shapes and bond angles of simple organic compounds
TRANSCRIPT
Shapes of and Bond Angles in Simple Organic Compounds
A. Miller
Simple Organic Compounds
Ethane
Etnene
Benzene
Simple Organic Compounds
Organic Compounds- consisting of carbon and hydrogen mostly
Recall
Overlapping of atomic orbitals
Formation of sigma bonds
The simple picture of overlap of half-filled atomic orbitals cannot be used to explain the geometry of all molecules especially organic molecules
Hybridisation
The mixing of orbitals Stronger orbitals are created
Methane -CH4
Structure
How Does Methane Forms Four Single Bonds
Ground state configuration 1s2 2s2 2p2
Methane
Needs to have four single bonds
Need four single electrons
Promotion of an electron from the 2s orbital to the 2p orbital
Mixing the 2s and 2p orbitals
Methane
Formation of sp3electronic configuration
Energy is required to do this
Promotion of electron and orbital mixing
hybridization
Mixing of Orbitals
Four single electrons
sp3 Hybrid Orbitals
The promotion electrons followed by the mixing of the orbitals create stronger orbitals
The s orbital mixes with the three p orbitals producing four equivalent sp3 orbitals
Each hybrid orbital contains 25% s character and 75 % p character.
The 4 sp3 hybrid orbitals each contains an electron
Will arrange themselves in a three dimensional space to get as far apart as possible (to minimize repulsion)
Electrons Arrangement in Carbon
Arrangement gives rise to a tetrahedral structure bond angle of 109.5
Overlapping of C and H orbitals
The sp3 hybrid orbitals of carbon overlap with the s orbital of hydrogen containing an electron.
Give rise to the C-H sigma bond
Formation of methane
Overlapping of orbitals
Structure of Methane
C-H bonds
Ethane
overlapping
Etnane
overlapping
Sp2 hybridization
Found in compounds such as alkenes
Formation of bonds to three other atoms (two hydrogens and one carbon)
Each carbon employs a set of sp2 hybrids
sp2 Hybridization
Electron promotion still occur in carbon
Mixing of the 2s and 2p orbitals.
Only two of the p orbitals are mixed with the s orbital.
sp2 Hybridization
The other p orbital remains pure (unhybridized)
Three sp2 hybrid orbitals are created
Two will overlap with hydrogen 1s orbital
Formation of Ethene
The third will overlap with a similar sp2 orbital on the other carbon atom.
Accounting for all the C-H bonds and the C-C sigma bond of the double bond
Each carbon has a pure p orbital containing an electron
Formation of Ethene
The orbitals are perpendicular to the plane of the sp2 orbitals-
Projects above and below the plane
Orbitals close proximity causes overlap sideways forming a pi bond
Ethene
Pi bonds are weaker than sigma bonds
sp2 Hybridization- mixing of orbitals
Hybridized Structure of Ethene
Ethene
Ethene
Benzene
Six carbon atoms in a ring
Shows resonance hybrid
Hexagonal in shape- at each apex there is a carbon bonded to a hydrogen
Benzene
Each carbon is bonded to three other atoms; a hydrogen and two other carbon atoms
Each carbon uses sp2 hybrid orbitals
Each carbon contains a pure p orbital perpendicular to the plane of the ring
Benzene
Each unhybridized p orbital overlaos with two other p orbitals, one on each of the two neighbouring carbon atoms
A large circular pi-type bond is formed above and below the plane
Electrons are delocalized in the benzene ring
Benzene
Overlapping of p orbitals
Benzene
Benzene
Canonical forms
Benzene
Hybridized structure
Structure of solids
Solids can either be
- Amorphous (non-crystalline) or
- Crystalline
Amorphous Solids
Particles have no orderly structure Lack well-defined faces and shapes Many are mixtures of molecules that do not
stack together Most composed of large complicated
molecules Example; rubber, glass
Crystalline Solids
Highly regular/orderly arrangement of atoms, molecules or ions in a crystal.
