Chapter 17 - Chemical Bonding: FACTS: o Charged things interact with other charged things o If the signs are opposite (protons and electrons), things attract. o Three types of bonds: Metallic, Ionic and Covalent 17.1 Metals and Alloys: Ion-an atom that has either lost or gained one or more electrons Metallic Bond: a fluid of electrons holds the positively charged metal ions together Alloy- any mixture composed of two or more metallic elements E.g.: Steel- iron, manganese and carbon 1 17.2 Ionic Bonds: The attraction between two oppositely charged ions Ionic Compound – any chemical compound made of ionically bonded ions E.g.: Sodium Chloride (Na is + and Cl is -) ♦ A positive superscript means that an electron has been LOST. (Na+) ♦ A negative superscript means that an electron has been GAINED. (Cl-) Ionic Crystal- any array of 2 dimensional ionic compounds 17.3 Covalent Bonds: 2 elements SHARING valence electrons (cosharing and valent-valence electrons) Covalent Compound - any group of atoms held together by one or more covalent bonds 2 E.g.: H2 -each H atom shares an electron with the other H atom Molecule- a group of atoms held tightly together by covalent bonds. 17.4 Covalent Polarity: Dipole- one side of a molecule is slightly positive & one side is slightly negative Electronegativity- how well atoms are able to pull electrons toward themselves E.g.: H and F, Fluorine is more electronegative & holds electrons closer & is Therefore lightly negative. Nonpolar: no dipole is formed (E.g. H2) Polar: Electronegativities are not equal & form a dipole 3 Percent Ionic Charter: o indicates the degree of polarity o determined by the difference in electronegativity 17.5 Molecular Polarity: Polar bonds create polar molecules. Chemical bonding is like a tug of war. Each atom is pulling on electrons. When one atom pulls harder than the other, the result is a polar molecule. E.g.: H2O, Oxygen is more electronegative than hydrogen and therefore “tugs” on electrons harder. This ends up forming a polar molecule The oxygen side is slightly negative. The hydrogen side is slightly positive. Polar molecules attract one another creating substances with a higher boiling temperature. E.g.: Liquid Nitrogen is nonpolar and boils at –196oC. Water is polar and boils at 100oC. 4 5