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The Atom

The Atom. The Building Block of Matter. 400 BC Democritus (Greek Philosopher) Atomos = “indivisible” …like a brick is used to build a building; an atom is used to build all matter…. First Atomic Theory. 1808 John Dalton (English Chemist)

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The Atom

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  1. The Atom

  2. The Building Block of Matter • 400 BC Democritus (Greek Philosopher) • Atomos = “indivisible” • …like a brick is used to build a building; an atom is used to build all matter…

  3. First Atomic Theory • 1808 John Dalton (English Chemist) • Using experiments formulates the first atomic theory • All elements are composed of indivisible particles called atoms • Atoms of the same elements are exactly the same • Atoms of different elements are different • Two or more elements combine to form compounds

  4. Subatomic Particles • The idea that the atoms was not a solid sphere, but a composition of small particles which came to be known as subatomic particles • Julius Plucker, William Crooks & J J Thomson • mid-1800’s

  5. J J Thomson • 1897 Discovers the electron

  6. Ernest Rutherford (English Physicist) • Gold Foil Experiments • 1908 Discovers that the atom is mostly empty space • Discovers a hard, dense center of the atom called the NUCLEUS

  7. The Gold Foil Experiment

  8. The atom is mostly empty space • Most of the particles passed straight through to gold foil. • First important discovery by Rutherford

  9. The NUCLEUS is Discovered • 1911 Rutherford proves that the particles that do not pass through are hitting a small, dense center of the atom called the nucleus. • Rutherford later goes on to discover the proton

  10. Electron Energy Levels • 1913 Niels Bohr (Danish physicist) discovers the electrons travel around the outside of the atom on different energy levels • The Bohr Model = solar system model

  11. The Neutron is Found • 1932 James Chadwick proves the existence of the neutron. • Only 4 years later the neutron is used to split the first atom • Why was the neutron’s existence more difficult to prove? • What evidence hinted of its existence?

  12. The Subatomic Particles

  13. Finding the Number of Subatomic Particles in an Atom • Atomic Number = the number of protons in the nucleus of an atom • Identifies each element • Hydrogen is 1 and it has 1 proton in its nucleus (only hydrogen has 1 proton) • Helium is 2 and it has 2 protons in its nucleus (only helium has 2 protons)

  14. Electrons • IFthe atom is neutral (same number positive charges as negative charges) then the number of electrons will be the same as protons. • ION = a charged atom (unequal number of protons and electrons) • +1 charge = the atom LOST one electron • -1 charge = the atom GAINED one electron • +2 charge = LOST 2 electrons • -2 charge = GAINED 2 electrons and so on

  15. Example of Ions • Sodium will lose one electron when it bonds • Na+1 or Na+ • Sodium’s atomic number is 11, so it has 11 protons. • The +1 charge means Na+1 has 10 electrons

  16. Another Example • Chlorine will gain an electron when it bonds • Cl-1 or Cl- • Chlorine’s atomic number is 17, so it has 17 protons • The -1 charge means Cl-1 has 18 electrons

  17. Mass Number • The two subatomic particles that have mass? • Proton and neutron, both found in the nucleus • Mass Number = # of Protons + # of Neutrons • Mass # - Atomic # = # of neutrons

  18. Practice Problems

  19. ISOTOPES • Atoms of the same element with a different number of neutrons. • Ex: carbon-12 & carbon-14 • Carbon-12 • 6 protons • 6 neutrons • 6 electrons • Carbon-14 • 6 protons • 8 neutrons • 6 electrons

  20. Isotopes of Hydrogen • Hydrogen-1 (protium) 0 neutrons • Hydrogen-2 (deuterium) 1 neutron • Hydrogen-3 (tritium) 2 neutrons

  21. The ELECTRON CLOUD • The electron cloud is separated by different energy levels. • Electrons with less energy travel on the levels closest to the nucleus. • Energy levels are divided into sub-levels • Sub-levels are divided into orbitals • All of these levels, sub-levels & orbitals can overlap.

  22. VALENCE ELECTRONS • Valence electrons = the outermost electrons • The electrons involved in bonding • Determines the chemical properties of an atom

  23. More about Electrons • Maximum # of electrons on each energy level • Level 1 = 2 electrons • Level 2 = 8 electrons • Level 3 = 18 electrons • Level 4 = 32 electrons

  24. the Stable 8 • Due to the overlapping levels, sub-levels and orbitals the maximum number of outer most electrons is EIGHT. • An atom is becomes stable when it outer-most energy levels is full of electrons • This explains the chemical bonding properties of the atoms • Atoms will do one of three things in order to fill their outer most energy levels. • gain electrons • lose electrons • share electrons

  25. Concepts Coming Up Next • The number of valence electrons an atom has determines the group it becomes to on the PERIODIC TABLE. • Groups or families of elements on the periodic table has similar chemical properties.

  26. Concepts Coming Up Next • Valence electrons determine how atoms will bond with other atoms in order to complete their outer-most energy level. • The Stable 8 • CHEMICAL BONDING • Ionic bonding (gaining/losing of electrons) • Covalent bonding (sharing of electrons)

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