Chapter 16: Covalent Compounds Ms. Knick HAHS

What is a Covalent Compound ? A covalent compound is a chemical bond formed between a 2 or more nonmetals.

Stability Nonmetals join with one another to obtain 8 electrons ( octet ). An atom with 8 electrons is considered to be stable. However, there are exceptions to the octet rule. –H : is stable with 2 electrons –B : is stable with 6 electrons –S : is stable with 12 electrons

Electrons Remember that in an ionic bond, electrons are transferred or donated. However, in a covalent bond, electrons are shared among both atoms in the bond.

Why Bond ? Potential Energy is minimized. Atoms in the bond are stable.

Lewis Structures Diagrams that show the bonding between atoms of a molecule and the lone pairs of electrons that may exist in the molecule. A Lewis structure can be drawn for any covalently bonded molecule

Examples:

Writing Lewis Structures for Charged Molecules Negative: Gained electrons; add to the number of your total valence electrons Positive: Lost electrons; subtract from the number of your total valence electrons

Molecular Geometry

Molecular Geometry and VSEPR (Valence Shell Electron Pair Repulsion Molecular Geometry is the 3-D arrangement of the atoms that constitute a molecule. VSPER is used to predict the geometry based upon the extent of electron-pair repulsion.

Number of Bonds attached to the central atom Number of Lone Pairs Around the Central Atom Shape of Molecule 20 Linear 21 Bent Trigonal Planar 31 Trigonal Pyramidal 40 Tetrahedral 50 Trigonal Bypyramidal 60 Octahedral

Molecular Geometry Lab Guidelines All students must complete the handout and turn it in before the end of class. This assignment will be graded, so do your best! When working with the kits: – Part I and II: Follow the color coding for atoms in the box; your drawings of the compounds should reflect the color coding. LONE PAIRS WILL BE REPRESENTED WITH A WOODEN STICK ATTACHMENT! – Part II: Be sure all drilled holes are filled for each model that you create!

Length of Bonds Triple bonds are the shortest in length; single bonds are the longest in length. Triple bonds require more of an orbital overlap in order to join the electrons in a bond making them the shortest in length.

Breaking Bonds Triple bonds require the most amount of energy to break the bond between atoms. Single bonds require the least amount of energy to break bond between atoms.

Two types of Covalent Bonds 1. Nonpolar Covalent : The bonding electrons are shared equally. The differences in electronegativity are Polar Covalent : The bonding electrons are shared unequally. (ONE ATOM IS NOT PLAYING NICE! ) The differences in electronegativity are greater than 0.3

Nonpolar vs. Polar Non-Polar Chlorine is not playing nice! 

Electronegativity Chart Classify the following as polar covalent or nonpolar covalent: H—Cl C—F N—O Xe—F O—O S—F

Covalent Compound Poster Project Select and Research a commonly used covalent compound. Draw the Lewis Structure (10 points). Explain the uses/property/characteristics (20 points). Label at least one polar bond and at least one nonpolar covalent bond (10 points). Make the presentation creative; Give it a creative title! (10 points) Can not use Ms. K’s example!

Need a kick start to your morning? It is most commonly consumed by humans in infusions extracted from the seed of the coffee plant, as well as from various foods and drinks containing products derived from the kola nut. In humans, caffeine acts as a central nervous system stimulant, temporarily warding off drowsiness and restoring alertness. It is the world's most widely consumed psychoactive drug, but unlike many other psychoactive substances, it is legal and unregulated in nearly all parts of the world. Polar bond Nonpolar

Writing Assignment The journal entry must be a minimum of 1 page (front). You should include: A summary of what you learned about covalent compounds (electrons, Lewis dot structures, molecular geometry, polar covalent, nonpolar covalent) You should include: An application to real world (THINK OF YOUR POSTER PROJECT). Refer to rubric for grading!