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Atoms, Molecules and Ions

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Daltons Atomic Theory (1808)

1. Elementsare composed of extremely small particles

called atoms

! All atomsof a "i#en element are identical, ha#in" the

same si$e, mass and chemical properties The atoms of

one element are different from the atoms of all other

elements

3. Compoundsare composed of atoms of more than one

element In any compound, the ratio of the num%ers of

atoms of any t&o of the elements present is either an

inte"er or a simple fraction

' A chemical reactionin#ol#es only the separation,

com%ination, or rearran"ement of atoms it does not

result in their creation or destruction!1

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!1

Daltons Atomic Theory

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8 X2Y16 X 8 Y+

!1

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Thomson, measured mass*char"e of e+

(10- .o%el /ri$e in /hysics) !!

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athode ay Tu%e

!!

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e-char"e 2 +1-0 x 10+1

Thomsons char"e*mass of e+2 +13- x 108*"

e-mass 2 10 x 10+!8"

Measured mass of e+

(1!4 .o%el /ri$e in /hysics)

!!

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(Uranium compound)

!!

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!!

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1 atoms positi#e char"e is concentrated in the nucleus

! proton (p) has opposite (5) char"e of electron (+)

4 mass of p is 18'0 x mass of e+(1-3 x 10+!'")

particle #elocity 6 1' x 103m*s

(67 speed of li"ht)

(108 .o%el /ri$e in hemistry)

!!

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atomic radius 6 100 pm 2 1 x 10+10m

nuclear radius 6 7 x 10+4pm 2 7 x 10+17m

Rutherfords Model of

the Atom

!!

9If the atom is the :ouston Astrodome, then

the nucleus is a mar%le on the 70+yard line;

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had&ic

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mass p 2 mass n 2 18'0 x mass e+

!!

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Atomic number(?) 2 num%er of protons in nucleus

Mass number(A) 2 num%er of protons 5 num%er of neutrons

2 atomic num%er (?) 5 num%er of neutrons

Isotopesare atoms of the same element (@) &ith different

num%ers of neutrons in their nuclei

@A?

:11 : (D)

!1 : (T)

41

!47

!

!48

!

Mass .um%er

Atomic .um%er=lement Bym%ol

!4

Atomic number, Mass number and Isotopes

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!4

The Isotopes of ydro!en

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- protons, 8 (1' + -) neutrons, - electrons

- protons, 7 (11 + -) neutrons, - electrons

Do Cou nderstand Isotopes

!4

:o& many protons, neutrons, and electrons are in 1'

-

:o& many protons, neutrons, and electrons are in 11

-

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/eriod

Eroup

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