Polarity and Intermolecular forces

Polarity of bond, Polarity of molecules, Intermolecular forces

1. P R E S E N T A T I O N O N P O L A R I T Y A N D B O N D S PRESENTED P R E S E N T E D B Y ; T O P A V A D H A A R A N I . K D r . T . P R A B H A

2. P h y sical p roperties The three main properties of a molecular substance include: L o w m e l ting point T e m p erature that indicates when a solid substance changes to a liquid; B o i l i ng p o int , or a temperature that indicates the point at which a liquid changes to a gas, or vapor; poor conductivity; and low solubility,

3. C h e mical p roperties Chemical bonds are the e l e c t r i c a l f o r c e s of attract i o n that hold atoms or ions together to form molecules. Different types of chemical bonds and their varying i n t e n s i t y are directly responsible for some of the p h y s i c a l properties of minerals such as hardness, melting and boiling points, solubility, and conductivity. Chemical bonds also influence such other properties as c r y s t a l s y m m e t r y a n d c l e a v a ge . S t r o n g b o n d s b e t ween atoms make them more difficult to separate and, in general, stronger chemical bonds result in greater hardness

4. P o l a r i t y of b o n d s the state of having two opposite or contradictory tendencies, opinions, or aspects

5. P o l a rity r e f e r s to the p h y sical p roperties o f c o m p o und s s u ch as b o i l i n g point , melting point and t h e i r s o l u b i l i t i es . The p o l a rity o f b o n d s i s caused d u e to i n t e r a c t i o n o f b o n d s b e tween m o l e c ules a n d a t o m s d i f f erent electronegativity. Polarity i n c h e m i stry i s n o t h i ng b u t the c o n c e pt of t h e s e p a ration of electric charges l e a d ing a m o l e c ul e to h a v e a p o s itive a n d n e g a tive e n d .

6. C o n s i d e r a n . E x a m ple . . I n a H - F b o n d , t h e f l u o r i n e a tom i s m o re e l e c t r o n e g a t i v e t h a n that o f h y d r ogen a t om . T h e e l e c t r o n s e v e n t u ally spend m o r e time a t the f l u o rine atom . H e n ce , t h i s F l o u r i n e atom s l i g h t ly b e c o m e s n e g a tive whereas t h e h y d r ogen atom t e n d s to b e come s l i g h tly p o s i t i v e

7. P o l ar m olecules Polar molecules occur when two atom s d o n o t s h a r e e l e c t r o n s e q u a l l y a covalent bond. A dipole forms, with part of the molecule carrying a slight positive charge and the other part carrying a slight negative charge. This happens when there is a d i f f e r e n c e b e tween the e l e c t r o n e g ativity o f each atom.

8. N o n p o l a r m o l ecules When molecules s h a r e e l e c t r o n s e q u a l l y in a covalent bond there is no net electrical charge across the molecule. In a nonpolar covalent bond, the electrons are evenly distributed. You can predict nonpolar molecules will form when atoms have the same or similar electronegativity.

9. T y p e s of b o n d s

10. Non p o l a r c o v a lent b o nds Nonpolar covalent bonds are a type of bond that occurs when t w o a t o m s s h a re a p a i r of e l e c t r o n s with each other. These shared electrons glue two or more atoms together to form a molecule . Like children who share toys, atoms involved in a nonpolar covalent bond equally share electrons . An example of a nonpolar covalent bond is the bond between t wo h y d r ogen a t o ms because they equally share the electrons. Another example of a nonpolar covalent bond is the bond between t w o c h l o r i ne a t o m s because they also equally share the electrons. Nonpolar covalent bonds are v e r y s t rong b o n d s r e q u iring a large amount of energy to break the bond.

11. Polar c o v alent bonding Polar covalent bonding is a type of chemical bond where a p a i r of e l e c t r o n s i s u n e q u a l l y s h a r e d between two atoms. In a polar covalent bond, the electrons are not equally shared because one atom spends more time with the electrons than the other atom. In polar covalent bonds, o n e a t o m h a s a s t r o n ger p u l l than the other atom and attracts electrons.

