Chapter 6 Chemical Bonding Section 2 Covalent Bonding

Chapter 6: Chemical Bonding Section 2: Covalent Bonding and Molecular Compounds

Overview • We will define molecule and molecular formula. • We will explain the relationships between potential energy, distance between approaching atoms, bond length, and bond energy. • We will state the octet rule. • We will see how to write Lewis structures. • We will explain why people use resonance structures.

Molecule • A neutral group of atoms that are held together by covalent bonds. • Molecular Compound – A chemical compound whose simplest units are molecules. • Chemical Formula – It indicates the number of atoms by using atomic symbols and subscripts. • Molecular Formula – Shows the types and numbers of atoms in a single molecule. • Diatomic Molecule – A molecule that has only two atoms.

Forming Covalent Bonds • Approaching electrons are attracted so there is a decrease in potential energy. • The nuclei also repel each other which increases potential energy. • See page 165, Figure 6 -5

Covalent Bond Characteristics • Bond Length – The distance between two bonded atoms at their minimum potential energy. AKA average distance between two bonded atoms. • Bond Energy – The energy required to break a chemical bond or form neutral isolated atoms.

Octet Rule • Chemical compounds tend to form so that each atom has an octet of electrons in its highest energy level by gaining, losing, or sharing electrons. • Exceptions: – Hydrogen and Helium only need two valence electrons. – Boron can have less than eight, others can have more than eight.

Electron-Dot & Lewis Structures • Electron Dot Notation – An atom’s atomic symbol with only dots representing the valence electrons. • An unshared pair or lone pair is two electrons that are not involved bonding. • Lewis Structure – The electron dot notation of a molecule showing bonds.

More Lewis Structures • Structural Formula – It indicates the kind, number, arrangement, and bond types, but not the unshared pairs. • Single Bond – A covalent bond with two electrons being shared. (Single Line) • Double Bond – A covalent bond with four electrons being shared. (Two Lines) • Triple Bond – A covalent bond with six electrons being shared. (Three Lines) • Multiple Bonds – A double or triple bond.

Resonance • The bonding of molecules that cannot be represented c • There is more than one way to assemble the same num

How do you make these?