Leska

• Empedocles


  Greek fundamental theory of matter - there are only four elements (earth, air, fire, water) that make up matter, and the properties of materials are imparted by the different proportions of these four elements
• Alchemy


  Intertwined chemical questions with mythical and spiritual concepts to try to transmute base metal into gold, discover a universal cure for diseases, and discover a means of prolonging life, but none of these aims succeeded. However, alchemy contributed numerous techniques and concepts to chemistry such as systematic logical approaches, knowledge of medicinal chemistry, and development of industrial chemistry. Practical and simple small-scale processes such as soap-making, glass manufacturing, charcoal production, and pigment and dye manufacturing originated during the period of alchemy.
• Democritus


  Believed that all matter is composed of very small particles called atoms, from the Greek word 'atomos' meaning 'indivisible' or 'uncuttable'
• Aristotle


  Did not believe in the existence of atoms, and asserted that all matter was continuous, an idea that was accepted for almost 2000 years
• Robert Boyle


  Published 'The Skeptical Chymist' in 1661, which led to the end of Aristotle's four-elements theory and the practice of alchemy, and to the development of the atomic theory of matter
• Dalton's Atomic Theory


  Postulates: 1) Elements are made up of small indivisible particles called atoms, 2) In any given pure element, the mass and other properties of all the atoms are the same, and atoms of different elements differ in mass and other properties, 3) Compounds are composed of atoms of more than one element in a consistent or constant whole number ratio, 4) In a chemical reaction, atoms are neither created nor destroyed, they simply combine, separate, or rearrange
• Dalton's concepts about matter and atoms are more detailed than those of Democritus
• Law of Definite Proportion


  When forming a compound, elements always combine in similar proportions by mass regardless of the size of the sample
• Law of Multiple Proportions

  If two or more different compounds are combined of the same two elements, then the ratio of the masses of the second element combined with a certain mass of the first element is always a ratio of small whole numbers
• Discovery of X-rays and Radioactivity

  In 1895, Wilhelm Rontgen discovered X-rays, and Antoine Becquerel started studying the fluorescent properties of some substances, accidentally learning that the darkening of thickly wrapped photographic plates occurs after exposing them to a uranium compound. Marie Curie proposed the term 'radioactivity' to describe the ability of material to undergo spontaneous emission of particles or radiation.
• 3 Types of Rays Emitted by Radioactive Materials

  • Alpha Rays (positively charged alpha particles)
  • Beta Rays (high-energy electrons)
  • Gamma Rays (high-energy, no charge, similar to X-rays)
• Plum Pudding Model of an Atom

  Proposed by Joseph John Thomson in 1897, this model explained the neutrality of an atom by illustrating how the negatively charged electrons (plum) are mixed with smeared-out positive charges (pudding)
• Rutherford's Experimental Design and Conclusions

  Rutherford discovered the proton, that most of the atom is empty, that the nucleus is very dense, very small, and positively charged, and that the electrons are located outside the nucleus
• James Chadwick's Experimental Design and Discovery

  In 1932, James Chadwick proved the presence of neutral subatomic particles, which he named neutrons
• Robert Millikan's Findings


  Found that an electron has a charge equal to -1.6022x10^-19 Coulombs, and a mass of 9.10x10^-28, 1840 times lighter than a proton

  
• Bohr's Model


  Proposed an atomic model that shows electrons move in concentric orbits around the nucleus
• Timeline of the Brief History on Matter and Atoms

  • 450 BC - Empedocles' four-element theory
  • 400 BC - Democritus' atomic theory
  • 380-320 BC - Aristotle's continuous matter theory
  • 1799 - Proust's law of definite proportion
  • 1808 - Dalton's atomic theory
  • 1869 - Mendeleev's periodic table
  • 1890s - Becquerel and Curie's discovery of radioactivity
  • 1895 - Rontgen's discovery of X-rays
  • 1897 - Thomson's discovery of the electron
  • 1904 - Thomson's plum pudding model
  • 1908-1917 - Millikan's electron charge measurement
  • 1910-1911 - Rutherford's atomic model
  • 1913 - Bohr's atomic model and Moseley's X-ray studies
  • 1919 - Rutherford's discovery of the proton
  • 1932 - Chadwick's discovery of the neutron
• Atomic Number


  The number of protons in the nucleus of each atom of an element

  
• Atomic Mass


  The total number of neutrons and protons present in the nucleus of an atom of an element

  
• Discovery of subatomic particles


  1. Prompted study of variations in characteristics of elements

  2. Henry Moseley found different metals bombarded with electrons produced varying X-ray frequencies

  3. Moseley attributed this to differences in positive charge in nucleus

  4. Moseley correlated frequencies to whole numbers, assigning atomic numbers

  
• Atomic number (Z)


  Identifies an atom, indicates number of protons and electrons in a neutral atom

  
• Atomic mass (A) is the total number of neutrons and protons in the nucleus

  
• Hydrogen has one proton but no neutrons

  
• Mendeleev arranged elements by atomic mass, leading to periodic table


  1869
• Moseley argued periodic table should be based on atomic number


  1913
• Periodic table is still arranged by atomic number
• Isotopes


  Atoms of the same element with different atomic masses
• Isotopes of hydrogen


  • Protium
  • Deuterium
  • Tritium

  
• Ions


  Atoms with a net positive or negative charge due to loss or gain of electrons
• Cations


  Positively charged ions
• Anions


  Negatively charged ions
• Charge of ion depends on whether number of protons or electrons is greater
• Atomic Number


  The number of protons in the nucleus of each atom of an element

  
• Atomic Mass


  The total number of neutrons and protons present in the nucleus of an atom of an element

  
• Discovery of subatomic particles


  1. Prompted study of variations in characteristics of elements

  2. Henry Moseley found different metals bombarded with electrons produced varying X-ray frequencies

  3. Moseley attributed this to differences in positive charge in nucleus

  4. Moseley correlated frequencies to whole numbers, which he assigned as atomic numbers

  
• Atomic number (Z)


  Identifies an atom, refers to number of protons in nucleus, equals number of electrons in neutral atom

  
• Atomic mass (A) is total number of neutrons and protons in nucleus
• Hydrogen has one proton but no neutrons
• Gaps in periodic table led to discovery of new elements
• Isotopes


  Atoms of same element with different atomic masses