Download Develo ment of the Atomic Theo John Dalton - (English 1766

Develo ment of the Atomic Theo
Democritus - (Greek philosopher) When matter it divided, eventually the
smallest particle would be obtained. He named this particle
the at~om, from the Greek word atomos, which means
indivisible. (No experimentation was done)
John Dalton - (English 1766-1844) Dalton’s Atomic Theo _ry (experiments)
All elements are composed of atoms
Atoms are indivisible (cannot be divided further)
Atoms of the same element are alike, atoms of different
elements are different.
Compounds are formed by the joining of atoms of two or
more elements
Which art of Da|ton’s Theo do we now know toda is false?
J. J. Thomson - (English 1854-1940) Thomson’s Plum Pudding_.Model
In 1897 he discovered the ~ by studying the
passage of an electric current through a gas sealed in a
glass tube lcathode ray tube). This proved that the atom
W~ ~.
He said that the atom was made ofa puddinglike positively
charged material with electrons scattered throughout it like
plunas in a pudding.
Ernest Rutherford - (English 1871 -1937) Rutherford Model
In 1911, discovered the nucleus of the atom.
When he shot a beam of positively charged
particles through gold foil, some bounced
offin different directions as if they had hit something.
(They were repelled by the positive nucleus).
Electrons surrounded the nucleus
The atom was mainly empty space.
,
Niels Bohr - (Danish 1885-1962) Bohr Model
Electrons move in definite orbits around the nucleus like
planets around the sun.
These orbits or energy levels are at certain fixed distances
fi’om the nucleus.
Modem Atomic Wave Model - (mathematical calculations)
Atoms have no definite shape
Electrons do no......__At have definite orbits
There are regions around the nucleus
where the electrons are most likely to be
found based on their energy.
Exact locations of electrons are not known
An atom has a small positively charged nucleus surrounded by a large
.region in which there are enough electrons to make the atom electrically
neutral.
Other Contributors to the Atomic Theory.
Robert Millikan- (American 1868-1953) Calculated a more accurate value
for the ~ and mass of the electron:
charge = 1 negative unit
mass = 1/1840 that ofhydroCen
E. Goldstein - (1886) Discovered the proton - positive particles in a
cathode ray tube traveling in the opposite direction of the
negative cathode ray
Sir James Chadwick - (English 1891-1974) He discovered the neutr in
1932
"~.
The First Periodic Table
Dmitri Mendeleev - Russian Scientist, known as the Father of the Periodic Table
First person to arrange the elements in the periodic table
He arranged the elements in order of increasing atomic mass
Mendeleev was able to predict the properties of elements before they were discovered.
Modern Periodic Table
When Mendeleev looked over his periodic table, he did notice that some of the
elements appeared to be misplaced in terms of their properties. He assumed that their
atomic mass was just calculated incorrectly.
50 yrs. later a British scientist - Henry Moseley discovered the atomic numbers of the
elements. He noticed that when the elements were rearranged in order of increasing
atomic numbers instead of their atomic masses all of the elements fell into place
correctly. This is the modem periodic table that we use today.
Vertical columns - groups or families, similar but not identical properties, same
number of valence electrons (outermost electrons - used in
chemical bonding between elements)
Can be referred to by a Roman Numeral IA - VIIIA ( representative elements)
Group B -transition metals ( middle of table) these are the more commonly known
Elements (ex. copper, gold, iron, lead, silver)
Or
The groups can be numbered 1 - 18 straight across the table which would include both
the A and B groups.
Some groups also have family names:
Groul~ IA - Alkali Metals - most active metals (especially with water)
Not found free in nature, but in compounds
G¢oul2 2A - Alkaline Earth Metals - 2nd most active metals, also not fouhd
free in nature, but in compounds
Group 8/Group 0 - Noble Gases/Inert gases - non reactive elements, these
elements react only under special conditions, traces of all
of these elements are found in the earth’s atmosphere
Group 7A - Halogens - most reactive non-metals, not found flee in nature
but in compounds
Horizontal Rows - Periods/Series (there are 7) These elements all have different
properties. Each period stands for another energy level.
The bottom two rows are series that have been removed fi:om the main body of the
table to make the table more compact. These can be called the inner transition
elements.. They are known as the rare-earth elements.
Most elements on the.periodic t~ble are metals. They are’found in the middle and to
the left side of the table. Groups 1A - 3A (including the transition metals)
Properties of metals: good conductors of heat/electricity
lose electrons when bonding
form positive ions
malleable (can be hammered into sheets)
ductile (can be pulled into thin wires)
shiny/luster ’
high densities & high melting points
corrode easily (they lose e" & react easily w/water vapor)
example: iron rusting
Nonmetals - found on the right side of the table, Groups 4A- 7A
Properties of nonmetals: poor conductors of heat/electricity
gain electrons when bonding
form negative ions
not malleable/ductile
dull
brittle
lower densities & lower melting points -~.
example: Nitrog.~-makes up 78% of the earth’s
atmosphere.(our air)
There is another small group of elements called metalloids or semimetals;
Metalloids/semimetals - contain the~ properties of both metals or nonmetals
(Exo- can be dull yet good conductors, or have a luster and
be a poor conducto0
They are found on the dividing line (staircase) between the metals and nonmetals.
They include the elements: B, Si, Ge, ~ Sb, Te, Po, & At.
Chemical Bonding
When atoms bond with each other, they either lose, gain or share electrons. The
electrons involved in bonding are called valence electrons and are found in the
outermost energy levels of the atoms. The number of valence electrons involved can
be indicated by a valence or oxidation number. There is a relationship between the
valence/oxidation number of an element and where it is located on the periodic table.
Label the following on your periodic table:
Group number = number of valence electrons (outermost elec,tr0ns)
0~x. group IIA has 2 Valence electrons, group VIIA has 7 valence electrons)
Group
IA
Valence# +1
(ele.charge) [
IIA
IIIA
IVA
+2
+3
+4
lose
electrons ’]
metals
VA VIA VIIA
VIIIA/0
-3
-2
-1
[ . gain electrons ]
nonmetals
0
o hydrogen is an exception because it can have either a +1 or-1 charge
Group B/transition elements - can have more than one charge or valence number
many have +1 or+2 (most common charge is a +2)
Each box on the periodic table contains the following basic information:
Symbol Atomic mass
Atomic number
--) Na.
sodium
22.99
Name