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Chapter 4 : Chemical bonds and Water

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1 Chapter 4 : Chemical bonds and Water
Prepared by : MDM NUR DIANA BT MAMAT Department of Science KPTM Kota Bharu

2 STRUCTURE BEHAVIOR OF ATOM
CHEMICAL BONDS AND WATER STRUCTURE BEHAVIOR OF ATOM CHEMICAL BONDS AND MOLECULES PROPERTIES OF WATER AQUEOS SOLUTION

3 Water : The importance All living organisms require water more than other substance Most cells are surrounded by water and cells themselves are about 70-95% water ¾ of earth surface is submerged in water Water is the only substance that exist in three physical states of matter Water is the major reason earth is habitable

4 4.1 Structure and behavior of atom
Subatomic particles Atomic number and atomic weight Isotopes Electron configuration Electron orbital

5 Subatomic particles Subatomic particles
Atom composed of small parts called subatomic particles Subatomic particles Proton (p)->positive Neutron (n)-> neutral Electron (e)-> negative

6 Atomic number and atomic weight
equal to the number of proton in the element P=e Atomic weight /mass number total mass of an atom or the atomic mass. p+n Neutron mass number –num. of proton

7 H F O 1 16 8 19 9 Mass number 16 Atomic number 8 Proton Electron
Neutron

8 Example Atom natrium 23Na has 11 proton, 11 electron and 12 neutrons
Atomic weight : 23 dalton (mass number)

9 Isotopes Atom that have same number of proton but differ number of neutron E.g. CI 35 17 CI 37 17 C 12 6 C 13 6 p 17 n 18 p 17 n 20 p 6 n p 6 n 7

10 Isotopes have same chemical behavior, different in physical behavior
Radioactive isotopes is unstable, it can decay spontaneously In decay, neutron is converted to a proton and electron

11 Electron configuration /electron shell
HYDROGEN (H) Atomic number = 1

12 NITROGEN (N) Atomic number = 7 (2.5)

13 OXYGEN (O) Atomic number = 8 (2.6)

14 Octet rule Molecular compounds appears that a full set of electrons in the outer shell (8ĕ)

15 Electron orbital/electron configuration
An orbital is a three dimensional space where an electron spends most of Its time Each orbital holds up TWO electron

16 4.2 Chemical bonds and molecules
Chemical bonds : interaction between atom, may result in atoms staying together for stability Types of bond: Covalent bonds Ionic bonds Hydrogen bonds (weak bonds) Strong bonds

17 Covalent bonds Sharing valence electrons by two atoms to fulfill their valence shells (between non-metal) Single Share a pair of electron Double Share two pairs of electron Strong chemical bonds Two types Polar Non-polar

18

19 Single Double Single

20 Polar & non-polar Polarity
Depending on their electronegativity Capability of an atom to attract the shared electrons in covalent bonds

21 Polar covalent bond One of the atoms is bonded to a more electronegative atom The electrons of the bond will not be shared equally

22 (- ) O H (+ ) ( + )

23 Non-Polar covalent bond
Atoms have similar electronegativity Electrons are shared equally E.g. :oxygen (O2)

24 ionic bonds Chemical bond that can often form between metal and non-metal ion bond formed by the attraction between two oppositely charged ions. The metal donates one or more electrons, forming a positively charged ion or cation electrons then enter the non metal, causing it to form a negatively charged ion or anion

25 Natrium chloride/salt
Cl =17

26 Na = 11 Cl =17

27

28 Hydrogen bond weakest of all chemical attractions
form when a hydrogen atom that is covalently bonded to an electronegative atom is attracted to another electronegative atom, generally either oxygen (O) or nitrogen (N).

29 H O N Electronegative atom Hydrogen bond

30 H O Hydrogen bond (-) (+)

31 Van der waals interaction
Weak Occur only when atoms and molecules are very close together

32 Chemical bonds and molecules
Covalent bond, Ionic bond, Hydrogen bond, Van der waals forces Biological importance of weak bonds

33 Chemical bonds and molecules
Chemical bonds : interaction between atom, may result in atoms staying together for stability Types of bond: Covalent bonds Ionic bonds Hydrogen bonds (weak bonds) Strong bonds

34 Covalent bonds Sharing valence electrons by two atoms to fulfill their valence shells (between non-metal) Single Share a pair of electron Double Share two pairs of electron Strong chemical bonds Two types Polar Non-polar

35

36 Single Double Single

37 Polar & non-polar Polarity
Depending on their electronegativity Capability of an atom to attract the shared electrons in covalent bonds

