Ionic Versus Covalent Bonding. Covalent Bonding. Covalent Bonding H 2. Covalent Bonding. Keywords:

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1 Keywords: Covalent Bonding Valence electron Covalent bonding Single, double and triple bonds Bonding electrons and Non-bonding electrons (lone pair of electrons) Bond energy and bond length Electronegativity Ionic Versus Covalent Bonding Ionic compounds are formed when electrons are transferred from one atom to another The transfer of electrons forms ions Each ion is isoelectronic with a noble gas Electrostatic force (ionic bond) holds atoms together Covalent bonding involves sharing of electrons to achieve noble gas configurations for the atoms involved Covalent bond = attractive force resulting from atoms attracted to a shared pair of electrons Covalent Bonding Covalent Bonding H 2 First, some background The octet rule: The atoms tend to gain, lose or share electrons to have eight electrons in the valence shells (electronic configuration of noble gas, stable configuration) Carbon (group IVA) would need to gain or lose 4 electrons to achieve noble gas configuration in an ionic compound Diatomic molecules, like O 2, Cl 2, I 2 do not transfer electrons to form ionic bonds Another type of bonding is at work here G N Lewis (1916) theorized that noble gas configurations could be attained by electron sharing For H 2 (a) Two noninteracting H atoms, each with one electron in its 1s orbital (b) As the two H atoms approach, the spins pair and the s orbitals merge into a molecular orbital, electrons are shared (c) Fully formed molecular orbital Cl - Cl +???? Does this look OK? (d) Each H atom is satisfied

2 Formation of Covalent Bond Distribution of electron density in H 2 Electron density is highest around and between the nuclei Covalent Bonding Cl 2 Multiple Covalent Bonds Each Cl atom has a 3p orbital that is singly occupied Bonding pairs Lone pairs 3p 3s 2p 2s Each Cl atom in Cl 2 achieves its octet with a single Cl-Cl bond or What about N? : Cl Cl : : Cl Cl : Ṅ Ṅ Ṅ Ṅ + Check the octets! Cl 1s : C l Cl : + : Cl Cl : How can nitrogen satisfy its octet? Which bond is stronger, that in Cl 2 or in N 2?

3 Types of Bond and Bond Order Bond energy and bond length Types of bond Bond order Bond formation: exothermic process, -E Bond breakage: endothermic process, +E Single (Cl 2, HCl) 1 Double (O 2 ) 2 Triple (N 2 ) 3 Bond length: distance between the nuclei between two bonded atoms Bonding pairs and lone pairs Lone pairs Cl : Cl : Bonding pairs Electronegativity and Bond Polarity Electronegativity and Bond Polarity Electronegativity A measure of the ability of an atom in a molecule to draw electrons to itself -An atom with large negative electron affinity and large ionization energy has large electronegativity Example: fluorine, oxygen i) Both men are equally strong ii) Both men are equally weak iii) One is stronger than the other No one will win The stronger will win

4 Electronegativity Scale Increases Electronegativity and Atomic Size Decreases Electronegativity is inversely related to atomic size Electronegativity and bond polarity Bond Polarity and Electronegativity Bond polarity increase as the value of χ increase > < 05 χ : difference in electronegativity values between the bonded atoms χ H 2 00 non-polar covalent ( χ = 0) HF 18 polar covalent (0 < χ <20) LF 30 ionic ( χ >20) Bond polarity order for hydrogen halides: HF ( χ = 18) > HCl ( χ = 10) > HBr ( χ = 08) > HI ( χ = 05)

5 Bond Polarity Use electronegativity values to classify the bonding in the following molecules (ionic, polar covalent, or nonpolar covalent) KF NO SiCl 4 K 2 O General rules Make sure the compound qualifies as a covalent molecule (and not ionic) Give the name of the least electronegative element first Give the stem name of the more electronegative element, ending with ide Indicate the number of each type of atom by the prefixes, mono, di, tri, tetra, penta, etc PCl 5 phosphorus pentachloride SO 2 sulfur dioxide N 2 O dinitrogen monoxide CO carbon monoxide CO 2 carbon dioxide CCl 4 NO SeF 4 S 2 O 7 CaCl 2 Diphosphorus pentoxide Sulfur trioxide Silicon tetrachloride Trihydrogen nitride Dihydrogen monoxide N 2 O 4