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Notes on the periodic table
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The Periodic Table of The
Elements
Elements are like a collection
As more and more elements were
discovered it became more important to
organize and classify them
Between the late 1700’s and mid
1800’s scientists, using mostly atomic
spectroscopy, doubled the number of known elements.
In early 1800’s, German chemist J.W. Dobereiner observed that several of the elements could be
classified into groups of three which he
called triads
Ca, Sr, and Ba
Li, Na, K
Cl, Br, IDobereiner based his triads on similar
chemical properties
In addition:
Many of the properties of the middle element
in each triad are approximate averages of the properties of the first and third
element
Element Atomic DensityMass (amu)
Cl 35.5 1.56 g/LBr 79.9 3.12 g/LI 126.9 4.95 g/L
Ca 40.1 1.55 g/cm3
Sr 87.6 2.6 g/cm3
Ba 137 3.5 g/cm3
In 1865, English chemist J.A.R
Newlands presented another way to classify and
organize the 62 elements known at
the time
Newlands placed the elements in order of
increasing atomic mass
He noticed that the properties of the eighth element were like those of the first, the ninth
like those of the second, and so on….
He called this repeating pattern of every eight
elements
THE LAW OF OCTAVES
After the eight notes of the musical scale
Because he linked chemistry to music, he was not taken
seriously!
It took 20 years for him to
receive credit for recognizing
periodicity
In 1869 Russian Chemist Dimitri
Mendeleev and German chemist Lothar Meyer
published nearly identical ways of
classifying
But Mendeleev is generally more credited with the 1st periodic table for 2 reasons:
He published first
He was better at explaining it than
Meyer
Mendeleev also saw the “periods”
Credited with publishing the first
“periodic table”
Mendeleev got lots of credit because he left gaps for missing elements!
In 1913, English Chemist James
Moseley Presented a way of organizing the elements that
we still use today.
Moseley was the first to put the elements in order of increasing
Atomic #
Atomic # represents the
number of protons in the nucleus of
each element
When he did this, he saw the same
repeating periodic pattern, without the
exceptions that Mendeleev had to switch around
Periodic LawWhen the elements are arranged in
increasing order by their atomic
numbers, their properties repeat
periodically
The
Modern
Periodic Table
Each Square Tells about a different element
H Element Symbol
HydrogenElement Name
Not always there
1 Atomic NumberRepresents the number of PROTONS in each atom of
this element
1.009Atomic MassRepresents the number of PROTONS AND AVERAGE NUMBER OF NEUTRONS in each atom
of this element
H
Hydrogen
1
1.009
Atomic Number 1:
1 proton (positive charge particles) in
nucleus of EVERY hydrogen atom
Atomic Number 1:
ALSO means 1 electron (negatively charged particle)
OUTSIDE the nucleus
Atoms are NEUTRAL: Same number of positives as negatives
Atomic Mass of 1.009 means that there is an average of 1.009 PROTONS AND NEUTRONS
