Classification of Elements 2 Flashcards
How would you justify the presence of 18
elements in the 5th period of the Periodic
Table?
When n=5, l = 0,1,2,3,4.
The orbitals that can be filled are 5s, 4d and 5p arrangedin orderof increaseing energy (aufbau order) 5s<4d<5p. Total umber of e-s accomodated in each subshell is 2, 10 and 6 respectively. total no of e-s present that can be accommodated is 18 and hence total number of elementa is 18.
how are the elements placed in a group similar
Elements in the same vertical column or group
have similar valence shell electronic
configurations, the same number of electrons
in the outer orbitals, and similar properties.
For example, the Group 1 elements (alkali
metals) all have ns1 valence shell electronic configuration as shown below. Thus it can be seen that the properties of
an element have periodic dependence upon its
atomic number and not on relative atomic
mass.
why do elements in the same group have similar properties
The elements in a vertical column
of the Periodic Table constitute a group or
family and exhibit similar chemical behaviour.
This similarity arises because these elements
have the same number and same distribution
of electrons in their outermost orbitals. We can
classify the elements into four blocks viz.,
s-block, p-block, d-block and f-block
depending on the type of atomic orbitals that
are being filled with electrons.
what is the helium anomaly?
Strictly, helium belongs to the
s-block but its positioning in the p-block along
with other group 18 elements is justified
because it has a completely filled valence shell
(1s2) and as a result, exhibits properties
characteristic of other noble gases.
what is the hydrogen anomaly
The other
exception is hydrogen. It has only one
s-electron and hence can be placed in group 1
(alkali metals). It can also gain an electron to
achieve a noble gas arrangement and hence it
can behave similar to a group 17 (halogen
family) elements. Because it is a special case,
we shall place hydrogen separately at the top
of the Periodic Table
describe the s block elements
The elements of group 1 ( alkali metals) and group 2 (alkaline earth metals) belong to s-block.
Their outermost electronic configuration is ns1 ( in case of grp 1) and ns2 ( in case of grp 2) where n=2-7.
They are all
reactive metals with low ionization enthalpies.
They lose the outermost electron(s) readily to
form 1+ ion (in the case of alkali metals) or 2+
ion (in the case of alkaline earth metals). The
metallic character and the reactivity increase
as we go down the group. Because of high
reactivity they are never found pure in nature.
The compounds of the s-block elements, with
the exception of those of lithium and beryllium
are predominantly ionic.
Most of these metals impart charcateristic colour their flame
They are excellent reducing agents ( since they lose e-s easily)
describe the s block elements
- The elements of group 1 ( alkali metals) and group 2 (alkaline earth metals) belong to s-block.
- Their outermost electronic configuration is ns1 ( in case of grp 1) and ns2 ( in case of grp 2) where n=2-7.
- They are all reactive metals with low ionization enthalpies.
- They lose the outermost electron(s) readily to
form 1+ ion (in the case of alkali metals) or 2+
ion (in the case of alkaline earth metals). - The metallic character and the reactivity increase as we go down the group.
- Because of high reactivity they are never found pure in nature.
- The compounds of the s-block elements, with
the exception of those of lithium and beryllium
are predominantly ionic. - Most of these metals impart charcateristic colour their flame
- They are excellent reducing agents ( since they lose e-s easily)
describe the p block elements
- Consists of elements from group 13 - group 18
- The outermost electronic configuration on the elements varies from ns2np1 to ns2np6 where ne2-7
- At the end of each period is a noble
gas element with a closed valence shell ns2np6
configuration. All the orbitals in the valence
shell of the noble gases are completely filled
by electrons and it is very difficult to alter this
stable arrangement by the addition or removal
of electrons. The noble gases thus exhibit very
low chemical reactivity. - Preceding the noble gas
family are two chemically important groups of
non-metals. They are the halogens (Group 17)
and the chalcogens (Group 16). These two
groups of elements have highly negative
electron gain enthalpies and readily add one
or two electrons respectively to attain the stable
noble gas configuration.
The non-metallic character incrases as we go left to right in the periodn and metallic charcater increases as we go down a group.
Their electron gain enthalipes are extremely high when compared to s-block elements. They are good oxidisng agents as they readily gain e-s. They exhibit various oxidation states. They mainly form covalent cpds.
Their oxidisng character increases from left to right in a period and their reducing character increases from top to bottom.
describe the d-block elements
- d-Block elements consists of groups 3-12
- They are characterised by the filling of the inner d- orbitals by electrons and hence the name
- Have geenral outer electronic configuration as
(n-2) d1-10 ns0-2 - The are all metals( hard,malleable,ductile, high mpt and bpt)
- They form coloured ions, exhibit variable oxidn states and paramagnetism( strongly attracted to magnets, due the presence of unpaired e-s)
- they form alloys and used as catlaysts
- hoever, zinc,cadmium and mercury which have outer eln cnfg as (n-1)d10ns2 do not share most of the propoerties that the d-block elemeents have.
- These elements form a transition from the highly reactuve s-block elements to the less reactive metals of the groups 13-14 and hence are commonly referred to as transition elements.
What are the f-block element s
- The two rows of elements at the bottom of the
Periodic Table, called the Lanthanoids,
Ce(Z = 58) – Lu(Z = 71) and Actinoids,
Th(Z = 90) – Lr (Z = 103) are characterised by
the outer electronic configuration
(n-2)f
1-14(n-1)d0–1ns2
. The last electron added to each
element is filled in f- orbital. - These two series
of elements are hence called the Inner-
Transition Elements (f-Block Elements).
They are all metals.
Within each series, the
properties of the elements are quite similar. The
chemistry of the early actinoids is more
complicated than the corresponding
lanthanoids, due to the large number of
oxidation states possible for these actinoid
elements.
Actinoid elements are radioactive.
Many of the actinoid elements have been made
only in nanogram quantities or even less by
nuclear reactions and their chemistry is not
fully studied.
The elements after uranium(92) are
called Transuranium Elements.
what are representative or main group elements
Elements of sblock and pblock
write a short note on metals
Metals
comprise more than 78% of all known elements
and appear on the left side of the Periodic
Table. Metals are usually solids at room
temperature [mercury is an exception; gallium
and caesium also have very low melting points
(303K and 302K, respectively)]. Metals usually
have high melting and boiling points. They are
good conductors of heat and electricity. They
are malleable (can be flattened into thin sheets
by hammering) and ductile (can be drawn into
wires).
write a short note on non-metals
In contrast, non-metals are located at
the top right hand side of the Periodic Table.
In fact, in a horizontal row, the property of
elements change from metallic on the left to
non-metallic on the right. Non-metals are
usually solids or gases at room temperature
with low melting and boiling points (boron and
carbon are exceptions). They are poor
conductors of heat and electricity. Most non-
metallic solids are brittle and are neither
malleable nor ductile. The elements become
more metallic as we go down a group; the non-
metallic character increases as one goes from
left to right across the Periodic Table.
what are semi-metals or metalloids
The elements (e.g., silicon,
germanium, arsenic, antimony and tellurium)
bordering this line and running diagonally
across the Periodic Table show properties that
are characteristic of both metals and non-
metals. These elements are called Semi-metals
or Metalloids.