12. P o l a r molecule A p o l a r m o lecules h a s a n e t d i p o l e m o m ent a s a result of the o p p o s i n g c h a r g e s ( i.e.partial p o s i t i v e a n d p a r t i a l n e g a tive c h a rges ) W a t e r i s a n e x a mple of p o l a r m o l ecules s i n ce i t h a s a s l i ght p o s i tive c h a r ge o n o n e s i d e a n d a s l i g h t n e g a tive c h a rge o n o t h e r .

13. T o c a l culate e l e c t r o n e gativity

14. P r o p e r ties o f p o l a r m o lecule I f the d i fference i n e l e c t r o n e g a t i v i t y f o r a t o m s i n a b o n d i s g r e a t e r t h a n . 4 w e consider t h e b o n d a s p o l a r if the d i fference i s l e ss t h an . 4 , t h e b o n d i s e s s e ntially n o n - polar I n p o l a r m o l e cule , t h e e n d s of the m o l ecule , called d i p o les , c a r r y a n u n e q ual c h a r ge . T h i s is a n important c o n c e p t b e c a use m a n y areas of the b o d y a r e e i ther w a t e r s o l u ble o r f a t s o l u ble . A p o l a r molecule is w a t e r s o l uble

15. M e l ting point The m e l ting point of a s u b s t a n c e is t h e t e m p erature a t w hich i t c h a n ges s t a t e f r om s o l id t o l i q uid . A t t h e m e l ting point t h e s o l i d and l iquid p h a s e e x i s t in e q u i l ibrium . T h e m e l ting point of a s u b stance depends o n p r e s s u r e and i s u s u a lly s p e c i f i e d a t a s t a n dard p r e s s ure s u c h a s 1 a t m When c o n s i d e r ed a s t h e t e mperature of the reverse c h a n g e f r om liquid t o s o l i d , i t i s r e f e r r ed to as the f r e e z i n g p o i nt o r c r y s tallization p o i n t .

16. However, substances can be c o o l e d b e l ow t h e i r f r e e z i ng p o int without the formation of a solid. Such liquids are known as s u p e r c o o l ed l i q u ids Because of the ability of some substances to supercool, the freezing point is not considered as a characteristic property of a substance.

17. M e l ting p o i n ts ( i n b l ue ) a n d boiling p o ints ( i n p i n k ) o f the f i rst e i ght c a r b o x ylic aci ds

18. P o l a rity of m o l ecules P o l a rity i n molecules i s t h e s e p a ration o f e l e c t r i c c h a rge l e a ding to a m o l ecule o r i t s c h e m i cal g r o u p s h a v i ng a n e l e ctric dipole m o ment , with a n e g a t ively c h a rged end a n d a p o s i t i v e l y c h a r g e e n d . P o l a r ity m o l e c u l es m u s t c o n t a in p o l a r b o n d s to d i f f erences i n e l e c t r o n e g a t ivity b e t ween the b o n d e d a t o m s .

19. K o f l e r B e n c h A Kofler bench is a m e t a l s t r i p with a temperature gradient (range from room temperature to 300 °C). Any substance can be placed on a section of the strip, revealing its thermal behaviour at the temperature at that point.

20. I n t e r m o l ecular f o rces I n t e r m o l ecular f o rces a re the f o r c e s w h i ch m e d i a t e i n t e r a ction between m o l ecule s , including f o r c e s of attraction o r r e p u l sion w h i ch a c t b e t ween m o l ecules a n d o t h er t y pes o f n e i g h b o u ring p a r t i c l es I n t e r m o l e c u l a r f orces a r e weak r e l a t i ve to i n t r a m o lecular f o r c e - t h e forc es w h ich h o l d a m o l ecule together . F or example , the c o v a l e nt bond , i n v o l v i n g s h a r ing e l e c t r o n pairs b e t w een a t o m s , i s m u c h s t r onge r t ha n the f o r c es p r e s e nt b e t w een n e i g hbouring m o l ecules . Both s e t s of f o r c e s a r e e s s ential p a r t s of force f i e l ds f r e q u ently u s e d in m o l e c u l a r m e c h a n i c s

21. The investigation of intermolecular forces starts from m a c r o s copic observations which indicate the existence and action of forces at a m o l e c u lar l e vel

