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Atoms and Periodic Table

Atoms and Periodic Table. Atoms. Atoms are made of protons, neutrons, and electrons. Atomic number. The atomic number (Z) of an element is the number of protons in the nucleus of an atom of that element.

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Atoms and 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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