A periodic table of the elements, in chemistry, the arranged array of all the chemical elements in ascending order with respect to the atomic number, that is the entire number of protons in the atomic nucleus. When the chemical elements are thus ordered, there is a repeating pattern called periodic law in their properties, in which elements in the same column such that the group has similar properties.
It was found in the second decade of the 20th century that the array of elements in the periodic system is that of their atomic numbers, the numbers of which are equal to the positive electrical charges of the atomic nuclei represented in electronic units. In the following years, great progress was made in the explanation of the periodic law in terms of the electronic structure of atoms and particles. This clarification has improved the value of the law, which is used enormously today.
There are 7 periods in the periodic table and 18 groups in the periodic table. Hence these are arranged in row and column format that is 7 rows and 18 columns. There are 4 blocks in the periodic table.
These four blocks are called s, p, d, and f. The Elements in each block have a specific color in the background graphics, the periodic tables, and the element arranged themselves.
Groups 1 to 2 except hydrogen and 13 to 18 are termed main group elements. Groups 3 to 11 are termed transition elements. Transition elements are those whose element atoms have an incomplete ‘d subshell’ or these element cations have an incomplete ‘d subshell’.
Main group elements in the first 2 rows of the table are called typical elements. The 1st row of the f-block elements is called lanthanides or, less desirably, lanthanides. The 2nd row of the f-block elements is called actinides or, less desirably, actinides.
The d-Block in the Periodic Table
The elements that fall in between the third and the twelfth group of the periodic table are referred to as the d-block elements. These elements that fall under the category of d-block are also called transition elements or transition metals. The d-block contains all the metals. Some of these elements have one or more active d-orbital electrons.
Distinguishing between d Block Elements and Transition Elements
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The d-block elements are incomplete or filled d-orbitals. The transition elements have incompletely filled d orbitals, or at least in one of their stable cations they form.
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The d-block elements are paramagnetic, ferromagnetic or diamagnetic. The transition elements are only paramagnetic or ferromagnetic.
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The block elements might or might not have filled d orbitals in their cations. Whereas the transition elements have incompletely filled d-orbitals in their stable cations.
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The elements in the d-block might or might not form coloured compounds. The transition elements always form coloured complexes.
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Some of the d-block elements are not solid at room temperature. Whereas all the transition elements are solid at room temperature.
Distinguishing between d Block and f Block Elements
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Depending upon their electron configuration, the d-block elements show a wide variety of oxidation states. The very most stable oxidation state of f-block elements is +3 and there can be other oxidation states as well.
s-Block Elements
The elements that have the electrons in the outermost s orbitals are defined as s block elements. All the s-block elements have one or two electrons in their outermost s orbital since the s-orbital can only keep a maximum of two electrons.
The electron configuration of the s-block elements ends with s orbital always.
p-Block Elements
The elements that consist of electrons in the outermost p orbitals are referred to as p-block elements. The p subshell approximately holds up about six electrons in number. The electron configuration of the p-block elements always ends with p orbital (np).
Distinguishing between S Block and P Block Elements
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The s-block elements have 0,+1, +2 oxidation states, whereas the p-block elements have varying oxidation states ranging from -3, 0 to +5.
Transition Elements
Transition elements are those elements that have partly or inadequately filled d orbital in their ground state or they have the most stable oxidation state. The partly filled subshells of ‘d block’ elements include (n-1) d subshell. All the d-block elements carry an equal number of electrons in their distant shell. Hence, they possess similar chemical properties.
General Properties
All transition elements have similar properties because of the same electronic configuration of their peripheral shell. This happens as each extra electron enters the penultimate 3d shell. This creates an efficient shield between the nucleus and the outer 4s shell. The peripheral shell arrangement of these elements is ns2. The common properties of the transition elements are as follows:
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They form stable complexes
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The transition element has high melting and boiling points
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They contain high charge/radius ratio
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They form compounds which are usually paramagnetic
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They are firm i.e. solid and possess high densities
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They form compounds with intense catalytic activity
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They show variable oxidation states
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They form colored ions and compounds.
Melting and Boiling Points of the Transition Element
These elements show high melting and boiling points. This is due to the overlapping of (n-1) ‘ d’ orbitals and covalent bonding of the electrons which are not paired d orbital electrons. Zn, Cd, and Hg have totally had completely filled (n-1) ‘d’ orbitals. They cannot form covalent bonds. Thus, they have an under melting point than other d-block elements.
They have various other properties such as Ionic Radii, Ionization Potential, electronic configuration, and oxidation states. But now we will concentrate on metallic nature.
Metallic Nature
As there is very less number of electrons in the outer shell, all the transition elements are metals. They exhibit the qualities of metals, such as ductility and malleability. They are great conductors of electricity and heat. Apart from Mercury, whereas Hg is fluid and delicate like alkali metals, all the transition elements are strong and fragile.
Note: Ductile is the property in whi
ch the metal is drawn into wire and Malleable is beating metal into sheets.
Metallic character of an element is said to be the easiness of its atom in losing electrons. According to the modern periodic table, the metallic character of an element decreases as we cross the periodic table from left to right. This occurs due to the fact that while we move from left to right in a period, the number of electrons and protons in an atom increases and this results in an increase in nuclear force on the electrons and hence losing an electron from the atom becomes difficult. Metallic character increases as we move down the group, and this appears because while moving down the group, the atomic radius increases exponentially and therefore it becomes easier to lose electrons. Most of these elements show the common metallic properties such as malleability, luster, ductility, high tensile strength, electrical conductivity, and high thermal etc. We have Zn, Cd, Hg, and Mn which are exclusions, in this case, the rest of the elements show 1 or more metallic characters at regular temperatures. Apart from the metals which are exemptions the rest of the elements are tough and possess low volatility.
Transition elements exhibit a metallic character as they have weak ionization energies and have different vacant orbitals in their outermost shell. This feature favors the creation of metallic bonds in the transition metals and so they show typical metallic properties. These metals are hard which shows the presence of covalent bonds. This occurs because transition metals have unpaired d-electrons. The d orbital which holds the unpaired electrons may overlap and make covalent bonds. Higher the number of unpaired electrons existing in the transition metals more is the number of covalent bonds created by them. This moreover increases the hardness of the metal and its strength.
The metals chromium (Cr), molybdenum (Mo) and tungsten (W) have the highest number of unpaired d-electrons. Hence these transition metals are very firm and hard. We have zinc (Zn), mercury (Hg) and cadmium (Cd)which are not very hard as they do not possess unpaired d-electrons. The transition elements are very hard and have their own metallic character; this shows that both metallic and covalent bonding exists together in these elements.
Answer the Following Questions:
1. Define the term periodic table?
2. List the blocks present in the periodic table?
3. List the properties of transition elements?
4. Explain about the melting and boiling point?
5. Explain about the metallic character of transition metals?
Fill in the Blanks:
1. There are totally ______ periods in the periodic table and totally ____ groups in the periodic table. (Ans: 7 periods and 18 groups)
2. The 1st row of the f-block elements is called ____________. (Ans: lanthanide)
3. ‘d block’ elements include ______ subshell. (Ans: (n-1) d)
4. _________ is the property in which the metal is drawn into wire and _________ is beating a metal into sheets. (Ans: Ductile , Malleable)
5. Mercury (Hg) is _________. (Ans: Fluid)