bl05a 1 chemical & physical phenom on en

8/3/2019 BL05A 1 Chemical & Physical Phenom on En

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LECTURE 1:

CHEMICALANDPHYSICAL PHENOMENA

(THATSUSTAINLIFE)1


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COURSE OUTLINE

Matter Atoms, molecules, ions, isotopes Elements, compounds, mixtures States of matter

Bonding: ionic, covalent, polar

Dispersion systems Homogenous & heterogenous Types of dispersions: Solutions, Colloids,

Suspensions2


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OBJECTIVES: ATTHEENDOFTHISLECTUREYOUSHOULDBEABLETO:

Define and give examples of atoms, molecules, ions, isotopes, elements, compounds, mixtures

Dispersions: solutions, colloids, suspensions

Explain the difference between homogenous &

heterogenous dispersions systems how different types of binding occur

ionic, covalent, polar3


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INTRODUCTION

There is great diversity in life but there aresome basic unifying substances.

The processes that sustain living things mustbe explored both in the visible and invisiblerealm.

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DEFINITIONS

Chemical phenomenon Any natural occurrence involving

changes to atoms or molecules

Chemical reactions occur to sustainlife.

Chemistry is therefore necessary forthe explanation of biological

properties. 5


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DEFINITIONS

Physical phenomenon

Any natural occurrence involving the

interaction of matter and energy

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ELEMENTS

Substances that cannot be split intosimpler substances by chemical means.

approx.109 identified,

92 occur naturally and

17 synthesized.

Living organisms contain only about 20.

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ELEMENTS

Elements are denoted by one or twoletters derived from their English or Latinnames

carbon (C), hydrogen (H), sodium (Na),calcium (Ca) and oxygen (O).

Four elements (C, H, O, N) make upover 90 percent of our bodys weight.

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ELEMENTS IMPORTANT TO LIFE

Element Importance

C Organic molecules (Proteins, Carbohydrates, Lipids)

H Organic molecules, Electron transfer

O Organic molecules, Cellular respiration

N Proteins, Nucleic acids, Chlorophyll

Ca Bones, teeth, Conduction of nerve impulses, Musclecontraction, Blood clotting

Na & K Cations (positive ion) in interstitial fluid, Nerve functions

Cl Anion (negative ion) in interstitial fluid

P Nucleic acids, ATP, Phospholipids (cell membranes)

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ATOMS

The smallest part of an element thatcan take part in a chemical change(atomos indivisible).

Atoms consist largely of empty space. Nucleus the centre of an atom, very small

volume

Virtually all of the weight of an atom iscompacted in the centre (occupying aspace equivalent to a marble in afootball field)

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STRUCTUREOFTHEATOM

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www.howstuffworks.com/atom.htm


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ATOMS - NUCLEUS

Nucleus comprised of positively chargedprotons and neutral neutrons Nucleus therefore positively charged.

Protons and neutrons have equal mass - about1 atomic mass unit (or 1.6 x 10-24) grams.

Mass number/atomic mass =Total mass of atom = # protons + # neutrons.

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ATOMS- NUCLEUS

Nucleus orbited by electrons ofnegligible mass.

Electrons negatively charged

Electrons about 1/1,800 the mass of a

proton

The smallest atom, an atom ofhydrogen, consists of one proton and

one electron.13


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ATOMS

Held together as a unit by the electricalattraction exerted between the oppositelycharged protons and electrons.

Overall charge of the atom is neutralsince number of protons equals the

number of electrons

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ATOMS

All consist of the same three types

of subatomic particles (protons,

neutrons and electrons).

They are therefore distinguished

by the atomic number.

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ATOMS

The atomic number is the number ofprotons in the nucleus of an atom.

For example, carbons atomic number

is 6

therefore, all carbon atoms have 6protons, and conversely, all atomswith 6 protons are carbon.

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ATOMS- ISOTOPES

Isotopes

Atoms which have the same number ofprotons (atomic number) but different

number of neutrons (therefore differentatomic mass).

In nature, a sample of an element willcontain a mixture of various isotopes.

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ATOMS- ISOTOPES

Example

Hydrogen has three isotopes with 0, 1 or 2neutrons.

Hydrogen therefore exists in three differentforms

Hydrogen: Proton = 1; Neutron = 0; Electrons =1

Deuterium: Proton = 1; Neutron = 2; Electrons =1

Tritium: Proton = 1; Neutron = 3; Electrons =1

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ISOTOPESOF HYDROGEN

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Hydrogen Deuterium Tritium

Atomic # 1 Atomic # 1 Atomic # 1Mass # 1 Mass # 2 Mass # 3

Symbol: Symbol: Symbol:


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ATOMS- ELECTRONS

ElectronsArranged in shells/ orbitals around the

nucleus.

