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7/26/2019 (3) Atoms & Atomic Properties
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ATOMS & ATOMICPROPERTIES
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All matter is composed of the
basic building blocks called at Atoms are basic unit of an elemecan enter into chemical combinati
An atom is composed of three subparticles.
TE ATOMIC STR!CT!RE
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The nucleus is a dense core that contains the pneutrons. Most of the mass of an atom resinucleus.
The electron cloud is composed of electrons
rapidly in the almost empty space surrounding tThe electron cloud com rises most of the vol
TE ATOMIC STR!CT!RE
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TE ATOMIC STR!CT!RE
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"I##IAMCROO$ES
Used a vacuum discharge tube called Crookes tube, to show
some kind of matter coming from the cathode that cause thefrom the glass in the anode ( electrode!
These particles were called CATO%E RAS because they the cathode.
istor' of Subatomic ParticCATO%E RAS
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TE E#ECTRO( SIR )OSEP )O(TOMSO(
established the particlenature of cathode rays.
"e concluded that cathoderays are negatively chargedfundamental particlesfound in all atoms.
Cathode rays are now called
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#obert Millikan, in $%&%, succeeded in measuring the c
electron by performing the oil'drop eperiment.
The E#ECTRO(Millikan*s oil+drop e,periment
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)ubse*uent eperiments led to the discoveryof positive particles (protons) and neutral
particles (neutrons) in the nucleus.
Protons were discovered in 1919 byRutherford.
Neutrons in $%+ by -ritish scientist )amesChad-ick($%$/$%0!.
Thus, the atom is composed of electrons,
protons, and neutrons.
The 1#2T23 4 35UT#23
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ATOMIC PROPERTIES
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E.er' atom of a gi.en t'pe of element ahas the same number of protons inucleus/
atomic number (Z)
TE ATOMIC STR!CT!RE
the atomic number tells us both the number in the nucleus and the number of electro
electron cloud of a neutral atom
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an element is a miture of isotopes, useful to know the a.eragemass, caatomic -eight (or atomic mass!,atoms in a sample.
ATOMIC "EI0T1MASS 2A3
TE ATOMIC STR!CT!RE
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is the sum of the number of protoneutrons.
both protons and neutrons contrthe mass of an atom.
MASS (!M4ER 2A3
TE ATOMIC STR!CT!RE
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which de6nes the mass of individ
atoms relative to a standard mass.
2ne atomic mass unit (amu)e*u
one'twelfth the mass of a carb
atom that has si protons and
neutrons7 $ amu 8 $.99$ $&/:g.
atomic mass unit
TE ATOMIC STR!CT!RE
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AT2M;C 3UM-5#, A3< MA)) 3UM-5#
TE ATOMIC STR!CT!RE
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SAMP#E E5ERCISE
=ive the complete chemical sfor the atom that contaiprotons, electrons, andneutrons.
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SAMP#E E5ERCISE%etermining the (umber of Subatomic Particles in Atoms
"ow many protons, neutronelectrons are in 2a3 an atom of2b3 an atom of strontium'%&>
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PRACTICE E5ERCISE
"ow many protons, neutand electrons are in 2a6:;4a atom9 2b3 an atom
phosphorus'+$>
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PRACTICE E5ERCISE
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