Kimia Dasar Bag 1

8/17/2019 Kimia Dasar Bag 1

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ATOMS, MOLECULES AND MOLES

- In ancient time, people believe in phlogiston theory

- Antoine Lavoisier (around the end of 18th

century)experiments comes into the conclusion of conservation

of mass law:

In any chemical reaction, mass is neither

created nor destroyed

- !oseph "roust (around the end of 18th century)

experiments results law of definite proportions

(composition: In any sample of a pure chemical substance, it

always finds the same elements in the same

definite proportions by mass

- "ostulates of the atomic theory (!ohn #alton,

beginning of 1$th century)%

1& 'atter is composed of tiny indivisible particles called

atoms&

& All atoms of given elements are identical, but differ

from atoms of other elements&

& A chemical compound is composed of the atoms of

its element in a definite fixed numerical ratio&

*& A chemical reaction merely consists of a reshufflingof atoms from one set of combinations to another&

+he individual atoms themselves, hoever, remain

intact and do not change&

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Lets see molecule A! here an atom of A is tice as

heavy as an atom !

umber of

'olecule

umber

of Atoms

of A

'ass of

A

umber

of Atoms

of .

'ass of

.

'ass /atio

('ass A)0

('ass .)

" " # $nits " " $nits #%"

# # & $nits # # $nits &%# ' #%"

" " #

$nits

" "

$nits

#%" '

#%"

) ) "

$nits

) )

$nits

"%)

' #%"

.y product of #altons atomic theory% T*e of m$ltiple

proportions:

If the masses of one element are the same in the twosamples, then the masses of the other element are in ratio

of small whole numbers

xample% 2or 34 and 345 ratio of 4 in 34 0 4 in 34 is 6

T*e Mole Concept

1 atom 3 7 1 atom 4 → 1 molecule 34

1 atoms 3 7 1 atoms 4 → 1 molecules 34

9&x1 atoms 3 7 9&x1 atoms 4 → 9&x1 molecules 34

1 mole atoms 3 7 1 mole atoms 4 → 1 mole molecules 34

1 3 7 1 4 → 1 34


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3 7 4 → 34

Atomic Mass:

3arbon-1 is assigned as exactly 1 u (units)

1 mole 3arbon-1 : 1& g

1 mole 3 (mixture of 3-1 and 3-1 in nature) : 1&11 g

- "ercentage 3omposition

- 'olecular 2ormula and 'olecular ;tructure

- /elative 'olecular 'ass and 'olecular 'ass


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3


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Is it correct to rite the reaction in the folloing ay

Ba34 7 1


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Calc$lation 0nvolvin 1rams

uired to react ith

& mol Al and ho many grams of Al4 ill be

produced in the reaction% Al 7 4 → Al4

Limitin2+eactant Calc$lations

In an experiment, 1& g of Cn is mixed ith 9&B g of ;

and alloed to react& =hich is the limiting reactant

T*eoretical 3ield and 4ercentae 3ield

actual yield

Percentage yield = x 100

theoretical yield

thylene, 3uation 3


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+eactions in Sol$tion


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Calc$latin t*e molarit6 of sol$tion

A & g sample of sodium hydroxide, a4< as

dissolved in ater to give a solution ith a volume of

exactly mL& =hat is the molarity of this solution

mass of an element

number of moles (n) :

relative atomic mass

mass of a compound

number of moles (n) :

relative molecular mass


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'&F : (mol0L) x L : mol

M"89" ' M#89#

uired to prepare B mL of & '


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+


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T*e modern view of t*e atom

Is atom indivisible particle

In the late of 1$th century, s$7atomic particles, proton

("8;/"2"


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'ass of an atom is primarily determined by the number of

protons and neutrons in its nucleus

ucleus is so tiny ith the density of about 11* g0cm

umber of proton in nucleus : atomic number of the atom

Atom is neutralGGG

umber of proton : number of electron

An atom represented symbolically by riting its mass number

as a superscript and its atomic number as a subscript X

A

Z

C : atomic number: number of protons

: number of electrons in (neutral) atom

A : mass number

A H C : number of neutrons

C 1(

9 and C 1)

9 are isotopes of car7on

Cu9)

($ and Cu9B($ are isotopes of copper hose the masses are

9&$$8 and 9*&$E8 u, respectively, and their abundance are

9$&$ D and &$1 D& =hat is the average atomic mass of this

element

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Atomic n$m7er and t*e modern periodic ta7le

