought about dividing much experiments by Lavoisier and matter into smaller Joseph L. Proust. pieces.  Laws of chemical combination:1) o Believed in smallest Law of conservation of mass 2) Law particles called Parmanu. of Constant Proportions  Pakudha Katyayama: o Added to Kanad's ideas. LAW OF CONSERVATION OF MASS o Said particles combine to  Statement  Law of form di erent matter. conservation of mass states that  Ancient Greek Philosophers: mass can neither be created nor destroyed in a chemical reaction.  Democritus and Leucippus:  Explanation: o Thought about dividing o During any chemical matter into smaller reaction, the amount of pieces. matter stays the same. o Matter can change forms, o Believed in indivisible but the total mass particles called atoms remains constant. (meaning indivisible).  Example: o Ideas were philosophical, o When water (H₂O) splits not tested until the 18th into hydrogen (H₂) and century. oxygen (O₂) through electrolysis, the mass of  18th Century Scientific water before the reaction Advancements: equals the combined  Scientists understood elements mass of hydrogen and and compounds. oxygen after the reaction.  Interested in how and why elements combine. LAW OF CONSTANT PROPORTIONS  Antoine L. Lavoisier:  Definition:  Laid the foundation of chemistry. o The Law of Constant Proportions states that a pg. 1 All rights reserved. Do not copy or transmit this material in any form without express permission of author. Legal action will be taken in case of violation of the copyright. Downloaded From: Telegram ID @ajinkyasolunke YouTube Channel: Ajinkya Solunke Instagram ID ajinkya_solunke chemical compound 2. Atoms are indivisible particles, always contains the same which cannot be created or elements in the exact destroyed in a chemical reaction. same proportion by mass, 3. Atoms of a given element are regardless of the source identical in mass and chemical or method of preparation. properties.  One-line explanation: A chemical 4. Atoms of di erent elements have compound always has the same di erent masses and chemical elements in the same fixed properties. proportion by mass. 5. Atoms combine in the ratio of  Explanation: small whole numbers to form o In any pure chemical compounds. compound, the ratio of 6. The relative number and kinds of the masses of the atoms are constant in a given elements is always the compound. same.  Example: o Water (H₂O) always WHAT IS AN ATOM ? contains hydrogen and  One-line explanation: Atoms oxygen in a mass ratio of are the tiny, fundamental 1:8. No matter where the building blocks of all matter, water comes from, this essential to everything in the ratio remains constant. world despite their minuscule o Mass of oxygen = 16 and size. mass of hydrogen = 1 o Mass ratio of hydrogen  Building Blocks of Matter: and oxygen = [2 x 1] / o Atoms are the = 2/16 = 1/8 fundamental building blocks of all matter. o Comparable to bricks in a building or grains of sand DALTON’S ATOMIC THEORY in an ant-hill. According to Dalton’s atomic theory, all  Size of Atoms: matter, whether an element, a o Extremely small, smaller compound or a mixture is composed of than anything we can small particles called atoms. The easily imagine. postulates of this theory may be stated o Millions of atoms stacked as follows: together form a layer barely as thick as a sheet 1. All matter is made of very tiny of paper. particles called atoms, which o Atomic radius measured participate in chemical in nanometres (nm): reactions.  1 nm = 10-9 m  1 m = 10⁹ nm pg. 2 All rights reserved. Do not copy or transmit this material in any form without express permission of author. Legal action will be taken in case of violation of the copyright. Downloaded From: Telegram ID @ajinkyasolunke YouTube Channel: Ajinkya Solunke Instagram ID ajinkya_solunke SYMBOLS OF ATOM Cobalt Co Copper Cu  One-line explanation: Element Fluorine F symbols are derived from their Gold Au names, using the first one or two letters, and standardized by IUPAC, ensuring each element Symbols for some elements has a unique symbol. Element Symbol Hydrogen H  Dalton's Contribution: Iodine I o