University:
Florida Gateway College
Course:
CHM 2045 | General Chemistry I
Academic year:

2024
Views:

260

Pages:

19
Author:

vdanihy8

Polarity • A polar molecule has charged ends, + and – (just like poles on a magnet) • The polarity of a bond is the function of the difference in electronegativity between two bonded atoms • Not every polar bond results in a polar molecule • Polarity is largely determined by molecular geometry Electronegativity • The measure of the attraction an atom has for the electrons in a bond • Pauling scale: ▫ ▫ ▫ ▫ Fluorine assigned a value of 4.0 (highest EN) All other elements are listed relative to this value Nonmetals greater than 2 Metals less than 2 Electronegativity Cont. • Atoms with different electronegativities pull on the bonding electrons differently • This results in an uneven distribution of electrons and therefore, a polar bond. • These polar bonds could result in a polar molecule Nonpolar bonds • If both bonding atoms have identical EN’s, the bond is NONPOLAR • All diatomic elements make nonpolar bonds and since there are only two atoms in the molecule the molecule is also nonpolar Polar bonds • If the bonding atoms have different EN’s, the resulting covalent bond will be polar • The bond is called a polar covalent bond and is referred to as a dipole • Ex: H-F EN of F: 4.0 EN of H: 2.1 Difference: 1.9 Polar molecules • If there are only two atoms in the molecule and they are different elements, the molecule is polar • If there are only two atoms in the molecule and they are the same, the molecule is nonpolar Polar molecules • If there are more than two atoms in the molecule, a bond being polar may or may not result in the entire molecule being polar • The geometry of the molecule must be considered Polarity • If the same atoms are covalently bonded to the central atom and there are no lone pairs on the central atom, the molecule will be nonpolar • The dipoles on the polar bond are pulled in equal but opposite directions and therefore cancel each other out. Nonpolar molecule Polarity • If all the atoms bonded to the central atom are not the same, or do not have the same EN, then the molecule will be polar. • The individual dipoles will not cancel each other out Polar molecule • Ex: CH3F Polarity • Lone pairs on the central atom tend to result in a polar molecule. • The lone pair distorts the symmetry of the molecule • The individual dipoles will not cancel each other out • Exceptions: linear (XeF2) and square planar geometries (XeF4) Polar molecule • Ex: H2O Polarity • Hydrocarbons are always nonpolar • Short chain (1-3 carbons) alcohols (-OH group) are usually polar • The carbon chain portion of the alcohol is nonpolar, so as the chain grows longer, the polarity diminishes. The polarity truth! • The polarity of a bond is a continuum rather than an either/or situtation • Bonds are classified as either covalent (nonpolar), polar covalent, or ionic based on the difference in electronegaitvity. Polarity continuum • An EN difference of 0.0 is considered nonpolar covalent • Both of the atoms share the electrons equally Polarity continuum • An EN difference less than 1.7 is considered a polar covalent bond. • Ex: H-Cl • The Cl has the electrons the majority of the time, but the H is not considered to have “lost” its valence electrons Polarity continuum • An EN difference greater than 1.7 is considered and ionic bond. • Ex: Na-Cl ▫ The Cl has the electrons the huge majority of the time and Na is considered to have “lost” its valence electrons ▫ Only in an aqueous solution the sodium is Na+ and chlorine is Cl-

Chem Polarity Electronegativity

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