Chemistry I Mr. Patel SWHS

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Nov 26, 2013 (3 years and 6 months ago)

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Chemistry I

Mr. Patel

SWHS


Learn Major Ions


Defining the Atom (4.1)


Subatomic Particles (4.2)


Atomic Structure (4.2)


Ions and Isotopes (4.3)


Nuclear Chemistry (25.1)


Atom


the smallest particle of an element
that retains its identity


Can not see with naked eye


Nanoscale

(10
-
9

m)


Seen with scanning

tunneling electron

microscope


Democritus was a Greek to first come up
with idea of an atom.



His belief: atoms were indivisible and
indestructible. = WRONG!



Atom comes from “
atmos


-

indivisible


2000 yrs later, John Dalton used scientific
method to transform
Democritus’s

idea into
a scientific theory



Dalton put his conclusions together into his
Atomic Theory (4 parts)

1.
All elements are composed of tiny,
indivisible particles called atoms.

2.
Atoms of the same element are identical.
Atoms of different elements are different

3.
Atoms of different elements can physically
mix or chemically combine in whole
number ratios.

4.
Chemical reactions occur when atoms are
separated, joined, or rearranged. Atoms of
one element can never be changed into
atoms of another element due to a
chemical reaction.


Particle with
negative

charge



Discovered by J.J. Thomson



Used cathode ray (electron) beam and a
magnet/charged plate.



Millikan found the charge and mass



An atom is electrically neutral



If there is a negative particle then there must
be positive particle



Proton


particle with
positive

charge



Chadwick discovered neutron


neutral

charge



Electrons distributed in a sea of positive charge


Plum Pudding Model




Performed Gold
-
Foil Experiment


Beam of Alpha particles with positive charge
shot at thin piece of gold foil


Alpha particles should have easily passed
through with slight deflection due to positive
charge spread throughout.


Results: Most particles went straight through
with no deflection. Some were deflected at
large angles.






The
nucleus

is the central part of the atom
containing protons and neutrons


Positive charge


Most of the mass



Electrons are located outside the nucleus


Negative charge


Most of the volume




An element is defined
only

by the number of
protons it contains



Atomic Number


number of protons



Number of protons = number of electron


For a neutral element



1.
Zinc (Zn)


2.
Iron (Fe)


3.
Carbon (C)


4.
Uranium (U)

1.
30


2.
26


3.
6


4.
92



Nucleus contains most of the mass


Rounded Atomic Mass


Mass Number


total protons and neutrons


Number of neutron = Mass #


Atomic #



1.
Lithium

(MN = 7)


2.
Nitrogen

(MN = 14)


3.
Fluorine

(MN = 19)


**
MN = Mass Number


1.
3 p
+

, 3 e
-
, 4 n
0



2.
7 p
+

, 7 e
-
, 7 n
0



3.
9 p
+

, 9 e
-
, 10 n
0



Different element: different number of protons



Ions


same number of proton, different
number of electrons



Isotope


same number of proton, different
number of neutrons


Different Mass Numbers



Nuclear Notation


Write the element symbol


On left side, superscript = Mass Number


On left side, subscript = Atomic Number



Isotope

Hyphen Notation


Write full name of element


On right side, put a dash


On right side put Mass Number after dash


Hydrogen
-

3


Atomic Mass Unit (
amu
)


one
-
twelfth of the
mass of the carbon
-
12 atom



Different isotopes have different
amu

(mass)
and abundance (percentage of total)



Atomic Mass


weighted

average mass of the
naturally occurring atoms.


Isotope Mass


Isotope Abundance





Percent Abundance


the number of desired particles
in 100 total particles of sample


Allows for comparison to
any

sample set





Relative Abundance


the number of desired particles
in the sample used


Specific to the sample used; not useful in
comparison


Convert % abundance to a decimal = relative
abundance






Desired particles

Total particles in sample

%
Ab

=

x

100%



Because abundance is considered, the most
abundant isotope is typically the one with a
mass number closest to the atomic mass.



Example, Boron occurs as Boron
-
10 and Boron
-
11.
Periodic Table tells us Born has atomic mass of
10.81
amu
.


Boron
-
11 must be more

abundant




Convert the Percent Abundance to Relative
Abundance (divide by 100)



Multiple atomic mass of
each

isotope by its
relative abundance



Add the product (from step above) of
each

isotope to get overall atomic mass.


Radioactivity


nucleus emits particles and rays
(radiation)



Radioisotope


a nucleus that undergoes
radioactive decay to become more stable



An unstable nucleus releases energy through
radioactive decay.


Nuclear force


the force that holds nuclear
particles together


Very strong at close distances



Of all nuclei known, only a fraction are stable


Depends on proton to neutron ratio


This region of stable nuclei called band of
stability


Half Life


the time required for one
-
half the
sample to decay


Can be very short

or very long


Symbol

Element

Radiation

Half
-
Life

Decay
Product

U
-
238

Uranium
-
238

alpha

4,460,000,00
0 years

Th
-
234

Th
-
234

Thorium
-
234

beta

24.1 days

Pa
-
234

Pa
-
234

Protactinium
-
234

beta

1.17 minutes

U
-
234

U
-
234

Uranium
-
234

alpha

247,000 years

Th
-
230

Th
-
230

Thorium
-
230

alpha

80,000 years

Ra
-
226

Ra
-
226

Radium
-
226

alpha

1,602 years

Rn
-
222

Rn
-
222

Radon
-
222

alpha

3.82 days

Po
-
218

Po
-
218

Polonium
-
218

alpha

3.05 minutes

Pb
-
214

Pb
-
214

Lead
-
214

beta

27 minutes

Bi
-
214

Bi
-
214

Bismuth
-
214

beta

19.7 minutes

Po
-
214

Po
-
214

Polonium
-
214

alpha

1
microsecond

Pb
-
210

Pb
-
210

Lead
-
210

beta

22.3 years

Bi
-
210

Bi
-
210

Bismuth
-
210

beta

5.01 days

Po
-
210

Po
-
210

Polonium
-
210

alpha

138.4 days

Pb
-
206

Pb
-
206

Lead
-
206

none

stable

(none)

Nuclear Reactions


Deals with nucleus



Can end up with new
atoms/elements



Mass is not strictly
conserved


Mass Defect


E = mc
2


Deals with electrons



Atoms/elements remain
unchanged


rearranged



Mass is strictly
conserved

Chemical Reactions


Alpha Radiation (Helium Atom)


Low penetrating power


Paper shielding



Beta Radiation (Electron)


Moderate penetrating power


Metal foil shielding



Gamma Radiation (Pure energy)



Very high penetrating power


Lead/concrete shielding


Transmutation


conversion from one element to
another through a nuclear reaction


Only occur by radioactive decay


Only when nucleus bombarded with a particle



Emissions


given off


Alpha Emission, Beta Emission, Positron Emission


Positron = beta particle with a positive charge



Captures


taken in


Electron Capture