Chapter 4 :Chemical bonds and Water

Prepared by :MDM NUR DIANA BT

MAMATDepartment of Science

KPTM Kota Bharu

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CHEMICAL BONDS AND

WATER

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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

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4.1 Structure and behavior of atoma) Subatomic particles b) Atomic number and atomic weightc) Isotopesd) Electron configuration e) Electron orbital

Subatomic particles

•Atom composed of small parts called subatomic particles

•Subatomic particlesProton (p)->positiveNeutron (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

H1

1 FO16

8

19

9

Mass numbe

r

16

Atomic numbe

r

8

Proton 8

Electron

8

Neutron

8

•Example•Atom natrium

23Na has 11 proton, 11 electron and 12 neutronsAtomic weight : 23 dalton (mass number)

Isotopes

•Atom that have same number of proton but differ number of neutron

•E.g.

CI3517

CI3717

C126 C1

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p 17

n 18

p 17

n 20

p 6

n 6

p 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▫Ionic bonds▫Hydrogen bonds (weak bonds)

Strong 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

(- ) (- )

OH H

(+ )( + )

Non-Polar covalent bond

•Atoms have similar electronegativity •Electrons are shared equally •E.g. :oxygen (O2)

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 = 11Cl =17

Na = 11Cl =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

HH

O

N

Electronegative atom

Hydrogen bond

H

HO

Hydrogen bond

(-)

(+)

(-)

(-)

(-) (+)

(+)

(+)

Van der waals interaction

•Weak •Occur only when atoms and molecules are

very close together

Chemical bonds and molecules Covalent bond, Ionic bond, Hydrogen bond, Van der waals forcesBiological importance of weak bonds

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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

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

(- ) (- )

OH H

(+ )( + )

Non-Polar covalent bond

•Atoms have similar electronegativity •Electrons are shared equally •E.g. :oxygen (O2)

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 = 11Cl =17

Na = 11Cl =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

HH

O

N

Electronegative atom

Hydrogen bond

H

HO

Hydrogen bond

(-)

(+)

(-)

(-)

(-) (+)

(+)

(+)

Van der waals interaction

•Weak •Occur only when atoms and molecules are

very close together

4.3 Properties of water

1. Cohesive and adhesive2. High specific heat3. High heat of vaporization4. Water expansion5. 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

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•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

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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 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

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•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

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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 25oC, need 580 cal of heat

•Ethanol need 210 cal/g, acetone with 130 cal/g

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•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

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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

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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

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•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

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AQUEOUS SOLUTIONS

Solute concentration

Acids and base

PH scale

Buffers

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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 1023)

•A mole of sucrose has 6.023 X 1023 molecules of sucrose = 342 gm. A mole of ethyl alcohol has 6.023 X 1023 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.

•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

• .

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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