Chapter 6A: Chemical Bonding General Chemistry Mr. Mata Cartoon courtesy of NearingZero.net

Standard 2a Atoms combine to form molecules by sharing electrons to form covalent or metallic bonds.

Essential Question How do electrons behave during bonding?

6-1 Chemical Bonds Forces that hold atoms together. make groups of atoms function as a unit. Ionic bonds – transfer of electrons. Metal + Nonmetal Ex: NaCl, Li2O Covalent bonds – sharing of electrons. Nonmetal + nonmetal Ex: H2O, CO2 Metallic bonds- electrons are free to move throughout material. Ex: Metals

Covalent Bonds Nonpolar-Covalent bonds (H2) Electrons are equally shared. Electronegativity (EN) values are used. H: EN value = 2.1; H-H; 2.1 – 2.1 = 0 EN difference (0 to 0.3). Polar-Covalent bonds (HCl) Electrons are unequally shared. H: EN value = 2.1; Cl: EN value = 3.0 3.0 – 2.1 = 0.9 EN difference (0.3 to 1.7)

Using Electronegativity differences NaCl /0.9 – 3.0/= 2.1 Cl = 3.0 (look on Periodic Table) Na = 0.9 1.7 or up = Ionic Bond

6-2 Covalent Bonding Molecule- smallest unit of matter that can exist & retain all properties of substance. Examples: H2O & O2, C12H22O11 Diatomic molecule- molecule containing 2 identical atoms. (H2 N2 O2 F2 Cl2 Br2 I2)

Comparing Monatomic, Diatomic, and Polyatomic Molecules

Characteristics of the Covalent Bond When two atoms form a covalent bond, their shared electrons form overlapping orbitals. Bonding of two H atoms allows each atom to have stable e - configuration of helium, 1s2.

Chemical Formula- represents relative # of atoms in a chemical compound by using symbols & subscripts. Example: H2O H=2 atoms O=1 atom Molecular compound (Covalent) - simplest formula unit are molecules. Have low melting & boiling pts. Molecular formula- shows types & #’s of atoms combined in a single molecule.

Bond Length- average distance between 2 bonded atoms. Bond Energy- energy required to break a bond. Gives info about strength of bond. Energy is stored in chemical bonds.

The Octet Rule Compounds form so that each atom has an octet (8) e-’s outer shell. By gaining, losing, or sharing e-’s. 8 is Great! H He

Electron-Dot Diagrams Keeps track of valence (outermost) e-’s. Valence e-’s of an atom shown by dots placed around the element’s symbol. Inner-shell e-’s are not shown.

Lewis Dot Shows how valence e-’s are arranged among atoms in a molecule. Stability of compound relates to noble gas e- configuration. CH4 H2O

Structural Formula Shows shared pair of e-’s by a dashed line.

Single bond- 1 pair of e-’s Double bond- 2 pair of e-’s Triple bond- 3 pair of e-’s Try a couple: O2 O = O N2 N N

Molecular/Covalent Compounds Write Lewis Structures for Molecular Compounds. Electrons are shared: H2 . . H + H H:H : : : : . : :Cl:Cl: Cl2 Cl. + Cl : : : : :

Lewis Structures Often bonding pairs of electrons can be represented with a line: HCl H2O : : . : . H Cl: H:Cl: + = H-Cl: : : : : : : : . + H : . H:O: = O: H-O: . : H H . . . H

Lewis Structures NH3 H . . 3H . H-N: + N: . H H . 4H . CH4 + . . C