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 Rutherford and his students (Hans Geiger and Ernest Marsden) bombarded very thin gold foil with α–particles. Rutherford’s famous α–particle scattering experiment is represented in Fig. 2.5. A stream of high energy α–particles from a radioactive source was directed at a thin foil (thickness ∼ 100 nm) of gold metal. The thin gold foil had a circular fluorescent zinc sulphide screen around it. Whenever α–particles struck the screen, a tiny flash of light was produced at that point. The results of scattering experiment were quite unexpected. According to Thomson model of atom, the mass of each gold atom in the foil should have been spread evenly over the entire atom, and α– particles had enough energy to pass directly through such a uniform distribution of mass. It was expected that the particles would slow down and change directions only by a small angles as they passed through the foil. It was observed that : (i) most of the α– particles passed through the gold foil undeflected. (i...

          Electron Discovery 1. J.J. Thomson's Experiment (1897): Thomson investigated cathode rays using a cathode ray tube. 2. Cathode Ray Tube: A vacuum tube with electrodes at both ends, where electricity passes through. 3. Observations:     - Cathode rays were deflected by electric and magnetic fields.     - Deflection indicated a negatively charged particle.     - Charge-to-mass ratio was calculated. 4. Conclusion: Electrons are negatively charged particles with:     - Charge: -1.602 x 10^-19 C     - Mass: 9.109 x 10^-31 kg     - Charge-to-mass ratio: 1.759 x 10^11 C/kg Proton Discovery 1. Ernest Rutherford's Gold Foil Experiment (1919): Rutherford bombarded gold foil with alpha particles. 2. Gold Foil Experiment:     - Alpha particles scattered by gold foil indicated a dense, positively charged nucleus.     - Scattering pattern revealed the nucleus's size and charge. 3. Observ...

1. Dalton's Atomic Theory  JOHN DALTON John Dalton proposed the modern atomic theory in 1803. Key points: 1. Atoms are indivisible: Atoms cannot be divided into smaller particles. 2. Atoms are identical: Atoms of the same element have identical properties. 3. Atoms have mass: Atoms have a specific mass. 4. Atoms combine in whole numbers: Atoms combine in simple whole-number ratios to form compounds. 5. Chemical reactions involve atom rearrangement: Atoms are rearranged during chemical reactions, not created or destroyed. Example Hydrogen gas (H2) consists of two identical hydrogen atoms. 2. Atomic Mass Atomic mass is the mass of a single atom of an element, measured in atomic mass units (amu). 1. Protons, neutrons and electrons: Atomic mass includes protons, neutrons and electrons. 2. Isotopes: Atoms with the same number of protons (atomic number) but different numbers of neutrons. 3. Average atomic mass: Weighted average of isotopic masses. Example Hydrogen atomic mass = 1.00794 a...

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  Laws of Chemical Combinations: Understanding the Basics Chemical combinations, or chemical reactions, occur when elements come together to form compounds. These reactions follow specific rules, ensuring predictable outcomes. Let's break down the five fundamental laws governing chemical combinations: 1. Law of Conservation of Mass - Chemical reactions follow predictable rules. - Elements combine in specific ratios. - Mass remains constant during reactions. Simplifying Complex Chemistry Understanding these laws provides a solid foundation for exploring chemistry. By recognizing patterns and relationships, you'll better grasp chemical reactions and compound formation. - Matter cannot be created or destroyed, only transformed. - Total mass before reaction = Total mass after reaction. Example: Burning wood (mass remains constant, only form changes) 2. Law of Definite Proportions - Compounds always contain elements in fixed ratio. - Composition remains constant, regardless of sour...