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Cerium(Z = 58)

Scandium(Z = 21)

Transition elements show variable state oxidation in their compounds because there is a very small energy difference in between (n-1)d and ns orbitals. As a result, electrons of (n-1)d orbitals as well as ns-orbitals take part in bond formation.

(i) Mn(Z-25) has the maximum number of unpaired electrons present in the d-subshell so it shows maximum oxidation states(+7).

(ii) Sc only exhibits a +3 oxidation state in these series.

This is due to electronic configuration. Mn²⁺ has (Ar)3d⁵ and Fe²⁺ has (Ar)3d⁶.Therefore, the loss of one electron from Fe²⁺ to Fe³⁺ requires low energy.

The transition elements show variable oxidation state due on to small energy difference between (n‐1) d &ns orbital as a result both (n‐1)d &ns electrons take part in bond formation.

The electronic configuration of Mn²⁺ is [Ar] 3d⁵, i.e. all five d‐orbitals are singly occupied. Thus this is stable electronic configuration and further loss of electron requires high energy .on other hand side the electronic configuration of [Fe]²⁺ is [Ar] 3d⁶, i.e. Loss of one electron r quires low energy.

An element which has partially filled (n‐1) d orbital is known as transition elements. Group 12 elements i.e. Zn, Cd, Hg have completely filled (n‐1) d‐orbital in atomic & ionic state & thus these elements are not considered as Transition Elements.

The E⁰ (M²⁺/M) values are not regular which can be explained from the irregular variation of ionization energy and sublimation energy of Mn due to half‐filled orbitals.

In a transition series, the oxidation state which lead to exactly half filled or completely filled is [Ar] 3d⁶ ,4s² orbitals are more stable.

e.g. the electronic configuration of Fe. It shows various oxidation state but Fe(III) is more stable than Fe(II).

i. Most of the transition elements are metals and thereby they show metallic properties such as ductility, malleability, electrical conductivity, high tensile strength and metallic lustre. 

ii. Except mercury which is liquid at room temperature, other transition elements have typical metallic structures. 

iii. Their compounds generally contain unpaired electrons, hence they are paramagnetic in nature and form coloured compounds. 

iv. They show variable oxidation states. 

v. They have tendency to form large number of complexes. 

vi. They have higher densities as compared to the metals of groups 1 and 2 (s-block). 

vii. They are heavy metals with higher melting and boiling point as well as higher heats of vaporisation. 

viii. Transition elements are less reactive than s-block elements due to their higher ionisation energy. 

ix. Most of the transition metals such as Mn, Ni, Co, Cr, V, Pt, etc., and their compounds are used as catalysts. 

x. They have good thermal and electrical conductivity. 

xi. They form alloys with different metals. 

xii. They form interstitial compounds with elements such as hydrogen, boron, carbon, nitrogen, etc. 

xiii. They form organometallic compounds.

Compounds of transition metal with relatively smaller non‐metals are known as interstitial compounds. These compounds are well known for transition metals because size of C, N, O, and B is similar to size of interstitial voids of transition metal.

Transition elements contain incompletely filled d subshell, i.e., their outer electronic configuration is (n-1) d^1-10 ns^1-2 , whereas non-transition elements have no d subshell or their d subshell is completely filled and they have the outer electronic configuration of ns^1-2 or ns² np^1-6 .

[Ar] = 1s² 2s² 2p⁶ 3s² 3p⁶

Transition metals and many of their compounds show paramagnetic behavior due to presence of unpaired electrons in (n‐1) d orbital.

Interstitial compounds are those which are formed when small atoms like H, N or C are trapped inside the crystal lattices of metals. They are usually non-stoichiometric and are neither typically ionic nor covalent. Interstitial compounds are well known for transition compounds due to its closed crystalline structure with voids in them. The atomic size of transition metals is very large hence have large voids to occupy these small atoms.

The general electronic configuration of a d-block elements is (n -1) d^1-10 ns^1-2.

Transition elements in its ground state or excited state will have a configuration of (n - 1) d^1-9 ns^0-2 ie. partly filled d orbitals whereas non transition elements will have a configuration of (n -1) d¹⁰ ns^0.2  i.e completely filled d- orbitals.

(i) Paramagnetic arises due to the presence of unpaired electrons, each such electron has a magnetic moment associated with it due to its spin angular momentum. Transition metals have in its ground state or ionised state have number of unpaired d-electrons which gives it a paramagnetic behaviour.

