I can #2 I can draw a Lewis structure

Rules for Lewis Structures 1. total number of valance electrons 2. central atom –Always C, Never H, Rarely O, or the one that is the least electronegative. 3. bond to central atom 4. add the valance electrons until u have a full shell of 2 (H) or 8. you may have some exceptions, incomplete, expanded, multi bond (C, N, O, S) 5. check your work

Chapter 6: Bonding & Molecular Shape

How will the placement of the bonds and lone pairs effect the structure and shape? I can –Define the different shapes –Label models for the shapes –Predict what molecules will form what shapes

Formulas Empirical Formula – The ratio of elements in a compound (CH 2 O) Molecular formula – gives the actual number of atoms in a compound C 6 H 12 O 6

Formulas

Structural Formulas – show which atoms are bonded to which. Molecular Shape – gives the angles of the bond

Formulas Ball-and-stick – Ball represents the inner atom, the sticks represent bonds Space filling – shows the actual shape of the molecule

VSEPR H9COZohttps:// H9COZo

How Do We Know This? VSEPR Theory – Valence-shell electron pair repulsion theory States that repulsion between the sets of valence electrons surrounding an atom causes these sets to be oriented as far apart as possible. In a small molecule, pairs of valence electrons are arranged as far apart from each other as possible. Lone pairs of electrons repel more than electrons in bonds Double bonds count as one pair!!

Effective Pairs Covalent bonds count as 1 effective pair. Double bonds and triple bonds count as 1 pair!! Lone pairs count as 1 pair.

Shapes of Small Molecules Linear – atoms connected form a straight line. Bond forms an angle of 180 o All single bonds are linear. Carbon dioxide and acetylene

Examples of Linear CO 2 BeF 2 Cl 2

Shapes of Small Molecules Trigonal Planar – 3 atoms connected to a central atom. Bond forms an angle of 120 o Boron trichloride & carbonate ion

Trigonal Planar CO 3 -2 BCl 3

Shapes of Small Molecules Tetrahedral – 4 atoms connected to a central atom. Bond forms an angle of o Methane & carbon tetrachloride

tetrahedral CH 4

trigonal bipyramidal AB 5 Makes five bonds No lone pairs

octahedral AB 6 This a bond of 6 atoms to a center. Expanded octet No lone pairs

Lone pairs on the Central atom This will cause more bending and therefore will make a different shape. Remember that lone pairs are unbounded electrons.

Shapes of Small Molecules Pyramidal – 3 sided pyramid Lone electron pair not involved in bonding. Bond forms an angle of o Ammonia, Phosphorous Trichloride

Pyramidal NH 3

Shapes of Small Molecules Bent – 3 atoms not in a straight line 2 lone electron pairs not involved in bonding. Bond forms an angle of o Water & Nitrite Ion

Bent H 2 O

Square pyramidal Bromine Pentafluoride (square pyramidal BrF 5 ) Beyond Tetrahedral

Beyond Tetrahedral T-Shaped Bromine Trifluoride (T- shaped BrF 3 )

Beyond Tetrahedral Phosphorus Pentachloride (trigonal bipyramidal PCl 5 ) Sulfur Tetrafluoride (see-saw SF 4 )

Beyond Tetrahedral Sulfur Hexafluoride (octahedral SF 6 ) Tetrachloroiodate Ion (square planar ICl 4 - )

Practice What shape is formed from –Nitrogen trichloride NCl 3 –Oxygen Difluoride OF 2 –BeF 2

Visual video on shape VlSZc4https:// VlSZc4

Polarity Molecules as well as bonds may be polar or nonpolar. Polar molecules are also called dipoles. Polarity is determined by the shape of the molecule as well as the polarity of each of the bonds.

Polarity Bond polarity is represented by vectors. Arrows point to the more electronegative atom. The polarity of the molecule is the sum of all the vectors.

Molecular Polarity –If electrons are not always evenly distributed between bonds, it would make sense that the electrons are not evenly distributed through the entire molecule. –Polar Molecules - molecule where the shared electrons are not evenly distributed throughout the molecule. These molecules are called dipoles since you have a partially negative and partially positive areas of the molecule. –Non-polar Molecule - molecule where the shared electrons are evenly distributed throughout the entire molecule.

Finding its polarity Key to figuring Molecular Polarity - Assume Polar, prove Non-polar –Since it is easier to have the electrons unevenly distributed throughout the molecule, polar molecules are statistically seen more often. Molecular polarity is a function of Bond Polarity and Shape of the Molecule. There are certain shapes (linear, trigonal planar, tetrahedral, trigonal bipyramidal, and octehedral) where polar bonds will cancel themselves out (due to the symmetry in the shape) so these bonds will act like non-polar bonds.

Polarity Rules –Determine the geometry of the molecule. If you have all non-polar bonds, you have a non-polar molecule If you have all polar bonds, you have a polar molecule, except for molecules that have symmetry (trigonal planar, linear, tetrahedral, trigonal bipyramidal, octahedral) since the polar bonds will cancel themselves out due to symmetry to form a non-polar molecule. For compounds with both polar & non-polar molecules, need to check to see if polar bond can themselves out due to symmetry to give non-polar molecules. Bent and pyramidal molecules will be polar For oil, grease, gasoline and fats (these compounds have CxHy), these compounds are all non-polar molecules since the C-H & C-C bonds are all non-polar.

Determine polarity with symmetry If a molecule is symmetrical then it is nonpolar. If a molecule is unsymmetrical it is polar.

Which of the following molecules is polar? a) b) c)

Practice Is it a polar molecule? –Chloroform (CHCl 3 ) –Methane –H2–H2 –H2S–H2S

Intermolecular forces Three main types of molecule attraction –Dipole- dipole or ion-dipole –Dipole induced (ion – nonpolar, or polar- nonpolar) –London Dispersion

Dipole-dipole force The force attraction between polar molecules

Induced dipole force Making a compound with out polarity have polarity.

London Dispersion Forces Weak intermolecular force It is a continuous motion of an electron that temporarily creates a dipole. This occurs between all molecules and compounds no matter if polar or nonpolar. They are the only force that is acting among noble-gas atoms. The strength will increase with increasing electrons, so the larger the atomic number the larger the London force.

Hydrogen Bonds The weak intermolecular forces between polar molecules creates Hydrogen bonds H bonds have 5% of the strength of a covalent bond Gives water unique properties

Polarity Determines Physical Properties Polar molecules will align in an electrical field. The more polar a molecule, then the higher the boiling point. Higher polarity gives a high surface tension

Polarity Determines Physical Properties Polar molecules will dissolve in polar solvents Hydrophobic - “water fearing” Hydrophilic – “water loving” Soap is an amphipathic molecule

Organic Chemistry Carbon makes 4 bonds Almost a limitless number of compounds may be formed Organic chemistry is the study of carbon compounds