Chapter 8 Covalent Bonding Honors Chemistry

Section 8.1 The Covelent Bond Why do atoms bond? Atoms in non-ionic compounds share electrons. The chemical bond that results from sharing electrons is a covalent bond.covalent bond A molecule is formed when two or more atoms bond.molecule Ex: Hydrogen Molecule H 2

Diatomic molecules (H 2, F 2 for example) exist because two-atom molecules are more stable than single atoms. There are 7 Diatomic molecules: H 2, N 2, O 2, F 2, Cl 2, Br 2, and I 2.

Types of Covalent Bonds: Single – 1 shared pair Double – 2 shared pair Triple - 3 shared pair

Section 8.2 Naming Molecules Naming Binary Molecular Compounds The first element is always named first using the entire element name. The second element is named using its root and adding the suffix –ide. Prefixes are used to indicate the number of atoms of each element in a compound.

You must remember these prefixes!!!

Naming Acids An acid is a substance that donates H + when in solution. There are two types of acids – binary and oxyacids. All binary acids have H + combined with one other nonmetal.

Naming Binary Acids The first word has the prefix hydro- followed by the root of the element plus the suffix –ic. The second word is always acid Ex: Hydrochloric acid is HCl

Naming Oxyacids An oxyacid is an acid that contains both a H + and an oxyanion.oxyacid Identify the oxyanion present. If the oxyanion ends in –ate, change -ate to -ic. If the oxyanion ends in –ite, change -ite to -ous.

Some molecular compounds are more known by their common names.

Naming Molecular Compounds

Section 8.3 Molecular Structures There are numerous ways to represent molecules:

Drawing Lewis Structures –Predict the location of certain atoms. –Determine the number of electrons available for bonding. –Determine the number of bonding pairs. –Place the bonding pairs. –Determine the number of non-bonding pairs remaining. –Determine whether the central atom satisfies the octet rule.

Atoms within a polyatomic ion are covalently bonded.

A coordinate covalent bond forms when one atom donates both of the electrons to be shared with an atom or ion that needs two electrons.coordinate covalent bond Ex: Chloric Acid, HClO 3

Resonance Structures ResonanceResonance is a condition that occurs when more than one valid Lewis structure can be written for a molecule or ion. Ex: This figure shows three correct ways to draw the structure for nitrate, NO 3 1-.

Two or more correct Lewis structures that represent a single ion or molecule are resonance structures. The molecule behaves as though it has only one structure.

Exceptions to the Octet Rule Some molecules do not obey the octet rule! 1. Incomplete Octet - a small group of molecules might have an odd number of valence electrons.

2. Suboctet - a few compounds form stable configurations with less than 8 electrons around the atom.

3.Expanded Octet - atoms with more than eight valence electrons. (Forms with elements in period 3 or higher with d-orbitals and can form more than 4 covalent bonds)

Assigning Formal Charges Formal Charges For each atom, count the electrons in lone pairs and half the electrons it shares with other atoms. Subtract that from the number of valence electrons from that atom: the difference is its formal charge.

The BEST Lewis structure… …is the one with the fewest charges. …puts a negative charge on the most electronegative atom.

VSEPR Model The shape of a molecule determines many of its physical and chemical properties. Molecular geometry (shape) can be determined with the Valence Shell Electron Pair Repulsion model, or VSEPR model which minimizes the repulsion of shared and unshared atoms around the central atom.VSEPR model Section 8.4 Molecular Shapes

We can refer to the electron pairs as electron domains. In a double or triple bond, all electrons shared between those two atoms are on the same side of the central atom; therefore, they count as one electron domain. VSEPR Model The central atom in this molecule, A, has four electron domains.

VSEPR Model - Electron Domain Geometry These are the electron-domain geometries for two through six electron domains around a central atom.

VSEPR Model (cont.) Electron pairs repel each other and cause molecules to be in fixed positions relative to each other. Unshared electron pairs also determine the shape of a molecule. Electron pairs are located in a molecule as far apart as they can be.

VSEPR Model (cont.)

HybridizationHybridization is a process in which atomic orbitals mix and form new, identical hybrid orbitals. Once you know the electron-domain geometry, you know the hybridization state of the atom.

Section 8.5 Electronegativity and Polarity Electronegativity and Bond Character Electronegativity measures the attraction for a shared pair of electrons in bonded atoms. Why aren’t values for the Noble Gases given???

EN Difference & Bond Character…

Polar Covalent Bonding Unequal sharing of electrons results in a polar covalent bond.polar covalent bond Bonding is often not clearly ionic or covalent. Polar Covalent Bonding in a Water Molecule Covalently bonded molecules are either polar or non- polar. Non-polar molecules are not attracted by an electric field, whereas polar molecules will always align with an electric field. H 2 O and CCl 4 both contain polar covalent bonds between atoms, but only one of these molecules is a polar covalent molecule. How can you tell?

Polar Covalent Bonds (cont.) Solubility is the property of a substance’s ability to dissolve in another substance. Polar molecules and ionic substances are usually soluble in polar substances. Non-polar molecules dissolve only in non-polar substances. LIKE DISSOLVES LIKE!!!!!

Properties of Covalent Compounds Many physical properties are due to intermolecular forces. Low melting and boiling points of molecular substances. Relatively soft solids. Molecules can align in a crystal lattice, similar to ionic solids but with less attraction between particles.

Properties of Covalent Compounds Solids composed of only atoms interconnected by a network of covalent bonds are called covalent network solids. Quartz and diamonds are two common examples of network solids.