BONDING Types of Bonding Covalent Bonding Nonmetal with

BONDING

Types of Bonding • Covalent Bonding – Nonmetal with nonmetal • Ionic Bonding – Metal with nonmetal • Metallic Bonding – Metal with metal

Covalent Bonds Why do covalent bonds occur? The electrons occupy a larger ‘cloud’ in the covalent bond than in the individual atomic orbitals. This larger cloud is more stable than the smaller clouds.

Covalent Bonds 1) Covalent bonds result when electrons in atomic orbitals are combined into a bonding orbital. 2) Each bonding orbital can contain two electrons. 3) Each atom has a stable ‘octet’ of electrons.

Lewis Dot Structures A simple method of accounting for electrons in compounds. Only valence electrons are shown. Dots are added as orbitals are filled. Valence electrons are represented using dots ( • ) Example 1: Lewis dot structure of a nitrogen atom Nitrogen has 5 valence electrons: • • • • N • Example 2: Lewis dot structure of a chloride anion Chloride anion has 8 valence electrons: • • – • • Cl • •

Lewis Electron Dot (cont) • Step 1 Step 2 Step 3 Step 4 • Step 5 Step 6 Step 7 Step 8

Lewis Dot Structures

Problems Write Lewis dot structures for the following atoms: a) beryllium c) strontium b) neon d) aluminum

Lewis Dot Structures The Lewis Dot picture can help one understand the formation of ionic compounds. Consider potassium bromide (KBr): element dot structure ion K K • K+ Br • • Br • • • Br- • • K • + • • Br • K+ • • Br • • dot structure K • • Br- • • fate loses electron gains electron

Covalent Bonds Examples: combine hydrogen atoms with oxygen, nitrogen, or carbon atoms to form stable molecules

Steps to Write a Lewis Dot Structure 1. Sum up all valence electrons of all atoms. 2. Choose a central atom (all compounds exhibit symmetry) 3. Place electrons(dots) around central atom to obey octet rule. 4. Place remaining electrons around outer atoms to obey octet rule (remember exceptions to the octet rule!)

PRACTICE!! • Water • Ammonia • Methane

Exceptions to the Octet Rule Elements on the 3 rd row or beyond often violate the octet rule. These elements have empty d-orbitals that can participate in bonding. Boron molecules often have empty atomic orbitals, and do not have a stable octet of electrons. Now, use the boards to draw the LDS!

Multiple Covalent Bonds In some cases, stable molecules are formed by sharing more than two electrons between two atoms. Consider the oxygen molecule (O 2) , which we all breathe in and depend on for life: double bond + • • lone pairs O = O • • • • The molecule O 2 contains a double bond that is represented with two lines connecting the atoms. Each bond contains two electrons, so a total of four electrons are counted in this bond. Each oxygen atom has a stable octet of electrons.

Multiple Covalent Bonds Ethylene (C 2 H 4): two carbon atoms, each contribute four valence electrons = 8 four hydrogen atoms, each contribute one valence electron= 4 12 e- total

Chemical Formulas A molecular formula indicates the atoms and numbers of each atom that contribute to form the molecule. The molecular formula does not provide information about the connectivity of the atoms in the molecule. Structural formulas show atoms are connected in the molecule. • • vs. H • • H 2 O O H * A molecular formula differs from a formula unit (for ionic compounds) since it is not the simplest ratio of atoms that make up the substance Ex: The molecule ethylene contains two carbon atoms and four hydrogen atoms in each molecule. Its molecular formula is C 2 H 4, not CH 2

Lewis Dot Structure Practice trichlorophosphide, PCl 3 ozone, O 3 (be careful)

Lewis Dot Structure Practice carbon dioxide, CO 2 nitrate ion, NO 3 -