Gist of Lesson for Quick Revision (By
JSUNIL)1. Periodic table: The table which classifies all the known elements on the basis of their properties in such a way that elements with similar properties are grouped together.
The first classification of elements was as metals and non-metals.
In 1789, Lavoisier first attempted to classify the elements into two divisions namely Metals and Non-metals
This served only limited purpose mainly because of two reasons:
(i). All the elements were grouped in to these two classes only. The group containing metals was very big.
(ii) Some elements showed properties of both-metals and non-metals and they could not be placed in any of the two classes.
2. All earlier attempts on the classification
of the elements were based on their atomic weights.
3. The first attempt towards the
classification of elements was made by Johann Dobereiner, a German chemist in
1829. He made sets of three elements which showed similar chemical properties and
he called it triads. as
their oxide are alkalies in nature and exist in the Earth
12. No Place were given for forth coming elements by Newland.
13. . Newland placed unlike elements in same slot like Co and Ni placed with F ,
Cl and Iodine
14. When Nobel gases were discovered in 1900 law of octave fail and
9th element became similar to 1st. in Newland Octave
4. The Triad was approximately the
mean of the atomic weights of the other two members and the properties of the
middle element were in between those of the other two members.
5. The
average of the atomic masses of Li and K =1/2(7+39 )= 23 (Na)
5. The major drawback of Dobereiner
classification was that the concept of triads could be applied to limited
number of elements. It was also possible to group quite dissimilar elements
into triads.
6. Lithium, Sodium, Potassium are called Alkalies
metal as they react with water and form alkalies (Caustic solution)
7.
Calcium, Strontium, Bromine are called Alkalies
Earth metal as they react with water and form salt and exist in the Earth.
8.
Chlorine, Bromine, Iodine are called Halogen as they are reactive non-metallic elements which form strongly acidic compounds with hydrogen from which simple salts can be made.
9. In
1864 John Alexander Newland, an English chemist noticed that “when elements
are arranged in the increasing order of their atomic masses. He found
that "every eighth element had properties similar to the first
element.”
10. Newland called this as the Law of Octaves
due to its similarity with musical notes .
11. Newland could arrange elements in this
manner only up to calcium (atomic mass 40 ) out of a total of over sixty
elements known at his time.
15. Doberenier‘s
triads also exist in the column of Newland octaves like Li, Na, K.
16. In1869 Mendeleev
a Russian chemist while trying to classify elements discovered that on
arranging in the increasing order of atomic mass, elements with similar
chemical properties occurred periodically.
17. A periodic function is the
one which repeats itself after a certain interval.
18. According to the periodic
law : The chemical and physical properties of elements are a periodic function
of their atomic masses.
19. Mendeleev believed that
atomic mass of elements was the most fundamental property. A tabular
arrangement of the elements based on the periodic law is called periodic table.
20. The Seven horizontal rows
present in the periodic table are called periods.
21. Properties of elements in
a particular period increase or decrease
from left to right.
22. The nine vertical columns
present in it are called groups and are
numbered from I to VIII and Zero (Roman numerals).
23. Mendeleev’s periodic table
had some blank spaces for undiscovered elements
24. Scandium, gallium and
germanium, discovered later, have properties similar to Eka – boron, Eka–aluminium
and Eka–silicon, respectively.
25. The Mendellev's periodic
table helped in correcting the atomic masses of some elements based on their
positions in the table.
26. Atomic mass of beryllium
was corrected from 13.5 to 9. With the help of this table, atomic masses of
indium, gold, platinum etc., were corrected.]
27. Mendeleev fail to give fixed position to hydrogen in
the Periodic Table. It was placed in group IA and group VI B.
28. Hydrogen resembled both the
alkali metals and the halogens. So, it was placed above both the groups and
could not be given a fixed position in Mendeleev’s Periodic Table.
29.
There is no place given for isotopes in Mendeleev’s Periodic Table
30. Different isotopes of same
elements have different atomic masses; therefore, each one of them should be
given a different position in the periodic table. On the other hand, because
they are chemically similar, they had to be given same position.