;ee the modern periodic table

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=ormation of ionic compo$nd

=hen to or more substances combine to form a single

product the reaction sometime called a com7ination reaction

a( s) 7 3l( g ) → a3l( s)

Atom of sodium loses one electron, hich is transferred to a

chlorine atom

;odium atom loses one electron, become positive ion, ith thecharge 17 called a cation, ritten as a7

3hlorine atom gains one electron, become negative ion,

chloride ion, ith the charge 1- called an anion, ritten as 3l-

NaCl is an ionic compo$nd

Metals tend to react wit* nonmetals to form ionic

compo$nds

roup number

0A 00A 000A 09A 9A 90A 900A

Li7

a7

J 7

/b7

3s7

.e7

'g7

3a7

;r 7

.a7

Al73

*-

;i*-

-

"-4

-

;-

;e-

+e-

2-

3l-

.r -

I-

1*


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T*e transition metals are a7le to form more t*an one ion

3ations formed by some transition elements

3hromium 3r 7 old Au7

3r 7 Au7

'anganes 'n7 Cinc Cn7

'n7 3admium 3d7

Iron 2e7 'ercury uals the total number of

negative charge5 the formula unit must be electrically

neutral&

& +he smallest set of subscripts that give electrical neutrality

is alays chosen&

xample%

+he compound form from 3a7 and 3l- is 3a3l+he compound form from 3a7 and 4- is 3a4

+he compound form from a7 and 4- is a4

+he compound form from Al7 and 4- is Al4

1B


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0ons can contain more t*an one atom

3ations


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Simple compo$nd of nonmetals wit* *6droen

roup IFA roup FA roup FIA roup FIIA

3


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Some properties of ionic and molec$lar (nonionic compo$nd:

1& 'elting point% ionic compounds have a high melting point&

a3l, an ionic compound, melts at 8 o3&

eicosane (3uids such as gasoline and paint thinner&

*& lectrical conductivity%

- .oth ionic and non-ionic compounds in the solid form do

not conduct electricity&

-'olten non-ionic compounds do not conduct electricity,molten ionic compounds does&

O/idation > red$ction reactions

2rom the time that oxygen as discover, the term o/idation

has been associated ith the reaction of this compound ith

another compounds or elements to form oxides compounds&

;ince @non that iron oxide could be bro@en don (reduced)

to give the free metal, recovery of metal from its oxide @non

as red$ction8

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*2e( s) 7 4( g ) → 2e4( s)

2e loses electrons to become 2e7

ach 4 in 4 molecule gains electrons to become 4-

O/idation is t*e loss of electron(s from a s$7stance

+ed$ction is t*e ain of electron(s from a s$7stance

'g( s) 7 4( g ) → 'g4( s)

product of this reaction is an ionic compound, 'g4, contains'g7 and 4-, so the reaction can be considered as

'g → 'g7 7 e (oxidation)

4 7 *e → 4- (reduction)

O# is o/idi?in aent, it ta@es electrons from the substancethat is oxidiKed& 4 itself is reduced in fact& M is red$cin aent, it gives electrons to the substance that

is reduced& 'g itself is oxidiKed in fact&

O/idation n$m7er

are numbers (either positive or negative) that e assign to

atoms in a compound so e can follo the changes that ta@e place in redox reaction

1$


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T*e o/idation n$m7er are assined accordin to a set of r$les

+$les for assinin o/idation n$m7ers

1& +he oxidation number of any element in its elemental form

is Kero (e,


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0dentif6in o/idation and red$ction in a reaction

1*


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3u7 cuprous ion 3u4 cuprous oxide

;n*7 stannic ion ;n(;4*) stannic sulfate

;n7 stannous ion ;n;4* ;tannous sulfate

3o7 cobaltic ion 3o(34) cobaltic carbonate

3o7 cobaltous ion 3o34 cobaltous carbonate

Stoc name (s6stem:

2e.r iron(000) bromide 3o(34) cobalt(000) carbonate

2e.r iron(00) bromide 3o34 cobalt(00) carbonate

3u;4* copper(0) sulfate "b(34*) lead(IF) oxalate

3u;4* copper(00) sulfate "b34* lead(II) oxalate

Non2metal compo$nds

4 nitrogen dioxide 34 carbon monoxide

4* dinitrogen tetroxide 34 carbon dioxide

4B dinitrogen pentoxide

"3l phosphorus trichloride

"3lB phosphorus pentachloride

Acids (hen they dissolved in ater)


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Stron and wea electrol6tes

3ompare the conductivity solutions of 31


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Ag7(aq) 7 3l-(aq) → Ag3l( s)

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