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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 &$1 D& =hat is the average atomic mass of this
element
1
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Atomic n$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)