Telluric screw
Alexander-Emile, a French geologist, was the first person to notice the periodicity of the elements, similar elements occurring at regular intervals when they are ordered by their atomic weights. In 1862 he gave an early form of periodic table, which he named the 'telluric helix', after the element Tellurium, which fell near the center of the diagram. With the elements arranged in a spiral on a cylinder by order of increasing atomic weight, Chancourtois saw that elements with similar properties lined up vertically.
Chancourtois plotted the atomic weights on the surface of a cylinder with a circumference of 16 units, the approximate atomic weight of oxygen. The resulting helical curve, which Chancourtois called a square circle triangle, brought similar elements onto corresponding points above or below one another on the cylinder. He was the first scientist to see the periodicity of elements when they were arranged in order of their atomic weights. He found out that the similar elements occurred at regular atomic weight intervals.
Chancourtois plotted the atomic weights on the surface of a cylinder with a circumference of 16 units, the approximate atomic weight of oxygen. The resulting helical curve, which Chancourtois called a square circle triangle, brought similar elements onto corresponding points above or below one another on the cylinder. He was the first scientist to see the periodicity of elements when they were arranged in order of their atomic weights. He found out that the similar elements occurred at regular atomic weight intervals.
History of Classification of Elements
In 1789, Antoine Lavoisier made the earliest attempt to classify the elements. He grouped the elements based on their properties. Several other attempts were made to group elements together over the coming decades. In 1829, Johann Dobereiner recognized triads of elements with chemically similar properties.
Earlier attempts for classification of elements
As different elements were being discovered, scientists gathered more and more information about the properties of these elements. They found it difficult to organise all that was known about the elements. They started looking for some pattern in their properties, on the basis of which they could study such a large number of elements with ease.After a number of attempts finally, modern periodic table was prepared which was the team work under the guidance of Moseley.
Dobereiner's Triad
Dobereiner arranged the element in increasing order of atomic masses. He found that the atomic mass of the middle element was approximately equal to the arithmetic mean (average) of the atomic masses of the other two elements of that triad when they are arranged in their increasing order of atomic mass,
e.g., Li, Na, K. The atomic mass of Li is 9 and K is 39. The average of two atomic number is 23 that is the atomic number of sodium.
e.g., Li, Na, K. The atomic mass of Li is 9 and K is 39. The average of two atomic number is 23 that is the atomic number of sodium.
Mendeleev's Periodic Table
Mendeleev's Periodic law: Physical ,and chemical properties of elements are a periodic function of their atomic masses. Periodic table is a chart of elements prepared in such a way that elements with similar properties occur in the same vertical column. It has seven horizontal rows and eight vertical columns.
Characteristics of mandeleev's periodic table
1.Elements were arranged in order of their increasing atomic weights in horizontal rows called periods.
2.Elements were arranged in vertical columns called groups according to their resemblance in properties.
3. The periodic table had 8 groups and 7 periods.
4.Since only 63 elements were known at that time, he had left gaps for undiscovered elements.
2.Elements were arranged in vertical columns called groups according to their resemblance in properties.
3. The periodic table had 8 groups and 7 periods.
4.Since only 63 elements were known at that time, he had left gaps for undiscovered elements.
Achievements of Mendeleev's Periodic Table
1. There was grouping of elements according to the chemical properties.
2. The periodic table has gaps for the undiscovered elements.
3. The prediction of properties of undiscovered elements were correct.
4. It helped in systematic study of elements
2. The periodic table has gaps for the undiscovered elements.
3. The prediction of properties of undiscovered elements were correct.
4. It helped in systematic study of elements
Limitation of Mendeleev's classification
Mendeleev's periodic table suffered few defects as follows:
The position of hydrogen was not correctly defined.
In some cases, Mendeleev placed elements according to their similarities in properties and not in increasing order of their atomic masses. Thus, the position of these elements was not justified
Isotopes were not given separate places in the periodic table although Mendeleev's classification is based on the atomic masses.
Some similar elements were grouped separately while some dissimilar elements were grouped together.
Mendeleev could not explain the cause of periodicity in the elements.
The position for lanthanides and actinides were not included in this table.
The position of hydrogen was not correctly defined.
In some cases, Mendeleev placed elements according to their similarities in properties and not in increasing order of their atomic masses. Thus, the position of these elements was not justified
Isotopes were not given separate places in the periodic table although Mendeleev's classification is based on the atomic masses.