22. T y p e s of f o r c e s A t t r a ctive i n t e r m o l ecular forces a r e c a t e g o rised into the f o llowing t y pes : H y d r ogen b o nding I o n i c b o n d ing I o n - i n d u c e d d i p o le f o r c e s I o n - d i p o l e f o r c e s V a n d e r Waals f o rce - k e e s o m f o r c e , D e b y e f o r c e , a n d L o n don d i s p e r sion f o r c e

23. H y d r o gen b o nding A hydrogen bond (often informally abbreviated H-bond) is a p a r t i a l i n t e r m o l ecular b o n d i n g i n t e r a ction between a lone pair on an electron rich donor atom, particularly the s e cond -r o w e l e ments nitrogen (N), oxygen (O), or fluorine (F), and the antibonding molecular orbital of a bond between hydrogen (H) and a more electronegative atom or group Such an interacting system is generally denoted by Dn-H . . . A c the solid line denotes a p o l a r c o v a lent b ond A nd the dotted or dashed line indicates the h y d r o gen bond

24. Hydrogen bonding is a s p e c i a l t y p e of d i p o l e -d i p o l e i n t e r a c tion that occurs between the lone pair of a highly electronegative atom This type of bond can occur in i n o r g a n i c m o l ecules s u ch a s w a ter , D N A a n d proteins I n t r a m o l e c u l a r hydrogen b o nding is partly responsible for the secondary and tertiary structures of p r o t e i ns a n d n ucleic acid . It also plays an important role in the structure of polymers, both synthetic and natural.

25. I o n i c b o n d i ng Ionic bonding is a type of c h e m i cal b o n ding t h a t involves the electrostatic attraction between oppositely charged ions, and is the primary interaction occurring in i o n i c c ompounds It is o n e o f t h e m a in t y pes o f b o n d i n g along with covalent bonding and metallic bonding. Ions are atoms (or groups of atoms) with an electrostatic charge. Atoms that g a i n e l e c t r o n s ma k e negatively charged ions (called anions). Atoms that l o s e e l e c t r o n s m a k e positively charged ions (called cations)

26. In the simplest case, t h e c a t i o n i s a m e t a l a t o m a n d t h e a n i o n i s a n o n m e t a l a t o m , but these ions can be of a more complex nature, e.g. molecular ions like NH 4 + a n d S O 4 2 - In simpler words, an ionic bond results from the t r a n s f e r o f e l e c t r o n s f r o m a m e t a l t o a n o n - m e t a l in order to obtain a full valence shell for both atoms.

27. I f t h e m e t a l a n d n o n - m e t a l s t a r t s to f o r m a b o n d , the o p p osite c h a rg es t h e y will c a n c e l e a c h other I n i o n ic b o nds , t o t a l p o s i t ive c h a r ge e q u a l s the t o t a l n e g a tive c h a rge t o f o r m a neutral i o n ic c o mpound T h e s e o p p o s i t e ly c h a rged i o ns are attracted to each other to form a l a t t ice i n t h r e e d i m ensions

28. I n e x a mple of N a c l , t h e m o l ecules i f d i s s o lved i n water , the N a m e t a l i s s u r r ounded by w a ter m o l ecules w ith oxygen m o l ecules o r i e nted t o wards i t , and t h e c l n o n - metal i s s u r r ounded by molecules o f h y d rogen . T h i s i s b e cause i f t h e s e oppositely charged m o l e cules w h e n d i s s olved conduct e l e ctricity . N o t all t h e i o n i c m o l e c u les are d i s s olved in water

29. C o m p a r i son of e l e c t r o n e g a tivity o f b o n d s T y p e of b o n d . D i f f erence i n e l e c t r o n egativit y N o n p o l a r c o v alent < . 4 P o l a r c o v a lent . . 4 - 1 . 7 I o n i c . > 1 . 7

30. I o n i n d u ced d i p o l e f o r c e s An ion-induced dipole attraction i s a w e a k a t t r a c t i o n that results when the approach of an ion i n d u c e s a d i p o l e in an atom or in a n o n p o l a r m o l e c u l e by disturbing the arrangement of electrons in the nonpolar species. The i o n i n d u c e d d i p o le f o r c e i s a p e r m a nent e f f ect i n p o l a r m o l ecules b e c a use o f p r e s e n c e o f d i p o l es E x : H 2 O t h e h y drogen c a r r i e s p o s i t i v e charge a n d o x y gen c a r r i es n e g a tive charge s o t h e r e is a d i p l o e already p r e sent there

