Bonding The Shape Of Organic Molecules 13n5y

SCH4U0 Bonding & the Shape of Organic Molecules Organic compounds are defined as compounds that are based on carbon. They usually contain carbon-carbon and carbon-hydrogen bonds. The Carbon Atom Due to the bonding properties of carbon, there are several million organic compounds (versus ¼ million inorganic compounds). • Each carbon atom has the ability to form up to 4 covalent bonds. Therefore, each carbon atom ca connect to as many as 4 other atoms (in organic chemistry, most notably hydrogen, oxygen, and nitrogen). • Carbon atoms can form strong single, double, or triple bonds with other carbon atoms.

Carbon’s unique bonding properties allow the formation of a variety of structures, including chains, rings or many shapes and sizes. Carbon compounds in which a carbon forms only single bonds (a saturated compound) have a different shape than compounds in which carbon forms double or triple bonds (unsaturated compounds). Common Molecular Shapes in Organic Molecules Central Atom Shape Tetrahedral – Carbon is in the centre of a tetrahedron where Carbon with 4 single bonds. 4 other atoms are at the vertices of the tetrahedron (109.5o from each other).

Carbon with 1 double bond & 2 single bonds.

Trigonal planar – Carbon is in the centre of a triangle where 3 other atoms are at the vertices of the triangle (120o from each other).

Carbon with 2 double bonds or 1 triple bond & 1 single bond.

Linear – Carbon is in the centre and 2 other atoms are stretched out to either side (180o from each other).

Diagram

Oxygen with 2 single bonds.

Bent – Oxygen forms 2 single bonds leaving 2 non-bonding pairs of electrons. The nonbonding electrons repel the bonding electrons to 2 vertices of a tetrahedron (104.5o from each other).

Nitrogen with 3 single bonds.

Trigonal pyramidal – Nitrogen forms 3 single bonds leaving 1 non-bonding pair of electrons. The non-bonding electrons repel the bonding electrons to 3 vertices of a tetrahedron (107o from each other).

Three-Dimensional Structural Diagrams In a three-dimensional diagram, wedges are used to give the impression that an atom or group is coming forward, out of the page. Dashed or dotted lines are used to show that an atom or group is receding, or being pushed back into the page. Molecular Shape and Polarity The 3D shape of a molecule is important, especially when the molecule contains polar bonds (0.5 < ∆EN < 1.7). Recall that every polar bond has a bond dipole (a partial negative change and a partial positive charge at opposite ends of a covalent bond). In organic chemistry, polar covalent bonds such as, C=O, C—O, O—H, and N—H are of particular importance. Predicting Molecular Polarity A molecule is considered to be polar when it has an overall imbalance of charge (i.e. has polar bonds and is asymmetrical). • If equal bond dipoles act in opposite directions in 3D space, they counteract each other.

• If the bond dipoles in a molecule do not counteract each other exactly, the molecule is polar.

Steps to Predicting Molecular Polarity

No Does the molecule have polar bonds?

Non-Polar molecule

No

Yes

Yes

Is there more than one polar bond?

No

Do the bond dipoles act in opposite directions?

Yes

Polar molecule

Homework Read Section 1.1 Bonding and the Shape of Organic Molecules (pg. 5 – 11) Answer Practice Problems #1 – 4. Answer Section Review #2 – 5.

Polar molecule

Non-Polar molecule