First to use symbols for Iron Fe elements in a specific Lead Pb sense. Magnesium Mg o Symbol represented a Neon Ne definite quantity: one atom of the element. Symbols for some elements Element Symbol Nitrogen N Oxygen O Potassium K Silicon Si Silver Ag Sodium Na Sulphur S Uranium U  Berzelius' Suggestion: Zinc Zn o Symbols derived from one or two letters of the  Naming of Elements: element's name. o Early names derived from places (e.g., copper from Cyprus). Symbols for some elements o Some names based on Element Symbol colors (e.g., gold from the Aluminium Al word meaning yellow). Argon Ar  IUPAC: Barium Ba o International Union of Boron B Pure and Applied Bromine Br Chemistry. Calcium Ca o Approves names, symbols, and units for Symbols for some elements elements. Element Symbol o Many symbols are the first Carbon C one or two letters of the Chlorine Cl pg. 3 All rights reserved. Do not copy or transmit this material in any form without express permission of author. Legal action will be taken in case of violation of the copyright. Downloaded From: Telegram ID @ajinkyasolunke YouTube Channel: Ajinkya Solunke Instagram ID ajinkya_solunke element's name in  Example (Carbon Monoxide): English: o Carbon (C) and Oxygen  First letter (O) combine in a fixed capitalized, ratio. second letter o 3g of Carbon combines lowercase (e.g., H with 4g of Oxygen. for hydrogen, Al for o Carbon combines with aluminum, Co for 4/3 times its mass of cobalt). Oxygen.  Symbol Formation:  Atomic Mass Unit (u): o From the first letter and o Initially defined as 1/16 another letter in the name the mass of an Oxygen (e.g., Cl for chlorine, Zn for atom. zinc). o Oxygen was chosen o Derived from Latin, because it reacts with German, or Greek names many elements and forms (e.g., Fe from ferrum for compounds. iron, Na from natrium for o Masses of most elements sodium, K from kalium for were near whole numbers potassium). using this unit.  Standard Reference (Carbon- 12): ATOMIC MASS o In 1961, Carbon-12 isotope chosen as  One-line explanation: Atomic standard. mass is the relative mass of an o One atomic mass unit (u) atom compared to 1/12th the equals 1/12th the mass of mass of a Carbon-12 atom, a Carbon-12 atom. providing a standard measure for o Relative atomic masses of comparing di erent elements. all elements are  Dalton's Atomic Theory: measured relative to o Proposed the concept of Carbon-12. atomic mass.  Analogy: o Each element has a o Fruit seller uses characteristic atomic watermelon as a standard mass. unit. o Explained the law of o Divides watermelon into constant proportions. 12 equal pieces.  Relative Atomic Mass: o Sells other fruits by o Individual atomic masses comparing their mass to are hard to measure. one piece of watermelon o Relative atomic masses (fruit mass unit, fmu). determined using laws of chemical combinations. pg. 4 All rights reserved. Do not copy or transmit this material in any form without express permission of author. Legal action will be taken in case of violation of the copyright. Downloaded From: Telegram ID @ajinkyasolunke YouTube Channel: Ajinkya Solunke Instagram ID ajinkya_solunke Atomic Masses of few elements o Shows all properties of Element Atomic Mass (u) the substance (element or Hydrogen 1 compound). Carbon 12  Formation: Nitrogen 14 o Atoms of the same Oxygen 16 element can form Sodium 23 molecules. Magnesium 24 o Atoms of di erent Sulphur 32 elements can also form Chlorine 35.5 molecules. Calcium 40 MOLECULES OF ELEMENTS HOW DO ATOMS EXIST ?  One-line explanation: Molecules of elements consist of  Atoms of most elements are not identical atoms, ranging from able to exist independently. single-atom molecules to Atoms form molecules and complex structures with many ions. atoms, with their atomicity  These molecules or ions indicating the number of atoms aggregate in large numbers to in each molecule. form the matter that we can  Composition: see, feel or touch. o Consist of the same type of atoms.  