Major Points*Of more than 100 different elements now known, only 9 account for about 98% of the total mass of the earth's crust, oceans, and atmosphere. In the human body, oxygen, carbon, hydrogen, and nitrogen are the most abundant elements.
*Elements are represented by symbols that usually consist of the first one ore two letters of the element's name. Sometimes, however, the symbol is taken from the element's original Latin or Greek name. *The law of constant composition states that a given compound always contains the same proportions by mass of the elements of which it is composed. *Dalton accounted for this law with his atomic theory. He postulated that all elements are composed of atoms; that all atoms of a given element are identical, but that atoms of different elements are different; that chemical compounds are formed when atoms combine; and that atoms are not created or destroyed in chemical reactions. *A compound can be represented by a chemical formula that uses the symbol for each type of atom and gives the number of each type of atom that appears in a molecule of the compound. *Atoms consist of a nucleus containing protons and neutrons, surrounded by electrons that occupy a large volume relative to the size of the nucleus. Electrons have a relatively small mass (1/1836 of the proton mass) and a negative charge. Protons have a positive charge equal in magnitude (but opposite in sign) to that of the electron. A neutron has a slightly greater mass than the proton but no charge. *Isotopes are atoms with the same number of protons but different numbers on neutrons. *The periodic table displays the elements in rows and columns in order of increasing atomic number. Elements that have similar chemical properties fall into vertical columns called groups. Most of the elements are metals. These occur on the left-hand side of the periodic table; the nonmetals appear on the right-hand side. *Each chemical element is composed of a given type of atom. These elements may exist as individual atoms or as groups of like atoms. *When an atom loses one or more electrons, it forms a positive ion called a cation. This behavior is characteristic of metals. When an atom gains one or more electrons, it becomes a negatively charged ion called an anion. This behavior is characteristic of nonmetals. A compound is always neutral overall-it has zero net charge. |
Online ResourcesPeriodic Table:
http://cnx.org/content/m38760/latest/ Atoms and Molecules: http://cnx.org/content/m15754/latest/ VideosWriting Ionic Compounds:
http://www.youtube.com/watch?v=vscoYh6m46M Writing Ionic Compounds #2: http://www.youtube.com/watch?v=ww_hvRH0Luk&feature=fvwrel Example Problems1. What element has thew atomic number of 7?
Nitrogen (N) 2. What is the formula for Ca(+2) and O(-2) CaO 3. What element has the symbol of Ar? Argon 4. How many neutrons does Si have? 28-14=14 14 neutrons 5. How many protons does Mg have? 12 6. How many electrons does Kr have? 36 7. How many electrons does O(-2) have? 10 8. How many electrons does Ca(+2) have? 18 9. What element has the symbol of Al? Aluminum 10. What is the mass number of Fe? 56 Activity
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