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Final NB 2016-2017 Turley

The Learning Goal for

The Learning Goal for this assignment is: Distinguish between bonding forces holding compounds together and other attractive forces, including hyrdrogen bonding and van der waals forces. Introduction to Ionic Compounds Those molecules that consist of charged ions with opposite charges are called IONIC. These ionic compounds are generally solids with high melting points and conduct electrical current. Ionic compounds are generally formed from metal and a non-metal elements. See Ionic Bonding below. Ionic Compound Example For example, you are familiar with the fairly benign unspectacular behavior of common white crystalline table salt (NaCl). Salt consists of positive sodium ions (Na + ) & negative chloride ions (Cl - ). On the other hand the element sodium is a silvery gray metal composed of neutral atoms which react vigorously with water or air. Chlorine as an element is a neutral greenish-yellow, poisonous, diatomic gas (Cl2). The main principle to remember is that ions are completely different in physical and chemical properties from the neutral atoms of the elements. The notation of the + and - charges on ions is very important as it conveys a definite meaning. Whereas elements are neutral in charge, IONS have either a positive or negative charge depending upon whether there is an excess of protons (positive ion) or excess of electrons (negative ion). Formation of Positive Ions Metals usually have 1-4 electrons in the outer energy level. The electron arrangement of a rare gas is most easily achieved by losing the few electrons in the newly started energy level. The number of electrons lost must bring the electron number "down to" that of a prior rare gas. How will sodium complete its octet? First examine the electron arrangement of the atom. The atomic number is eleven, therefore, there are eleven electrons and eleven protons on the neutral sodium atom. Here is the Bohr diagram and Lewis symbol for sodium: 58

This analysis shows that sodium has only one electron in its outer level. The nearest rare gas is neon with 8 electron in the outer energy level. Therefore, this electron is lost so that there are now eight electrons in the outer energy level, and the Bohr diagrams and Lewis symbols for sodium ion and neon are identical. The octet rule is satisfied. Ion Charge? What is the charge on sodium ion as a result of losing one electron? A comparison of the atom and the ion will yield this answer. Sodium Atom Sodium Ion 11 p+ to revert to 11 p + Protons are identical in 12 n an octet 12 n the atom and ion. Positive charge is 11 e- lose 1 electron 10 e- caused by lack of 0 charge + 1 charge electrons. Formation of Negative Ions How will fluorine complete its octet? First examine the electron arrangement of the atom. The atomic number is nine, therefore, there are nine electrons and nine protons on the neutral fluorine atom. Here is the Bohr diagram and Lewis symbol for fluorine: This analysis shows that fluorine already has seven electrons in its outer level. The nearest rare gas is neon with 8 electron in the outer energy level. Therefore only one additional electron is needed to complete the octet in the fluorine atom to make the fluoride ion. If the one electron is added, the Bohr diagrams and Lewis symbols for fluorine and neon are identical. The octet rule is satisfied. 59

Chemistry Notebook - Torres
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