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Ionic, Covalent and Metallic Bonding The type of bond that atoms form between them affect the substances properties Why do atoms form bonds • Atoms form bonds in order to have a stable electron configuration. • You will recall that Noble Gases are the least reactive (most stable) elements. They have 8 valence electrons making them very stable. • All atoms try to obtain a stable octet (8 electrons) in their outer energy level by either gaining electrons, losing electrons or sharing electrons. Bonds can Stretch and Bend • Because bonds are formed from the attraction between the nucleus of an atom and the electrons of another atom the bond is not a rigid structure but rather a flexible spring-like attraction. • The electrons are in constant motion causing the forces of attraction and repulsion to constantly change, resulting in the distance between two bonded atoms to constantly change. Ionic Bonds • Formed between ions of opposite charges. • The nucleus of one ion attracts the electrons of the other ion. • Ionic bonds are usually formed by the transfer of electrons from a metal to a nonmetal. • Cations must free up electrons for the anions to accept. Ionic Compounds • Ionic compounds are a network of ions and not molecules. • The simplest ratio of ions that combine to form an ionic compound is called a formula unit • The ratio of ions in an ionic compound depends on the charges of the ions Characteristics of Ionic Compounds • Ionic Compounds: • are always solids at room temperature • conduct electricity when dissolved in water or in the molten state • have high melting and boiling points • are brittle • are usually white and crystaline Metallic Bonds • Metallic bonds: • only exist between atoms of two different metals or atoms of the same metal element. • Are formed by delocalized valence electrons, (electrons that do not belong to only one nucleus but are free to move from nucleus to nucleus) Metallic bonds cont. • Metals atoms also have an arrangement called close packed stacking in which atoms stack in layers with the atoms on the top layer sitting between atoms on the lower layer. Characteristics of metallic bonds • Properties of Metals: • Malleable ( can be hammered into a thin sheet) • Ductile (can be drawn into a wire) • Can conduct heat and electricity easily • Shiny • All these properties can be attributed to the delocalized electrons and the close stacking of atoms Covalent Bonding • Covalent Bonds: • Often form between two nonmetals • Formed by the sharing of electrons • Polar covalent bonds are formed when atoms do not share electrons equally like in a water molecule oxygen attracts the electrons more strongly than hydrogen. • Nonpolar covalent bonds the atoms share the electrons equally two identical atoms have nonpolar covalent bonds Covalent bonds cont. • Atoms can share more than one pair of electrons. These multiple bonds usually occur between carbon, oxygen, sulfur, or nitrogen atoms. • The more bonds two atoms share the stronger the bond is and the more energy that is required to break it. • Longer bonds are weaker than shorter bonds Polyatomic ions • A group of nonmetals that are covalently bonded with an overall charge. • Polyatomic ions are found in ionic compounds • Most polyatomic ions have a negative charge with the exception of ammonium which is positively charged NH4+1 • When there is more than one of a polyatomic ion in a compound it must be place in parentheses and the subscript put outside of the parentheses • (NH4)2SO4 is the correct formula for ammonium sulfate.
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