PHYSCI CM1 REVIEWER

• The most basic concepts in Chemistry are atoms and elements
• The idea of atoms can be traced back to the Ancient Greeks
• Atomos


  Indivisible, very small particles (according to Democritus)
• Democritus believed that all things are made up of small particles
• Democritus believed that when matter is repeatedly broken down, it will reach a point when the pieces cannot be further broken down
• Democritus' ideas were rejected by Aristotle, the most influential philosopher of the time
• Elements believed to be the building blocks of matter (by the Greeks)

  • Water (Thales)
  • Fire (Anaximenes)
  • Water, air, fire, earth (Empedocles)
• Aristotle's idea of the four elements as the composition of matter is supported by some phenomena like the burning of wood
• Robert Boyle debunked the Aristotelian concept of four elements during the 17th century
• Elements (according to Boyle)

  Pure substances that cannot be broken down into simpler substances
• The ideas of atoms and elements do not contradict each other, they give different points of view on the composition of matter
• Law of Conservation of Mass (Lavoisier)


  The total amount of the reactants is the same with the amount of the products
• Law of Definite Composition (Proust)

  Compounds contain exactly the same elements with the same proportion by mass, regardless of the source
• Dalton's Atomic Theory was based on the Laws of Conservation of Mass and Definite Composition
• Postulates of Dalton's Atomic Theory

  • All matter is composed of atoms
  • Atoms of the same element are identical
  • Atoms of different elements combine in definite ratios to form compounds
  • No atoms are created or destroyed during chemical reactions

  
• Dalton's atomic model is compared to billiard balls - small, hard spheres which cannot be further broken down

  
• Dalton's postulate that atoms of the same element have the same properties is not true anymore, as isotopes have different masses
• The discovery of electrons as a component of an atom is contrary to Dalton's idea of an indivisible atom
• Plum pudding atomic model (Thomson)

  An atom is made up of positively charged particles where the negatively charged particles (electrons) are embedded
• Experiments by Hertz, Lenard, and Rutherford showed that an atom is mostly empty space
• Rutherford's alpha-particle scattering experiment


  1. Fired alpha particles from helium atoms at a gold foil

  2. Most particles were able to pass through

  3. Many particles were scattered at wide angles

  4. Only a small number of particles were deflected at very large angles
• Plum pudding atomic model

  An atom is made up of positively charged particles where the negatively charged particles are embedded just like a plum pudding
• Cathode ray experiment by Heinrich Hertz and Philipp Lenard


  • Cathode ray penetrated thin, metal sheets
  • Majority of an atom is empty space
• Rutherford's alpha-particle scattering experiment


  1. Fired alpha particles from helium atoms at a gold foil

  2. Most particles were able to pass through

  3. Many of the undeflected particles were scattered at wide angles

  4. There was only a small number of particles which bounced back
• Rutherford's atomic model


  • The atom is mostly empty space
  • The atom has a core (nucleus) that is very small and is made up of the positive particles of the atom
  • The electrons are in constant motion around the nucleus occupying most of the atom's volume

  
• Proton


  Positively charged particle in the nucleus, discovered by Eugene Goldstein
• Neutron


  Neutral particle in the nucleus, discovered by James Chadwick
• Nucleons


  Protons and neutrons combined by a strong force in the nucleus
• Atomic number (Z)


  Number of protons in an atom, exclusive to an element
• Mass number (A)


  Sum of the number of protons and neutrons in an atom
• Isotopes


  Atoms of the same element with different number of neutrons
• Quarks


  Smaller particles that make up protons and neutrons
• Democritus claimed that matter is made up of indivisible particles called atomos
• Dalton's atomic theory postulates

  • All matter is composed of atoms
  • The atoms of the same element are identical
  • Atoms of different elements combine in definite ratios to form compounds
  • No atoms are created or destroyed during chemical reactions

  
• Protons, electrons, and neutrons were discovered to be the smallest particles of matter until the discovery of quarks
• The number of protons in an atom is equal to the number of electrons for non-electrically charged atoms
• Henry Moseley established the basis for arranging elements in the periodic table using the atomic number