Chemical Bonding Chapter 13 Covalent Bonds Section 3

Covalent Bonds A chemical bond is formed when two atoms share valence electrons is called a covalent bond. Covalent bonds form between two or more nonmetals. In a covalent bond, both atoms attract the two shared electrons at the same time. Ex: two fluorine atoms share a pair of e- so they each have full valence shells.

Covalent Bonds and Molecules molecule – two or more atoms chemically combined in a specific ratio, smallest piece of a compound molecular compounds consist of molecules having covalently bonded atoms Characteristics of Molecular Compounds: Much weaker than ionic bonds Have much lower melting/boiling points. All nonmetals Most molecular compounds are poor conductors of electricity and are often used as insulators. Ex: plastic and rubber Pure water does not conduct electricity.

Diagramming Covalent Bonds Electron-dot diagram – (also known as a valence dot diagram) the symbol for the element surrounded by as many dots as there are valence electrons How to Write Them The dots are written in pairs. Begin at the right of the element with single dots, add dots to the top, left side and bottom. Then begin adding a second dot to each side with any remaining valence e-.

Diagramming Covalent Bonds Cont… The # of valence e- needed to fill the valence shell is the # of bonds the element can form. Oxygen has 6 valence e-, so it can form 2 bonds. Nitrogen has 5 valence e-, so it can form 3 bonds. Double bond -- when 2 pairs of e- are shared between atoms Triple bond -- when 3 pairs of e- are shared between atoms

The Simplest Covalent Molecules The simplest molecules are made up of two bonded atoms. Two atoms of the same element bonded together are called diatomic molecules. Elements found in nature as diatomic molecules are known as diatomic elements. More Complex Molecules Carbon has 4 valence electrons, leaving 4 empty spaces in its outer shell, so carbon can form ___ covalent bonds.

Metallic Bonds Electrons in the outer energy levels of metals are not held tightly to the atom. They form a “shared pool” of electrons. Metallic bonds are formed when the positive metal atoms attract the pooled electrons. Movement of Electrons Throughout a Metal The valence shells of the metal atoms overlap, allowing electrons to flow freely throughout the metal.

Properties of Metals Conducting Electrical Current Reshaping Metals Since electrons are free to move between atoms, metallic bonding allows metals to conduct electricity very easily. Reshaping Metals Ductility/malleability – since electrons slide easily throughout metals Bonding Without Breaking Moving electrons allow metals to bend and keep the new shape.

Ionic Bonds Covalent Bonds Metals and Nonmetals Nonmetals and nonmetals Gain or Lose Electrons Share Electrons High melting points Low melting Points Ions conduct electricity. Solid ionic compounds do not. Does not conduct electricity; insulators Stronger bond and stronger charges Weaker bond