Johann Wolfgang Dobereiner’sJohann Wolfgang Dobereiner’s
Triads (1817)Triads (1817)
He grouped the elements, which
exhibit very similar characteristics
The atomic weight of the second
element was found to be the
average of the first and third
Atomic weight could be used to
determine the position of the
elements in the periodic table.
Berzelius (1828)Berzelius (1828)
published his table of atomic masses
containing 54 elements. Most of his
values conform with those in the
modern periodic table.
John Newlands (1864)John Newlands (1864)
an English chemist, arranged the
elements in an order of increasing
He arranged elements in groups
with seven members each similar to
the octave of the musical scale.
Referred to as Newlands’ Law of
Julius Lothar Meyer (1830-1895)Julius Lothar Meyer (1830-1895)
o He was working on his periodic table
consisting of 56 elements.
o He maintained that the properties of
the elements were functions of their
atomic mass and prepared a graph
wherein he plotted the atomic
volume of the elements against its
Dmitri MendeleevDmitri Mendeleev
In 1869, he created the first acceptedIn 1869, he created the first accepted
version of the periodic table.version of the periodic table.
He arranged the elements in order ofHe arranged the elements in order of
increasing atomic weight providingincreasing atomic weight providing
intervals on periods which were notintervals on periods which were not
always of the same length. always of the same length.
Blank spaces were left open to addBlank spaces were left open to add
the new elements he predicted wouldthe new elements he predicted would
The early periodic tables were
arranged according to increasing
atomic weights and this misplaced
several elements, such as Argon, Ar
(A= 40)and Potassium, K (A=39),
Cobalt, Co (A= 58.9) and Nickel, Ni
(A= 58.7), Tellerium, Te (A= 128) and
Iodine, I (A=127) in the periodic
Henry Moseley (1911)Henry Moseley (1911)
He suggested that it was the charge
of the nucleus and not the atomic
weight that accounted for the
periodic trends in the properties of the
elements. Thus, the position of
elements in the periodic table is
showed by the atomic number.
This concept gave rise to the Modern
The Modern Periodic LawThe Modern Periodic Law
states that there is a periodicstates that there is a periodic
repetition of chemical and physicalrepetition of chemical and physical
properties of the elements whenproperties of the elements when
they are arranged in increasingthey are arranged in increasing
atomic number.atomic number.
Features of the PeriodicFeatures of the Periodic
The periodic table is divided into
horizontal rows called PERIODS or
SERIES and the vertical columns are
called GROUPS or FAMILIES.
Periods are assigned in Arabic
numerals 1 to 7.
Families are assigned in Roman
numerals (paired with A or B)
IA to VIIIA and IB to VIIIB
Metals, Non-Metals andMetals, Non-Metals and
Elements can be classified as metals,
non-metals and metalloids.
Metals are elements that are good
conductors of heat and electricity,
generally shiny, solid at room
temperature, malleable and ductile.
Non-Metals are elements that are
poor conductors of electricity and
heat and generally gases and brittle
Metalloids are elements that exhibit
some properties of metals and
some properties of non-metals.
The elements in the periodicThe elements in the periodic
table divided into groupstable divided into groups
1.1. Main-group (representative)Main-group (representative)
2.2. Transition elementsTransition elements
3.3. Inner transition elementsInner transition elements
Alkali Metals (Li, Na, K, Rb, Cs, Fr)
The alkali family is found
in the first column of the
Alkali metals are found
in Group 1A or 1
Atoms of the alkali
metals have a single
electron in their
outermost level, in other
words, 1 valence
Alkali Metals They are the most
They react with
water to release
Alkali metals are
never found as
free elements in
nature. They are
Alkaline Earth Metals
(Be, Mg, Ca, Sr, Ba, Ra)
They are found in Group IIA or 2
They have two valence electrons.
They are very reactive, but not as much as
the alkali metals.
The Boron Family is
named after the first
element in the family.
They are found in
Group IIIA or 13.
Atoms in this family
have 3 valence
B, Al, Ga, In, Tl are
the elements belong
to the group.
Atoms of this family
have 4 valence
They found in Group IVA
This family includes C, Si,
Ge, Sn, Pb
The nitrogen family is
named after the
element that makes up
78% of our atmosphere.
