7.1 – NOTES Intro to Covalent Bonding

A. Why do atoms bond? Obtain the e- configuration of a noble gas; I. The Covalent Bond A. Why do atoms bond? Obtain the e- configuration of a noble gas; 8 outer e-; octet rule; B. What is a covalent bond? Formation of a covalent bond – bond in which atoms share electrons; - shared electrons are counted as valence e- for each atom; formed between two nonmetallic elements; - when electrons are shared a molecule is formed - lone pairs – unshared pairs of e-

C. Single covalent bonds Lewis structures – use e- dot diagrams to show how e- are arranged in a molecule;

Sigma (σ) bond – name given to single covalent bonds occurs when the electron pair is shared in an area centered between the two atoms found in all covalent molecules every covalent single bond has a σ component

D. Multiple covalent bonds – occurs between N, O, C, and S double bond – formed when two pairs of electrons are shared triple bond – three shared pairs of electrons Pi (π) bond – formed when parallel p orbitals overlap multiple bonds consist of one sigma bond and at least one pi bond double bond – one sigma and one pi bond triple covalent bond – one sigma bond and two pi bonds pi bond always accompanies a sigma bond;

1 sigma, 1 pi! 1 sigma 2 pi!

E. Strength of covalent bonds Bond dissociation energy (bond energy) (BE) Definition: the energy required to break a specific covalent bond; always a positive value b/c bond breaking always requires energy (endothermic!); more energy is needed to break shorter, stronger bonds;   What factors make a bond stronger? Strength depends on distance b/t bonded nuclei;

Bond length vs. bond strength: bond length – distance between the two bonding nuclei determined by the size of the atoms and how many electron pairs are shared as # shared electron pairs increases, bond length decreases shorter the bond length, the stronger the bond; longest (weakest) shortest (strongest) Single triple

II. Naming molecules A. Naming binary molecular compounds Use prefixes to indicate how many of each atom are present. The first element keeps its name and has a prefix if more than one atom is present. The second atom will end in –ide and always has a prefix.   1 – mono 2 – di 3 – tri 4 – tetra 5 – penta 6 – hexa 7 – hepta 8 – octa 9 – nona 10 – deca

Examples: NO nitrogen monoxide PCl5 phosphorus pentachloride N2O3 dinitrogen trioxide B. Common names of some molecular compounds Methane – CH4 Ammonia – NH3