CHAPTER 13 SECTION 3

Covalent & Metallic Bonds

Objectives:

Explain how covalent bonds form

Describe molecules

Explain how metallic bonds form

Describe the properties of metals

Covalent Bonds

Most things are held together by covalent bonds

Ex: water, sugar, oxygen, wood…

Properties: low melting & boiling points; brittle in solid state

Covalent bond: when atoms share one or more pairs of electrons

Covalent Bonds:

Two atoms of nonmetals – large amount of energy is required for either atom to lose an electron

Therefore, they do not transfer they share

Covalent Bonds:

http://vinstan.wikispaces.com/file/view/covalent_bonding.gif/46392209/covalent_bonding.gif

Covalent Bonds & Molecules:

Substances containing covalent bonds consist of individual particles called molecules

Molecule: 2 or more atoms joined together in a definite ratio

Ex: Oxygen (O2)

Most molecules are composed of atomsof 2 or more elements

Covalent Bonds in a Water Molecule:

H2O

http://sayee.ca/image/water%20molecule.gif

Electron Dot Diagrams:

Shows only the valence electrons in an atom

Helps to predict how an atom might bond

Place the 1st four dots alone on each side, then pair up any remaining dots

Electron Dot Diagram of H2O

http://www.fordhamprep.org/gcurran/sho/sho/images/lewdot11.jpg

Practice with Electron Dot Diagrams:

Draw the electron dot diagram for the following elements/compounds: Carbon Oxygen Krypton H2

Covalent Compounds & Molecules:

A molecule is the smallest particle into which a covalently bonded compound can be divided and still be the same compound

http://www.chemlin.net/news/2007/mar2007/images/water-molecules.jpg

The Simplest Molecules:

Molecules are composed of at least 2 covalently bonded atoms

The simplest are made of 2 bonded atoms – called diatomic molecules

Elements found in nature as diatomic molecules are called diatomic elements Ex: Oxygen, nitrogen, fluorine, chlorine, hydrogen,

iodine…

Diatomic Elements: Oxygen

http://image.wistatutor.com/content/chemical-bonding/oxygen-forming-covalent-bond.gif http://dkreutz.basd.k12.wi.us/O2.jpg

More Complex Molecules:

Important molecules are also complex molecules

Ex: soap, plastic bottles, proteins…

Carbon atoms are the basis for many complex molecules

Each carbon makes 4 covalent bonds

More Complex Molecules:

http://www.worsleyschool.net/science/files/sugar/sugarmolecule2.gif

Metallic Bonds:

A bond formed by the attraction between positively charged metal ions and the electron in the metal

Metals therefore have properties such as malleability

Ex: metal sculptures can be made

Movement of Electrons Through Metal:

Bonding in metals: atoms are very close together; outermost energy levels overlap

Valence electrons can therefore move throughout the metal

Metal – made of positive ions with enough electrons “swimming” around to keep the ions together

Metallic bonds extend throughout the metal in all directions

Movement of Electrons:

http://sites.univ-provence.fr/~wcalup/fichiers_images/metallicblue.gif

Properties of Metals:

Electrical Conductivity Electrons moving through copper wire

Malleability & Ductility Atoms in metals can be rearranged Metals can be reshaped Malleability – into sheets Ductility – into wires

Bending without breaking When metal is bent some ions are forced closer

together Moving electrons maintain the metallic bonds

Reference:

Holt Science and Technology: Physical Science. New York: Henry Holt & Co, 2007. Print.