the periodic table the how and why…. early in the 19th century, scientists began to seek ways of...
TRANSCRIPT
The Periodic Table
The how and why…The how and why…
Early in the 19th century, scientists began to seek ways of classifying elements.
1817, Dobereiner found the properties of metals calcium, barium and
strontium were very similar
he noted the atomic mass of strontium was about midway between those of
calcium and barium he grouped these three elements together and
called them a triad later he found other groups with similar
properties
Examples of Dobereiner’s Triads
Triad 1 Triad 1 Triad 1 Name At. Mass Name At. Mass Name At. Mass 1st Elem’t Calcium 40 Chlorine 35.5 Sulfur 32 3rd Elem’t Barium 137 Iodine 127 Tellurium
127.5 AVE. AVE. AVE. 2nd Elem’t Strontium 87.6 Bromine 79.9 Selenium 79.2
1863- John Newlands arranged elements in order of
increasing atomic mass noted their appeared a repetition of
similar properties ever eighth element arranged the 49 elements known into
seven groups of seven each
Called LAW OF OCTAVES
Newland’s Law of Newland’s Law of OctavesOctaves1 2 3 4 5 6 7 1 2 3 4 5 6 7
Li Be B C N O FLi Be B C N O FNa Mg Al Si P S ClNa Mg Al Si P S ClKK
Just 6 years later, 1869
Demitri Mendeleev proposed a similar idea
Felt similar properties occurred after periods(horizontal rows) of varying length.
placed seven elements in 1st two periods, seventeen elements in the next two
Mendeleev and a German chemist Lothar Meyer each working alone-
made an eight column table of the elements
However, Mendeleev had to leave some blank spots in order
to group all the elements with similar properties in the same column----
to explain these spots, he suggested there must be other elements which had not yet been discovered
he predicted properties and atomic masses of these unknown elements
TODAY- the other elements have been discovered
Mendeleev’s predictionsMendeleev’s predictions
Ekasilicon GermaniumEkasilicon Germanium
Predicted properties Actual PropertiesPredicted properties Actual Properties
Atomic mass= 72 Atomic mass= 72.6Atomic mass= 72 Atomic mass= 72.6High Melting point Melting pt. 958High Melting point Melting pt. 958 oo CCDensity = 5.5 g/cmDensity = 5.5 g/cm33 Density= 5.36 g/cm Density= 5.36 g/cm33
Dark gray metal Gray metalDark gray metal Gray metalSlightly dissolved in HCl Not dissolved in HClSlightly dissolved in HCl Not dissolved in HClWill form oxide EsOWill form oxide EsO22 Forms oxide GeO Forms oxide GeO22
Mendeleev arranged elements in order of increasing atomic masses
He showed the properties of the elements repeated as a function of their atomic
masses.
CALLED PERIODIC LAW Mendeleev called
FATHER OF THE PERIODIC TABLE
MENDELEEV KNEW HIS TABLE HAD PROBLEMS-
Tellurium and iodine seemed to be in the wrong columns
SWITCHING THEIR POSITIONS WOULD PLACE THEM IN THE RIGHT
COLUMNS BUT HE DIDN’T KNOW WHY...
Cobalt and Nickel also need to be reversed
Henry Mosely- found a reason In 1913- his X-ray experiments showed
the nucleus had a integral + charge, the ATOMIC NUMBER
he arranged the periodic table by ATOMIC NUMBER and everything fell into the right column
The Modern Statement of the Periodic Law is
the properties of the elements are a periodic function of their
atomic numbers.
THE MODERN TABLE Elements are still grouped by
properties. Similar properties are in the same
column. Order is in increasing atomic number. Added a column of elements Mendeleev
didn’t know about. The noble gases weren’t found because
they didn’t react with anything.
Horizontal rows are called periods There are 7 periods
Vertical columns are called groups.
Elements are placed in columns by similar properties.
Also called families
1A
2A 3A 4A 5A 6A7A
8A0
The elements in the A groups are called the representative elements
The group B are called the transition elements
These are called the inner transition elements and they belong here
Group 1A are the alkali metals Group 2A are the alkaline earth metals
Group 7A is called the Halogens Group 8A are the noble gases
Why? The part of the atom another atom
sees is the electron cloud. More importantly the outside
orbitals. The orbitals fill up in a regular
pattern. The outside orbital electron
configuration repeats. The properties of atoms repeat.
1s1
1s22s1
1s22s22p63s1
1s22s22p63s23p64s1
1s22s22p63s23p64s23d104p65s1
1s22s22p63s23p64s23d104p65s24d10 5p66s1
1s22s22p63s23p64s23d104p65s24d105p66s2
4f145d106p67s1
H1
Li3
Na11
K19
Rb37
Cs55
Fr87
He2
Ne10
Ar18
Kr36
Xe54
Rn86
1s2
1s22s22p6
1s22s22p63s23p6
1s22s22p63s23p64s23d104p6
1s22s22p63s23p64s23d104p65s24d105p6
1s22s22p63s23p64s23d104p65s24d10
5p66s24f145d106p6
Alkali metals all end in s1
Alkaline earth metals all end in s2
really have to include He but it fits better later.
He has the properties of the noble gases.
s2s1 S- block
Transition Metals -d block
d1 d2 d3s1
d5 d5 d6 d7 d8s1
d10 d10
The P-block p1 p2 p3 p4 p5 p6
F - block inner transition elements
f1 f5f2 f3 f4
f6 f7 f8 f9 f10 f11 f12 f14
f13
Each row (or period) is the energy level for s and p orbitals.
1
2
3
4
5
6
7
D orbitals fill up after previous energy level so first d is 3d even though it’s in row 4.
1
2
3
4
5
6
7
3d
f orbitals start filling at 4f
Ne is 1s22s22p6
so Al is [Ne] 3s23p1
1
2
3
4
5
6
7 4f
5f