Covalent Bonds

Chemical Bond Force of attraction that holds atoms together Valence electrons are somehow altered creating an attractive force In chemical reactions, bonds are formed and/or broken

Three Types of Bonds Exist Ionic, Covalent, and Metallic In covalent bonds, electrons are shared between two atoms

Generalizations Two non-metals usually form covalent bonds Metal and non-metal atoms usually form ionic bonds Metal and metal atoms usually form metallic bonds

Terminology Molecule – two or more atoms held together by covalent bonds Diatomic Molecule – molecule containing only 2 atoms Molecular Formula – shorthand notation for a covalently bonded substance showing the number and type of atoms

Atoms held together by covalent bonds can only be separated by chemical reactions Organic elements tend to form covalent bonds Octet Rule – bonds tend to form so that an atom has an octet (8) of electrons in its last main energy level

Forming the Bond Orbitals overlap to form a bond When 2 atoms approach the nucleus of one attracts the electron orbitals of the other

Multiple Bonds Single Bond – share 1 pair of electrons Double Bond – share 2 pair of electrons Triple Bond – share 3 pair of electrons

Bond Length and Energy Bond length is distance between two bonded atoms Bond energy is energy needed to break the bond As bond length increases, the bond energy decreases (long bonds weaker)

Molecular Nomenclature Naming molecular compounds Based on a system of prefixes

One mono-sixhexa- Twodi-sevenhepta- Threetri-eightocta- Fourtetra-ninenona- Fivepenta-tendeca-

Examples of Molecular Names CO 2 CO P 2 O 5 CCl 4

Drawing Covalent Molecules Lewis structure – formula that uses symbols to represent atoms, dots for valence electrons and dashes for covalent bonds Unshared pair – pair of electrons that do not form a bond H and He are exceptions to the octet rule – they only want 2 electrons

Draw the following CH 3 Cl SiF 4 SO N 2