31. There are anomalous pairs of
elements in Mendeleev’s Periodic Table : At certain places, an element of
higher atomic mass has been placed before an element of lower atomic mass. For
example, Argon (39.91) is placed before potassium (39.1)
32. Disimilar elements placed together:
Noble metals like Cu, Ag and Au are placed along with chemically dissimilar
alkali metals in Group I . Similarly, Mn possessing very few similarities with
halogens have been placed in VII group.
33. Similar elements separated: In
Mendeleev's periodic table, certain chemically similar elements such as copper
and mercury; gold and platinum have been placed in different groups.
34. Anomalous pairs : In the
Mendeleev's Table based on atomic weight, the positions of certain pairs , e.g.
Argon( at. wt = 39.94) and potassium ( at. wt = 39.1) : Cobalt( at wt =58.93 )
and nickel ( at wt = 58.71 ) ; Tellurium at wt = 127.60) and iodine (atomic
weight = 126.90 ) would be reversed. In other words, certain pairs of elements
are misfit in the periodic table, if atomic weight is the basis of
classification.
35. The formulae for the oxides of
the following elements: K, C, AI, Si, Ba. according to Mendeléev’s Periodic
Table are: K(potassium) belongs to group
I. Thus, formula of its oxide is K2O, similarly CO2, Al2O3, SiO2,, BaO.
36. The criteria used by Mendeleev in creating his periodic
table are:
(1) The chemical and physical properties of an element is the
periodic function of its atomic mass
.(ii) The elements were arranged in a
period such that their properties changed from metallic to non-metallic.(iii)
The elements were arranged in groups, such that all the elements have same, but
graded physical and chemical properties.
37. The noble gases are placed in a separate group because (a)
Noble gases are chemically inactive and hence constitute a separate group.(b)2.
Noble gases as a group offer a perfect dividing line for starting a new period
in the periodic table.
38. Moseley showed that the atomic number of an element is a
more fundamental property. The ModernPeriodic Law can be stated as : ‘Properties of elements are a
periodic function of their atomic number.’
39. The Modern Periodic Table has 18 vertical columns known as
‘groups’ and 7 horizontal rows known as ‘periods’.
40. The elements present in any one group have the same
number of valence electrons. The number of electrons in the valence shell
determines the group of the element. If the element has 1 or 2 electrons, then
it belongs to group 1 or 2, respectively. If the element has 3 to 8 electrons,
then its group is equal to 10 + number of valence electrons.
41. Elements with the same number
of occupied shells are placed in the same period. For example, if an element has 4
electron shells, it belongs to the 4th period.
42. The atomic size depends on the
distance between the centre of the nucleus and the outermost shell of an
isolated atom.
43. The atomic radius decreases in moving
from left to right along a period. This is due to an increase in nuclear
charge (increase in no. of proton without increasing shell) which tends to pull
the electrons closer to the nucleus and reduces the size of the atom.
44. The atomic size increases
down the group. This is because new shells are being added as we go down
the group. This increases the distance between the outermost electrons and the
nucleus so that the atomic size increases in spite of the increase in nuclear
charge.
45. The valencies of all elements
of the same group are the same. The valence of an element with respect to
oxygen is equal to its group number.
46. The melting points and boiling
points decrease while moving down in group of metals.
47. The melting points and boiling
points increases while moving down in group of non-metals.
48. Metallic character of
the element decreases along a period because the effective nuclear charge
acting on the valence shell electrons increases due to decrease in atomic size.
49. Metallic character of
the element Increases while moving down in group because the effective nuclear charge
experienced by valence electrons is decreasing as the outermost electrons are
farther away from the nucleus(due to increase in atomic size).
50. Metals tend to lose electrons
while forming bonds. That is why they
are electropositive in nature.
51. Non-metals are electronegative as
they tend to form bonds by gaining electrons.
52. The tendency to gain electrons increases
in a period due to decrease in atomic
size.
53. The tendency to lose electrons increases
in a group due to increase in atomic
size
54. Non metallic character decreases
down in group because of decrease in tendency to gain electron which is due to increase
in atomic size.
55. Non metallic character increases
left to right in group because of increase in tendency to gain electron which
is due to decrease in atomic size.
