Covalent Bonding Guided Notes. A covalent bond is a chemical bond in which 2 atoms a pair of valence electrons.

Transcription

1 Unit 6: Covalent Bonding Name: What is a covalent bond? Covalent Bonding Guided Notes A covalent bond is a chemical bond in which 2 atoms a pair of valence electrons. A covalent bond occurs between 2 nonmetals. Electrons want to be in pairs. Draw how F-F share electrons to create a bond. Representing Covalent Bonds Molecules of Elements A molecule is a neutral group of atoms that are joined together by one or more covalent bonds. The attractions between shared electrons and the protons in each nucleus hold the atoms together in a covalent bond. Diatomic means atoms. Many nonmetal elements exist as diatomic molecules. Atoms of the same element will share bonding electrons equally. Double Bonds: Since each are sharing two pairs Double Bond! Draw CO 2 below to show the double bonds. 1

2 Naming & Writing Formulas Writing Formulas 1. Write the symbol for the element. 2. The prefixes in the name will tell you the subscript of each element in the formula. Example: Carbon dioxide, mono di tri tetra penta hexa hepta octa nona deca Naming Covalent Molecules 1. Confirm that it is composed of two nonmetals. 2. Name the elements in the order listed in the formula. 3. Use prefixes to indicate the number of each kind of atom (Omit mono- for one atom in the first element) 4. Suffix of the name on the second element is ide mono di tri tetra penta hexa hepta octa nona deca Practice: 1. Name the following molecules: a. H 2 O b. CO 2. Write the formula for the following molecules: a. Trinitrogen pentafluoride b. Nonasulfur dioxide 2

3 Drawing Lewis Structures Label a bonding pair and nonbonding pair on the Lewis structure below: Bonding pair any pair of electrons that results from the formation of a covalent bond. Nonbonding pair any pair of electrons that are in the electron-dot structure of the individual atom. Drawing Lewis Structures: 1. Total all valence electrons. 2. Draw the skeleton structure and add bonds between each atom. 3. Add electrons around each atom until every atom has 8 electrons (except H gets 2 e - ) 4. Count all of your electrons on your structure. 5. Check your answer! Practice: Draw the Lewis structure for CF4 Practice: Draw the Lewis Structure for H 2 O Practice: Draw the Lewis structure for CCl 4 3

4 Unequal Sharing of Electrons Bond Polarity Nonpolar Covalent Bond sharing of electrons This happens in 2 identical atoms bonded together. Example: O 2 and N 2 Polar Covalent Bond sharing of electrons. This happens when different atoms bond together. Example: CO 2 and CH 4 Polar Covalent Bonds Sometimes the electron pair is not equally shared between the two atoms. If an element has a electronegativity value then it will have a stronger pull on the electron pair. This is called a covalent bond. When atoms form a polar covalent bond, the atom with the greater attraction for electrons has a partial negative charge. The other atom has a partial positive charge. Label the partial charges on the HCl molecule Bond Polarity: Bonds are never completely ionic or covalent. Difference in electronegativity will determine the type of bond. 4

5 Example: Will HF be polar or nonpolar? Example: Will the bonds in NO 2 be polar or nonpolar? Polar & Nonpolar Molecules Molecules are either polar or nonpolar. The type of atoms in a molecule and its are factors that determine whether a molecule is polar or nonpolar. Label the pictures below as either polar or nonpolar Just because a molecule has a covalent bond doesn t mean that it will be a covalent molecule. Example: H 2 O and CCl 4 both contain polar bonds (because of the electronegativity difference). However, only H 2 O is a polar molecule. 5

6 Attractions between Molecules There are forces that are within a molecule and there are forces between 2 molecules. The forces within a molecule are called molecular forces. This includes ionic and covalent bonds. The forces between 2 molecules are called molecular forces. These forces are much weaker than intramolecular forces. Polar Molecules Polar molecules electrically attract one another (the positive end of one molecule is attracted to the negative end of another). It makes it relatively difficult to separate the molecules. Polar molecules can be thought of as being. Attractions between polar molecules are stronger than attractions between nonpolar molecules. Properties of Covalent Molecules 6