31. In this e x a mple , t h e i o n h a s t o b e p r e s ent t o i n d u c e a d i p o l e t h a t c a u s e s t h e n e u t r a l m o l ecule t o o c c upy p o s i tive c h a rge o n o n e s i d e a n d n e g a tive c h a rge on o ther s i d e

32. I o n d i p o l e f o r c e s An ion-dipole force is an a t t r a c t i v e f o r c e s results from the electrostatic attraction between an i o n a n d a n e u t r al m o l e c u l e that has a dipole. Most commonly found in s o l u t i o n s . Especially important for solutions of ionic compounds in polar liquids. A p o s itive i o n (cation) attracts the partially n e g a t i v e e n d a neutral polar molecule. A n e g a t i v e i o n (anion) attracts the partially p o s i t i v e e n d a neutral polar molecule. Ion-dipole attractions become s t r o n g e r a s either the c h a r g e o n i o n i n c r e a ses as the magnitude of the dipole of the polar molecule increases.

33. V a n d e r Waals forces Van der Waals forces include a t t r a c t i o n a n d repulsion between atoms, molecules, and surfaces, as well as other intermolecular forces. They differ from covalent and ionic bonding in that they are caused by correlations in the fluctuating polarizations of nearby particles Being the w e a k e s t o f t h e c h e m i cal f o r c e s , with a s t r e n g t h b etween . 4 a n d 4 k J / m o l , they may still support an integral structural load when multitudes of such interactions are present. The force results from a transient shift in electron density I t e x i sts in all m o l ecules b u t m o r e d o m inant i n n o n - p o l a r m o l e c u les

34. The main characteristics of van der Waals forces are They are w e a k e r t h a n n o r mal c o v a l e nt a n d i o n i c b o n ds . Van der Waals forces are additive and cannot be saturated. They h a v e n o d i r e c t i o n a l characteristic . They are all short-range forces and hence o n l y i n t e r a c t i o n s b e t ween t h e n e a r est p a r t i c l e s need to be considered (instead of all the particles). Van der Waals attraction is greater if the m o l e c u l e s are c l o s e r Van der Waals forces are independent of temperature except dipole – dipole interactions.

35. I n the e x a m ple shown the non-polar m o l e c ule , t h e e l e c t r o n s a r e e q u ally d i s tributed i n e l e c t r o n c l o u d w i t h p o s itiv ely charged n u c l e u s a t centre A s t h e e l e c trons s t a rt to m o v e t h e r e is d i s t r ibution o f c h a rges , , s o o n e side of the a t o m b e c o me s + a n d o t h er s i de b e c omes - a n d f i n a l l y i t b e c omes p o l a r i s e d I t c a u s e s t h e o t h e r a t o m t o b e come p o l a r i s e d i n t h e s a m e the w a y , t h e + c h a rge o f t h e s e c ond a t o m f a c e s t h e - c h a rge o f f i r s t a t o m a n d vice-versa I f e l e c t r o n s i n a n a t o m i n c r e ases t h e m o l e c u l a r w e i ght i n c r e a s e s w h i c h i n t urn i n c r e ases the v a n d e r w a a l s f o r c e .

36. B o i l i ng point The boiling point of a substance is the temperature at which the v a p o u r p r e s s ure o f a l i q u id e q u a l s the p r e s s ure s u r r o unding the l i q u i d and the liquid changes into a vapor. The boiling point of a liquid varies depending upon the surrounding e n v i ronmental p r e s s ure . A liquid in a partial vacuum has a lower boiling point than when that liquid is at atmospheric pressure. A liquid at h i g h p r e s s ure h a s a h i g h e r b o i l i n g p o i nt than when that liquid is at atmospheric pressure. For example, water boils at 100 °C (212 °F) at sea level, but at 93.4 °C (200.1 °F) at 1,905 metres (6,250 ft) altitu de