Some similar elements were grouped separately while some dissimilar elements were grouped together.
Mendeleev could not explain the cause of periodicity in the elements.
The position for lanthanides and actinides were not included in this table.
Occurrence of Elements in Earth’s Crust
The most abundant element in the earth's crust is oxygen, making up 46.6% of the earth's mass. Silicon is the second most abundant element (27.7%), followed by aluminum (8.1%), iron (5.0%), calcium (3.6%), sodium (2.8%), potassium (2.6%). and magnesium (2.1%). These eight elements account for approximately 98.5% of the total mass of the earth's crust.
Occurrence of Elements in Atmosphere
The atmosphere is composed of several gases in a certain amount. Nitrogen accounts for 78% of the atmosphere, oxygen 21%, and argon 0.9%. Carbon dioxide accounts for about a 90% of the 0.1% trace gases. Water vapor concentration varies from 0-4% of the atmosphere depending upon location and time.
Features of long form of periodic table
1. 18 vertical columns known as groups.
2. 7 Horizontal rows known as periods.
3. Light metals These are elements of periodic table of group 1 and 2.
4. Heavy metals or Transition metals - These are elements of periodic table of group 3, 4, 5, 6, 7, 8, 9, 10, 11 and 12.
5. Non-Metals These are elements of periodic table of group 13, 14, 15, 16 and 17.
6. Zero group These are elements of periodic table of group 18.
2. 7 Horizontal rows known as periods.
3. Light metals These are elements of periodic table of group 1 and 2.
4. Heavy metals or Transition metals - These are elements of periodic table of group 3, 4, 5, 6, 7, 8, 9, 10, 11 and 12.
5. Non-Metals These are elements of periodic table of group 13, 14, 15, 16 and 17.
6. Zero group These are elements of periodic table of group 18.
Modern Periodic Table
There are 18 vertical columns in the periodic table. Each column is called a group. All elements in a group have similar chemical and physical properties because they have the same number of outer electrons.
In periodic table elements are arranged in a series of rows. Elements of the same period have the same number of electron shells.
In periodic table elements are arranged in a series of rows. Elements of the same period have the same number of electron shells.
Position of Elements in the Periodic Table
Location of Metals, Non-metals, Metalloids and Noble Gases are as follows:
- Elements on the left and middle are Metals
- Elements on the right are Non-metals
- Metalloids form the narrow stair-step area between metals and non-metals
- The last group (18) to the right are Noble gases
Moseley's Periodic table
Moseley found and measured a property linked to Periodic Table position. Hence atomic number became more meaningful and the three pairs of elements that seemed to be in the wrong order could be explained. Moseley used what was then brand-new technology in his experiments. A device now called an electron gun had just been developed. He used this to fire a stream of electrons (like machine gun bullets) at samples of different elements. He found that the elements gave off X-rays. (This is how the X-rays used in hospitals are produced.)
Moseley measured the frequency of the X-rays given off by different elements. Each element gave a different frequency and he found that this frequency was mathematically related to the position of the element in the Periodic Table he could actually measure atomic number. Moseley plotted the square root of the X-ray frequency against atomic number.
Moseley measured the frequency of the X-rays given off by different elements. Each element gave a different frequency and he found that this frequency was mathematically related to the position of the element in the Periodic Table he could actually measure atomic number. Moseley plotted the square root of the X-ray frequency against atomic number.
Determine the period number of elements
All of the elements in a period have the samenumber of atomic orbitals. For example, every element in the top row (the first period) has one orbital for its electrons. All of the elements in the second row (the second period) have two orbitals for their electrons.
Determine the group number of elements
The group number is an identifier used to describe the column of the standard periodic table in which the element appears. Groups 1-2 (except hydrogen) and 13-18 are termed main group elements. Groups 3-11 are termed transition elements.
Electronic configuration of Sodium is 2, 8, 1. So the number of group is 1
Electronic configuration of Sodium is 2, 8, 1. So the number of group is 1
Group number in a periodic table
1. In any group, outermost shell electron are known as valance electrons and these electrons are same so main properties of elements of group is similar.
2. Elements are divided into four blocks, which is s, p, d, f according to valance electrons.
3. s-block elements elements of 1 and 2 group.
4. p-block elements elements of 13 to 18 group.
5. d-block elements elements of 3 to 12 group.
