Priyank Joshi (PJ Sir) – JEE | NEET Chemistry

  Class 9 Science Chapter 8 Journey Inside the Atom – NCERT Solutions & Easy Notes Part 4 | PJ Sir Part 4: Isotopes, Isobars & Average Atomic Mass Part 1 me humne Dalton, Thomson aur Rutherford ke atomic models samjhe. Part 2 me Bohr Model, electron, proton, neutron, atomic number aur mass number padha. Part 3 me electronic configuration, 2n² rule, valence electrons, octet aur valency samjhi. Ab Chapter 8 ke final part me hum padhenge: Isotopes Isobars Average Atomic Mass Important Numericals Complete Chapter Revision 1. What Are Isotopes? Hum jaante hain: Atomic Number (Z) = Number of Protons Aur: Mass Number (A) = Number of Protons + Number of Neutrons Kabhi-kabhi same element ke atoms me protons ki sankhya same hoti hai, lekin neutrons ki sankhya different hoti hai. Aise atoms ko Isotopes kehte hain. Definition of Isotopes Atoms of the same element having the same atomic number but different mass numbers are called isotopes. In simple words: Same Element Same Atomic Num...

  Class 9 Science Chapter 8 Journey Inside the Atom – NCERT Solutions & Easy Notes Part 3 | PJ Sir Part 3: Electronic Configuration & Valency Made Easy Part 1 me humne Dalton, Thomson aur Rutherford ke atomic models ko samjha. Part 2 me humne Bohr Model, subatomic particles, atomic number aur mass number padha. Ab ek important question: Atom me electrons different shells me arrange kaise hote hain? Aur kisi atom ki valency kaise pata lagti hai? Part 3 me hum Electronic Configuration, 2n² Rule, Valence Electrons, Octet aur Valency ko easy way me samjhenge. 1. Distribution of Electrons in Different Energy Levels Bohr Model ke according electrons nucleus ke around different energy levels or shells me present hote hain. These shells are represented as: K, L, M, N... or n = 1, 2, 3, 4... Electrons ko shells me arrange karne ke liye Bohr and Bury ne kuch rules suggest kiye. 2. The 2n² Rule Kisi shell me maximum kitne electrons aa sakte hain, ise calculate karne ka formula hai: ...

Class 9 Science Chapter 8 Journey Inside the Atom – NCERT Solutions & Easy Notes Part 2 | PJ Sir Part 2: Inside the Atom – Bohr Model, Subatomic Particles, Atomic Number & Mass Number Part 1 me humne atomic models ki journey samjhi — Dalton se Thomson aur Rutherford tak. Rutherford ne bataya ki atom ke centre me ek very small, dense and positively charged nucleus hota hai aur atom ka most part empty space hota hai. Lekin Rutherford ka model ek important question ka answer nahi de paya: Electrons nucleus me girte kyon nahi hain? Isi problem ko samjhane ke liye Niels Bohr ne atom ka ek improved model propose kiya. 1. Bohr’s Model of the Atom In 1913 , Niels Bohr proposed a new model to explain the stability of atoms. According to Bohr: Electrons nucleus ke around randomly move nahi karte. They move only in certain fixed circular paths . These fixed paths are called: Stationary States Orbits Shells Each shell has a definite amount of energy, so these shells are also called: Energ...

  Class 9 Science Chapter 8 Journey Inside the Atom – NCERT Solutions & Easy Notes Part 1 | PJ Sir Part 1: Journey of Atomic Models – From Dalton to Rutherford Atoms are the building blocks of matter. Everything around us—living as well as non-living—is ultimately made up of atoms. But scientists did not always know what was present inside an atom. For a long time, atoms were considered indivisible. As experiments improved, scientists discovered electrons and the nucleus, and the model of the atom changed step by step. In Part 1, we will understand this fascinating journey in simple language. 1. Early Idea of the Atom The idea that matter is made of extremely small particles is more than 2,000 years old. Acharya Kanada Ancient Indian thinker Acharya Kanada suggested that if matter or dravya is divided repeatedly, eventually we reach particles that cannot be divided further. He called these smallest particles parmanus . His ideas are recorded in the Vaisesika Sutras . Accordin...

  Class 9 Science Chapter 9 Atomic Foundations of Matter – NCERT Solutions & Easy Notes Part 4 | PJ Sir Exploration – Grade 9 Science | Chapter 9 Part 4: Properties of Ionic & Covalent Compounds, Molecular Mass & Formula Unit Mass By Priyank Joshi (PJ Sir) Chemistry Educator & Mentor | 18+ Years of Teaching Experience In Part 1, we learnt the Laws of Chemical Combination and Dalton’s Atomic Theory . In Part 2, we understood Covalent and Ionic Bonding . In Part 3, we learnt Ions, Valency, Polyatomic Ions and Writing Chemical Formulae . Now, in the final part of Chapter 9, we will understand: Properties of Ionic & Covalent Compounds Solubility Electrical Conductivity Melting & Boiling Points Molecular Mass Formula Unit Mass Important Numericals 1. Properties of Ionic and Covalent Compounds Ionic and covalent compounds are formed differently, so their properties are also different. The chapter compares substances such as sodium chloride, copper sulfate, sugar, ...

  Class 9 Science Chapter 9 Atomic Foundations of Matter – NCERT Solutions & Easy Notes Part 3 | PJ Sir Exploration – Grade 9 Science | Chapter 9 Part 3: Chemical Formulae Made Easy – Ions, Valency & Criss-Cross Method By Priyank Joshi (PJ Sir) Chemistry Educator & Mentor | 18+ Years of Teaching Experience In Part 2, we understood how atoms combine through covalent and ionic bonds . Now we will learn another very important skill: How do we write the correct chemical formula of a compound? For example: Why is magnesium chloride written as MgCl₂ and not MgCl? Why is aluminium oxide Al₂O₃ ? Why do we use brackets in Ca(OH)₂ ? Once you understand ions, valency and the criss-cross method , writing chemical formulae becomes much easier. 1. What is an Ion? When an atom loses or gains electron(s), it can form a charged species called an ion . There are two important types: Cation → Positively charged ion Examples: Na⁺, K⁺, Ca²⁺, Mg²⁺, Al³⁺ Anion → Negatively charged ion Exampl...

Class 9 Science Chapter 9 Atomic Foundations of Matter – NCERT Solutions & Easy Notes Part 2 | PJ Sir Exploration – Grade 9 Science | Chapter 9 Part 2: Chemical Bonding Made Easy – Covalent & Ionic Bonds By Priyank Joshi (PJ Sir) Chemistry Educator & Mentor | 18+ Years of Teaching Experience In Part 1, we understood the Law of Conservation of Mass, Law of Constant Proportions and Dalton’s Atomic Theory . Now comes one of the most interesting parts of Chemistry: Why do atoms combine? What is a chemical bond? Why does hydrogen form H₂ while oxygen forms O₂? How is common salt NaCl formed? Let us understand all of this step by step. 1. What is a Molecule? Atoms of the same element can combine to form a molecule of that element. For example: H + H → H₂ Two hydrogen atoms combine to form one hydrogen molecule. Atoms of different elements can also combine to form molecules of compounds. For example: H + Cl → HCl A molecule is an electrically neutral entity consisting of more than...