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Chapter 5

Chapter 5. The Atom. First Theory. Democritus 4 th Century B.C. Believed the atom was indivisible and indestructible. His theory does not describe chemical behavior and no experimental evidence had been used. 2 nd Theory. John Dalton

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Chapter 5

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  1. Chapter 5 The Atom

  2. First Theory • Democritus • 4th Century B.C. • Believed the atom was indivisible and indestructible. • His theory does not describe chemical behavior and no experimental evidence had been used.

  3. 2nd Theory • John Dalton • Late, middle 1800’s he performed experiments that resulted in: Dalton’s Atomic Theory

  4. Dalton’s Atomic Theory • 1. All elements are composed of tiny indivisible particles called atoms. • 2. All atoms of the same element are identical and atoms of one element are different from atoms of another element. • 3. Atoms of different elements can physically mix together or chemically combine in simple whole number ratios.

  5. Dalton’s Atomic Theory, cont. • 4. Chemical reactions occur when atoms are separated, joined, or rearranged. • Atoms of one element cannot change into atoms of another element. • What idea out of his theory can we now disprove?

  6. Atoms • Atoms • Consist of: • Protons: positively charged • Neutrons: neutrally charged, mass of neutron = mass of protons • Electrons: negatively charged, smallest subatomic particle • They are tiny!!! • 100,000,000 Cu atoms = 1 cm long

  7. Rutherford’s Experiment • Rutherford bombarded alpha particles, at a thin sheet of foil • He thought they would pass through with a slight deflection due to the opposite charges. • Some bounced off at sharp angles, some even bounced straight back, however, the majority went straight thru. • What did this prove?

  8. Rutherford, cont. • The atom is mostly EMPTY SAPCE!!!!!!!!

  9. Atomic Math • Atomic number: • Equal to the number of protons. • Mass number: • Equal to the number of protons PLUS neutrons. • Number of neutrons = mass # - atomic # • Example: • Atomic number = 100 • Number of neutrons = 50 • What is the mass number? • So, why are there decimals on the periodic table?

  10. Because of Isotopes! • On the periodic table, the decimals are an average of the Isotopes: • (Remember: An isotope is the same element, just has different numbers of neutrons.) • They are chemically similar because protons and electrons are responsible for chemical behavior.

  11. Isotopes, cont. • Example: Hydrogen • Most common isotope has a mass = 1 11H • 2nd most common has a mass of 2 21H • 3rd most common has a mass of 3 31H • Other ways to write it: Hydrogen -1, Hydrogen -2, Hydrogen -3

  12. Atomic Mass Unit: • Used as a standard to compare isotopes when calculating average atomic mass. • Calculating Average Atomic Mass • Isotope A (abundance) + Isotope B (abundance) + Isotope C (abundance) + etc.

  13. Average Atomic Mass Example • Example: Micekium is an element with several different isotopes. Micekium – 99 (mass = 99.00 amu) is found 42.35% of the time, Micekium– 102 (mass = 102.00) is found 51.24% of the time, and Micekium– 101 (mass = 101.00) is found 6.41% of the time. What is the average atomic mass? • 99.00(0.4235) + 102.00(0.5124) + 101.00(0.0641) = 100.66 amu

  14. Periodic Table • Dmitri Mendeleev in the mid-1800’s arranged the 70 known elements into a systematic way. • First arranged them in a column of increasing atomic mass. • Then put elements with similar properties side by side. He left blank spaces where he didn’t know the element for the spot. • By doing this, he constructed the first periodic table.

  15. Modern Periodic Table • 1913 – Henry Moseley discovered the atomic numbers for the elements. • He then arranged the elements by order of increasing atomic number instead of atomic mass. This is the current periodic table.

  16. Parts of the Periodic Table • Periods: • Rows • Periodic Law: • Patterns everywhere! • Groups: (a.k.a. Families) • Columns • Numbered 1 – 18 or into Groups A and B

  17. Parts of the Periodic Table, cont. • Representative Elements: • The tall parts of the periodic table – the A Group. • These can be divided into 3 groups: • Metals • Nonmetals • Metalloids

  18. Metals • High electrical conductivity • High luster • Ductile • Group I A = alkali metals • Group II A = alkaline earth metals • Transition elements (Group B) and Inner Transition elements are also metals, but are not part of Group A. • Most are solid at room temperature • 80% of all elements are metals

  19. Nonmetals • Upper right portion of the periodic table • Generally nonlusterous • Generally poor conductors of electricity • Some are gases at room temperature and some brittle solids • One is even a liquid at room temperature • Group VII A is called the Halogen Group • Elements in Group VIII A (0) are called the Noble Gases • Noble Gases are inert

  20. Metalloids • These border the stair step, except for aluminum • These have properties of both metals and nonmetals

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