Covalent Bonds As presented by : Group 8

Lam Winn Sen (015681)Tan Di Ken (012861)Alvin Chiew Jing Jie (015154)Oswald Chai Ming Yang (013421)Table of contentsIntroduction to covalent bondsLam Winn Sen presents :Introduction to covalent bondsWhat is a covalent bond?A chemical bond that involves the sharing of electron pairs between atoms.Covalency is greatest between atoms of similar electronegativity.Definition of covalent Co- : to mean jointly/together.- -valent : to denote electrons involved in chemical bonding.Types of covalent bonds include :- -bonding, -bonding, metal-to-metal bonding and etc.Covalent bond is stronger than intermolecular forces, and generally the strongest among the intramolecular force because it keeps both atoms in close proximity.Covalent bond is an intramolecular force, same as ionic and metallic bond. Forms general between two non-metals. 4The most typical example of covalent bonding

Image above titled Covalent bond hydrogen by Jacek FH is licensed under Creative Commons License Attribution-ShareAlike 3.0 Unported(CC BY-SA 3.0)

Octet rule, single bonds & double bondsTan Di Ken presents :Octet RuleShare electronEight electrons in valence shellAtoms seek the most stable electron configurationRequires eight electrons because it is the amount needed to fill the s and p orbital

Gilbert N. LewisExceptions to the Octet RuleElements in periods 3 or higher can hold more than an octet.More than 8 electrons in valence shellBoron hold less than an octet

Chlorine has 10 electrons in valence shell

Boron has 6 electrons in valence shell

First discovered binary compound of a noble gasXenon has 12 electrons in valence shell

Single bondsOne electron pair is shared between two atoms.The bond is weaker.Smaller density.Most stable.

Basic + ComplexDouble bondsTwo electron pairs are shared between the two atoms.

EthyleneElaidic acid

Double bondsMain features of double bondsBoth atoms are connected by two covalent bonds, therefore:Not flexible

Cannot rotate

Requires more energy to break

Triple bonds,Coordinate bondsOswald Chai Ming Yang presents :Triple BondsThree covalent bonds between two atoms

Main features of triple bondsBoth atoms are connected by three covalent bonds, therefore :Less flexible

Cannot rotate

Requires more energy to break

Bonds are shorter

Larger electron density

Least stable among the covalent bonds

Video?Coordinate Bonds (A.K.A Dative Covalent Bonds)Where the electrons being shared come from one atom.Typically occurs in inorganic complexes.

Follows the octet rule.

Example of coordinate bonding in formation of Ammonium (NH4+ Ion)

NH3 + HCl >>> NH4+ + Cl- Ammonia + Hydrogen Chloride >>> Ammonium Ion + Chloride IonNote : Arrow points away from the lone pair which forms the bondCoordination complexes

[Fe(H2O)6]2+ ionHexaaquairon (II) ionLone pairs in the oxygen atom of water form coordinate bonds with the central Fe2+ ion.

In this case :Water molecules are ligands.

Resulting ion is a complex ion.

Co-ordination number : 6 , because it has 6 coordinate bonds to the central metal ion.

1 water molecule forms 1 coordinate bond with the central metal ion. Therefore, water is a monodentate ligand.- & - bonding,polar & non-polar bondingAlvin Chiew Jing Jing presents :-bondingSigma ( ) bond: orbitals overlap head-on (1 Bond)Strongest type ofcovalent bonds due to the direct overlap of orbitals.

There is no more than 1 sigma bond between any two atoms.

-bondingPi bond ( ) bond: orbitals overlap sideways ( >1 Bond)

Weaker than bond.Can only form after the formation of a -bond.

Single bond: -bond

Double bond: -bond + -bond

Triple bond: -bond + 2 -bond

Polar bondsA covalent bond between 2 different Atoms.One with +ve charge, the other with ve charge.Unequal sharing of electrons, which means they are polarised.Chemically more reactive ( HO universal solvent).

+ X Y -Polar MoleculesA molecule which has both small +ve and ve charge at two ends.We call it Dipole.It has polarised bond and might not be symmetrical.

+H

C

Cl Cl Cl- --How do we differentiate them?Non-Polar MoleculeMust be symmetrical.Must not contain lone pair.

Polar Molecule- Contains lone pair - Not symmetrical

In general, the higher the electronegativity difference, the more polar are the bonds.

Eg. H-F and H-O are very polar.DRAWING SESSION!(CH, CO)( H & Cl on CHCl) ( HS )Orbital hybridizationLam Winn Sen presents :Orbital hybridisation (sp3)Carbons ground state electron configuration :

According to the valance bond theory, carbon should form two covalent bonds, resulting in a CH2.In reality, CH2 highly reactive and CH4 is the one that is formed.

We can excite the 2s electron into the 2p orbital to give :

This would result in a formation of CH4. But, it also means that the C-H bonds have different energies due to the overlapping of different orbitals (2s , 2p).

In reality, all four of CH4s C-H bonds have equal energy. Therefore, it can only be explained if the 2s and 2p orbitals combine to form sp3 hybrid orbitals.

- Four sp3 hybrid orbitals from Carbon overlaps with Hydrogens 1s orbitals.

- 4 -(sigma) bonds as 4 individual covalent bonds of equal bond length and energy.CH4 structure by Maksim licensed under CC BY-SA 3.0ReferencesL. PaulingThe Nature of the Chemical Bond(3rd ed., Oxford University Press 1960) p.111-120.Steric numbers 2-6 from R.H. Petrucci, W.S. Harwood and F.G. Herring, General Chemistry (8th ed., Prentice-Hall 2002) Table 11.1, pp.413-414.ISBN 0-13-014329-4Moore, John; Stanitski, Conrad L.; Jurs, Peter C.Principles of Chemistry: The Molecular Science

External Links : http://www.chemguide.co.uk/atoms/bonding/covalent.htmlhttp://ibchem.com/IB/ibnotes/full/bon_htm/14.2.htmhttp://www.science.uwaterloo.ca/~cchieh/cact/c120/bondel.htmlhttp://chemistry.about.com/od/chemistryglossary/g/Double-Bond-Definition.htmhttp://www2.chemistry.msu.edu/faculty/reusch/VirtTxtJml/intro3.htmhttp://chemwiki.ucdavis.edu/Theoretical_Chemistry/Chemical_Bonding/General_Principles/Covalent_Bondshttp://en.wikipedia.org/wiki/Orbital_hybridisationhttp://en.wikipedia.org/wiki/VSEPR_theoryhttp://en.wikipedia.org/wiki/Covalent_bondhttp://en.wikipedia.org/wiki/Sigma_bondhttp://en.wikipedia.org/wiki/Pi_bondhttp://en.wikipedia.org/wiki/Dipolar_bondhttp://chemwiki.ucdavis.edu/Organic_Chemistry/Fundamentals/Hybrid_Orbitals

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