chem 1,2,3 lessons

• Chemistry


  The study of the properties and behaviour of matter
• Matter


  The physical substance in which the universe is made up of
• Atom


  The simplest form of matter
• Smallest particle


  Involved in a chemical reaction
• Atom


  The simplest and neutral particle in which matter can be divided into
• Sub atomic particles


  • Electrons
  • Protons
  • Neutrons
  • Mesons
  • Positrons

  
• Nucleons


  Protons and neutrons
• Nucleus


  The (+) charged area where the nucleons are located

  
• Electrons


  Revolve around energy levels (shells) located around the nucleus

  
• Atomic radius is about 10-10 m while the radius of the nucleus is about 10-15 m - 10-14 m. That means the atom is 10,000 – 100,000 times larger than the nucleus.
• A live prototype which depicts the atom can be studied by scanning the following QR code.

  
• Electron


  Symbol: e, Charge: -1.6 x 10-19 C, Mass: 9.107 x 10-31 kg
• Neutron


  Symbol: n, Charge: 0, Mass: 1.674 x 10-27 kg
• Empedocles believed that everything was made out from the four elements fire, water, air and sand.
• Democritus explained that the materialistic world was made up from very small, invisible, indivisible particles and used the word 'atomos' (atoms) for that which meant 'indivisible' or 'unbreakable'.
• Dalton's atomic theory


  • Elements are made up from 'atoms' which are extremely small particles that cannot be divided further
  • All atoms of an element are similar in mass and size while atoms of different elements are different to each other
  • Atom of one element cannot be converted to an atom of another element by means of a chemical reaction
  • Two or more atoms of different elements combine together in simple numerical ratios to form compounds

  
• Dalton's atomic model is known as the 'golf ball model'.
• Johnstone G. Stoney gave the name 'electron' for the basic particle in electricity in 1891.
• Cathode ray experiment


  1. Large voltage supplied

  2. Pressure decreased by removing some air

  3. Invisible ray formed from cathode and travelled towards anode

  4. Ray collided with surface and emitted colour
• Properties of cathode rays

  • Negatively charged
  • Particulate
  • Moves from cathode to anode in a straight path
  • Produced perpendicular to surface of cathode
  • Possesses a constant charge/mass (e/m) ratio
  • Ability to penetrate thin metal sheet
  • Collide upon metals with high mass numbers and produce X rays
• Cathode rays possessed the same nature irrespective of the type of material that the cathode is composed of and the type of gas present within the tube.
• Thompson model (Plum pudding model)


  Nucleus is a (+) charged solid sphere and (-) charged electrons are embedded throughout the nucleus

  
• Positive ray (canal ray) experiment

  1. High voltage applied

  2. Ions in air accelerated

  3. Ions collide with gas molecules, ionizing them and forming more cations

  4. Cations attracted towards negative cathode, some pass through pores
• Properties of positive rays

  • Positively (+) charged
  • Particulate
  • Moves in a linear path towards the cathode
  • e/m ratio varies according to the gas used
• The (+) rays that are obtained when H2 is used, possess a type of (+) particles that is common in matter. This particle was termed as the proton by Rutherford.
• Types of radioactive radiation

  • Alpha (α)
  • Beta (β)
  • Gamma (γ)
• Alpha (α) rays


  Equal to a He nucleus
• Beta (β) rays


  Equal to an electron
• Gamma (γ) rays


  Electromagnetic waves
• Gold leaf experiment


  1. Majority of rays/particles penetrated thin gold leaf with minimal/no deflection

  2. Some particles refracted with considerably large angles upon incidence

  3. Minimum reflected back upon incidence
• Rutherford expressed a new model for the atom based on the deductions, that major space of an atom is empty and all positive charges of an atom is confined to a small charged space which is called as the nucleus.

  
• Bohr compacted the ideas that prevailed at that era and came to a conclusion that the electrons orbit around the nucleus of an atom in a manner similar to the revolution of planets around the sun. This is the first nuclear model about atom.

  
• Bohr stated that for electrons to specifically exist in atomic orbitals, the electrostatic forces that exist between the nucleus and the electrons must be equal to the centrifugal force that is exerted on that specific electron.

  
• James Chadwick discovered the neutron based on the experimental evidence that revealed the mass of the atom to be greater than the aggregate of the masses of the protons and the electrons.
• When the metal Be is collided with α rays, neutral particles or rays are produced.
• Rutherford-Bohr structure


  Atomic structure expressed by Bohr
• The non-continuous nature of matter is
• Drawbacks of planetary model

  • No explanation about how all the protons in an atom stay together without any repulsion
  • No explanation about how electrons orbiting the nucleus do not get attracted towards the nucleus
• Neutrons


  Neutral particles or rays produced when metal Be is collided with α rays
• Neutron discovery


  James Chadwick discovered the neutron based on the experimental evidence that revealed the mass of the atom to be greater than the aggregate of the masses of the protons and the electrons