(ii) Transition metals have very high interatomic metallic interaction due to the involvement of greater number of electrons from (n - 1)d in addition to the ns electrons. Greater the number of valence electrons, stronger is the resultant bonding due to the greater overlapping of half filled orbitals. Hence, more amount of energy is required to break these metallic bond. Thus enthalpy of atomisation of transition metal is very high.

(iii) Colour of transition metal - compounds is due to the excitation of an electron from a lower energy d-orbital to a higher energy d orbital. The energy of excitation corresponds to the frequency of light absorbed and the colour observed corresponds to the complementary colour of the light absorbed (whose frequency lies on the visible region). The frequency of the light absorbed depends on the nature of ligand. Transition metals form coloured compounds due to presence of vacant d-orbitals for the d-d transition of e’ which causes the colour.

(iv) The catalytic activity of transition metals is ascribed to their’ability to adopt multiple oxidation states and to form complexes. Catalyst at a solid surface involve the formation of bonds between reactant molecules and atoms of the surface of the catalyst this has the effect of increasing the concentration of the reactants at the catalyst surface and also weakening of the bonds in the reacting molecules (activation energy is lowered. Transition metals have d and s orbitals to from these bonds.

i. The atomic radii for transition metals are smaller than their corresponding s-block elements. 

ii. The atomic radii of the elements of a given series decrease with the increase in atomic number but this decrease becomes small after middle of the series.

In the first transition series, the atomic radius gradually decreases from scandium to chromium but from chromium to copper, it is nearly the same. Similar behaviour has been observed in the second and third transition series.

iii. The decrease in atomic radii in each series, in the beginning, is due to an increase in nuclear charge across the period, which tends to pull the ns electrons inward, i.e., it tends to reduce the size.

iv. The addition of extra electrons to (n1) d-orbitals provides the screening effect. As the number of d-electrons increases, the screening effect increases. Thus, there are two operating effects namely screening effect and nuclear charge effect which oppose each other. In the midway onwards of the series, both these effects become nearly equal and thus, there is no change in atomic radii inspite of the fact that atomic number increases gradually.

v. The values of atomic radii at the end of each series are slightly higher which is due to electronelectron repulsions among (n1) d-electrons. These repulsions become predominant at the end of each series and thus resulting in the increase in size.

vi. In a vertical row, the atomic radii is expected to increase from top to bottom. Therefore, the atomic radii of transition metals of second series have larger values than those of the first transition series. However, the transition metals of third series except the first member, lanthanum, have nearly the same radii as metals of second transition series above them which is due to the lanthanoid contraction.

The lanthanoids have an electronic configuration of 6s² common with variable occupancy of 4f level. These elements have only one oxidation state(+3).

The 4d and 5d series of transition elements in each group have the same atomic radii. This is due to lanthanide contraction.

The steady decrease in the size of the atoms or ions from lanthanum to lutetium is known as lanthanide contraction.

As the atomic number increases in the lanthanide series, the new electron goes to the inner 4f orbitals. The shielding effect of a 4f electron is poor. As a result, the attraction of the outer electrons by the nucleus increases and this tends to a decrease in the size.

Chemical Formula - The chemical formula of a substance is the symbolic representation of the actual number of atoms present in one molecule of that substance.

Explanation:

(a) Formula of one molecule of water is H₂O. It shows that one molecule of water is made up of 2 atoms of hydrogen and one atom of oxygen.

(b) Formula of one molecule of sulphuric acid is H₂SO₄. It shows that one molecule of sulphuric acid is made up of 2 atoms of hydrogen, 1 atom of Sulphur and 4 atoms of oxygen.

Due to comparable energies of 5f, 6d and 7s orbitals and the relative stabilities of f⁰, f⁷ and f¹⁴ occupancies of the 5f orbitals.

The common stable oxidation state of lanthanides is +3.However some members also show oxidation states of +2 & +4.

In the transition elements, there is a little difference in the energy of (n‐1) d‐orbitals and ns‐ orbitals.Thus,  incoming electron can occupy either of shell. Hence, transition elements  exhibit  many irregularities in their electronic configurations. 

In KMnO₄, Mn exhibits the highest oxidation state of +7.

Oxygen and fluorine act as strong oxidising agents because of their high electronegativities and small sizes. Hence, they bring out the highest oxidation states from the transition metals. In other words, a transition metal exhibits oxidation states in oxides and fluorides. For example, in OsF₆ and V₂O₅, the oxidation states of Os and V are + 6 and respectively.

