Chapter 4 : Chemical bonds and Water

Prepared by : MDM NUR DIANA BT MAMAT Department of Science KPTM Kota Bharu 1

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

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 3

4.1 Structure and behavior of atom a) Subatomic particles b) Atomic number and atomic weight c) Isotopes d) Electron configuration e) Electron orbital

Subatomic particles

• • Atom composed of small parts called subatomic particles

Subatomic particles

 Proton (p)->positive  Neutron (n)-> neutral  Electron (e)-> negative

Atomic number and atomic weight

•

Atomic number

 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

1 1 Mass number Atomic number Proton Electro n Neutro n 1 6 8 16 8 8 8 8 9 1 9

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

Isotopes

• • Atom that have same number of proton but differ number of neutron E.g.

3 5 1 7 p 17 3 7 1 7 p 17 p 1 2 6 1 3 p 6 n 18 n 20 n 6 n 7

• • • 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

Electron configuration /electron shell

Electron HYDROGEN (H) Atomic number = 1

NITROGEN (N) Atomic number = 7 (2.5)

OXYGEN (O) Atomic number = 8 (2.6)

Octet rule

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

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

4.2 Chemical bonds and molecules

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

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

Single Double Single

Polar & non-polar

• Polarity ▫ Depending on their electronegativity Capability of an atom to attract the shared electrons in covalent bonds

Polar covalent bond

• • One of the atoms is bonded to a more electronegative atom The electrons of the bond will not be shared

equally

(



- ) H (



+ ) O (



- ) H (



+ )

Non-Polar covalent bond

• • • Atoms have similar electronegativity Electrons are shared equally E.g. :oxygen (O 2 )

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

Natrium chloride/salt

Na = 11 Cl =17

Na = 11 Cl =17

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).

H H H N H O H Electronegative atom Hydrogen bond

Hydrogen bond (-) (+) H (+) (-) (-) O (+) H (+) (-)

Van der waals

interaction

• • Weak Occur only when atoms and molecules are very close together

 Covalent bond,  Ionic bond,  Hydrogen bond,  Van der waals forces  Biological importance of weak bonds 32

Chemical bonds and molecules

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

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

Single Double Single

Polar & non-polar

• Polarity ▫ Depending on their electronegativity Capability of an atom to attract the shared electrons in covalent bonds

Polar covalent bond

• • One of the atoms is bonded to a more electronegative atom The electrons of the bond will not be shared

equally

(



- ) H (



+ ) O (



- ) H (



+ )

Non-Polar covalent bond

• • • Atoms have similar electronegativity Electrons are shared equally E.g. :oxygen (O 2 )

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

Natrium chloride/salt

Na = 11 Cl =17

Na = 11 Cl =17

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).

H H H N H O H Electronegative atom Hydrogen bond

Hydrogen bond (-) (+) H (+) (-) (-) O (+) H (+) (-)

Van der waals

interaction

• • Weak Occur only when atoms and molecules are very close together

4.3 Properties of water

1.

2.

3.

4.

5.

Cohesive and adhesive High specific heat High heat of vaporization Water expansion Versatile solvent

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Cohesive and Adhesive

• • • • • Cohesive ▫ 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 50

• 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 51

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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 1 0 C • The specific heat of water is 1 calorie per gram per 0 C or 1 cal/g/ 0 C • High specific heat compared to other substance. Eg: Ethyl alcohol 0.6 cal/g/ 0 C 53

• • 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 54

High heat of vaporization

• 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 25 o C, need 580 cal of heat Ethanol need 210 cal/g, acetone with 130 cal/g 55

• 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 56

Water expansion

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

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 58

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

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 Solute concentration  Acids and base  PH scale  Buffers 61

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

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 10 23 ) • A mole of sucrose has 6.023 X 10 sucrose = 342 gm. A mole of ethyl alcohol has 6.023 X 10 23 23 molecules of molecules of EtOH = 46 gm • Molarity = the number of moles of solute per liter.

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 10-14 M or [H+][OH-] = 10-14 M2 • An increase in 1 pH unit means a solution is ten times more acidic.

• pH values of 0-7 are acidic.

• pH values of 7-14 are basic.

• Neutra l 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

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

THE END……

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