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The Atom

The Atom. Basic Atomic Theory. Atom = “indivisible” in Greek Atoms are indivisible and indestructible Atoms of same element are identical Compounds are formed by a combination of two or more different kinds of atoms Chemical reactions cannot change one element into another

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The Atom

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  1. The Atom

  2. Basic Atomic Theory • Atom = “indivisible” in Greek • Atoms are indivisible and indestructible • Atoms of same element are identical • Compounds are formed by a combination of two or more different kinds of atoms • Chemical reactions cannot change one element into another • Atoms only rearrange

  3. Atoms are Indivisible and Indestructible? • Not true! • Why? • Nuclear reactions • Subatomic particles

  4. Electrons • Discovered by J.J. Thompson using a cathode ray tube • Negatively charged (-1) • Electron’s mass is 1/1840 • Free moving around the nucleus

  5. Protons • Discovered by Moseley • Positively charged (+1) • Proton’s mass is 1 (About 2000 times more than an electron) • Atomic # = # protons • No 2 elements have the same # of protons • Found in the nucleus of an atom

  6. Neutrons • Discovered by Chadwick • No charge • Same mass as proton (1) • Found in the nucleus of an atom

  7. Atomic Number • Whole number • Atomic # = # of proton • Atomic # = # of electrons (neutral) • Atomic # = Z • Shorthand nuclear symbol • Unique for every element

  8. Atomic Number

  9. Mass Number • Whole number • Mass # = # of protons + # of neutrons • Mass # = A • Shorthand nuclear symbol • Isotopes of the same element have different mass # • Isotopes are the different kinds of atoms within one element (C-12 and C-13)

  10. Mass Number

  11. Using Mass Number • Mass # = # of protons + # of neutrons • To find # of protons • # protons = # electrons (neutral atom) • Need to know mass # and # of neutrons • To find # of neutrons: • Need to know mass # and # of protons

  12. Nuclear Shorthand • Top number is A (mass #) • Element symbol in the middle • Bottom number is Z (atomic #) A Element Symbol Z

  13. Atomic Mass • Listed on periodic table • Does not equal mass # • Given in atomic mass units (amu) • 1 amu = 1/12 the mass of C-12 atom • Is not a whole number • Due to relative abundance of naturally occurring isotopes • Weighted average

  14. Finding Atomic Mass • To calculate the atomic mass of an element • Multiply the mass of each isotope by its percent abundance (expressed as a decimal) • The quantity of a specific isotope that occurs in a natural sample of an element • Add the masses together • Also called average atomic mass

  15. Very Funny… but what is wrong with this?

  16. Isotopes • Atoms of the same element • Have the same # of protons and electrons • Have a different number of neutrons • Have a different mass number • Have the same physical and chemical properties and undergo the same chemical reactions • Have differing nuclear qualities • Some isotopes of an element may be radioactive • Average atomic mass takes all of the isotopes into consideration

  17. Isotopes

  18. Ions • Atoms are neutral • Equal number of protons and electrons • Atoms can become charged by gaining or losing an electron • Called ions • Ions are indicated with a (+) or (-) sign • Cations are positive • Anions are negative

  19. Cations and Anions

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