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The Atom and Elements

The Atom and Elements. Development of Atomic Theory:. Democritus (460-370 BC). Extremely small particles in motion.

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The Atom and Elements

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  1. The Atom and Elements

  2. Development of Atomic Theory: Democritus (460-370 BC) Extremely small particles in motion Proposed that matter was made of small particles he called atoms. In Greek this means indivisible or cannot be divided. He believed different atoms would vary in size and would be in constant motion. John Dalton (1766-1844) • Published the atomic theory: • Elements were composed of atoms. • Atoms of a given element are identical. • Atoms of different elements have different properties. • Atoms don’t change, but can be combined and rearranged with other atoms. • Compounds are formed when atoms of more than one element combine. Atom as solid object Joseph John Thomson (1856-1940) Atom as solid object with a positive center and electrons embedded in the atom Identified the electron, which carries a negative charge. He thought that electrons were embedded in the atom like raisins in raisin bread.

  3.            Development of Atomic Theory: Ernest Rutherford (1871-1937) Used high speed lightweight atoms called alpha particles to bombard very thin gold foil. Most of these alpha particles passed through the gold foil. The fact that these particles went through the foil lead to his theory that atoms have mostly empty space. Alpha particles went through spaces. Neils Bohr (1885-1962) Described the electrons moving around the nucleus in fixed orbits. Each orbit has a set amount of energy. We use this model for a basic understanding of the atom’s structure. However, more recent research has shown that electrons move around the nucleus in waves rather than elliptical orbits. Electrons are better represented as an “electron cloud.” Electrons move so fast that scientists prefer the atom model where electrons are represented by a cloud. James Chadwick (1891-1974) Solved the problem of “missing mass” in the atom by discovering the neutron.

  4. 1AMU 1AMU 1AMU 1AMU Basic Structure of an Atom Proton Positive Charge + + Neutron No Charge Electron AMU is an atomic mass unit. Electrons do not have much mass compared to protons and neutrons. Negative Charge

  5. Notice the Pattern of the Periodic Table.

  6. What Do You Notice? 1 H 1.01 2 He 4.0 3 Li 6.94 4 Be 9.01 5 B 10.81 6 C 12.01 7 N 14.01 8 O 16.00 9 F 19.00 10 Ne 20.18 11 Na 22.99 12 Mg 24.31 13 Al 26.98 14 Si 28.09 15 P 30.97 16 S 32.07 17 Cl 35.45 18 Ar 39.95 19 K 39.10 20 Ca 40.08

  7. Element Name Beryllium 4 Atomic Number Be (# of protons and electrons) Element Symbol Atomic Mass 9.01 (# of neutrons and protons) Atomic Mass-Atomic Number=# of neutrons 9 - 4 = 5 + + 5 Neutrons + +

  8. What are the numbers of protons, electrons and neutrons? Nitrogen 7 N P = E = N = 7 7 7 14.01

  9. What are the numbers of protons, electrons and neutrons? Fluorine 9 F P = E = N = 9 9 10 19.00

  10. What are the numbers of protons, electrons and neutrons? Chlorine 17 Cl P = E = N = 17 17 19 35.45

  11.   Protium Deuterium Tritium Isotopes Elements usually have differing amount of neutrons. These different forms are called isotopes. Let’s take hydrogen as an example: 1 Hydrogen H 1.01 As you can see from the atomic mass (1.01) the most naturally abundant form of hydrogen does not have a neutron. However, in rare instances isotopes form. Below are the isotopes of hydrogen: …. are isotopes of hydrogen.

  12. Energy Level Max # of Electrons 15 18 1 2 4 2 8 3 17 14 3 8 1 11 P = 5 12 2 N = 8 10 7 9 6 16 The Bohr Model 13 Valence Electrons – The electrons on the outer shell

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