37. For a given pressure, different liquids will boil at different temperatures. The normal boiling point (also called the a t m o s p h eric b o i ling p o int or atmospheric p r essure b o i ling point ) of a liquid is the special case in which the vapor pressure of the liquid equals the defined a t m o s p h e r i c p ressure a t s e a l e v e l , o n e a t m

38. S o l u bility Solubility is a property referring to the a b i l i t y of the g i v e n s u b s tance the solute, to dissolve in a solvent. It is measured in terms of the m a x i m u m a m ount of s o l u t e dissolved in a solvent at equilibrium. The resulting solution is called a s a t u r a ted s o l u tion . S o l u bility d e p ends on the t e m perature and p r essure a n d i t a l s o d e pends on n a t u r e o f s o l u t e a n d s o l v e nt . , i t h a s n o u n i t s A s o l u t e d i s s olves in a s o l v e nt i f i n t e r m o l ecular interactions a r e s i m i lar in t w o s u b stance

39. I n s a t u r a ted s o l u tion , if d i s s olution process is e x o t h e rmic ( ∆ H i s -v e ) , solubility d e c r e ases with i n c r e a s e i n t e m perature . I f d i s s o l u t i o n p rocess i s endothermic ( ∆ H i s + v e ) solubility i n c r e a s e s with i n creasing t e m perature . S i n ce l i q uids a n d s o lids a r e h i ghly i n c o m p r essible , pressure h a s no e f f ect o n d i s s olution o f s o l i ds o r l i q uids i n l i q u id s o l v e nt , many g a s e s a r e s o l u b l e in water .

40. S o l u bility of g a s i n w a ter g e n e r a l l y d e c r e a s e s with i n c r e a s e in t e mperature a n d p ressure , the n o of g a s e ous m o l ecules p e r u n it v olume o v e r s o l u t i on i n c r eases A t c o n s t ant t e mperature , the s o l u b i l i t y of g a s i n liquid is d i r e ctly proportional to p r e s s ure of gas

41. H e n r y w a s t h e first t o g i ve q u a n t i t a tive r e l a t i o n s h i p between the s o l u bility and p r e ssure o f g a s w h i ch is k n own a s . H e n r y ' s l a w C = K × P C i s t h e c o n c e n tration of l i q uid K is Henry's c o n s t a nt P is p a r t i a l p r e ssure

42. D a l t o n , c o n c l u d e d t h at s o l u b i l i t y o f g a s i n liquid i s a f u n ction o f p a r t i a l p r e s s ure of g a s P t = P a + P b + P c P t i s t o t a l p r e ssure P a i s p r e s s u r e o f g a s 1 P b is pressure of g a s 2 P c i s p r e s s u r e o f g a s 3

43. I o n i c a n d n o n - i o n i c c o m p o u n d I o n ic c o m pounds a r e t w o o r m o re i o n s h e l d together by a t t r a c t i o n . A n e x a m ple o f a n i o n i c c o mpound i s t a b l e s a l t . I t c o n s i s ts of p o s i tive s o d i um i o n s and n e g a tive chloride i o n s t h a t is a c r y s tal t h a t c a n be s e e n w ith t h e naked eye . I f i t l o o ks like it is a p o w d e r i t is j u st b e c a use t h e c r y s tals a r e t o o s m a l l to a c t u ally b e seen . T h e y h a v e h i g h m e l ting a n d b o i l ing point a n d a r e h a r d o r b r i t t l e , t h e y c a n a l s o be d i s s olved i n w a ter E x : N a c l

44. Ions in ionic compounds are primarily held together by the e l e c t r o s t a tic a t t raction b e tween the charge distribution of these bodies, In particular the ionic bond resulting from the l o n g long-ranged C o u l o m b a t t r a ctio n between the net negative charge of the a n i o n s and net positive charge of the c a t i o n s In a reaction between m e t a l s to l o s e e l e c t r o n s a n d n o n m e t a l s t o g a i n e l e c t r o n s t o complete t h e ir o c t e t . Metals and non-metals generally react to form i o n i c c ompound .

