Chemical Bonding Chapter 6

Substances Elements are substances that cannot be further decomposed by ordinary chemical means. Compounds are substances that can be decomposed into two or more simpler substances by ordinary chemical means.

Examples of Compounds HClNaCl H 2 OCaCl 2 NH 3 AlCl 3 HCl – one atom of hydrogen and one atom of chlorine Can you make any generalization concerning these formulas?

Questions 1. What is the “goal” of every atom? 2. What makes an atom chemically stable? 3. Why do you suppose noble gases like He, Ne, or Ar, do not react under most circumstances? 4. Why does He only have two electrons and Ne and Ar has eight in the outer shell?

Electrons Valance electrons are the electrons in an incomplete highest energy level; often involved in chemical bonding. The core electrons are all electrons in an atom other then the valance electrons.

Bonding Chemical bonds – the linkage between atoms produced by transfer or sharing of electrons. 1. Ionic bonding – electrons transfer due to electrostatic attraction between metals (cation) and nonmetals (anion). 2. Covalent bonding – electrons sharing usually between nonmetals.

Ionic Bonding Electrons are transferred from the highest energy level of one atom to the highest energy level of a second atom, attaining the electron configuration of a noble gas.

Formation of NaCl, MgO, CaCl 2, and K 2 O Highlight address, left click, open hyperlink to see the formation of several ionic compounds. bonding/ionic_bonds.htm Na 1+ - lose one electron becomes isoelectronic with Ne. Cl 1- - gains one electron becomes isoelectronic with Ar. Name the ions and the noble gas that it is isoelectronic with for the following compounds: MgO, CaCl 2, K 2 O.

Formulas Chemical formula – is a shorthand method of representing the composition of a substance by using chemical symbols. Empirical formula – indicates: 1. The kinds of atoms in the compound formed; 2. The simples whole-number ratio of the atoms in the compound. (Bonding between metal and nonmetal) NaCl is the chemical and empirical formula for sodium chloride. Ratio – 1:1, Na:Cl; 2:1:4, K 2 SO 4 – Ionic compounds

Molecular formula – substances existing as simple molecules. (Bonding between nonmetals and nonmetals) 1. The kind of atoms in the compound formed; 2. The number of atoms in a molecule. Formula unit – represents a definite amount of a compound.

Particles Depending on the type of bond formed by their atoms, compounds can have two kinds of particles: 1. Ionic bonds - Ions: + or -; 2. Covalent bonds - Molecules

Naming Ionic Compounds Write the cation then the anion. NaCl If the element has more than two or more ions use roman numerals to indicate the charge. Common Ions Tables 6.2 p.143, 6.3 p.144, and 6.4 p.147 Copy onto index cards – front write name, back write symbol Memorize cations then anions. Quiz to follow.

Binary compounds Compound that consist of two elements. Drop the last syllable in the second element’s (anion) name, add –ide. NaCl – sodium chloride Li 3 P – lithium phosphide

Writing Ionic Formulas Iron (III) oxide 1. Write the chemical symbols for the cation then anion. Fe 3+ O Crisscross charge numbers (3 or 2) only, not the + or – signs. Fe 2 O 3

Polyatomic Ions An ion made of two or more atoms. Act as a single ion. Some contains oxygen which ends –ite (less oxygen) and –ate (more oxygen). Sulfite (SO 3 2- ), Sulfate (SO 4 2- ) Nitrite (NO 2 1- ), Nitrate (NO 3 1- ) Some contain hydrogen and started prefixed mono- (one) and di- (two) in front of the word. Table 6.4 p. 147

Writing Polyatomic Ionic Formulas Iron (III) chromate 1. Write the chemical symbols for the cation then anion. Fe 3+ CrO Crisscross charge numbers (3 or 2) only, not the + or – signs. When there are two or more polyatomic ions, parentheses must be used to indicate the number. Fe 2 (CrO 4 ) 3

3. Compound must be neutral. Check 2Fe 3+ = 6+ 3CrO 4 2- = 6- Fe 2 (CrO 4 ) 3 = 0

Assignments 1. Sample and Practice Problems pp. 145, 146, 151, 153, 155, 156, 156, 2. Section Review pp. 148, 156, 160, and Complete “Ionic Bonding” worksheet. 4. “Ionic Compounds” worksheet 5. “Polyatomic Ions” worksheet 6. “Stable ions” worksheet

Covalent Bonding When atoms of nonmetals combine with each other, they tend to share one or more electrons to form a molecule. Example: H, N, O, F, Cl, Br, and I (halogens) 1. By themselves they are unstable – H 2. When bonded or combined with an identical atom they are stable – H 2 forms a diatomic molecule.

Formation of Covalent Compounds Highlight address, left click, open hyperlink to see the formation of several covalent compounds. ons/03bonding/mleebonding/covalent_bonds. htm

Nonpolar Covalent bonds A covalent bond in which both atoms have the same attraction for the shared electrons Only nonpolar bonds are between identical atoms) H 2, N 2, O 2, F 2, Cl 2, Br 2, and I 2. Even electron distribution. See board for examples of single, double, and triple bonds.

Polar Covalent Bonds A covalent bond in which there is an unequal attraction for the shared electrons and a resulting unbalanced distribution of charge. Polar covalent bonds are between different elements (CO, H 2 O, NH 3 etc…). See board for examples.

Dipole A molecule of part of a molecule that contains both positively and negatively charged regions. Uneven electron distribution. The Greek symbol delta (δ) means partial. Example: δ+ HCl δ-

Assignment 1. “Covalent Bonds” worksheet 2. “Naming Molecular Compounds” worksheet 3. “Names of Covalent Compounds” worksheet

Electronegativity The relative value of the electron-attracting ability of atoms. 1. Related to nuclear charge and atomic size. 2. Increase in the nuclear charge and decrease in the atom’s radius. 3. Nonmetals have a relatively high electro negativity and metals a relatively low electro negativity.

Polarity To find the degree of polarity subtract the electronegativities of the elements  Bonds with more than or equal to 1.7 electronegativity difference are considered ionic.  Bonds with between 0.4 – 1.6 electronegativity difference are polar.  Bonds with 0 – 0.3 electronegativity difference are nonpolar.

Examples: Calculate the degree of polarity for the following: a. Na = 0.9 Cl = 3.0 (NaCl) b. C = 2.5 O = 3.5 (CO) a. Cl-Na = 3.0 – 0.9 = 2.1 ionic b. O-C = 3.5 – 2.5 = 1.0 polar

Assignment 1. Cl-Cl in Cl 2 2. H-S in H 2 S 3. Ca-Br in CaBr 2 4. C-Cl in CCl 4 5. K-O in K 2 O 6. I-I in I 2 7. H-O in H 2 O “Determining Bonds Types” worksheet

Assignment Of the 4 compounds below: 1. Which compound has bonds with the greatest degree of polarity (most polar)? 2. Which compound has bonds with the least degree of polarity (least polar)? CO 2 SiO 2 NO 2 NCl 3 “Polarity of Molecules” worksheet