Atoms and Molecules

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The Law of Conservation of Mass states that mass can neither be created nor destroyed in a chemical reaction. This means the total mass of reactants equals the total mass of products in any chemical r…

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The Law of Definite Proportions states that in a pure chemical compound, elements are always present in definite proportions by mass. For example, in water (H₂O), hydrogen and oxygen are always presen…

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John Dalton proposed the atomic theory in 1808. Main postulates: (1) All matter is made of tiny particles called atoms (2) Atoms are indivisible and indestructible (3) Atoms of the same element are id…

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An atom is the smallest particle of an element that cannot usually exist independently and retains all the chemical properties of that element. Atoms are the basic building blocks of all matter. They …

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Atoms are extremely small with radius measured in nanometers (10⁻⁹ m). A hydrogen atom has a radius of about 10⁻¹⁰ m. More than millions of atoms stacked together would make a layer barely as thick as…

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Atomic mass unit (u) is the standard unit for measuring atomic masses. It is defined as exactly 1/12th the mass of one atom of carbon-12 isotope. All atomic masses are measured relative to this standa…

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A molecule is the smallest particle of an element or compound that is capable of independent existence and shows all the properties of that substance. It is formed when two or more atoms are chemicall…

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Atomicity is the number of atoms present in one molecule of an element. Examples: Monoatomic - Argon (Ar), Helium (He); Diatomic - Oxygen (O₂), Hydrogen (H₂), Nitrogen (N₂); Tetra-atomic - Phosphorus …