45. N o n ionic c o mpound The d e f i nition f o r a n o n i o n ic c o mpound is s i m p ly m e a ns t hat the c h e m i cal b o n ds are n o n i o n i c All the compounds having non-ionic bonds such as the L o n d o n f o r c e s , covalent bonds etc are known as a non-ionic compound. These compounds are formed by the sharing of e l e c t r o n s between the atoms. F o r example : H 2 , O 2 e t c

46. P r o t i c s o l v e n t protic solvent is a solvent that has a h y d r o g e n atom bound to an oxygen (as in a hydroxyl group), a nitrogen (as in an amine group), or fluoride (as in hydrogen fluoride). In general terms, any solvent t h a t c o n t a ins a l a b i l e H + i s c a l l ed a p r o t i c s o l v e nt . The molecules of such solvents readily d o n a t e s p r o t o n s ( H + ) to solutes, often via hydrogen bonding. Water is the most common protic solvent. E x : w a t e r , e t h a n o l , methanol , ammonia

47. A p r o t i c s o l v e nt Conversely, aprotic solvents c a n n ot d o n a t e e l e c t r o n . A p r o t i c s o l v e nt i s a s o l v e nt that d o e sn't h a v e O - H a n d N - H b o n d . T h e " a " m e a n s w i t h o u t a n d " p r o t i c " r e f e r s t o p r o t o n o r h y d r o gen m e a n s that they d o not f o r m h y drogen bonds b u t t h e y c a n a c c e pt h y d r ogen bonds . E x : a c e t o n e , acetonitrile

48. I o n p a i r s ion association is a chemical reaction whereby ions o f o p p o s ite e l e c t r i c a l c h a rge come together in solution to form a distinct chemical entity. Ion associates are classified, according to the n o of i o n s that associate with each other, as i o n p a i r s , i o n t r i p l e t s Ion pairs are also classified according to the n a t u r e of i n t e r a ction as c o n t a c t , solvent -sh a r e d , o r s o l v e nt -s e p a r a t e d . I o n pairs d o e s n o t e x i st i n i d e a l s o l u tion b e c ause a l l i o n s are separated f r om o n e a n o ther b y s o l v ent m o l ecules

49. The most important factor to determine the extent of ion association is the d i e l e c tric c onstant o f m o l ecule . Ion associates have been characterized by means of vibrational spectroscopy. The concept was introduced by N i e l s B j e r r u m .

50. By an IUPAC definition, solvation is an i n t e r a c t i o n of a s o l u t e w ith the s o l v e n t which leads to stabilization of the solute species in the solution

51. When there is about one solvent molecule between c a t i o n a n d a n i o n and, the ion pair may be termed s o l v e n t s h a r e d .

52. when the ions are in c o n t a c t with e a c h other , ion pair is termed a c o n t a c t i o n p a i r . Even in a contact ion pair, however, the ions retain most of their solvation shell.

53. Ion pairs are formed when a c a t i o n a n d a n i o n are present in a solution of an ionizable substance, c o m e t o gether to form a discrete chemical species. There are three distinct types of ion pairs, depending on the extent of solvation of the two ions. For example, magnesium sulphate exists as both contact and solvent-shared ion-pairs in seawater. Mg2+(aq) + SO42-(aq) ⇌ Mg(SO4)(aq)

54. I o n s o f opposite c h a r g e naturally a t t r a c t e d to e a c h other b y the e l e c t r o s t a t i c f o rce . T h i s i s described b y c o u l o mb 's l a w : F = q1 × q 2 ÷ € × r w h e r e F i s t h e f o r c e of a t t r a ction , q 1 a n d q 2 i s m a g n i t u d e of e l e c t r i c c h a r g e s , € i s t h e d i e l e ctric constant of m e d i u m a n d r is the d i s tance b etween the i o n s .

55. Ion association will increase as: the magnitude(s) of the e l e c t r i cal c h a r g e s q1 and q2 i n c r e ases the magnitude of the d i e l e c t r i c c onstant ε , d e c r e a s e s the s i z e of i o n d e c r e a s e s so that the d i s t a nce r between c a t i o n a n d a n i o n d e c r e a s e s .

56. https://youtu.be/c3g3maYegBk for v i d e os https://g.co/kgs/Hmbd9i f o r t h e o r y R e f e r ence