Lesson 1: Introduction to Chemical Bonding Covalent Bonding Unit
TargetsI can define chemical bond.I can describe covalent bonding.I can classify bonding type according to electronegativity differences.
DefinitionsChemical Bond – mutual electrical attraction between the nuclei and valence electrons of different atoms that bind the atoms togetherValence electrons – outermost electrons that are available to be lost, gained, or shared to form a chemical bond
Chemical Bond A force that holds groups of 2 or more atoms together and makes them function as a unit Atom – smallest unit of an element Molecule – Group of covalently bonded atoms Atoms Molecule
Types of Chemical BondsIonic Bonding – (covered in next chapter) a type of bond in which a metal and a nonmetal transfer electronsCovalent Bonding – type of bond in which 2 or more nonmetal atoms share electrons
ElectronegativityElectronegativity - measure of an atom’s ability to attract electrons.Electronegativities tend to increase across a period and decrease down a group
Classifying Chemical BondsThe polarity of a bond depends on the difference between the electronegativity values of the atoms forming the bonds.Nonpolar covalent – 0 to 0.3Polar covalent – 0.4 to 1.7Ionic – greater than 1.8
Electronegativity ValuesIncreases from left to right across a periodDecreases down a group of representative elements
PracticeUse electronegativity values to classify the following bonds: a. Sulfur and Hydrogen b. Lithium and Fluorine c. Potassium and Chlorine d. Iodine and Bromine e. Carbon and Hydrogen
PracticeUse electronegativity values to classify the following bonds: a. Sulfur and Hydrogen 2.5 – 2.1 = 0.4; polar covalent b. Lithium and Fluorine 4.0 – 1.0 = 3.0; Ionic c. Potassium and Chlorine 3.0 – 0.8 = 2.2; Ionic d. Iodine and Bromine 2.8 – 2.5 = 0.3; Nonpolar covalent e. Carbon and Hydrogen 2.5 – 2.1 = 0.4 ; polar covalent
Covalent BondingCovalent Bonding and Molecular Compounds
TargetsI can explain why most atoms form chemical bonds.I can explain the relationships among potential energy, distance between approaching atoms, bond length and bond energy.I can state the octet rule.I can determine the number of valence electrons for a given atom.
Formation of a Covalent BondNature favors chemical bonding because most atoms have lower potential energy when they are bonded to other atoms.
Formation of a Covalent BondEach atom has a positive nucleus in the center and negative electrons surrounding the nucleus in a spherical pattern.The positively charged nuclei are attracted to the negatively charged electrons.
Formation of a Covalent BondAs the atoms approach each other, the charged particles interact: nucleus on one atom attracts electrons on the other atom.
Formation of a Covalent BondAs the atoms approach one another, the potential energy decreases.A bond forms when the potential energy is at a minimum.
Formation of a Covalent BondIf the atoms continue to approach one another once the bond forms, the nuclei will begin to repel one another and the potential energy will start to increase.
Characteristics of the Covalent Bond Bond length – distance between two bonded atoms at their minimum potential energy or the average distance between two bonded atoms Bond energy – energy required to break a chemical bond and form neutral isolated atoms - kilojoules per mole (kJ/mol) Bond lengths and bond energies vary with the types of atoms that have combined
The Octet RuleThe octet rule states that atoms tend to lose, gain or share electrons until they are surrounded by 8 electrons in their valence shell.The number of valence electrons is equal to the group number. (Groups 13-18; Group # -10)LABEL YOUR PERIODIC TABLE 1A 8A 2A 3A 4A 5A 6A 7A
PracticeWhat is the relationship between bond energy and bond length?
PracticeWhat is the relationship between bond energy and bond length? The bond length decreases as the strength of the bond increases.
PracticeArrange the following in order of increasing bond strength: C–Cl, C–I, H–F, and I–ISKIP
PracticeArrange the following in order of increasing bond strength: C–Cl, C–I, H–F, and I–I I-I, C-I, C-Cl, H-F
Practice ProblemsWhich pair of bonded atoms has the strongest bond?
Practice ProblemsWhich pair of bonded atoms has the strongest bond? H – F
Practice ProblemsWhich pair of bonded atoms has the weakest bond?
Practice ProblemsWhich pair of bonded atoms has the weakest bond? I – I
Practice ProblemsArrange the following bond lengths in order of increasing bond strength: 72 pm, 149 pm, 53 pm, and 398 pm SKIP
Practice ProblemsArrange the following bond lengths in order of increasing bond strength: 72 pm, 149 pm, 53 pm, and 398 pm 398 pm, 149 pm, 72 pm, 53 pm
Practice ProblemsDetermine the number of valence electrons in each of the following atoms. Lithium Sulfur Carbon Neon
Practice ProblemsDetermine the number of valence electrons in each of the following atoms. Lithium - 1 Sulfur - 6 Carbon -4 Neon - 8