Importance of Chemistry:
Chemistry is the branch of science that deals with the composition, properties, and interactions of matter. It helps us understand the nature and behavior of various substances and forms the foundation for multiple scientific and industrial fields.
Nature of Matter:
Matter is anything that has mass and occupies space. It exists in different states: solid, liquid, and gas. Matter can be classified into pure substances (elements and compounds) and mixtures (homogeneous and heterogeneous). Elements consist of one type of atom, while compounds are composed of two or more types of atoms chemically combined in fixed ratios.
Properties of Matter and Their Measurement:
Properties of matter can be categorized as physical (e.g., melting point, boiling point, density) and chemical (e.g., reactivity, flammability). Measurement of these properties involves using various units and instruments, ensuring precision and accuracy. SI units are the standard units used in scientific measurements.
Uncertainty in Measurement:
All measurements have some degree of uncertainty, which is influenced by the limitations of measuring instruments and human error. Significant figures are used to express the precision of measurements, and rules are applied to determine the number of significant figures in a calculated result.
Laws of Chemical Combinations:
1. Law of Conservation of Mass: Mass is neither created nor destroyed in a chemical reaction. The mass of reactants equals the mass of products.
2. Law of Definite Proportion: A pure compound always contains the same elements combined in the same proportion by mass.
3. Law of Multiple Proportions: When two elements form more than one compound, the masses of one element that combine with a fixed mass of the other are in simple ratios.
4. Gay Lussac’s Law of Gaseous Volumes: Gases react in volumes that bear simple ratios to each other and the volumes of the products, provided all measurements are at the same temperature and pressure.
5. Avogadro’s Law: Equal volumes of gases at the same temperature and pressure contain an equal number of molecules.
Chemistry Class 11 Dalton's Atomic Theory
Dalton proposed that matter is composed of small indivisible particles called atoms. Atoms of the same element are identical, while atoms of different elements differ in mass and properties. Atoms combine in simple whole-number ratios to form compounds. However, modern discoveries have modified some of Dalton's postulates.
Difference Between Atomic and Molecular Masses
Atomic Mass: The mass of an atom, typically expressed in atomic mass units (amu), where 1 amu is defined as one-twelfth the mass of a carbon-12 atom.
Molecular Mass: The sum of the atomic masses of all atoms in a molecule. It is a relative number and can be expressed in grams as molar mass.
Mole Concept and Molar Masses:
Mole: The amount of substance containing as many entities (atoms, molecules) as there are in 12 grams of carbon-12. One mole equals 6.022 * 10^23 entities (Avogadro's number).
Molar Mass: The mass of one mole of a substance, usually expressed in grams per mole (g/mol)
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Percentage Composition:
The percentage composition of a compound is calculated by dividing the mass of each element by the total molecular mass of the compound and multiplying by 100. This helps in determining the empirical and molecular formulas of compounds.
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Stoichiometry and Stoichiometry Calculations:
Stoichiometry involves the calculation of reactants and products in chemical reactions using balanced chemical equations. It helps in understanding the quantitative relationships between substances involved in reactions. Key concepts include the limiting reagent, theoretical yield, and per cent yield.
These study notes provide an overview of fundamental concepts in chemistry, helping Class 11 students build a strong foundation for advanced topics in the subject.