Molecular Geometry

• A molecule is the smallest particle of a substance that exists independently.
• Molecules of elements are atoms of the same element that are chemically joined together, also called diatomic molecules.
• Examples of molecules of elements include H2, O2, N2, Cl2, I2, Br2, F2.
• Molecules of compounds are atoms of different elements that are chemically joined together.
• Examples of molecules of compounds include NO, H2O, NO2, CO2.
• Covalent bonds are much weaker than ionic bonds.
• Molecular compounds have much lower melting and boiling points.
• Molecular compounds are solid, liquid, or gas at room temperature.
• Molecular compounds are non-conductors in any state.
• Molecular geometry is the three-dimensional structure or arrangement of atoms in a molecule.
• Polarity, phase of matter, and reactivity of a compound can be determined with the understanding of the molecular structure of a compound.
• Bond lying on the surface is a line that connects the central atom C to A.
• Bond directed in front of the plane is a wedge shaped bond that connects to B (thick end toward the observer).
• Bond directed in back of the plane is a hatched bond or the dashed bond that connects to D.
• Valence Shell Electron Pair Repulsion (VSEPR) Theory predicts the geometry of individual atoms from the number of electron pairs surrounding their central atoms.
• The Lewis Dot Structure (LDS) shows which atoms have lone pairs of electrons.
• The Valence Shell Electron Pair Repulsion can predict the shapes of many molecules and polyatomic ions but cannot provides information about bond lengths or the presence of multiple bonds.
• If a metal is involved, only nonmetals are involved in the bond.
• A non-polar molecule is one in which the electrons are distributed more symmetrically and thus does not have an abundance of charges at the opposite sides.
• Examples of non-polar molecules are hydrocarbons, diatomic molecules, noble gases and CO 2 .
• A polar molecule is a molecule that has one end with a slightly positive charge and one end with a slightly negative charge ( without symmetry ).
• According to Linus Pauling, electronegativity is the power of an atom in a molecule to attract electrons to itself.
• Pauling developed a numerical scale of electronegativities.
• The molecular geometry of water ( H 2 O ) can be drawn by drawing the Lewis dot Structure of H 2 O.
• Opposite directions of dipole moments cancel out.
• Examples of predicting the type of bond between atoms are Cl 2 ( Nonpolar covalent ), NaF ( Ionic ), and O - H ( Polar covalent ).
• Each dipole of CCl 4 is shown clearly, however, the symmetry of the molecule cancels out the dipole moments and results in a non-polar.
• C: 4(1) = 4, O: 6(2) = 12, Total = 16 valence e- used in bonds - 8 e- remaining e- = 8e-2.
• Electronegativity values are useful in classifying the bond as nonpolar covalent, polar covalent or ionic.
• General Rule: Symmetrical molecules are non-polar, while asymmetrical molecules are polar.
• Examples of polar molecules are Hydrogen fluoride ( partially negative, partially positive dipole moment ), and Hydrogen chloride ( partially negative, partially positive dipole moment ).
• Formula for VSEPR: A - central atom, X - 2 atoms are attached to A, E - lone pair.