Name Covalent Bonding and Nomenclature: Unit Objective Study Guide Class Period Date Due 1. Define chemical bonding. What is chemical bonding? Chemical bonding is the combining of elements to form new substances. 2. Explain why atoms chemically bond and describe the factors that determine whether or not two atoms will chemically bond. Why do most elements form chemical bonds? Most elements form chemical bonds in order to decrease potential energy and become more chemically stable. What factors determine whether or not a chemical bond will form? Two factors that determine whether or not a chemical bond will form are the electron configurations of the atoms involved and the attraction the atoms have for electrons. 3. Define electronegativity. Electronegativity - a measure of the ability of an atom to attract electrons when chemically bonding to another element. Why are there no electronegativity values given for most of the noble gases? The noble gases are stable and do not need to chemically combine with other elements. For this reason they do not attract electrons from other atoms and do not have electronegativity values. Which element on the periodic table is the most electronegative? Fluorine 1
4. Given a chart of electronegativities, calculate the difference of electronegativities of two atom two determine the degree of electron sharing and type of bond formed. Type of Bond EN (difference in electronegativity) Nonpolar Covalent 0.2 Polar Covalent 0.2-1.7 Ionic 1.7 Elements Elements Electronegativity EN Bond Type Bonding Hydrogen 2.1 H and O 1.4 Polar Oxygen 3.5 Li and Cl H and H Lithium 1.0 Chlorine 3.0 Hydrogen 2.1 Hydrogen 2.1 2.0 Ionic 0 Nonpolar 5. Identify which classes of elements form covalent bonds and which classes of elements form ionic bonds. Completion. A bond formed between a metal and a is generally classified as ionic. An example of this would be the bond formed between lithium and fluorine. In an ionic bond the electrons are between atoms. A bond formed between a nonmetal and a is generally classified as covalent. The bond could be classified as covalent if the electrons are shared equally. An example of this would be the bond formed between two nitrogen atoms to form the diatomic molecule N 2. The bond would be classified as covalent if the electrons are shared unequally. An example of this would be the bond formed between the hydrogen and chlorine atoms in HCl. 2
6. Define dipole in terms of binary compounds. Also identify the negative dipole and positive dipole when given a compound. Dipole oppositely charged regions of a molecule due to uneven sharing of valence electrons. Compound Negative Dipole (δ - ) Positive Dipole (δ + ) HBr bromine hydrogen NO oxygen nitrogen 7. Draw Lewis (electron) dot diagrams for atoms. Draw a Lewis dot diagram for each of the following atoms. Na Mg Al Si P S Cl Ar 8. Define single, double, triple and coordinate covalent bonds. Single Covalent Bond a bond formed when a pair of electrons is shared en atoms. Double Covalent Bond a bond formed when two pairs of electrons are sh ared between atoms. Triple Covalent Bond a bond formed when two pairs of electrons are shared between atoms. 10. Using prefixes, name binary molecular compounds given their formulas. 11. Write formulas for binary molecular compounds, given their names. Name Formula Carbon tetrachloride CCl 4 Dinitrogen monoxide N 2 O pentaphosporus decoxide P 5 O 10 Sulfur hexafluoride SF 6 Boron trichloride BCl 3 3
9. Draw Lewis (electron) dot diagrams and structural formulas for molecules. 12. Draw Lewis (electron) dot diagrams and structural formulas for exceptions to the octet rule. Draw the Lewis (electron) dot diagram or structural formula for each of the following molecules or polyatomic ions. CH 4 HCN H 2 O SH 6 C 2 H 6 CO 2 CH 3 COO - BeH 2 13. Draw resonance structures for molecules. What are resonance structures? Resonance structures are one of two or more equally valid electron dot structures for a molecule or polyatomic ion; the actual bonding is a hybrid, or mixture, of the resonance structures. Draw the resonance structures for sulfur dioxide (SO 2 ). Sulfur is the central atom. atoms; this value is usually expressed in kj per mole of a substance. 4
14. Define VSEPR and given a chemical formula of a simple molecule, identify the geometric shape as linear, trigonal planar, angular, tetrahedral, trigonal pyramidal, trigonal bypyramidal, or octahedral. 15. Using the shape of a molecule and electronegativities of its atoms, determine the polarity of the molecule. Formula Electron Dot Diagram or Structural Formula Shape of the Molecule Molecular Polarity (polar or nonpolar) CH 3 Cl AsF 5 CO 2 SCl 2 H 2 CO NI 3 SCl 6 5
16. Define van der Waals forces, dipole-dipole forces, hydrogen bonds, and London forces and give an example of each. van der Waals forces a term used to describe the intermolecular forces that occur between molecules. dipole-dipole forces an intermolecular force of attraction between polar molecules. hydrogen bonds a relatively strong intermolecular attraction in which a hydrogen atom that is covalently bonded to a very electronegative atom (O, N, F) is attracted to an unshared pair of electrons of an electronegative atom in a nearby molecule. Hydrogen bonding is a type of dipole-dipole force of attraction. London forces (dispersion forces) the weakest kind of intermolecular attraction; this attraction is thought to be caused by the motion of the electrons. 17. Given a molecule, identify the dominant type of intermolecular force of attraction. Describe the intermolecular forces that must be overcome to convert each of the following from a liquid to a gas. a. Cl 2 b. CH 3 OH c. H 2 S 18. Given chemical formulas for two substances, identify which type of intermolecular forces they exhibit and compare their boiling and freezing points. Br 2 has a boiling point of 59 C and ICl has a boiling point of 97 C. Rationalize the differences in boiling points between the two substances. HF has a boiling point of 20 C and HCl has a boiling point of -85 C. Rationalize the differences in boiling points between the two substances. CHCl 3 has a boiling point of 61 C and CHBr 3 has a boiling point of 150 C. Rationalize the differences in boiling points between the two substances. 6