Chemical Bonding And Intermolecular Forces

Chemical Bonds Forces of attraction that hold atoms or groups of atoms together and allow them to function as one unit. Type of attractive force directly related to the molecule’s physical properties, melting point, hardness, electrical and thermal conductivity and solubility.

Breaking up is hard to do! Most of the chemical substances you know are compounds and not elements. Matter favors systems that have positions of lowest energy. Being bound requires less energy than existing in elemental form.

Types of Bonds 1. Ionic A.Characteristics 1. Electrons that are transferred between atoms having large differences in electronegativity. 2. Contain a metal and a nonmetal. 3. Strong electrostatic attractions between positive and negative atoms 3. Formulas in simplest ration of elements (empirical formula; NaCl)

Ionic Bonds Continued 4. Formulas given in the simplest ratio of elements (empirical formula; NaCl) 5. Crystalline structures that are solids at room temperature. 6. Ions that form a crystal lattice structure. 7. Compounds that melt at high temps.

Ionic Bonds Continued. 8. Good conductors of electricity in molten or dissolved state.

2. Covalent A. Characteristics 1. Share electrons between atoms having small differences in electronegativity. 2. Nonmetals with nonmetals 3. Formulas are in the true ratios of atoms (molecular formulas; C 6 H 12 O 6 ) 4. Melt at low temps

Covalent Continued 5. Substances exist in all states of matter. 6. Nonconductors of electricity.

3. Metallic Bonding A. Characteristics 1. Substances are metals 2. Sea of electrons surrounding a positively charged metal center. An attraction between metal ions and surrounding electrons.

Metallic Bonding Cont. 4. Formulas written as a neutral atom (Mg, Pb) 5. Solids with a crystalline structure at room temperature. 6. Range of melting points(depends on # of valence electrons 7. Excellent conductors of electricity because electrons in the “sea” are free to move.

Your Turn! Predict the type of bond in the following: 1. NaCl 2. H Ca

What part of atom is involved in bonding? Valence electrons- The Non Core electrons on the outermost shell

Your Turn!! Write the Lewis Diagrams for the following elements 1. Li 2. Ba 3. B 4. Si 5. N 6. C 7. Br 8. Ne

Valence Bond Theory The valence bond theory focuses on the atomic orbitals that must have overlapped or blended in order to obtain a particular molecular geometry

Methane CH 4 Look at the electron configuration for carbon. Where are the valence electrons? We have a 2s orbital full two of the p-orbitals are half full and the third p orbital is empty. Now draw the Lewis Diagram.

How can the central atom be using it’s four electrons to bond if 2 are in the s orbital? The second energy level has two types of orbitals available for bonding, s and p. So we will blend the one s orbital and the three p orbitals to create four spaces so that each valence electron can bond with each Hydrogen. The new orbitals are not s or p so they are call sp 3. Now each orbital is equal in energy.

Polarity- Separation of Charge Covalent bonds are polar if the electronegativity difference between the atoms is greater than.4 but less than Dipole Moment results in an unequal force Symmetrical vs. Asymmetrical

Intermolecular Attractive Forces IMF’s are forces that exist between molecules. The attraction between neighboring molecules NOT chemical bonds

IMF’s Melting and boiling points are a result of IMF’s. The lower the boiling point the weaker the IMF The higher the boiling point the stronger the IMF

Types of IMF’s 1. Dipole-dipole- two polar molecules attract each other 2. Hydrogen bonding- force of attraction between the hydrogen atom of one molecule and an unshared electron pair on F, O, or N of a neighboring molecule. Not the same as a bonded hydrogen,

Types of IMF’s 3. Dipole-induced dipole- polar and nonpolar molecule’s attraction. The polar molecule induces a temporary dipole in the nonpolar molecule. Larger molecules are more likely to form induced dipoles. 4. London Dispersion Forces- force of attraction between two nonpolar molecules due to the fact they can form temporary dipoles.