Chemical Bond http://education.jlab.org/frost/electroscope.html Forms when 2 or more atoms rearrange valence electrons to increase stability Electrical attraction between the valence electrons of one atom and the nucleus of another Episode 501

Ionic Bond Forms when valence electrons are transferred from one atom to another Cation Atom loses electrons to become (+) charged Anion Atom gains electrons to become (-) charged In ionic compounds the ions are arranged in a crystal lattice; strong forces hold the ions together. Episode 501

Properties of Ionic compounds High melting and boiling points Hard – not easily crushed Conduct electricity when melted or dissolved because the ions are free to move Episode 501

Covalent Bond Electrons are shared , forming molecules Covalent compounds have weaker forces holding the molecules together Properties of covalent compounds Lower melting and boiling points Many covalent compounds are volatile liquids or gases Softer – easier to crush Are not conductors of electricity Episode 501

Electronegativity Property that tells how strong an atom’s attraction is for electrons Oxygen en. = 3.5 Hydrogen en. = 2.1 Since oxygen has a greater electronegativity than hydrogen, oxygen holds onto the electrons stronger, giving oxygen a partial negative charge and the hydrogen a partial positive charge. Episode 501

Nonpolar Covalent Bond Electrons are shared unequally creating partially charged ends or poles Nonpolar covalent bonds Electrons are shared equally because the atoms have the same or nearly the same electronegativities Electronegativity difference Type of Bond Greater than or equal to 1.7 Between 1.7 and 0.3 Less than or equal to 0.3 Ionic Bond Polar Covalent Bond Nonpolar Covalent Bond Episode 501

Examples: Problem Set #1 Li and Cl? C and O? Na and Cl? Cl and Br? Mg and F? Mg en.= 1.2 F en.= 4.0 4.0 – 1.2 = 2.8 Ionic S and Cl? S en.= 2.5 Cl en.= 3.0 3.0 – 2.5 = 0.5 Polar covalent Problem Set #1 Li and Cl? C and O? Na and Cl? Cl and Br? S and H? Episode 501