38 Polar covalent bond One of the atoms is bonded to a more electronegative atom The electrons of the bond will not be shared equally

39 (- ) O H (+ ) ( + )

40 Non-Polar covalent bond
Atoms have similar electronegativity Electrons are shared equally E.g. :oxygen (O2)

41 ionic bonds Chemical bond that can often form between metal and non-metal ion bond formed by the attraction between two oppositely charged ions. The metal donates one or more electrons, forming a positively charged ion or cation electrons then enter the non metal, causing it to form a negatively charged ion or anion

42 Natrium chloride/salt
Cl =17

43 Na = 11 Cl =17

44

45 Hydrogen bond weakest of all chemical attractions
form when a hydrogen atom that is covalently bonded to an electronegative atom is attracted to another electronegative atom, generally either oxygen (O) or nitrogen (N).

46 H O N Electronegative atom Hydrogen bond

47 H O Hydrogen bond (-) (+)

48 Van der waals interaction
Weak Occur only when atoms and molecules are very close together

49 4.3 Properties of water Cohesive and adhesive High specific heat
High heat of vaporization Water expansion Versatile solvent

50 Cohesive and Adhesive Cohesive Due to hydrogen bonding
Def : A substance that have the capacity to stick with each other tightly Due to hydrogen bonding Contributes to the transportation of water and nutrient against gravity in plants. Water transport from root to leaves via a water conducting cells. In plant Process happening during evaporation / transpiration

51 Contribute to water transportation
Adhesion Def : Ability if water molecules to cling to other substances. Contribute to water transportation Ensure water molecules move upward to every part of higher plants

52

53 High specific heat Specific heat
The amount of heat that must be absorbed or lost for 1 g of that substance to change its temperature by 10C The specific heat of water is 1 calorie per gram per 0C or 1 cal/g/0C High specific heat compared to other substance. Eg: Ethyl alcohol 0.6 cal/g/0C

54 Water need more energy because to break the hydrogen bond first
Allow water to absorb or release large amount of heat without changing its temperature drastically Water need more energy because to break the hydrogen bond first Importance : Stabilizes the ocean temperature Sustain favorable environment for marine life Keep earth tempt within limit

55 High heat of vaporization
The quantity of heat must absorb for 1 g of water to convert from liquid to gaseous state Water has a high heat of vaporization, to evaporate 1 g of water at 25oC, need 580 cal of heat Ethanol need 210 cal/g, acetone with 130 cal/g

56 Advantages: Moderate the earth’s climate Provide evaporating cooling Evaporative cooling contributes to the stability of temperature in lakes and ponds Provide a mechanism that prevents terrestrial organisms from overheating

57 Water expansion Water expands as it freezes
Water contract when it is cooled until it reached 4oC, after that it expands until it reaches freezing point Become less dense as solid thus, ice tend to float

58 Versatile solvent Due to the polarity
Polarity – polar covalent bond when water molecules posses partial positive and partial negative charges One water molecules can form 4 hydrogen bond with its neighboring water molecules

59 Hydrophilic – water loving
Hydrophobic – water fearing NaCl interact with water, Na+ attracted to oxygen and Cl- attracted to hydrogen The region around water molecules around the dissolved ions – Hydration shell

60

61 AQUEOUS SOLUTIONS Solute concentration Acids and base PH scale Buffers

62 ACIDS, BASES AND SALTS Acid = a substance that releases a H ion into solution Base = a substance that combines with a H ion in solution

63 a)Solute concentration
Mole = molecular weight of substance in daltons. # atoms or molecules that will give you avogadro's number of atoms or moleucles (6.023 X 1023) A mole of sucrose has X 1023 molecules of sucrose = 342 gm. A mole of ethyl alcohol has X 1023 molecules of EtOH = 46 gm Molarity = the number of moles of solute per liter.

64 b)PH scale The pH scale is based on concentration of H ions in solution (moles/l) pH scale goes from 0 to 14 The greater the H ion concentration, the lower the pH. pH = -log [H+], where [H+] = hydrogen ion concentration In any solution, the product of the H+ and the OH- concentrations is constant at M or [H+][OH-] = M2 An increase in 1 pH unit means a solution is ten times more acidic.

65 pH values of 0-7 are acidic.
pH values of 7-14 are basic. Neutral pH = 7 Human blood has a pH of 7.4. A change in blood from 7.4 to 7.8 for even a short time can be fatal .

66 BUFFERS Buffers are molecules that help regulate pH within a fairly narrow range, protecting life. One example of a buffer is carbonic acid. Found in blood. H2CO3 = HCO3- + H+ carbonic acid bicarbonate

67 THE END……


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