Single-Atom Molecules: WHAT IS A MOLECULE ? o Some elements, like  One-line explanation: A argon (Ar) and helium molecule is the smallest particle (He), have molecules with of a substance, consisting of two only one atom. or more atoms chemically  Diatomic Molecules: bonded, capable of independent o Molecules with two existence and retaining the atoms, e.g., oxygen (O₂). substance's properties.  Triatomic Molecules:  Definition of molecule: o Molecules with three o Group of two or more atoms, e.g., ozone (O₃). atoms chemically  Atomicity: bonded. o The number of atoms in a o Held together by molecule. attractive forces.  Complex Structures:  Characteristics: o Metals and elements like o Smallest particle capable carbon have large, of independent existence. pg. 5 All rights reserved. Do not copy or transmit this material in any form without express permission of author. Legal action will be taken in case of violation of the copyright. Downloaded From: Telegram ID @ajinkyasolunke YouTube Channel: Ajinkya Solunke Instagram ID ajinkya_solunke indefinite numbers of RATIOS bonded atoms. For water (H2O) following are the mass ATOMICITY OF SOME ELEMENTS by mass ratio and ratio by number of Type pf Name Atomicity atoms element Non- Argon Monoatomic  Mass by mass ratio for water: Metal o Mass of hydrogen = 2 x 1 = Helium Monoatomic 2 Oxygen Diatomic o Mass of oxygen = 16 Hydrogen Diatomic o Ratio of mass of hydrogen Nitrogen Diatomic and mass of oxygen = 2:16 Chlorine Diatomic = 1:8 Phosphorus Tetra-atomic  Number of atom ratio for water Sulphur Poly-atomic o Number of atoms of hydrogen = 2 MOLECULES OF COMPOUNDS o Number of atoms of oxygen = 1  One-line explanation: o Ratio of number of atoms Molecules of compounds are of hydrogen and number formed by atoms of di erent of atoms of oxygen = 2:1 elements combining in definite mass ratios.  Formation: WHAT IS AN ION ? o Atoms of di erent elements join together in  One-line explanation: Ions are definite proportions. charged particles that can be  Examples and Combining Ratios: single atoms or groups of atoms, o Water (H₂O): with negatively charged ions  Elements: called anions and positively Hydrogen and charged ions called cations. Oxygen  Definition of ion:  Combining ratio by o Charged species in mass: 1:8 compounds of metals and o Ammonia (NH₃): nonmetals.  Elements: Nitrogen o Can be a single charged and Hydrogen atom or a group of atoms  Combining ratio by with a net charge. mass: 14:3  Types of Ions:  Carbon Dioxide (CO₂): o Anion: Negatively charged o Elements: Carbon and ion. Oxygen o Cation: Positively charged o Combining ratio by mass: ion. 3:8  Example: pg. 6 All rights reserved. Do not copy or transmit this material in any form without express permission of author. Legal action will be taken in case of violation of the copyright. Downloaded From: Telegram ID @ajinkyasolunke YouTube Channel: Ajinkya Solunke Instagram ID ajinkya_solunke o Sodium Chloride (NaCl): 2 Sulphate SO42-  Positively charged sodium ions (Na⁺). Valency Name of Symbol  Negatively charged ion chloride ions (Cl⁻). Metals  Polyatomic Ions: 3 Aluminium Al3+ o Groups of atoms carrying 3 Iron (III) Fe3+ a charge. Non-Metallic Element 3 Nitride N3- Polyatomic ions Valency Name of Symbol 3 Phosphate PO43- ion Metals 1 Sodium Na+ WRITING CHEMICAL FORMULAE 1 Potassium K+  One-line explanation: The 1 Silver Ag+ chemical formula of a compound 1 Copper (I) Cu+ represents its composition using Non-Metallic Element 1 Hydrogen H+ element symbols and valencies, 1 Hydride H- with rules for balancing charges, 1 Chloride Cl- order of elements, and notation 1 Bromide Br- for polyatomic ions. 1 Iodide I-  Definition: Polyatomic Ions o Symbolic representation 1 Ammonium NH4+ of a compound's 1 Hydroxide OH- composition. 1 Nitrate NO3-  Symbols and Combining 1 Hydrogen HCO3- Capacity: Carbonate o Valency: The combining power or capacity of an Valency Name of Symbol element. ion o Used to determine how Metals atoms of di erent 2 Magnesium Mg2+ elements combine. 