Chemistry Chapter 4 Forces Between Particles

Dispersion Forces

- Very weak attractive forces acting between the particles of all matter. They result from momentary nonsymmetric electron distributions in molecules or atoms.

Nonpolar Covalent Bond

-A covalent bond in which the bonding pair of electrons is shared equally by the bonded atoms. -An electron pair shared by two identical atoms is attracted equally to each of the atoms, thus the electrons spend exactly the same amount of time associated with each atom. -When the e/n difference (ΔEN) b/t bonded atoms is 0.0, it is classified as nonpolar covalent (electrons shared equally). -Compounds between non-metals can be non-polar.

Polar Covalent Bond

-A covalent bond that shows bond polarization; that is, the bonding electrons are shared unequally. -The more electronegative atom acquires a partial charge of (-) and the less e/n atom has a partial (+) charge. -Molecule as a whole has no net charge, just an uneven charge distribution -When ΔEN is b/t 0.0 and 2.1, the bond is classified as polar covalent (unequally shared electrons and bond is polarized). -Compounds formed between non-metals can be polar.

Nonpolar Molecules

-A molecule that contains no polarized bonds, or a molecule containing polarized bonds in which the resulting charges are distributed symmetrically throughout the molecule. - Symmetrical charge distribution throughout the molecule. Identical atoms with identical attractions for their shared electron pairs.

Bond Polarization

-A result of shared electrons being attracted to the more electronegative atom of a bonded pair of atoms. -Bonding shared by two different electrons shared by two different atoms are shared unequally. Electrons spend more time near the atom with the higher electronegativity.

Network Solid

-A solid in which the lattice sites are occupied by atoms that are covalently (shared pair of e-) bonded to each other.

Polar Molecules

-AKA dipoles. A molecule that contains polarized bonds and in which the resulting charges are distributed nonsymmetrically throughout the molecule. -Nonsymmetric charge distribution throughout the molecule. -Unlike atoms exert unequal attractions for their shared electrons.

Metallic Bond

-An attractive force responsible for holding solid metals together. It originates from the attraction between positively charged atomic kernels that occupy the lattice sites and mobile electrons that move freely through the lattice.

Binary Ionic Compounds

-Composed of ions with two different elements. One a metal and the other a non-metal.

Binary Covalent Compounds

-Composed of two different nonmetal elements.

Polyatomic Ions

-Ion that contains more than 1 atom and are considered one.

Bonds (3) and Molecules (2)

-Only 3 types of bonds: Nonpolar covalent (ΔEN=0) * Between 0.0 - 0.4 = Non polar Polar covalent (ΔEN=0.1 - 2.0) * Between 0.4 - 1.8 = Polar Ionic covalent (ΔEN=2.1 or greater) * Between 1.8 + = Ionic -Only 2 types of molecules: Polar and nonpolar Ionic bonds do NOT form molecules.

Dipolar Force

-The attractive force that exists between the positive end of one polar molecule and the negative end of another.

Hydrogen Bonding

-The result of attractive dipolar forces between molecules in which hydrogen atoms are covalently bonded to very electronegative elements (O, N, or F). -Bonding occurs in gases, liquids, and solids composed of polar molecules in which H atoms are covalently bonded to highly electronegative elements (generally O, N, or F).

Electronegativity

-The tendency of an atom to attract shared electrons of a covalent bond. -Different atoms generally have different tendencies to attract shared electrons of a covalent bond. -Follows trends in the periodic table. Increases L to R and decreases from top to bottom. -Used to determine the direction of bond polarity which can be indicated in the Lewis structure by replacing the short line for the bond with a modified arrow |-->) pointed towards the more electronegative atom.

Ionic Covalent Bond

-When ΔEN is 2.1 or greater (electrons are transferred). -Change from purely covalent to completely ionic compounds is gradual and continuous as ΔEN changes. -Compounds formed by a reaction of a metal with a non-metal are generally ionic. - Ionic covalent bonds do NOT form molecules.

Diatomic Molecules

Composed of only two atoms, of either the same or different chemical elements. Ions that do not have a central atom.

Tetrahedral

Four pairs of shared electrons (no pairs of lone (unshared) electrons around the atom. Bond angle is approximately 109.5 degrees. o SP3 hybridized molecules are tetrahedral. AX4 = SP3 (four bonds attached to the central atom, therefore is tetrahedral in shape)

Molecular Geometry

Geometric patterns that allow electron pairs to get as far away as possible (which minimizes the repulsive forces between them). VSEPR theory

Trigonal Planar

Three groups of shared electrons around a central atom. Two of these groups are single bonds and one groups is a double bond made up of two pairs of shared electrons. There are no unshared electrons around the atom. Bond angle us 120 degrees. o SP2 hybridized molecules are trigonal planar AX3 = SP2 are trigonal planar

Trigonal Pyramidal

Three pairs of shared electrons and one pair of unshared electrons around a central atom. o SP3d hybridized molecules are trigonal bypyramidal AX5 = SP3D are trigonal bypyramidal

Bent

Two groups of shared electrons (in a single or double bonds) and one or two pairs of unshared electrons.

Linear

Two groups of shared electrons, usually double bonds with two shared electron pairs between two atoms, and no unshared electrons around a central atom. When there are only two atoms in a molecule or ion, and there is no central atom (HBr, for example), the geometry is also linear. Bond angle is 180 degrees. o SP hybridized molecules are linear AX = hybridization/SP Shape/Linear

VSEPR Theory

Used when some of the valence electrons around the atom are unshared to predict changes in spacial arrangements of molecules (3D).