The first classification of elements was as metals and non-metals.
This served only limited purpose mainly because of two reasons:
(i). All the elements were grouped in to these two classes only. The group containing metals was very big.
12. No Place were given for forth coming elements by Newland.
13. . Newland placed unlike elements in same slot like Co and Ni placed with F , Cl and Iodine
14. When Nobel gases were discovered in 1900 law of octave fail and 9th element became similar to 1st. in Newland Octave
4. The Triad was approximately the mean of the atomic weights of the other two members and the properties of the middle element were in between those of the other two members.
5. The average of the atomic masses of Li and K =1/2(7+39 )= 23 (Na)
6. Lithium, Sodium, Potassium are called Alkalies metal as they react with water and form alkalies (Caustic solution)
8. Chlorine, Bromine, Iodine are called Halogen as they are reactive non-metallic elements which form strongly acidic compounds with hydrogen from which simple salts can be made.
9. In 1864 John Alexander Newland, an English chemist noticed that “when elements are arranged in the increasing order of their atomic masses. He found that "every eighth element had properties similar to the first element.”
10. Newland called this as the Law of Octaves due to its similarity with musical notes .
11. Newland could arrange elements in this manner only up to calcium (atomic mass 40 ) out of a total of over sixty elements known at his time.
15. Doberenier‘s triads also exist in the column of Newland octaves like Li, Na, K.
16. In1869 Mendeleev a Russian chemist while trying to classify elements discovered that on arranging in the increasing order of atomic mass, elements with similar chemical properties occurred periodically.
18. According to the periodic law : The chemical and physical properties of elements are a periodic function
19. Mendeleev believed that atomic mass of elements was the most fundamental property. A tabular arrangement of the elements based on the periodic law is called periodic table.
20. The Seven horizontal rows present in the periodic table are called periods.
21. Properties of elements in a particular period increase or decrease from left to right.
22. The nine vertical columns present in it are called groups and are numbered from I to VIII and Zero (Roman numerals).
23. Mendeleev’s periodic table had some blank spaces for undiscovered elements
24. Scandium, gallium and germanium, discovered later, have properties similar to Eka – boron, Eka–aluminium and Eka–silicon, respectively.
25. The Mendellev's periodic table helped in correcting the atomic masses of some elements based on their positions in the table.
26. Atomic mass of beryllium was corrected from 13.5 to 9. With the help of this table, atomic masses of indium, gold, platinum etc., were corrected.]
27. Mendeleev fail to give fixed position to hydrogen in the Periodic Table. It was placed in group IA and group VI B.
28. Hydrogen resembled both the alkali metals and the halogens. So, it was placed above both the groups and could not be given a fixed position in Mendeleev’s Periodic Table.
29. There is no place given for isotopes in Mendeleev’s Periodic Table
30. Different isotopes of same elements have different atomic masses; therefore, each one of them should be given a different position in the periodic table. On the other hand, because they are chemically similar, they had to be given same position.
31. There are anomalous pairs of elements in Mendeleev’s Periodic Table : At certain places, an element of higher atomic mass has been placed before an element of lower atomic mass. For example, Argon (39.91) is placed before potassium (39.1)
32. Disimilar elements placed together: Noble metals like Cu, Ag and Au are placed along with chemically dissimilar alkali metals in Group I . Similarly, Mn possessing very few similarities with halogens have been placed in VII group.
33. Similar elements separated: In Mendeleev's periodic table, certain chemically similar elements such as copper and mercury; gold and platinum have been placed in different groups.
34. Anomalous pairs : In the Mendeleev's Table based on atomic weight, the positions of certain pairs , e.g. Argon( at. wt = 39.94) and potassium ( at. wt = 39.1) : Cobalt( at wt =58.93 ) and nickel ( at wt = 58.71 ) ; Tellurium at wt = 127.60) and iodine (atomic weight = 126.90 ) would be reversed. In other words, certain pairs of elements are misfit in the periodic table, if atomic weight is the basis of classification.
