PERIODIC TABLE OF ELEMENTS
In 1869, Mendelee a Russian
scientist was the first to construct table. But he arranged the element in
other of increasing on atomic mass. He pointed out that element with similar property
kept re-occurring at regular interval or period.
The
mendelee periodic table had may gapes which he predicted that there were
un-discovered element which will these gapes, he even predicts the possible property
of that element. But with the discovery of the electronic structure, it became
clear that element do not vary with their atomic mass but atomic number. They even
found a new element e.g. scandium, gallium etc. which have the predicted property
of mendelee.
Therefore, the modern periodic law
states that element are arranged according to their atomic number.
However,
the following are the terminology to understand when dealing with periodic
table.
GROUP
This can easily be known as the vertical
column of element which comprise eight columns in periodic table ranges from
0-7.
Note: element in the same group
must have the number of valency electron at their outermost shell.
However, the element hydrogen does
not fit to belong to any group, but for convenience, it is placed in group one
of because of its lone electron.
In
group 0, helium has two electrons while other have eight electrons each in
which they are un=reactive element known as rare or noble gas because of their
complete shell when configured.
In
between group 2 and 3, there are some sets of elements lying within called
transition group of element.
PERIOD
This
can be best described as the horizontal row of element on the periodic table
which are numbered from 1 – 7. However, element in the same period have the
same number of electron shell or orbital. Example, element in period 2 have two
electron shell (K L).
Note: the number of valency
electron increased by one across the period provided they are in the same
period from left to right.
PROPERTIES OF A PERIODIC TABLE
1. Atomic
and ionic size: Atomic size can be easily means atomic radius i.e. distance
between nucleus to the electron revolving around the orbit or shell/. It can
also be defined as one half the distance closest approach between the nucleus
of atom in the element substances
2. IONIC
SIZE: These are also similar to that of atomic size but it will be measured by
the distance between the center of one ion and the center of its nearest neighbor
of opposite charge.
This property shows ionic radius decrease across the
period while it increases down the groups as an increase in atomic number.
3. MELTING
AND BOILNG POINT: Discovery from periodic table shows that some element are
metals, metalloids and non-metal. Hence, element in group 1. 2, 3, have strong
metallic ability i.e. metallic bond that will held them together. Therefore, their
melting and boiling are very high.
Note: Group 4 element shows high melting and boiling
point because the element has simple covalent bond that interlink the atoms
together to form giant three-dimensional crystalline lattice e.g. diamond.
4. Electrical
and thermal conductivity: they decrease across the period and increase down
the group
5. IONIZATION
ENERGY: they are energy requires to remove a valency electron from an atom of elements
to form an ion. Thus, ionization energy increase across a period and decrease
down the group.
6. ELECTRON
AFFINITY: These are the energy required to gain a valency electron from an atom
of the element to form univalent negative electron. Thus electron affinity decreases
across the period while it increased down the group.
7. ELECTRON
GRAVITY: it is the power of that atom in is molecule to attract electron. Thus it
increases across the period and decrease down a group. The most electro
negative elements are F, Cl, Br, I
BRIEF PROPERTIES OF FAMILIES OF ELEMENT.
GROUP 1 ELEMENT
All
element that belong to these group have similar behavior e.g. Na, K, L, are the
similar one. They are known as ALKALI
METALS.
FEAUTRES OF GROUP 1 ELEMENT
1.
They are univalent element since they have one
valency electron at their outermost shell.
2.
They are family of electrovalent when they are ionized
3.
They are good reducing agent
4.
They are good conductor of electricity
5.
They are electropositive i.e. they donate
electron
K+
Na+
6.
They react with cold water vigorously to liberate
hydrogen and form alkalis
FEATURES OF GROUP 2 ELEMENT
1.
They are divalent element
2.
They form electrovalent
3.
They are reducing agent
4.
The most familiar ones are calcium and magnesium
5.
They are also referred to as ALKALINE EARTH
METAL
FEATURES OF GROUP 3 ELEMENT
1. They
are trivalent
2. Its
reducing agent is nil.
3. Their
oxide is insoluble in water
4. Aluminum
as a member react with steam above 600 Celsius to liberate hydrogen
5. Both
oxide and hydroxide are amphoteric in nature
FEAUTRES OF GROUP 4 ELEMENT
1.
They are tetravalent element
2.
They are increased in metallic property down the
group
3.
They have oxidation number of t2 and t4
4.
Carbon and silicon as a member form covalent
compound with hydrogen e.g. CH4
5.
Carbon does not react with water in any form
FEATURES OF GROUP 5 ELEMENT
1.
They are non-metallic i.e. they cannot conduct
electricity
2.
They have two oxidation number of t3 and t5 from
several oxides which have parallel characteristics e.g.
N2O3 Nitrogen(III)oxide
P4O6 Phosphorus (III)oxide
N2O5 Nitrogen(V)oxide etc.
NOTE: They are all acidic and will combined with water to form acid.
FEATURES OF
GROUP 6 ELEMENT
The most common element in this group are oxygen and they
exhibit some characteristics both physically and chemically.
1.
They are electron acceptor
2.
Oxygen as a member is slightly soluble in water
while Sulphur as a member is insoluble.
3.
Both oxygen and Sulphur react directly with
hydrogen to yield water and hydrogen, sulphide respectively
FEATURES OF GROUP SEVEN ELEMENT
The element in this group are referred
to as HALOGEN FAMILY. They are most reactive non-metals. There features
as follows
1. They are
all non-metals
2. They are
diatomic molecules
3. They are
coloured
4. They ionize
to form univalent negative ions
5. Their electronegativity
decreases down the group
6. Their melting
and boiling point increased progressively
FEATURES OF GROUP 0 ELEMENTS (SOME
MAY REFERRED TO THIS AS GROUP 8)
This group are known as rare or noble gases.
1. They have
no bonding electron at their outer most shell
2. They are
radiative element
3. Their melting
and boiling point increase down the group
4. Their ionization
energy decreases down the group
5. They consist
about 1% of composition of air
TRANSITION ELEMENT
FEATURES
They are all elements found within
group 2 and 3
1. They are
all metallic and possess all metallic properties
2. They are
coloured ionize
3. They can
form complex ion.
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