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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