Lecture 3sf

Lecture 3sf - Ions Ions are charged particles. Ordinary...

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Ions Ions are charged particles. Ordinary atoms are uncharged (neutral); they have an equal number of protons and electrons. An atom may become an ion by losing or gaining electrons. Positive ions (cations) are formed when an atom loses electrons. Negative ions (anions) are formed when an atom gains electrons. Na + is an ion of sodium. It contains 11 protons and 10 electrons. Cl - is an ion of chlorine. It contains 17 protons and 18 electrons. The Periodic Table The periodic table organizes the elements in order of their atomic number. The arrangements is such that every column of elements (called a group) has similar properties. The reason for this is that every element in a group has the same number of outer shell electrons, and forms ions of similar charge. The shell picture of electrons is something we will investigate in more detail in future chapters. Rows in the periodic table are called periods. Columns in the periodic table are called groups. Some groups have particular names. Group 8A. Noble Gases. These gases have what is roughly called a complete shell of electrons. They are chemically very unreactive. Group 1A Alkali Metals. These are soft, low-density metals which are very reactive. They have one outer shell electron (one more than previous noble gas), and form 1+ ions in their compounds. Group 2A Alkaline Earth metals. These are reactive metals with two outer shell electrons (two more than the previous noble gas), and form 2+ ions in their compounds. Group 7A
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Lecture 3sf - Ions Ions are charged particles. Ordinary...

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