Each shell can hold a specific amount ofelectrons. 1st shell can hold 2 electrons,

2nd shell 8

When one shell is filled, additional electronsgo into the next shell farther away from thenucleus.

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ATOMS- ELECTRONS

Example

Chlorines 17 electrons are held

2 in 1st shell,

8 in the next shell and

7 in the last.

Chlorines electron configuration may be

written (1s22s82p7).

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ELECTRONS

Nitrogens seven

electrons areaccommodated 2 in1st shell, 5 in thenext shell

N= 7 (2:5)

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www.webelements.com/


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ATOMS- ELECTRONS

Elements with their outermost shell full ofelectrons are

usually unreactive e.g., helium, neon.

called the noble gases because they seldomform compounds with other atoms.

All other elements have a tendency to wantto obtain a full shell through reaction withother elements.

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MAIN ELEMENTSIN LIVING MATTER

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Atomic # Electron Shells Valency Mass #

C 6 1s2 2s2 2p2 4 12

H 1 1s1 1 1

O 8 1s2 2s2 2p4 2 16

N 7 1s2 2s2 2p3 3 or 5 14

P 15 1s2 2s2 2p6 3s2 3p3 3 or 5 31

S 16 1s2

2s2

2p6

3s2

3p4

2 or 6 or 4 32

Valency= # of H atoms that the element can combine with

Atomic #=# of protons (+ charge) =# of electrons (- charge)


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MOLECULES + COMPOUNDS

The atoms of most elements can interactwith similar or other atoms to form larger,more complex structures called molecules.

Eg. H2

A molecule containing two or more types ofelements chemically combined is called a

compound e.g., water (hydrogen & oxygen);

glucose (carbon, hydrogen & oxygen);

sodium chloride (sodium & chlorine)

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COMPOUNDS

Different atoms are combined inspecificproportions, with a specific bond. Eg.,

All samples of pure H2O contain, by mass, H:O

in the ratio1:8 When H reacts with O to produce water, relative

amounts of H and O that combine are alwaysthe same.

If 1.0g of H reacts, 8.0g of O is always used.

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BONDS27


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BONDS

Atoms in compounds are held together bybonds

The main types of chemical bonds are ionic (transfer of electrons) and

covalent (sharing of electrons) but

there are other types

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IONICBONDS(TRANSFEROFELECTRONS)

Some atoms are so electron attracting(electronegative) that they can capture electrons

from the outer shell of other atoms

Electrons end up being transferred from one atom toanother.

E.g. Formation of Sodium Chloride (NaCl)

Atoms of sodium are being bonded to chlorine

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Number and arrangement of electrons:

Na = 11 (2: 8: 1); Cl = 17 ( 2: 8: 7)

Chlorine will capture the one electron in theouter shell of sodium.

Cl now has 17 protons and 18 electrons (anet negative charge). Cl- anion

Na is left with 11 protons and 10 electrons(a net positive charge). Na+cation

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Oppositely charged ions attract one another,forming a linkage called the ionic bond.

Electrically charged particles are called ions. Positive ions = cations; negative ions = anions.

Ionic bonds usually form between charged

groups that are of large, complex biologicalmolecules e.g., proteins.

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COVALENTBONDS(SHARINGELECTRONS)

Electrons in this type of bond are sharedbetween atoms, so that each has a stablecomplete outer energy shell.

The number of bonds that are formeddepend on the number of electrons neededto fill the outer shell.

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COVALENTBONDS(SHARINGELECTRONS)

Eg., hydrogen molecule (H2) consistsof two atoms of hydrogen.

Hydrogen has a single electron in itsouter shell and so can combine withanother hydrogen atom.

This is a single covalent bond.

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COVALENTBONDS

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Hydrogen

Molecule

Oxygen molecule(double covalent bond)

ChlorineMolecule


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COVALENTBONDS

Double (e.g, O2) and triple covalent bonds(e.g., N3) also occur.

Different atoms can be covalently bonded to eachother. Eg. methane has H bonded with C.

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POLARBONDS

Formed during the sharing of electrons betweentwo atoms of different electronegativity e.g., water(H2O).

Waters single O atom attracts electrons much

more than its two H atoms.

The electrons associate more with O which

becomes slightly negative as a result; H atomsbecome slightly positive.

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POLARBONDS

Molecules with unequal chargedistribution are said to be polar(unequal sharing of electrons).

Polar molecules possess distinctpositive and negative regions, or poles,

and attract each other leading to theformation of the bond Eg. hydrogen bond

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HYDROGENBONDS

Hydrogen bonding occurs when an atom ofhydrogen is attracted by rather strong forcesto two atoms instead of only one, so that it

may be considered to be acting as a bondbetween them

Eg. Partially positively charged hydrogen atom

lies between partially negatively charged oxygenor nitrogen atoms

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POLARBONDS (HYDROGENBOND)

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Red ball = hydrogenWhite ball = oxygen


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COMPOUNDS

MIXTURESDISPERSION SYSTEMS

SOLUTIONS

SUSPENSIONCOLLOIDSEMULSION

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MIXTURES

Mixtures differ from molecules andcompounds in that they may be ofvariable composition.

