An Introduction to Bonding and Octet Rule

Slide 1: Unit 3: Compounds Octet Rule for Bonding

Slide 2: Objectives • Why do some substances drop and bounce and some substances drop and break? • Why do some substances remain solid when they are heated, while others liquefy quickly? • The answers to these questions are found in the electronic structure of the atoms involved.

Slide 3: Objectives • The physical and chemical properties of elements and compounds depend on the bonds that hold them together. • In this unit we will examine the relationship between: electronic structure/chemical bonding/properties of a substance

Slide 4: Quick Vocabulary • Molecule = compound (made up of more than one atom of an element) • Ionic Bond – two atoms attracted through opposite electric charge • Metallic Bond – a bond between two metals • Covalent Bond – two atoms that share electrons • Lone Pairs – unshared electrons

Slide 5: Chemical Bonding • A chemical bond is a force of attraction that holds two atoms together. • Bonds are formed and broken during chemical reactions. • Bonds form between atoms to achieve stability. • Bonding involves only the valence

Slide 6: Three Types of Bonds: Ionic Bonds • electrostatic forces between particles of opposite charge. • formed by the transfer of electrons. • formed between a metal (+) and a nonmetal (-) • or with polyatomic ions (groups of atoms that behave as a unit and carry a charge.

Slide 7: Three Types of Bonds: Covalent Bonds • sharing of electrons between two atoms. • formed between two nonmetals • Pure Covalent - two atoms with similar electronegativity values. • Polar Covalent - two atoms with an intermediate electronegativity difference. • polar bonds behave as if one end is negative and the other end is positive.

Slide 8: Three Types of Bonds: Metallic Bond • force of attraction that holds metals together. • positive metal ions are uniformly arranged in a sea of electrons made up of the valence electrons of metal atoms.

Slide 9: Lewis Diagram of the Molecule G. N. Lewis 1875-1946 American Chemist Drew structures that help us to visualize a molecule.

Slide 10: Lewis Symbols Lewis symbols show the valence electrons as dots arranged around the atomic symbol. H· hydrogen: Na · sodium: ·· Cl ·· · ·· chlorine:

Slide 11: Valence Electrons • the outer electrons which participate in bonding • For the representative elements the number of valence electrons is equal to the group number. • Atoms often gain, lose, or share electrons in order to achieve the same number of valence electrons as the noble gas closest to them in the periodic table.

Slide 12: Valence Electrons • Noble gases are stable as evidenced by their high ionization energies, low affinity for additional electrons, and general lack of chemical reactivity. • This observation has lead to the octet rule: atoms tend to gain, lose, or share electrons until they are surrounded by eight valence electrons.

Slide 13: Lewis Structures Octet Rule In compound formation an atom gains or loses electrons, or shares pairs of electrons, until its valence shell has eight electrons. Bonding pairs will have a multiple of 8 electrons between them.

Slide 14: Example 1: C2 (diamond) C2 How many valence electrons? 4 How many times? x2 8 Is it a multiple of 8? Yes = single bond No molecule

Slide 15: Octet Rule Single Bonding Puzzle Reconstruct the original rectangle by matching the sides who fulfill the octet rule.