Ch 1 Chemistry Class 11 Notes

• Here are the detailed ch 1 class 11 chemistry notes to help you prepare for your exams.
• Definition of Isotopes with examples and also explain it.
• Determination of Relative Atomic Mass of Isotopes by Mass Spectrometer
• Definition of Empirical Formula with examples.
• Steps to Calculate Empirical Formula
• Define and explain of Combustion Analysis with its diagram and working.
• Formulas to calculate the percentages of the elements:
• Definition of Molecular Formula with examples
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• Compounds with Same Molecular Formula and Empirical Formula
• Definition of Avogadro’s Number with examples
• Definition of Stoichiometry with examples
• Definition of Limiting Reactant with examples
• Definition of Actual Yield and Theoretical Yield
• Why Actual Yield less than Theoretical Yield?
• Definition of Efficiency of Reaction  
• Solutions of Numerical of Ch 1 Some Basic Concepts of Chemistry Notes.
• Atoms of the same element can possess different masses but same atomic numbers. Such atoms of an element are called isotopes. Explanation This phenomenon of isotopy was first discovered by Soddy. Isotopes are different kind of atoms of the same element having same atomic number, but different atomic masses due to same number of protons and electrons but different number of neutrons. The isotopes of an element possess same chemical properties and same position in the periodic table. Examples • Carbon has three isotopes written as 6C 12 , 6C 13 and 6C 14 and expressed as C-12, C-13 and C-14. Each of these have 6-protrons and 6 electrons. These isotopes have 6, 7 and 8 neutrons, respectively. • Hydrogen has three isotopes written as 1H 1 , 1H 2 and 1H 3 called protium, deuterium and tritium. • Oxygen has three, nickel has five, calcium has six, palladium has six, cadmium has nine and tin has eleven isotopes. Relative Abundance of Isotopes The percentage of one isotope of an element as compared to other isotopes of the same element occurring naturally is called relative abundance of isotopes. The properties of a particular element mostly correspond to the most abundant isotope of that element. The relative abundance of the isotopes of elements can be determined by mass spectrometry.
• Facts about Isotopes • At present above 280 different isotopes occur in nature. • They include 40 radioactive isotopes as well. • About 300 unstable radioactive isotopes have been produced through artificial disintegration. • The elements like arsenic, fluorine, iodine and gold etc have only a single isotope. They are called mono-isotopic elements. • The elements of odd atomic number almost never possess more than two stable isotopes. • The elements of even atomic number usually have larger number of isotopes and isotopes whose mass numbers are multiples of four are particularly abundant. • For example, O-16, Mg-24, Si-28, Ca-40 and Fe-56 form nearly 50% of the earth’s crust. • Out of 280 isotopes that occur in nature, 154 have even mass number and even atomic number.
• Important long questions according to past papers.
• 1. Define mass spectrometer. Explain the construction and working of mass spectrometer.
• 2. Describe combustion analysis. OR How can the %age of Carbon, Hydrogen and Oxygen in the given organic compound be estimated by combustion analysis?
• 3. What is the difference between actual yield and theoretical yield?
• 4. Define limiting reactant. How is it helpful to control chemical reaction?
• 5. What is stoichiometry? Give its assumptions and relationships studied. Mention two important laws which help to perform the stoichiometric calculations.
• 6. Example# 5, 10, 11, 12, 13
• 7. Exercise Numerical 16, 17, 20, 21