A solution of sodium chloride (NaCl,table salt) in water is a mixture of twosubstances.

There can be any amount of water andany amount of sodium chloride.

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MIXTURES

Separation of mixtures can beaccomplished by some physical process(as opposed to a chemical reaction).

Eg. Sodium chloride in water

If left to evaporate, water will leave the saltbehind.

Most materials found in nature are not purebut are mixtures. 42


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DISPERSIONSYSTEMS- SOLUTIONS

SolutionsCommon in nature

Extremely important in both life & industrialprocesses.

Vary in concentration

Body fluids (eg. blood and urine) of all life formsare solutions;

the concentrations of the solutes give valuableclues on the state of health.

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True solutions consist of a solvent andone or more solutes

Proportions of solute and solvent vary

from one solution to another (whereaspure substance has fixed composition).

The solventis the medium in which the

solutes are dissolved.

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DISPERSION SYSTEMS SOLUTIONS


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The fundamental units of solutes are usually

molecules or ions.

Molecules 2 or more atoms heldchemically combined in a definitearrangement. Eg. O2

Ions - atoms, groups of atoms that wouldnormally be neutral but now have becomecharged by the gain or loss of an electron.

Negative ions (anions) have more electrons in itsshells than protons in its nucleus. Eg. O2-

Positive ions (cations) have less electrons in its

shells than protons in its nucleus. Eg. H+ 45


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Homogenous mixture have the solutemolecules relatively small incomparison to the solvent molecules.

Solutions may involve many differentforms of matter; a solid, liquid, or gascan act as either a solvent or solute.

Most common kinds of solutions haveliquids as the solvent.

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DISPERSIONSYSTEMS- SOLUTIONSEg. of common solutions with non-liquid

solvents: Air is a solution of gases (with variable

composition).

Dental fillings are liquid in solid; solutions ofliquid mercury dissolved in metals.

Alloys are solid solutions of solid metalsdissolved in one another.

The solutes in solutions are relativelysmall in comparison to the solventmolecules. 47


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DISPERSIONSYSTEMS- SUSPENSIONS

SuspensionA heterogeneous mixture in which

the large solute-like particlesimmediately settle out after mixing

with a solvent like phase.

For example, sand is stirred into

water. The solute does not dissolve.

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DISPERSIONSYSTEMS- COLLOIDSColloids, colloidal suspensions, or colloidal

dispersions

Intermediate kind of a mixture (between

homogenous, solution and totallyheterogeneous, suspension) in whichthe solute like particles, or dispersedphase, are suspended in the solvent-like

phase or dispersing medium.

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DISPERSIONSYSTEMS- COLLOIDS

The particles of the dispersed solute are large incomparison to the solvent but small enough toremain suspended and settling is negligible.

Solute neither dissolves nor sediments

Solute particles large enough to make the mixtureappear cloudy (or opaque) because light is

scattered as it passes through the colloid.Suspension therefore heterogenous.

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If left for a long time, flocculation occurs,that is, the particles come together thensettle out.

Colloid Classification

hydrophilic (water loving) or

hydrophobic (water hating)based on the surface characteristics of the

dispersed particles. 51


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Hydrophilic ColloidsProteins eg. haemoglobin form hydrophilic sols

when they are suspended in saline aqueousbody fluids eg. blood plasma.

These proteins fold and twist in an aqueoussolvent so that polar groups are exposed to thefluid, while non-polar groups are encased.

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Hydrophilic Colloids

Gels are special types of sols (solid in liquidcolloid) in which the solid solutes join

together in a semi-rigid network structurethat encloses the solvent.

Protoplasm in human cells are examples ofgels. The solute are mainly proteins andcarbohydrates and the solvent aqueous)

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Hydrophobic Colloids

Hydrophobic solutes cannot exist in polarsolvents without the presence of emulsifying

agents.Emulsifiers coat the solute to prevent their

coagulation into a separate phase.

In milk, the fat is emulsified by casein.

In mayonnaise, the vegetable oil isemulsified by egg yolk. 54


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EMULSIONS

Two liquids are immiscible andthere do not dissolve in each other.

Liquid in liquid colloide.g., oil and water.

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COLLOIDS

AdsorptionThe adhesion of the molecules of liquids,

gases, and dissolved substances to thesurfaces of solids (as opposed to absorption, in which the

molecules actually enter the absorbingmedium).

Colloidal particles suspended in a solutionmay adsorb much of the solvent.

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ADSORPTION

Charcoal, for example, is used inindustry to remove colors fromsolutions, since they adsorb many

coloring materials and carry these withthem when separated from thesolution.

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