pda104t_01 polarity, dipole moment

©M. S. Ramaiah University of Applied Sciences

1Faculty of Engineering & TechnologyFaculty of Pharmacy ©M. S. Ramaiah University of Applied Sciences

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Lecture No. 1Structure & Physical Properties

- Polarity, Melting & Boiling Point

• At the end of this lecture, student will be able to

– Define electronegativity, polarity and dipole moment– Differentiate between polar and non polar covalent bond– Relate dipole moment with the geometry of the molecule– Relate melting and boiling point with the structure of the

molecule



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Electronegativity

• Tendency of an atom to attract electrons• Increases from left to right across a period on the periodic

table• High for the nonmetals with fluorine as the highest• Low for the metals • Differences in electronegativity between two atoms -

used to predict the type of covalent bond



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Electronegativity Contd… • Electronegativities of selected elements



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Electronegativity Contd… • Electronegativity and bond types



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Bond Polarity

• Polar covalent bond

– Unequal sharing of electrons– Difference in electronegativity– Example



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Bond Polarity Contd…

• Non polar covalent bond

– Equal sharing of electrons– No difference in electronegativity– Example

H: H



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Bond Polarity Contd…



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Dipole Moment

• Dipole – negative end and positive end

• Measurement of polarity• Dipole moment μ = exd e = charge in esu d = distance between the charges• Unit – Debye



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Dipole Moment Contd…

• Represented by • Example

• Molecular polarity

• Dipole moment in a molecule depends on– Individual bond dipole moments– Geometry of the molecule



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Dipole Moment Contd… • Dipole moments of commonly encountered bonds



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• Polarity and shape of the molecule

Molecular Polarity



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Molecular Polarity Contd…



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Molecular Polarity Contd…

• Dipole moment in H20 & NH3

• Importance of dipole moment



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Melting Point

• Ionic compounds• Strong interionic forces• More energy required to overcome the interionic

forces• High melting point

Melting of an ionic crystal – units are ions



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Melting Point Contd…

• Non ionic compounds• Weak intermolecular forces• Low melting point

Melting of a non ionic crystal – units are molecules



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Boiling Point • Ionic compounds

• Strong interionic forces• More energy required for the ions to break away from

the liquid• High boiling point

Boiling of an ionic liquid – units are ions & ion pairs



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Boiling Point Contd…

• Non ionic compounds• Weak intermolecular forces• Low boiling point

Boiling of a non ionic liquid – units are molecules



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Summary

• Electronegativity is the tendency of an atom to attract electrons

• Covalent bond is polar if it joins atoms that differ in electronegativity

• Extent of polarity is measured by dipole moment • Dipole moment in a molecule depends on the individual bond

dipole moments and the geometry of the molecule• Melting point, boiling point of a compound depends on the

kind of bonds that holds its atoms together

pda104t_01 polarity, dipole moment

Documents

molecule faculty of

h faculty of pharmacy

bond types faculty of

dipole momentdifferentiate

electronegativity example

boiling point

periodic tablehigh

metals differences