Download presentation
Presentation is loading. Please wait.
Published byRudolph Snow Modified over 8 years ago
1
H δ+δ+ δ-δ- AS Chemistry POLAR COVALENT BONDS H Cl H
2
GAS N2N2N2N2CO MELTING POINT / K Introduction6374 Explain the difference in the melting points above.
3
Both non-metal + non-metal expect COVALENT bonding LOW melting points N 2 and CO have SAME M r (28) WHY NOT? Explained by BOND POLARISATION expect SIMPLE MOLECULAR structure expect SAME INTERMOLECULAR FORCES expect SAME MELTING POINT
4
POLARISATION OF COVALENT BONDS This depends on different atoms having slightly different ELECTRONEGATIVITY DEFINITION: What type of bonding would you expect if combining atoms’ electronegativities are; (a)Very DIFFERENT eg Na and Cl (b) SIMILAR eg C and H (c) SLIGHTLY DIFFERENT eg O and H The ELECTRONEGATIVITY of an atom is a measure of its tendency to ATTRACT the electron pair(s) from a covalent bond Learn!
5
What type of bonding would you expect if combining atoms’ electronegativities are; (a) Very DIFFERENT eg Na and Cl (b) SIMILAR eg C and H (c) SLIGHTLY DIFFERENT eg O and H
6
If combining atoms’ electronegativities are: (a)Very DIFFERENT eg Na and Cl ionic bonding Na + Cl - (b) SIMILAR eg C and H covalent bonding CH 4 (b) SLIGHTLY DIFFERENT eg O and H POLAR covalent bonding H 2 O
7
Pauling Electronegativity Index used to measure electronegativity. H 2.1 Li 1.0 Be 1.5 TRANSITION B 2.0 C 2.5 N 3.0 O 3.5 F 4.0 Na 0.9 Mg 1.2 ELEMENTS Al 1.5 Si 2.1 P 2.1 S 2.5 Cl 3.0 K 0.8 Ca 1.1 ALL SIMILAR Ga 1.6 Ge 1.9 As 2.0 Se 2.4 Br 2.8 Rb 0.7 Sr 1.0 IN RANGE Sn 1.8 I 2.5 Cs 0.6 Ba 0.9 1.5 - 2.0 Pb 1.7 Explain the trend – across a period Explain the trend – down a group
8
Increases across periods Decreases down groups because number of nuclear attracting protons (+) acting on bond e - increases because distance and shielding from attracting protons acting on bond e - increases
9
For a “normal” covalent bond EQUAL sharing of the electron pair occurs This occurs for atoms with similar electronegativities Such bonds are called NON-POLAR bonds Examples H-HF-FCl-Cl O=O NNNNNNNNC-H Most bonds are POLAR !!!!!
10
Polar Covalent Bonding Occurs when electron pair shared UNEQUALLY This occurs for atoms of dissimilar electronegativities Bond electrons NOT centralised between the atoms e- pair pulled towards more electronegative atom (Y) and away from less electronegative atom (X). slight negative charge ( -) on Y, and slight positive charge ( +) on X. Represented by X Y ++ -- NB The molecule is still NEUTRAL overall because + and - cancel. H-ClF-BrC-O I - Br O-SC-F ++ -- ++ -- ++ -- -- ++ -- ++ ++ -- Insert the dipole on each of the following: - called a “dipole”
11
H-Cl Polar bonds more IONIC character ++ -- ++ -- stronger attractions between neighbouring molecules higher m pt / b pt than expected N N N N C O C O ++ -- ++ -- N 2 and CO have same M r (28) but mpt CO > mpt N 2 because of polarity of CO. called DIPOLE-DIPOLE inter- molecular forces
12
The End
Similar presentations
© 2025 SlidePlayer.com. Inc.
All rights reserved.