Chapter 8 – Covalent Bonding

Review of Chapter 7 In Chapter 7, we learned about electrons being transferred (“given up” or “stolen away”) This type of bond between a METAL and NONMETAL is called an IONIC BOND

george-zaidan-and-charles-morton

Chapter 8.1 – Molecular Compounds In this chapter, you will learn about another type of bond in which electrons are shared Covalent Bonds are atoms held together by SHARING electrons between NONMETALS

Covalent Molecules A group of atoms joined together by a covalent bond is called a MOLECULE

Properties of Molecular Compounds Lower Melting Points than Ionic Compounds (which means that they are weaker than ionic) Liquids or gases at room temperature

Molecular Formulas The Molecular Formula is the formula of a molecular compound It shows how many atoms of each element a molecule contains H 2 O contains 3 atoms (2 atoms of H, 1 atom of O) C 2 H 6 contains 8 atoms (2 atoms of C, 6 atoms of H)

Practice: True or False 1. All molecular compounds are composed of atoms of two or more elements. 2. Molecular compounds are composed of two or more nonmetals. 3. Atoms in molecular compounds exchange electrons. 4. Molecular compounds have higher melting and boiling points than ionic compounds.

Ionic versus Covalent IONICCOVALENT Name of fundamental particle Formula UnitMolecule Bonding TypeTransfer e - Share e - Types of Elements Metal & Nonmetal Nonmetals Physical StateSolidSolid, Liquid, or Gas Melting PointHigh (above 300ºC) Low (below 300 ºC) Solubility Dissolves in Water Varies ConductivityGoodPoor

Chapter 8.2 – Covalent Bonding Remember that ionic compounds transfer electrons in order to attain a noble gas electron configuration Covalent compounds form by sharing electrons to attain a noble gas electron configuration Regardless of the type of bond, the Octet Rule still must be obeyed (8 valence electrons)

Single Covalent Bond A Single Covalent Bond consists of two atoms held together by sharing 1 pair of electrons (2 e - )

Electron Dot Structure

Double Covalent Bonds A Double Covalent Bond is a bond that involves 2 shared pairs of electrons (4 e - ) Sometimes atoms attain noble gas configuration by sharing 2 or 3 pairs of electrons

Triple Covalent Bond A Triple Covalent Bond is a bond that involves 3 shared pairs of electrons (6 e - )

Chapter 8.4 – Polar Bonds and Molecules There are two types of covalent bonds Nonpolar Covalent Bonds (share equally) Polar Covalent Bonds (share unequally)

Polar Covalent A Polar Covalent Bond is unequal sharing of electrons between two atoms (HCl) In a polar covalent bond, one atom typically has a negative charge, and the other atom has a positive charge

Nonpolar Covalent Bond A Nonpolar Covalent Bond is equal sharing of electrons between two atoms (Cl 2, N 2, O 2 )

Classification of Bonds You can determine the type of bond between two atoms by calculating the difference in electronegativity values between the elements Type of BondElectronegativity Difference Nonpolar Covalent 0  0.4 Polar Covalent 0.5  1.9 Ionic 2.0  4.0

The electronegativity of an element indicates its relative ability to attract electrons in a chemical bond.electronegativity Electronegativity decreases down a group and increases left to right across a period. Electronegativity

Practice What type of bond is HCl? (H = 2.1, Cl = 3.1) Your Turn To Practice N(3.0) and H(2.1) H(2.1) and H(2.1) Ca(1.0) and Cl(3.0) Mg(1.2) and O(3.5) H(2.1) and F(4.0) Difference = 3.1 – 2.1 = 1.0 Therefore it is polar covalent bond.

Intermolecular forces Intermolecular attractions are weaker than ionic, and covalent bonds Besides ionic and covalent bonds, there are also attractions between molecules

Hydrogen Bond A hydrogen bond is the attraction between polar molecules. It occurs when hydrogen (H) atom in one molecules is attracted to nitrogen (N), oxygen (O) or fluorine (F) in another molecule.

Hydrogen Bond Hydrogen Bonds have about 5% of the strength of an average covalent bond Hydrogen Bond is the strongest of all intermolecular forces

Intermolecular forces Hydrogen Bonds

Weak Dipole Forces- van der Waal’s forces

London’s Dispersion forces

Chapter 8.3 – VSPER Theory Valence shell electron pair repulsion (VSEPR) theory

VSEPR Theory VSEPR Theory predicts the 3D shape of molecules According to VSEPR, the repulsion of electrons causes the shape of the molecule to adjust so that the electrons are far apart

Shared versus Unshared Electrons A Shared Pair is a pair of valence electrons that is shared between atoms and participates in the formation of covalent bond An Unshared Pair is a pair of valence electrons that is not shared between atoms

VSEPR Theory Both shared and unshared pairs of electrons are important in predicting the shapes of molecules Each bond (single, double, or triple) or unshared pair is considered a steric number Use the steric number to predict the molecular geometry

Practice Methane (CH 4 ) – tetrahedral Ammonia (NH 3 ) – pyramidal Water (H 2 O) – bent Carbon Dioxide (CO 2 ) - linear