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Understanding Atoms and the Periodic Table

Explore the basics of atoms, isotopes, atomic mass, and the Periodic Table, including elemental properties and mass spectroscopy. Learn about metals, non-metals, and metalloids.

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Understanding Atoms and the Periodic Table

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  1. Atomsand Periodic Table

  2. Atoms Atoms are made of protons, neutrons, and electrons.

  3. Atomic number • The atomic number (Z) of an element is the number of protons in the nucleus of an atom of that element. • Since atoms are electrically neutral, the number of electrons (-) must equal the number of protons (+).

  4. Atomic symbol Periodic Table

  5. Isotopes • Isotopes: same # protons, different # neutrons • Symbol:

  6. Atomic mass • Atomic mass is a weighted average mass of the atoms in a naturally occurring sample of the element. • Calculate: multiply the atomic mass of an isotope by its percentage/100. • Do this for every isotope. • Add the atomic masses found.

  7. Isotopes • Gallium is a metallic element found in small lasers used in compact disc players. In a sample of gallium, there is 60.2% of gallium-69 (68.9 amu) atoms and 39.8% of gallium-71 (70.9 amu) atoms. What is the atomic mass of gallium?

  8. Ga-69 68.9 amu x 60.2 = 41.5 amu for 69Ga 100 Ga-71 70.9 amu x 39.8 = 28.2 amu for 71Ga 100 Atomic mass Ga = 69.7 amu

  9. Abundance • Percent abundance: % of total • Relative abundance: Most abundant isotope set at 100 %, other relative to most abundant one.

  10. Mass Spectroscopy Mass spectroscopy provides an accurate way of measuring the mass of atoms and molecules.

  11. Periodic Table • horizontal rows: periods • vertical columns: groups or families • groups 1 and 2 (1A and 2A) and groups 13-18 (3A – 8A) are called representative elements • groups 3-12 are the transition metals • Lanthanides and Actinides

  12. Periodic Table • Three main classes of elements: 1. metals 2. nonmetals 3. metalloids

  13. Metals • Most elements are metals. Properties: • Good conductors of heat and electricity • Solid at room temperature (except Mercury) • Reflect light (shiny) • Lose electrons in reactions

  14. Non-metals • Located in the upper right corner of PT • Greater variation among these than metals. • Most are gases at room temperature. • A few are solids (C, S, P) and one is a liquid (Br) • Tend to have properties opposite of metals. • Gain electrons in reactions.

  15. Metalloids • Generally have properties similar to metals and nonmetals. • An element in this group may behave like a metal under certain conditions, and then behave like a nonmetal under different conditions. • For example, the metalloid Silicon is a poor conductor of electricity, but it becomes a good conductor when it is mixed with another metalloid, Boron.

  16. Main groups • Group IA  alkali metals • Group IIA  alkaline earth metals • Group VIIIA  noble gases • Group VIIA  halogens – “salt formers” • Group VIA  chalcogens • Group VA  Nitrogen group • Group IVA  IVA group • Group IIIA  IIIA group

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