They can be found in
Group VA or 15
Atoms in the nitrogen
family have 5 valence
electrons. They tend to
share electrons when
Other elements in this
family are phosphorus,
arsenic, antimony, and
Atoms of this family have
6 valence electrons.
They belong to Group VIA
Most elements in this
family share electrons
This family includes S, Se,
The elements in
this family are
They can be found
in Group VIIA or
Halogens have 7
They react with alkali
metals to form salts.
elements in the B
These are the metals
you are probably
most familiar: copper,
tin, zinc, iron, nickel,
gold, and silver.
They are good
conductors of heat
The compounds of transition metals are usually
brightly colored and are often used to color
Transition elements have 1 or 2 valence electrons,
which they lose when they form bonds with other
Noble Gases are colorless gases that are extremely
One important property of the noble gases is their
inactivity. They are inactive because their
outermost energy level is full.
Because they do not readily combine with other
elements to form compounds, the noble gases are
The family of noble gases includes helium, neon,
argon, krypton, xenon, and radon.
All the noble gases are found in small amounts in
the earth's atmosphere.
Rare Earth Elements
The thirty rare earth
composed of the
One element of the
and most of the
elements in the
actinide series are
means synthetic or
Electron Configurations and theElectron Configurations and the
Periodic TablePeriodic Table
Elements belonging to the same
group have the same number of
Elements belonging to the same
period have the same number of
The s, p, d and f blocks ofThe s, p, d and f blocks of
Elements are easily differentiated
from one another because of
differences in the number of their
The first 2 columns to the right of the
periodic table fill up the nsns orbitals
and are referred to as s-block
o The last 6 columns fill up the npnp
orbitals and are called the p-block
o Between the s-block and the p-block
elements are 10 columns which fill up
the (n-1)d orbitals. These are the d-
o On the lower part of the Periodic
Table are two series of elements
which fill up the (n-2) f orbital and are
called the f-block elements.
Predicting Periods and GroupsPredicting Periods and Groups
The period and groups of an element
can be predicted from the electron
configuration of that element.
The following guidelines can help in
determining the period and group of
If the electron configuration of the element ends in
s or p, then the element belongs to family A;
otherwise, the element belongs to family B.
The outermost energy of the element corresponds
to its period.
For an element belonging to family A, the number
of electrons in the outermost energy level
corresponds to the group of the elements.
For an element belonging to B (provided that the
electron configuration does not end in f the total
number of electrons in the outermost energy in
level and the incomplete inner sub-level is equal to
the group number except for the following sums
whose corresponding groups are indicated.
Noble Gas Core Notation
This is the shorthand way of writing
the electronic configuration of an
The noble gas that precedes a given
element is called the core element of
the given element.
Steps in Writing the Noble
1. Put symbol for noble gas from the
previous row in brackets.
2. Start at the beginning of the row
where the element is located.
3. Move to the right, writing down any
sublevels (blocks) that you move
Trends in theTrends in the
Periodic TablePeriodic Table
are specific patterns that are present
in the periodic table that illustrate
different aspects of a certain element,
including its size and its electronic
1. Atomic Size
Usually expressed as an atomic
radius measured in picometers.
Atomic radius is equal to half the
distance between the nuclei of two
atoms of the same element when
they are joined.
Atomic size increases as you move
down a group.
Going down a row adds another
energy level of electrons.
Atomic sizes decreases as you
move from left to right across a
Moving from left to right there is an
increase in protons causing greater
attraction to electrons.
2. Ionization Energy
is the energy required to remove
an electron from an atom.
-- when inner electrons block the
positive charge from outer
Ionization energy tends to
decrease down a group in the
The farther, the distance of an
electron from the nucleus the
more easily it can be removed.
Ionization energy tends to
increases from left to right across a
Atoms with fewer electrons hold
on to the more tightly.
is the ability of an atom to attract
electrons to itself.
Electronegativity decreases from
top to bottom and increases from
left to right of the periodic table.
4. Electron Affinity
is the amount of energy released or
exerted when an atom gains an
The electron affinity of an atom can be
described either as the energy gained
by an atom when an electron is added
Down a group the electron affinity of
the elements decreases.
Electron Affinity increases within a
5. Metallic Property
Within a period of the periodic
table, the elements become more
nonmetallic from left to right across
Within a group or from top to
bottom metallic properties
Periodic Properties of the elements
Atomic properties and the periodic table a summary