(i) The transition elements exhibit high enthalpies of atomisation because they have large number of unpaired electron in their atoms. Due to this they have stronger inter atomic interaction and hence stronger bonding between atoms.

(ii) Many transition metals and their compounds acts as catalyst the catalytic activity is due to their ability to exhibit multiple oxidation states, eg. V₂O₅ in contact process and finely divided iron in Haber process.

(iii) The actinoid contraction is similar to lanthanoid contraction. This contraction is due to poor shielding by 5f electrons in the actioids than that by 4f electrons in the lanthanoids.

(iv) Much larger third ionisation energy of Mn (where the required change is Cl₅ and d⁴) is mainly responsible for this. This also explains that +3 state of Mn is of little importance.

(v) Scandium (Z = 21) has incompletely filled 3d orbitals in the ground state. (3d) Hence, it is considered as a transition element.

Steps for writing Chemical Equation

Step I: Writing skeletal Equation

A word-equation shows change of reactants to products through an arrow placed between them (→). The arrow may be read as "to yield" or "to form" or "to give" and shows the direction of the reaction.

The reactants are placed on the left hand side (LHS) of the arrow and the products on the right hand side (RHS). The different reactants as well as products are connected by a plus sign (+). A complete chemical equation represents the reactants, products and their physical states symbolically and is a balanced account of a chemical transaction.

Step II: Balancing of Chemical Equation

An equation in which number of atoms of each element is equal on both the sides of the equation is known as balanced chemical equation.

A chemical equation is balanced so that the numbers of atoms of each type involved in a chemical reaction are the same on the reactant and product sides of the equation.

There are 206 bones present in our body.

The joint between the upper jaw and the skull is the fixed joint.

These bones are so hard they are made of calcium and phosphorus.

The displacement of an entire body from one place to another is called locomotion.

The stream-lined body, fins in fish; wings, legs in birds; ribs in the snake; muscular foot in snail are useful in locomotion.

The biggest bone is the femur.

There are more than 650 muscles in our body.

Locomotion helps for protection and food gathering.

The biggest muscle is Gluteus Maximus.

The smallest muscle in our body is Stapedius.

Muscles are connected to bones either directly or with the help of tendons.

Interestingly the muscle of the heart works without rest.

Muscles work in pairs. When one of them contracts, the bone is pulled in that direction and the other muscle of the pair relaxes.

The point where two bones meet is called a joint.

1. It’s funny to imagine our body without a skeleton. 

2. Without a skeleton, muscles don’t have support. 

3. So the body does not have a shape. 

4. The body becomes a fate round ball.

Different bones of our body combine together to form the skeleton.

1. The different bones of different parts of the body combine together to form a single structure or system. This structure is called the skeleton. 

2. The skeletal system provides base and shape to our body. 

3. It provides protection to internal organs. 

4. It also help in blood formation.

In a simplified form, circulation of current means that if field \(\vec B\) is directed along the tangent to every point on the perimeter L of a closed curve and its magnitude is constant along the curve. Then BL = µ₀I

Amoeba is reproduces by  Binary fission.

Linear path.

Reproduction results in the production of offspring similar to parents in body design and form. The exact blue prints of body design is inherited in the offspring due to DNA replication/DNA copying. The imperfect DNA copying results in genetic variations that can be both useful or harmful for the offspring. The useful variations gets selected in nature and helps organism to survive in the changing environment while harmful variation gets eliminated.

If each new generation is to be the combination of the DNA copies from two pre-existing individuals, then each new generation will end up having twice the amount of DNA that the previous generation had. In sexual reproduction, the gametes usually contain half number of chromosomes and same numbers present in the body cells. These haploid gametes when fuse produces a new cell with double number of chromosomes than the gametes and same as the body cells. In this way organisms restrict doubling of DNA and maintain the chromosome number.

One ampere current is defined as the constant current which is maintained in two straight parallel conductors of infinite length at a distance 1 metre apart placed in vacuum of negligible circular cross section, would produce between these conductors a force equal to 2 × 10^-7 N/m of length.

Alternating Current: If the current changes direction after equal intervals of time, it is called alternating current. The positive and negative generator. polarities of AC are not fixed.

Direct Current: If the current always flows in the same direction, it is called direct current. It can be obtained from a cell or a battery. The positive and negative polarities of DC are fixed for long distance transmission. AC is preferred as it caused minimum loss of energy during transmission.