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Transcript
ATOMIC THEORY
IN THE BEGINNING




Atoms originally named by Democritus
Believed the a substance could be divided over
and over again only to a point
If divided further it would not be that substance
anymore
His atoms were solid, _________________________
LAVOISIER: LAW OF CONSERVATION OF
MASS


Precisely measured masses of reactants and
products of chemical rxns
Law of conservation of __________- mass is
neither created or destroyed in chemical rxn

Mass of reactants equals the mass of the products
PROUST: LAW OF DEFINITE PROPORTIONS

All samples of a particular compound have the
same _______________

Elements have the same proportion by mass in each
sample
DALTON: LAW OF MULTIPLE
PROPORTIONS

If two or more compounds containing the same
two elements are examined (for example: CO and
CO2)

Then the ratio of masses of the element that changes
in both compounds (in our example: O) is a small
whole number
Law of Multiple Proportions (cont.)

Four different oxides of nitrogen can be formed by
combining 28 g of nitrogen with:
16 g oxygen, forming Compound I
 48 g oxygen, forming Compound II
 64 g oxygen, forming Compound III
 80 g oxygen, forming Compound IV

What is the ratio 16:48:64:80
expressed as small whole numbers?

Compounds I–IV are N2O, N2O3, N2O4, N2O5
JOHN DALTON
Proposed atomic theory in 1803
 Four ideas

All matter is composed of indivisible particles called
atoms.
 All atoms of one element are alike in mass and other
properties, but the atoms of one element are different
that the atoms of other elements.
 Compounds are formed when atoms of elements unite
in fixed proportions.
 No atoms are created, destroyed, or broken apart in
chemical reactions. Atoms are just rearranged


His atom is also a solid, _____________________
Dalton’s Theory Satisfies Laws
Six fluorine atoms and four
hydrogen atoms before reaction …
… six fluorine atoms and four
hydrogen atoms after reaction.
Mass is conserved.
HF always has one H atom
and one F atom; always
has the same proportions
(1:19) by mass.
J.J. THOMSON AND CATHODE RAYS
Worked with cathode ray tubes (made by Sir
William Crooke) in the late 1800’s
 Found that all matter had negative particles
(___________________)
 Calculates _______________ ratio of e
J.J. THOMSON’S MODEL
Atoms have negative particles, but overall they are
neutral
 His atom has a positive sphere with negative particles
embedded (often called the _______________________)

Robert Millikan’s Oil Drop Experiment
Calculated the charge of an e Made it possible to calculate the mass of the e
Charged droplet can
move either up or down,
depending on the charge
on the plates.
Radiation ionizes
a droplet of oil.
Magnitude of charge on
the plates lets us calculate
the charge on the droplet.
RUTHERFORD’S EXPERIMENT
Often called the ____________ experiment
 Expected almost all  particles to pass straight
through the gold
 Although many did, some particles were reflected
back

RUTHERFORD’S CONCLUSION
Atom must have positive particles
(_______________) concentrated in the center
 Center is called the ______________
 Electrons gravitate around the nucleus
 A lot of _________________ between nucleus and
electrons

JAMES CHADWICK


Discovered neutrally charged particles
(_________________)
Particle was also found in the ______________
NIELS BOHR
Refined Rutherford’s atom model
 Put the electrons in fixed _______ (like
planets orbiting around the sun)
 Electrons could temporarily get excited and jump
levels

MODERN ATOMIC MODEL
Electron behave like _________________________
 Can’t be tied down to a orbit like a planet
 Instead scientist show where an electron is likely
to be a any one point in time
 Forms an electron __________

COMPARING THE PARTICLES

In the nucleus

Protons
Charge= ________
 Mass = ___________________


Neutrons
Charge= ______
 Mass= ______________________


Surrounding the nucleus

Electron

Charge= ________

Mass= _______________________
ELEMENTS
Composed of only one type of _________
 Identity is based on ___________ number
 Atomic number (___)- number of protons found
in that atom (ID number for elements)



Elements are ordered in periodic table according to
this number
Mass Number (___)- mass of atom in atomic unit
Really the mass of the __________________________
 Electrons are so tiny that they don’t count

CALCULATING PNE (GROUND STATE)

# of protons= __________________

# of electrons= _________________

# of neutrons= _______________________________
ISOTOPES
Different forms of the same atom type
 Differ by number of ____________ (so therefore
differ by mass as well)
 Isotope names- element name – mass number
Lithium-6
Lithium-7
Lithium-8

IONS
Atoms that lose or gain ___________ form ions
 Ions have a charge

Cation- ion with a ____________ charge
 Anion- ion with a _____________ charge

CATIONS

Forms when atoms _________ electrons
ANION

Forms when atoms __________ electrons
NAMING IONS

Cations
“Name of the element” ion
 For example, Ca+2 is calcium ion


Anions

“Name of the element with ending changed to –ide”
ion

For example Cl is chloride ion
-
CALCULATING PNE (IONS)

# of protons= atomic number

# of electrons =
atomic number – charge for cations
 Atomic number + charge for anions


# of neutrons= mass number – atomic number
ATOMIC MASSES ON THE PERIODIC TABLE

Atomic masses on periodic table are an average
of all naturally occurring ___________ based on
their abundance
Calculating Atomic Mass

Need
Mass of each isotope
 Fractional abundance of each isotope (must change to
fraction if given as %)


For each isotope
Multiple the mass and the fractional abundance
 Add all of the answers together to get the atomic
mass

DMITRI MENDELEEV




Proposed period table (1869)
Arranged elements according
to ________________
Grouped elements by similar
properties
Left holes for undiscovered
elements and predicted their
properties
GERMANIUM PREDICTION
STRUCTURE OF MODERN PERIODIC
TABLE




Elements are arranged by
_____________________
Elements occur in rows (or
_________)- 7 periods in all
Elements occur in columns (or
___________________) with similar
chemical properties- 18 in all
______________ law- elements can
be organized into patterns in the
table based on chemical and
physical properties
PERIODIC GROUPS
OTHER PERIODIC GROUPINGS
WHERE DO THEY BELONG?

The two series actually belong in the table like
this, but we put them at the bottom to save space
METALS, NONMETALS, AND
METALLOIDS

Metal





Good conductor of electricity
Malleable
Ductile
Shiny
Nonmetal
Poor conductor of heat and
electricity
 Often gas or dull, brittle
solid


Metalloid

Properties in between the
other two
NATURAL STATES OF ELEMENTS



Most occur as
solids
Br and Hg can
occur as a liquid
Other occur as gas
NATURAL STATES OF ELEMENTS
(CONT)


Many elements can exist in different forms
naturally
Carbon

Both graphite and diamond are carbon, the atoms
are just arranged differently
DIATOMIC ELEMENTS


Element occurs naturally in pairs
7 elements







Hydrogen (H2)
Nitrogen (N2)
Oxygen (O2)
Fluorine (F2)
Chlorine (Cl2)
Bromine (Br2)
Iodine (I2)