CHEMICAL BONDING

Why do bonds form? To complete the valence or outer energy level Octet Rule – 8 is great! A bond forms when 2 atoms attract the same electron or electron pair

Bond Characteristics Attractive Forces pull atoms together: - (+ ) Nucleus of one atom attracts (–) electrons of another atom - Opposite charges attract = ELECTROSTATIC ATTRACTION Bond Energy - When bonds form Energy is released = Exotherimc - When bonds break Energy is absorbed = Endothermic - When 2 atoms are held together by a chemical bond they are at a LOWER energy condition than when they are separate!

Bond Characteristics (cont.) Bond Stability - Compounds with LOW energy are STABLE - Compounds with HIGH energy are UNSTABLE - Chemical Change = the rearrangement of atoms to form low energy and stable compounds Bond Strength - Weak Bond – when a small amount of energy is released - Strong Bond – when a large amount of energy is released

In nature: Exothermic reactions are favored (bond formation) UNSTABLE  STABLE REACTIVE  UNREACTIVE HIGH ENERGY  LOW ENERGY WEAK BOND  STRONG BOND

Electronegativity – Table S An atom’s ability to attract electrons Highest EN value = 4.0 = Fluorine (non-metal) Lowest EN value = 0.7 = Francium (metal) The difference in EN values of two bonded atoms can tell you the bond type

ELECTRONEGATIVITY DIFFERENCE AND BOND TYPE If the EN Difference is between: 4.0 – – – 0.0 Ionic BondPolar CovalentNon-Polar Covalent Examples: BaOCH 4 Cl 2

BOND TYPES Ionic Covalent: - Polar Covalent - Non-Polar Covalent - Coordinate Covalent Metallic

Ionic Bonds Electrons are TRANSFERRED from one atom to another Transfer from a metal to a nonmetal Metals lose electrons to the nonmetals (gain e-) High EN Diff. – the greater the difference, the stronger the ionic character Form ionic solids called Ionic Crystals (crystal lattice) Example: Which of the following has the strongest ionic bond? MgONaClLiF

Characteristics of Ionic Compounds High Melting Point High Boiling Point Conducts electricity when dissolved in solutions Does not conduct electricity in the solid phase! Soluble in water Forms crystals in solid phase

Metal Hydrides Are ALWAYS IONIC Occurs when Hydrogen bonds with a group 1 or 2 element Examples: LiHNaHKH H behaves as a nonmetal and is written second in the formula

Covalent bonds When 2 atoms SHARE electrons in the same orbital Possible to have single, double, triple bonds (1, 2, or 3 shared e- pairs) Occurs between 2 nonmetals Includes the Diatomic Molecules (B O FINCH) 2 types of Covalent Bonds 1. POLAR Covalent – sharing of e- is uneven 2. NONPOLAR Covalent – sharing of e- is even

Polar Covalent Bonds There is an uneven distribution of + and – charges due an uneven sharing of electrons in the bond EN Difference is between 0.2 – 1.6 Examples: HClH2O

Non-Polar Covalent Bonds Even distribution of + and – charges due to even sharing of electrons EN Diff = 0.0 – 0.1 ALL Diatomic molecules have nonpolar covalent bonds

Coordinate Covalent Bonds Occurs when only one atom contributes BOTH electrons in forming a bond Occurs with the polyatomic ions (see Reference Table E) Polyatomic Ions – 2 or more atoms that act as a single unit and have one charge on the entire group Ex. NH 4 + H 3 O + NO 3 - SO 4 -

Characteristics of Molecular Substances Can exist as solids, liquids, or gases SOFT in the solid phase Poor conductors of heat and electricity *Good insulators Low melting and boiling points Does not dissolve in water Soluble in Benzene or Ether (organic molecules)

Network Solids In molecular solids, the the covalently bonded atoms are linked into a GIANT NETWORK throughout the entire solid MACROMOLECULES EXTENSIVE WEB OF COVALENT BONDS (3-D FISHNET) Examples: Diamond, Silicon Dioxide, Asbestos PROPERTIES: -HIGH melting points -HARD solids -Poor conductors of heat and electricity

Metallic Bonds Bonds between metal atoms Valence electrons drift from atom to atom “SEA OF MOBILE ELECTRONS” Properties: - Very malleable - Good Conductors of Heat and electricity - Has Luster - Tenacity

Summary of Bond Types Ionic Bonds Metal – Nonmetal Forms Crystal Compound Exists as solids EN Diff = 1.7 – 4.0 High Melting/Boiling Pt Conducts electricity when in solution Soluble in water Covalent Bonds Nonmetal – Nonmetal Forms Molecule Exists as solids, liquids, gases EN Diff = 0.2 – 1.6 Polar 0.1 – 0.0 NonPolar Lo Melting/Boiling pt Does not conduct electricity in solutions Not soluble in water (dissolves in Benzene)

Summary of Bond Types Metallic Bonds Metal – Metal Sea of Mobile Electrons Good Conductors of Heat & Elec Malleable, Luster High melting/boiling points Network Solids Covalently bonded clusters of atoms Macromolecule Poor Conductors of Heat & Elect Hard Solids High melting point

ATTRACTIVE FORCES BETWEEN MOLECULES also known as IMF’s – Intermolecular Forces 2 TYPES OF MOLECULES 1. Polar Molecules – molecule has a (+) end and a (-) end - uneven or asymmetrical distributions of Bond angle is less than 180 degrees - also called DIPOLES Ex. H 2 0, NH 3, HCl 2. NonPolar Molecules – symmetrical, bond angle = All of the DIATOMIC MOLECULES - B O FINCH

*Important Note* All molecules with polar covalent bonds are dipoles EXCEPT: CF4CCl4CO2 A molecule can have polar covalent bonds but be a NONPOLAR molecule Example: Draw Lewis Dot Diagram of CCl4 (Carbon Tetrafluoride), CO2, H2O

Attraction Between POLAR Molecules Dipole-Dipole Attraction - When + end of one molecule is attracted to the – end of another molecule - Very strong attractiongives a high boiling point due to energy needed to break the force of + - attraction Hydrogen Bond NOT A BOND Occurs when H is covalently bonded to an atom which has a -Small atomic radius -Hi Electronegativity -H is bonded to N, O, F (NH3, H2O, HF)

Non-Polar Force of Attraction WEAK attractive forces Van der Waals Forces OR London Dispersion Forces Occurs between: Diatomic Molecules (B O FINCH) NonPolar Molecules Noble Gases *Force increases as they get closed together: Distance btwn molecules decreases OR Size of molecules increases

Molecule – Ion Attraction EXAMPLE: NaCl dissolves in H2O Hydration of the ions Draw diagram