6. f-block elements elements of the Lanthanide and Actinide series.
7. Representative Elements elements of s-block and p-block collectively called as Representative elements also known as Normal elements or Typical elements.
8. Transition Elements elements of d-block.
9. Inner Transition Elements elements of f-block, also known as Rare Earth Elements.
10. Alkali Metals elements of 1st group.
11. Alkaline Earth Metas elements of 2nd group.
2. Elements are divided into four blocks, which is s, p, d, f according to valance electrons.
3. s-block elements elements of 1 and 2 group.
4. p-block elements elements of 13 to 18 group.
5. d-block elements elements of 3 to 12 group.
6. f-block elements elements of the Lanthanide and Actinide series.
7. Representative Elements elements of s-block and p-block collectively called as Representative elements also known as Normal elements or Typical elements.
8. Transition Elements elements of d-block.
9. Inner Transition Elements elements of f-block, also known as Rare Earth Elements.
10. Alkali Metals elements of 1st group.
11. Alkaline Earth Metas elements of 2nd group.
Trends in different properties of elements in a periodic table
In periodic table elements are placed in periods and groups.In periods like atomic number increases but electrons enters in same shell hence atomic size do not increases on moving Left to Right in periods but in group as atomic number increases number of electrons enters into new shells hence atomic size increases.
Long form of periodic table
The periodic table is a tabular arrangement of the chemical elements, ordered by their atomic number , electron configuration, and recurring chemical properties. This ordering shows periodic trends such as elements with similar behavior in the same column. It also shows four rectangular blocks with some approximately similar chemical properties. In general, within one row (period) the elements are metals on the lefthand side, and non-metals on the righthand side.
The rows of the table are called periods, the columns are called groups. Six groups (columns) have names as well as numbers: for example, group 17 elements are the halogens and group 18, the noble gases. The periodic table can be used to derive relationships between the properties of the elements, and predict the properties of new elements yet to be discovered or synthesized.
The rows of the table are called periods, the columns are called groups. Six groups (columns) have names as well as numbers: for example, group 17 elements are the halogens and group 18, the noble gases. The periodic table can be used to derive relationships between the properties of the elements, and predict the properties of new elements yet to be discovered or synthesized.
Cause of periodicity
The modern periodic table is based on the electronic configuration of the elements. The properties of an element are determined largely by the electrons in its outermost or valence shell. Valence electrons interact with other atoms and take part in all chemical reactions, while inner shell electrons have little influence on the properties of elements. When elements are placed in the order of their increasing atomic number, the elements having the same number of valence shell electrons is repeated in such a way, so as to fall under the same group. Since, the electronic configuration of the valence shell electrons is same they show similar properties.
Method of prediction of period , group
By knowing the electronic configuration. example: sodium(atomic no-11)-
electronic configuration 2 , 8 , 1. Sodium have one electron in the last orbit hence it is the member of first group. There are 3 shells occupied by electrons, hence it is the member of 3rd period.
electronic configuration 2 , 8 , 1. Sodium have one electron in the last orbit hence it is the member of first group. There are 3 shells occupied by electrons, hence it is the member of 3rd period.
Prediction of block of a given element
The sub-shell in which the differentiating electron enters represents block to which the given element belongs. Differentiating electrons are the electrons which would distinguish one atom or the other.
Example : Scandium 21 .
As the differentiating electron enters in d-sub shell it belongs to d-block.
Example : Scandium 21 .
As the differentiating electron enters in d-sub shell it belongs to d-block.
Types of Elements - s, p ,d and f Blocks
Elements in the group exhibit similar chemical behaviour. The similarity is because of two factors:
- Same number of electrons in outermost orbital
- Same distribution of electron in their outermost orbitals.
Properties of individual atoms
The periodic variation in electron configurations as one moves sequentially through the Periodic Table from H to heavier elements produces a periodic variation in a variety of properties. The periodic properties are:
- Atomic size
- Electron affinity
- Electronegativity
- Ionization enthalpy
- Metallic and Non metallic character
Properties of groups
Elements within different groups within the periodic table have different physical and chemical properties. This determines the kinds of reactions these elements have. Different groups also show different trends, in terms of reactivity, as you move down a group. This can also determine how violently a reaction occurs - or whether it happens at all.
Elements Used in Day-to-Day Life
Following is the list of some elements we use in our daily life.
