CHAPTER 6: COVALENT COMPOUNDS Section 1: Covalent Bond Section 2: Drawing and Naming Section 3: Molecular Shapes

Objectives Draw Lewis structures to show the arrangement of valence electrons among atoms in molecules and polyatomic ions. Explain the differences between single, double, and triple covalent bonds. Name binary inorganic covalent compounds by using prefixes, roots, and suffixes. Section 2 Drawing and Naming Molecules Chapter 6

Lewis Electron-Dot Structures A Lewis structure is a structural formula in which valence electrons are represented by dots and dashes (shared electron pairs). Use 4 positions around the atom: top, bottom, right, left. Example: Cl2, Section 2 Drawing and Naming Molecules Chapter 6

A Step-By-Step Approach To Writing Lewis Structures (electron-dot diagrams) Page Step 1: Total number of valence e- in the compound Step 2: Identify the central atom first atom or single atom or atom can bond more than once. Carbon always, Never Hydrogen, never halogens Step 3: Distribute the dots. each atom satisfies the octet rules. (H, Li, Be, B=duet rule) Sample problem Draw a Lewis structure for

Drawing Lewis Structures with Single Bonds Sample Problem A Draw a Lewis structure for CH 3 I. Section 2 Drawing and Naming Molecules Chapter 6 1. Draw each atom’s Lewis structure, and count the total number of valence electrons. number of dots: 14 Arrange the Lewis structure so that carbon is the central atom.

Drawing Lewis Structures for Polyatomic Ions Section 2 Drawing and Naming Molecules Chapter 6 1. Add the valence e- --> Total e- For negative ions, add e- For Positive ions, subtract e- 2. Identify the central atom 3. Distribute the e- so atoms follow octet rule (H = duet rule) 4. For PAI, Bracket the ion and place the charge on the outside.

Drawing Lewis Structures for Polyatomic Ions Sample Problem B Draw a Lewis structure for the sulfate ion. Count electrons for all atoms. Add two additional electrons to account for the 2  charge on the ion. Section 2 Drawing and Naming Molecules Chapter 6 number of dots: = 32 Distribute the 32 dots so that there are 8 dots around each atom.

Lewis Electron-Dot Structures A single bond is a covalent bond in which two atoms share one pair of electrons The electrons can pair in any order. However, any unpaired electrons are usually filled in to show how they will form a covalent bond. Section 2 Drawing and Naming Molecules Chapter 6

Multiple Bonds For O 2 to make an octet, each atom needs two more electrons. The two atoms share four electrons. Section 2 Drawing and Naming Molecules Chapter 6 A double bond is a covalent bond in which two atoms share two pairs of electrons.

Multiple Bonds, continued For N 2 to make an octet, each atom needs three more electrons. The two atoms share six electrons. Section 2 Drawing and Naming Molecules Chapter 6 A triple bond is a covalent bond in which two atoms share three pairs of electrons.

Drawing Lewis Structures with Multiple Bonds Sample Problem C Draw a Lewis structure for formaldehyde, CH2O. Draw each atom’s Lewis structure, and count the total dots. Section 2 Drawing and Naming Molecules Chapter 6 number of dots: 12 Arrange the atoms so that carbon is the central atom. O HC H

Drawing Lewis Structures with Multiple Bonds Sample Problem C Solution, continued Distribute one pair of dots between each of the atoms and the rest, in pairs, around the atoms. C does not have an octet. To get an octet, move an unshared pair from the O to between the O and the C. Section 2 Drawing and Naming Molecules Chapter 6 Change each bonding pair to a long dash. Two pairs of dots represent a double bond.

Naming Covalent Compounds Binary covalent compounds: 2 non metals, use prefixes to tell number of atoms. Don’t use “mono” on the first element. The second element named has the ending -ide. Drop the vowel at the end of some of the prefixes when naming oxide. (all but Tri and Di) Section 2 Drawing and Naming Molecules Chapter 6

Prefixes Mono Di Tri Tetra Penta Hexa Hepta Octa Nona Deka, deci Not to hard, people love this naming method

Naming Covalent Compounds, continued This system of prefixes is used to show the number of atoms of each element in the molecule. Section 2 Drawing and Naming Molecules Chapter 6

Naming Covalent Compounds, continued Prefixes can be used to show the numbers of each type of atom in diphosphorus pentasulfide. Section 2 Drawing and Naming Molecules Chapter 6

Objectives Predict the shape of a molecule using VSEPR theory. Associate the polarity of molecules with the shapes of molecules, and relate the polarity and shape of molecules to the properties of a substance. Section 3 Molecular Shapes Chapter 6

Determining Molecular Shapes The valence shell electron pair repulsion (VSEPR) theory is a theory that predicts some molecular shapes based on the idea that pairs of valence electrons surrounding an atom repel each other. Section 3 Molecular Shapes Chapter 6

Determining Molecular Shapes Electron pairs are negative, so they repel each other. Therefore, the shared pairs that form different bonds repel each other and remain as far apart as possible. Section 3 Molecular Shapes Chapter 6

Predicting Molecular Shapes Sample Problem D Determine the shape of H 2 O. Section 3 Molecular Shapes Chapter 6 1. Draw the Lewis structure for H2O. 2. Count the number of shared and unshared pairs of electrons around the central atom. H 2 O has two shared pairs and two unshared pairs.

Predicting Molecular Shapes 3. Find the shape that allows the shared and unshared pairs of electrons to be as far apart as possible. The water molecule will have a bent shape. Section 3 Molecular Shapes Chapter 6 Molecular Shape Affects a Substance’s Properties Shape Affects Polarity

Section 3 Molecular Shapes If two dipoles are arranged in opposite directions, they will cancel each other. If two dipoles are arranged at an angle, they will not cancel each other. Chapter 6 Molecular Shape Affects Polarity

Section 3 Molecular Shapes Chapter 6 Atomic orbitals - represent the ways that electrons can arrange themselves in atoms. s, p, d, f orbitals A bonding orbital - The space taken up by bonded electrons. When bond forms atomic orbital hybridize. Hybridization

Atomic orbitals - represent the ways that electrons can arrange themselves in isolated, individual atoms. The space taken up by bonded electrons is called a bonding orbital.