2 Calcium Ca2+  Analogy: 2 Zinc Zn2+ o Valency can be thought of 2 Iron (II) Fe2+ as the "arms" of an atom. 2 Copper (II) Cu2+ o Example: Octopus (O) Non-Metallic Element with 8 arms and humans 2 Oxide O2- (H) with 2 arms. 2 Sulphide S2- o If an octopus (O) holds 4 Polyatomic ions humans (H), the formula 2 Carbonate CO32- is OH₄. 2 Sulphite SO32- pg. 7 All rights reserved. Do not copy or transmit this material in any form without express permission of author. Legal action will be taken in case of violation of the copyright. Downloaded From: Telegram ID @ajinkyasolunke YouTube Channel: Ajinkya Solunke Instagram ID ajinkya_solunke  Rules for Writing Chemical Formulas: o Balancing Valencies/Charges:  Charges on ions must balance. o Metal and Non-metal 4. Formula of magnesium chloride Compounds:  Metal name or symbol written first.  Examples: Calcium oxide (CaO), Sodium chloride (NaCl). 5. Formula for aluminium oxide  Polyatomic Ions: o Indicate number of ions with brackets and a subscript. o Example: Magnesium hydroxide (Mg(OH)₂). o For one polyatomic ion, brackets are not needed. 6. Formula for calcium oxide Example: Sodium hydroxide (NaOH). FORMULLAE OF SIMPLE COMPOUNDS Formula: CaO 1. Formula of hydrogen chloride 7. Formula of sodium nitrate 2. Formula of hydrogen sulphide 8. Formula of calcium hydroxide 3. Formula of carbon tetrachloride pg. 8 All rights reserved. Do not copy or transmit this material in any form without express permission of author. Legal action will be taken in case of violation of the copyright. Downloaded From: Telegram ID @ajinkyasolunke YouTube Channel: Ajinkya Solunke Instagram ID ajinkya_solunke  Relative molecular mass of water (H2O) : o Atomic mass of hydrogen =1u o Atomic mass of oxygen = 16 u 9. Formula of sodium carbonate o Molecular mass = Total Atomic mass of hydrogen + Total atomic mass of Oxygen = [2x1] + 16 = 18 u  Relative molecular mass of HNO3: o Atomic mass of hydrogen =1u o Atomic mass of nitrogen = 10. Formula of ammonium sulphate 14 u o Atomic mass of oxygen = 48 u o Molecular mass = Total Atomic mass of hydrogen + Total Atomic mass of nitrogen + Total Atomic mass of oxygen = 1 + 14 + [3x16] = 63 u MOLECULAR MASS  One-line explanation: FORMULAE UNIT MASS Molecular mass is the total of the atomic masses of all atoms in a  One-line explanation: Formula molecule, expressed in atomic unit mass is the sum of atomic mass units (u). masses in a formula unit of an  Definition: The sum of the ionic compound, calculated atomic masses of all atoms in a similarly to molecular mass. molecule.  Definition:  Calculation: o The sum of atomic o Add the atomic masses of masses of all atoms in a each atom in the formula unit of a molecule. compound.  Expression:  Calculation: o Expressed in atomic mass o Add the atomic masses of units (u). each atom in the formula  Purpose: unit. o Represents the relative o Similar to calculating mass of a molecule. molecular mass. pg. 9 All rights reserved. Do not copy or transmit this material in any form without express permission of author. Legal action will be taken in case of violation of the copyright. Downloaded From: Telegram ID @ajinkyasolunke YouTube Channel: Ajinkya Solunke Instagram ID ajinkya_solunke  Usage: calculated calculated o Used for substances by summing similarly by atomic summing whose constituent masses. atomic particles are ions. masses. o Example: Sodium chloride Expression Expressed Expressed (NaCl). in atomic in atomic  Example Calculation: mass units mass units o Sodium chloride (NaCl): (u), e.g., (u), e.g., H₂O = 18 u. NaCl = 58.5  Sodium (Na): 23 u u.  Chlorine (Cl): 35.5 u  Formula unit mass = 1 × 23 + 1 × 35.5 = 58.5 u o Calcium chloride (CaCl2)  Calcium (Ca) = 40 u  Chloride (Cl) = 35.5 u  Formula unit mass = 40 + [2 x 35.5] = 40 + 71 = 111 u MOLECULAR MASS Vs. FORMULA UNIT MASS Aspect Molecular Formula Mass Unit Mass Definition Sum of Sum of atomic atomic masses of masses of all atoms in all atoms in a molecule. a formula unit. Type of Applies to Applies to Substance molecular ionic compounds compounds (e.g., water, (e.g., NaCl, CO₂). MgO). Constituent Molecules. Ions or Particles formula units. Calculation Total mass Total mass of a of a formula molecule, unit, pg. 10 All rights reserved. Do not copy or transmit this material in any form without express permission of author. Legal action will be taken in case of violation of the copyright.