Usually have flat surfaces, or faces that make definite angle with one another
Example; quartz, diamond
Lattice Structure
Consists of repeating units called unit cell Solid can be represented by a three
dimensional array of points called crystal lattice
Each point in the lattice is called a Lattice points
Lattice Structure
Structural units in the lattice are held by;
- electrostatic forces in ionic crystals
- van der Waals forces in simple
molecular crystals
- hydrogen bonds as in ice
Lattice Structure
Structural units in lattice are held by;
- Covalent bonds as in giant molecular structures as in silicon dioxide (quartz), giant atomic structures as in diamond and graphite
- metallic bond as in metallic crystals such as copper
Ionic Solid-sodium chloride
Face-centred cubic structure
Lattice points are occupied by ions
Each Na+ surrounded by 6 Cl- ions as next nearest neighbour and vice-versa
Strong forces of attraction between oppositely charged ions
Ionic Structure- Sodium Chloride
Blue- chloride ions
Red-sodium ions
Simple Molecular structure
Atoms held by strong covalent bonds
Molecules held by weak van der Waals
forces
Gases or liquids at room temperature
Simple Molecular-Iodine
Atoms covalently bonded in pairs as I2
molecules
Discrete molecules held by weak van der Waals forces
Shiny in appearance due to regular arrangement of molecules
Iodine
Very slightly soluble in water
Dissolve freely in organic solvent
Does not conduct electricity- no separation of charge
Face-centred Cubic Structure
Simple Molecular-Iodine
Molecules in corners and face of unit cell
Giant Molecular-Silicon dioxide
Formed by strong, directional covalent bonds, and has a well-defined local structure
Each silicon atom can bond to four oxygen atoms, giving rise to a giant covalent network structure
Silicon dioxide
Each Si is bonded to four oxygens and each O to two silicon atoms.
The bonding between the atoms goes on and on in three dimensions.
Four oxygen atoms are arrayed at the corners of a tetrahedron around a central silicon atom:
Giant Molecular-Silicon dioxide
Three dimensional structure
Silicon dioxide
bonding
Metallic Structures
Consist entirely of metal atoms.
Usually have hexagonal close-packed, cubic close-packed (face-centred cubic) or body-centred cubic structures
Each atom typically has 8 or 12 adjacent atoms.
Metallic Structure
Bonding due to valence delocalized electrons throughout the entire lattice
i.e. positive ions immersed in a sea of delocalized valence electrons.
Metallic StructureBody-centerd Cubic
There is one host atom (lattice point) at each corner of the cube and one host atom in the center of the cube: Z = 2.
Each corner atom touches the central atom along the body diagonal of the cube
Metallic Structure
Body-centred cubic
Body-centred
Unit cell
Cubic Close-packed/ Face-centred
Arranging layers of close-packed spheres such that the spheres of every third layer overlying one another gives cubic close packing
Cubic Close-packed/Face-centred Cubic
Unit cell has one host atom at each corner and one host atom in each face.
Each corner atom contributes one eighth of its volume to the cell interior
Each face atom contributes one half of its volume to the cell interior (and there are six faces), then Z = 1/8.8 + 1/2.6 = 4.
Cubic Close-packed/ Face-centred eg. Copper
Face-centred cubic
Hexagonal Close-packed
The unit cell consists of three layers of atoms.
The top and bottom layers contain six atoms at the corners of a hexagon and one atom at the center of each hexagon.
The middle layer contains three atoms nestled between the atoms of the top and bottom layers
Hexagonal Close-packed
layers
Giant Atomic Structures
Covalent-network solids
Consist of atoms held together in large network or chains by covalent bonds
Solids are much harder and have higher melting points than molecular solids.
Giant Atomic Structure
Two examples are; diamond and graphite.
Diamond and graphite are two allotropes of carbon
Diamond
Lattice points occupied by carbon atoms
Each carbon atom is bonded to four other carbon atoms in a tetrahedral arrangement.
Interconnected three-dimensional array of strong C-C single bonds
Diamond
Diamond is very hard as a result.
Multitude of covalent bonds causes diamond to have a very high melting point 3550 degree Celsius
Does not conduct electricity- no free electrons.
Diamond
Insoluble in water and organic solvents.
No possible attractions which could occur between solvent molecules and carbon atoms which could outweigh the attractions between the covalently bound carbon atoms
Giant Atomic Structure- Diamond
C-C single bonds
Diamond
Tetrahedral arrangement
Giant Atomic Structure- Graphite
Each carbon is covalently bonded to three other in a trigonal planar arrangement.
Each carbon has a single electron that is delocalized and free to move about in the lattice.
Hence graphite conducts electricity along the layers
Giant Atomic Structure- Graphite
Lattice structure consists of layers of interconnected hexagonal rings
Layers are held by weak van der Waals forces
Layers readily slide past each other when rubbed. Giving a greasy feel.
Hence used as a lubricant and in lead pencils
Giant Atomic Structure- Graphite
Insoluble in water and organic solvents - for the same reason that diamond is insoluble.
Attractions between solvent molecules and carbon atoms will never be strong enough to overcome the strong covalent bonds in graphite.
Giant Atomic Structure- Graphite
Layers of carbon atoms
Graphite
Van der Waals forces between layers
Structure of Ice