Atomic theory


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Atomic theory

  1. 1. Atomic Theory• Democritus (440 BCE)- realized that if you continued to cut something, eventually you would end up with something that couldn’t be cut anymore, atomos – meaning not able to divide• Atoms are the smallest particle that an element can be divided and still be the same substance• All matter is made of atoms
  2. 2. John Dalton (1803)• realized that atoms combine in very specific proportions (ratios) based on mass• all substances are made of atoms and they can not be created, divided or destroyed because they were made of a single substance• All atoms of the same element are exactly alike and different from other elements, they are unique• Atoms join with other atoms to form new substance
  3. 3. J. J. Thomson (1897)• discovered that there were small particles inside the atom, meaning that atoms can be divided into smaller substances• Electrons – negatively charged particles attracted to positively charged particles• Plum pudding model – electrons are mixed throughout the atom, soft blobs of matter
  4. 4. Ernest Rutherford (1909)• Discovered that an atom contains a nucleus with positively charged particles and that the electrons must be “floating” around the nucleus
  5. 5. Niels Bohr (1913)• Proposed that electron moved around the nucleus in energy levels (shells), but no electrons between the energy level (think ladder)• Electrons can jump from one level to another• Travel in a definite path
  6. 6. Modern Atomic Theory• Erwin Shrodinger & Werner Heisenberg• Electrons have no predictable pattern and move in a region where electrons are likely to be found called the electron cloud
  7. 7. Atoms• All atoms have a nucleus – protons (+), – neutrons (no chg) – electrons (-)• Same number of protons and electrons an atom has no charge• More protons (+) than electrons (-) the atom has a positive ion is formed (more positives than negatives)• More electrons (-) than protons (+) a negative ion is formed (more negatives than positives)
  8. 8. • 117 different element that are unique and all things known to exist come from a combination of these elements in specific mass ratios• Simplest atom is made of one proton, and 1 electron – hydrogen (has no neutrons)
  9. 9. • All additional element will have protons, neutrons and electrons• The atomic number of an element is determined by the number of protons, – 1 is hydrogen, 6 is carbon, hydrogen has 1 proton, carbon has 6 protons (you can not change the number of protons)• To find neutrons take the mass number (rounded) and subtract the protons.
  10. 10. Isotopes• Isotopes have the same number of protons but additional neutrons which causes the atomic mass to be different• Isotopes can be stable (maintain there structure) and unstable (fall apart over time)• Unstable isotopes are radioactive and will decay over time giving off particles and energy (radioactive)
  11. 11. • Mass number determines the isotope, the number of protons and neutrons added together• Most elements have isotopes• All isotopes of an element have the exact properties of the element
  12. 12. Forces in atoms• Gravitational force – pulls objects toward each other—depends on mass and distances between the objects—very small force in atoms• Electromagnetic force –– proton (+) and electrons (-) have strong attraction which keeps the electrons in motion around the nucleus of atoms
  13. 13. • Strong force – force which keeps protons from flying apart due to close distance between protons and neutrons• Weak force – relevant to radioactive atoms- allows neutrons to change into proton and electron