Chemical Bonding

Review: valence electrons Valence electrons are the electrons found in the outermost energy level of the atom Valence electrons are responsible for forming chemical bonds TO THE RIGHT: Atoms of nitrogen have 5 valence electrons

Review - Octets When an atom has eight valence electrons it has an octet Octets are chemically stable Atoms want to be stable, so they will gain, lose or share electrons to have an octet (BONDING)

Why do atoms bond? We learned that octets (a full valence electron shell) are very stable. Atoms desire stability, so they will combine with other elements in order to achieve a full octet of valence electrons. To become more stable by filling their outer energy level with electrons (8)

Valence Electrons and the Periodic Table The periodic table is divided into groups which are columns of elements with similar properties Elements in the same group will have the same number of valence electrons (exception: transition metals)

Three Main Types of Bonding Ionic bonding –a metal and a nonmetal Covalent bonding – a nonmetal and a nonmetal Metallic bonding –a metal and a metal

What type of bond is it? a) Ca & S b) Li & Pt c) C & Cl Find the following elements on the periodic table and determine their bond type: a) Ca & S b) Li & Pt c) C & Cl

Ionic Bonding Metal and non-metal (one is way more electronegative than the other) Metal loses e- and becomes positive (“cation”) Nonmetal gains e- and becomes negative (“anion”) Opposites attract: the ions bond via opposite charges

PROPERTIES OF IONIC COMPOUNDS Crystalline solids – usually hard crystals High melting and boiling points – because of strong forces in the bond Soluble in water – water molecules attract the ions Conduct electricity (electrolyte)

Covalent Bonding Two or more nonmetals (not a large electronegativity difference) SHARE electrons (the outer energy levels overlap) 1, 2, or 3 electrons shared (single, double, or triple bond)

COVALENT COMPOUNDS: Soft and brittle Low melting and boiling points – because covalent bonds are weak Insoluble in water – except if dipole moment Do NOT conduct electricity - non-electrolyte

Metallic Bonding Metal and a metal Metals are held together in rigid shapes The nuclei are attracted to delocalized electrons from other atoms

Review Questions: Why do atoms bond? Which type of bond shares electrons? What is a cation? Does the metal or the nonmetal become the cation? What is a triple bond? What types of compounds are soft? Do they conduct electricity? What is an electrolyte?