Chemical BondingChapter 8

Covalent and Metallic Bonds

Section 3

Covalent Bonds

• A covalent bond forms when atoms share one or more electrons.

• Atoms with almost a full set of electrons in their outer energy levels enter into covalent bonds with each other.

• Substances that have covalent bonds tend to have low melting points and boiling points and are brittle in the solid state.

Covalent Bonds and Molecules

• Substances that have covalent bonds make up particles called molecules.

• A molecule is usually made of two or more atoms joined in a definite ratio.

Electron-Dot Diagrams

• An electron-dot diagram is a way to represent the valence (outer energy level) electrons of an atom or molecule.

• Place the first four dots alone on each side, then pair up any remaining dots.

Covalent Compounds and Molecules

•The molecule is the smallest particle of a covalently bonded compound can be divided into and still be the same compound.•The simplest molecules are composed of at least two covalently bonded atoms.•They are called diatomic

molecules. e.g. H2, O2, N2, F2,Cl2, Br2, I2

•Other molecules are morecomplex.

Metallic Bonds• A metallic bond is a bond formed by the

attraction between positively charged metal ions and the electrons surrounding these ions.

• Positively charged metal ions form when metal atoms lose electrons.

Properties of Metals• Electrical Conductivity – The free valence

electrons allow metals to conduct electricity (current is the flow of electrons).

• Malleability and Ductility– because the electrons move freely around the metal ions, the atoms in metals can be rearranged.

• Bending without Breaking – The moving electrons maintain the metallic bonds no matter how the shape of the metal changes.

It’s lab time! Covalent Bonds