35. The formulae for the oxides of the following elements: K, C, AI, Si, Ba. according to Mendeléev’s Periodic Table are: K(potassium) belongs to group I. Thus, formula of its oxide is K2O, similarly CO2, Al2O3, SiO2,, BaO.
37. The noble gases are placed in a separate group because (a) Noble gases are chemically inactive and hence constitute a separate group.(b)2. Noble gases as a group offer a perfect dividing line for starting a new period in the periodic table.
38. Moseley showed that the atomic number of an element is a more fundamental property. The ModernPeriodic Law can be stated as : ‘Properties of elements are a periodic function of their atomic number.’
39. The Modern Periodic Table has 18 vertical columns known as ‘groups’ and 7 horizontal rows known as ‘periods’.
40. The elements present in any one group have the same number of valence electrons. The number of electrons in the valence shell determines the group of the element. If the element has 1 or 2 electrons, then it belongs to group 1 or 2, respectively. If the element has 3 to 8 electrons, then its group is equal to 10 + number of valence electrons.
41. Elements with the same number of occupied shells are placed in the same period. For example, if an element has 4 electron shells, it belongs to the 4th period.
42. The atomic size depends on the distance between the centre of the nucleus and the outermost shell of an isolated atom.
43. The atomic radius decreases in moving from left to right along a period. This is due to an increase in nuclear charge (increase in no. of proton without increasing shell) which tends to pull the electrons closer to the nucleus and reduces the size of the atom.
44. The atomic size increases down the group. This is because new shells are being added as we go down the group. This increases the distance between the outermost electrons and the nucleus so that the atomic size increases in spite of the increase in nuclear charge.
45. The valencies of all elements of the same group are the same. The valence of an element with respect to oxygen is equal to its group number.
46. The melting points and boiling points decrease while moving down in group of metals.
47. The melting points and boiling points increases while moving down in group of non-metals.
48. Metallic character of the element decreases along a period because the effective nuclear charge acting on the valence shell electrons increases due to decrease in atomic size.
49. Metallic character of the element Increases while moving down in group because the effective nuclear charge experienced by valence electrons is decreasing as the outermost electrons are farther away from the nucleus(due to increase in atomic size).
50. Metals tend to lose electrons while forming bonds. That is why they are electropositive in nature.
52. The tendency to gain electrons increases in a period due to decrease in atomic size.
53. The tendency to lose electrons increases in a group due to increase in atomic size
54. Non metallic character decreases down in group because of decrease in tendency to gain electron which is due to increase in atomic size.
55. Non metallic character increases left to right in group because of increase in tendency to gain electron which is due to decrease in atomic size.
Periodic properties
|
Left to right in period
|
Down a group
|
Atomic size
|
Decreasing
|
Increasing
|
Tendency to lose Electron
|
Decreasing
|
Increasing
|
Tendency to gain Electron
|
Increasing
|
Decreasing
|
Metallic Character
|
Decreasing
|
Increasing
|
Non - metallic Character
|
Increasing
|
Decreasing
|
Distance b/w Valance Electron and Nucleus
|
Decreasing
|
Increasing
|
Force of attraction b/w Valance Electron and Nucleus
|
Increasing
|
Decreasing
|
56. Alkali Metals: Lithium, sodium,
potassium, rubidium, caesium and francium have one electron in the valence shell.
They are called alkali metals because their hydroxides are strong alkalis.
57. Halogens: The elements placed in group 7 (VIIA) and have seven
electrons in their valence shell and so are mononvalent.All these elements form
salts called halides, e.g. NaCl, NaI, KCl, KI etc. Halogen is an ancient Greek
word meaning 'salt producer.
58. Transition Elements: Elements belonging to 3 to 12 groups are called
transition elements. They are called transition elements because they are
placed between the most reactive metals on the left and non-metals on the
right.
59. Inner-transition Elements:
The 6th period consists of elements that
have atomic numbers 58 to 71. They are called Lanthanides.
The 7th period
consists of elements that have atomic numbers 90 to 105. They are called
Actinides. Both of them are called inner transition elements.
60. The group VIA elements are called chalcogens because most ores
of copper (Greek chalkos) are oxides or sulfides, and such ores contain traces
of selenium and tellurium.
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