in the nucleus… Since there is
already 1 proton (AND THAT CAN NOT
CHANGE AND STILL BE HYDROGEN) That means
that the average atom of Hydrogen has
0 Neutrons!
He
Helium
2
4.003
Let’s do another4 Particles
2 MUST BE Protons
4-2 = 2 Neutrons in nucleus
Each block tells us about the element…
The periodic table arranges the
elements into rows and columns based on
similarities
Vertical columns are called groups.Vertical columns are called groups. Elements are placed in columns by Elements are placed in columns by
similar properties.similar properties. Also called familiesAlso called families
Alkali MetalsAlkali Metals
Group 1Group 1
ALL elements in Group 1 ALL elements in Group 1 have 1 electron in their have 1 electron in their outer regionouter region
Alkali Earth MetalsAlkali Earth Metals Group 2Group 2
ALL elements in Group 2 ALL elements in Group 2 have 2 electrons in their have 2 electrons in their outer regionouter region
Boron FamilyBoron Family
Group 13Group 13
ALL elements in Group 13 ALL elements in Group 13 have 3 electrons in their have 3 electrons in their outer regionouter region
Carbon FamilyCarbon Family
Group 14Group 14
ALL elements in Group 14 ALL elements in Group 14 have 4 electrons in their have 4 electrons in their outer regionouter region
Nitrogen FamilyNitrogen Family
Group 15Group 15
ALL elements in Group 15 ALL elements in Group 15 have 5 electrons in their have 5 electrons in their outer regionouter region
Oxygen FamilyOxygen Family
A.K.A. the ChalcogensA.K.A. the Chalcogens
Group 16Group 16
ALL elements in Group 16 ALL elements in Group 16 have 6 electrons in their have 6 electrons in their outer regionouter region
HalogensHalogens
Group 17Group 17
ALL elements in Group 17 ALL elements in Group 17 have 7 electrons in their have 7 electrons in their outer regionouter region
Noble GassesNoble Gasses
Group 18Group 18
ALL elements in Group 18 ALL elements in Group 18 have 8 electrons in their have 8 electrons in their outer regionouter region
Lanthanide SeriesLanthanide Series Actinide SeriesActinide Series
Horizontal rows are called “Periods”Horizontal rows are called “Periods” Each period also shows something Each period also shows something
in commonin common
Period 1Period 1 Each element has one region of Each element has one region of
space for electrons around itspace for electrons around it
Period 2Period 2 Each element in this period has two Each element in this period has two
regions of spaceregions of spacearound it for around it for electronselectrons
Period 3Period 3 Each element in this period has 3 Each element in this period has 3
regions of spaceregions of spacearound it for around it for electronselectrons
Period 4Period 4 Each element in this period has 4 Each element in this period has 4
regions of spaceregions of spacearound it for around it for electronselectrons
Period 5Period 5 Each element in this period has 5 Each element in this period has 5
regions of spaceregions of spacearound it for around it for electronselectrons
Period 6Period 6 Each element in this period has 6 Each element in this period has 6
regions of spaceregions of spacearound it for around it for electronselectrons
The Lanthanides are part of period 6The Lanthanides are part of period 6
Period 7Period 7 Each element in this period has 7 Each element in this period has 7
regions of spaceregions of spacearound it for around it for electronselectrons
The Actinides are part of period 7The Actinides are part of period 7
The periodic table can also show larger “Groups”
METALS Non-METALS
METALLOIDS
Tall columns are collectively Tall columns are collectively referred to as the “representative referred to as the “representative elements”elements”
Short, center groups are collectively Short, center groups are collectively referred to as the “transition referred to as the “transition elements”elements”
Two long rows on bottom are Two long rows on bottom are collectively referred to as the “inner collectively referred to as the “inner transition metals”transition metals”
Periodic Trends
Atomic SizeAtomic Size First problem where do you start First problem where do you start
measuring.measuring. The electron cloud doesn’t have a The electron cloud doesn’t have a
definite edge.definite edge. They get around this by measuring They get around this by measuring
more than 1 atom at a time.more than 1 atom at a time.
Atomic SizeAtomic Size
Atomic Radius = half the distance between Atomic Radius = half the distance between two nuclei of a diatomic molecule.two nuclei of a diatomic molecule.
}Radius
Trends in Atomic Size Trends in Atomic Size
Influenced by two factors.Influenced by two factors. Energy LevelEnergy Level Higher energy level is further away.Higher energy level is further away. Charge on nucleusCharge on nucleus More charge pulls electrons in More charge pulls electrons in
closer.closer.
Group Group trendstrends
As we go down a As we go down a groupgroup
Each atom has Each atom has another energy another energy level,level,
So the atoms get So the atoms get bigger.bigger.
HLi
Na
K
Rb
Periodic TrendsPeriodic Trends As you go across a period the radius As you go across a period the radius
gets smaller.gets smaller. Same energy level.Same energy level. More nuclear charge.More nuclear charge. Outermost electrons are closer.Outermost electrons are closer.
Na Mg Al Si P S Cl Ar