University:
Felician University
Course:
CHEM-001 | Basic Chemistry
Academic year:

2022
Views:

66

Pages:

14
Author:

Clint W.

Lewis Structures For Monatomic Ions • We subtract the charge on the ion from the number of valence e- and show these around the element symbol • We enclose the symbol in brackets and indicate the charge • for Na+ ion 1-1=0 [ Na ]+ • for O2- ion, 6-(-2)=8 [ O ]2- 16 Ionic Compounds – Lewis Structures Ionic compounds are formed by the attraction between oppositely charged ions • show each ion, separately, alternating charges • for the ionic compound K2S: [ K ]+ [ S ]2- 17 [ K ]+ Chemical Bonds - Covalent • Covalent bonds form when atoms share valence electrons in the region of space created by orbital overlap Nonmetal - nonmetal bonds are shared or covalent bonds because neither element easily loses eH : H 18 In a Covalent Bond, atoms SHARE electrons to form stable pairs. Nonbonding lone pair Before bonding н Н• Н• Ammonia molecule, NH 3 (а) Before bonding Н· н Н· (Ь) н н Methane molecule, СН4 Molecules Often Obey The Octet Rule • Share e- to gain octet • May form single, double or triple bonds • Each atom has 8 esurrounding it 21 Many nonmetals occur as diatomic molecules Representations of Molecules Structural Formula Ball and Stick Condensed Structural Formula CH3CH2CH3 Structural Formulas – Derived from Lewis Structures Show how atoms are attached to one another. Electron Pairs in Lewis Symbols •Symbolized by a line between the atoms •May include up to three pairs of e-: One pair forms a single bond X-Y Two pairs form a double bond X=Y Three pairs form a triple bond X≡Y Not All Atoms Share Electrons Equally • While electrons in a covalent bond are shared, the electrons are not evenly distributed between the two nuclei • Electronegativity is a measure of the attractive force that one atom in a covalent bond has for the electrons of the bond Bond Dipoles • Atoms with different electronegativity values will share electrons unequally • Electron density is uneven, with a higher charge concentration around the more electronegative atom • Bond dipoles indicate with delta (δ) notation that a partial charge has arisen • Partial negative (δ-) charge is assigned to the more electronegative element • Such a bond is termed a polar bond 27 Electronegativity • The polarity of a bond depends on the difference between the electronegativity values of the atoms forming the bond Differences in Electronegativity Indicate Bond Polarity Type of Bond Difference in Electronegativity Non-Polar Covalent less than 0.5 Polar Covalent between 0.5 and 2.1 Ionic greater than 2.1