- Hydrogen - Water, air
- Sodium - As a salt in food
- Potassium - Used in food
- Calcium - Present in fruits
- Iron - Present in meats
- Copper - Utensils
- Silver - Jewellery
- Gold - Jewellery and Computers
- Mercury - Thermometer
- Aluminium - Kitchen supplies
- Carbon - Organic Materials like paint, coal, etc
- Silicon - Memory card, glass
- Tin - Cans
- Lead - Batteries
- Oxygen - Air, Water
Merits of Modern Periodic Table over Mendeleev's periodic table
The advantages of Modern periodic table over Mendeleev's periodic table are : Modern periodic table is based on the most fundamental property, the atomic number of elements, while Mendeleev's periodic table is based upon the atomic masses of elements. In the modern periodic table, elements are arranged in accordance with their electronic configurations. The elements having similar electronic configurations are placed in the same group. Hence, elements in given group show similar properties. Elements with different electronic configurations are grouped separately, hence they show different properties. Mendeleev's periodic table does not provide any reason for the similarity and the difference in properties of elements. In Mendeleev's periodic table there are several anomalies, e.g. the position of isotopes, wrong order of atomic masses of some elements etc. In the long form of the periodic table, these anomalies have been removed. In the long form of the periodic table, elements have been clearly separated as normal elements, transition elements and noble gases. Metals and non-metals are also separated. But in Mendeleev's periodic table there is no such separation of different types of elements.
Defects of Modern Periodic table
- Position of hydrogen still dicey. It is not fixed till now.
- Position of lanthanides and actinides has not been given inside the main body of periodic table.
- It does not reflect the exact distribution of electrons of some of transition and inner transition elements.
Factors which affect atomic size
Factors affecting atomic size are:
a) Screening effect- caused by mutual repulsion between electrons in the inner shell with those in the outer shell.
b.) Nuclear charge- more the number of protons in the nucleus.more will be the pull on electrons closer to the nucleus which causes the atomic size to decrease
a) Screening effect- caused by mutual repulsion between electrons in the inner shell with those in the outer shell.
b.) Nuclear charge- more the number of protons in the nucleus.more will be the pull on electrons closer to the nucleus which causes the atomic size to decrease
Metallic and Non-metallic properties
The tendency of an element to lose electrons and form positive ions (cations) is called electropositive or metallic character. The tendency of an element to accept electrons to form an anion is called its non-metallic or electronegative character. In each period, metallic character of elements decreases as we move to the right. Elements to the left of the periodic table have a pronounced metallic character while those to the right have a non-metallic character. Conversely, non-metallic character increases from left to right.
As we move down the group the number of shells increases. This causes the effective nuclear charge to decrease due to the outer shells being further away: in effect the atomic size increases. The electrons of the outermost shell experience less nuclear attraction and so can lose electrons easily thus showing increased metallic character.
As we move down the group the number of shells increases. This causes the effective nuclear charge to decrease due to the outer shells being further away: in effect the atomic size increases. The electrons of the outermost shell experience less nuclear attraction and so can lose electrons easily thus showing increased metallic character.
Size of atoms and molecules
Most molecules and atoms are far too small to be seen with the naked eye, but there are exceptions. DNA, a macromolecule, can reach macroscopic sizes, as can molecules of many polymers. Molecules commonly used as building blocks for organic synthesis have a dimension of a few angstroms () to several dozen , or around one billionth of a meter.
Different Atomic Radius Definitions
In a practical way, it is difficult to measure the size of an individual atom. But we can estimate the radii of the atom by the bonds it forms. But still, there is no fixed radius of an atom.
We can understand atomic radius by three definitions:
We can understand atomic radius by three definitions:
- Covalent Radius: If an element is non-metallic
- Metallic Radius: If an element is metallic
- van der Waals Radius: If an element is a noble gas.
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ReplyDeleteClassification of elements in groups provides us a fixed pattern in which the elements change their properties periodically. The periodic table made the study of the physical and chemical properties of elements simple and organised. This science topic is necessary to learn for all school students to score well in their exams. Classification of elements is necessary to make their study easy. By the process of classification of elements, we group together the elements with the same characteristics. As it is impossible to study each element separately and deal with their different properties so they are grouped together in the periodic table.
ReplyDeleteSuch an helpful resource for classification of elements. I'm also an science tutor and looking for helpful resource like this to share with my students. thank you for this amazing post.
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