Chapter 02: Atomic Structure

Mg has two valence electrons. And it is easy to remove two valence electrons, but for 3r electron a much bigger amount of energy required due to disturbance in octet rule. That's why Is is much bigger than I2. Among the elements Li, K, Ca, S and Kr which one has the lowest first ionization energy? Which has the highest first ionization. The least first ionization energy is of alkali metals. And among alkali metals it decreases downward. So, among the given elements lowest ionization energy is of K and highest value of Kr which is a noble gas that ionization has complete octet, as energy increase from left to night in period. the

See Q5. from theory.

19K= 1s 2s 2p°3s-3p°4s (ii) Explain why the 4s subshell is filled before the 3d subshell in potassium, even though the principal quantum number of the 3d subshell is lower. Ans. Electrons are filled according to n+ l rule. The values of 4s is n+ l=4+0=4, while that of 3d, the values of n+ l= 3+2 = 5. So, because the values of 4s of nt! is smaller than 3d that's why electrons are filled in 4s first then in 3d. (i) An atom of element X has an 05. atomic number of 17 and a mass number of 35. Determine the number of protons, and electrons in this atom. An element X has atomic number 17 Ans. means it has 17 protons and 17 electrons because X has no charge. While neutrons are 18 (n = A-Z) Z=17 p = 17 e = 17 X has no charge n= 18 n = A-Z= 35-17 (ii) If this element forms an ion with a charge of -1, how many protons, neutrons, and electrons will be present in the ion? Ans. 35x Z = 17 p = 17 e = 18 XI-= 17+1=18 n = 18 n= A-Z= 35-17 = 18 Because of -1 charge, it have total of 18 electrons.

See Q6. from theory. chemical properties among groups of elements. Electronic Configuration and Semi- conductors

See Q4. from theory

80 Hg: 3d"' 4p' 5s 1s 2s 2p' 3s 3p° 45 Atomic orbitals with n= 3 3s 3p' 3d!° Electrons = 2+6+10 = 18 (i) How many electrons occupy 4d atomic orbitals? Ans. As per ground state configuration: 4d electrons = 10 (wii) How many electrons occupy 4p. atomic orbitals? Ans. As per ground state configuration: 4pz electrons = 2 Because maximum electrons that can occupy an orbital are 2. (iv) How many electrons in the valence shell have spin "up" s=-! state to ground Ans. According configuration: Total electrons are 80, the total number of valence electron are 12. The total spin "up" - - valence electrons (-1 are 06.

The massive difference between 2nd and 3r ionization energies show that 3rd electron is removed from inner shell. It means atom has two electrons in its valence shell. And has total four electrons so, it should be Be and it is of alkaline earth metals s-block (LIA).

The trend in ionization energies as given is in increasing order as the electrons are removed, because of increasing attraction of nucleus and valence electrons. Al< Al3+ < Al?+ < AC3+ (i) Explain the large increase between 13 and 14. Ans. The large increase between Is and I4 is due to the difference in their shells. Is is of valence shell while I4 is of inner shell, that's why it has large difference and massive jump can be seen. Al has 3 electrons in its valence shell. (wii) List the four aluminium ions given in the order of increasing size, and explain your ordering. Ans. The increasing order of size of ions is: Alt4 < Al3+ < Al3+ < Al3+. It is due to the removal of electrons and increase in effective nuclear charge, the sizes are smaller with increase in the sign. Greater is the size smaller will be the charge. 09. (i) State the general order of filling orbitals up to the 4p subshell. Ans. The general order of filling orbitals up to 4p is: 1s 2s 2p° 3s 3pó 45 3a'° 4p° SLO BASED SHORT QUESTION ANSWER Atomic Number, Atomic Mass

It is a relationship between frequency of a particular line in the x-rays and atomic number of element Vo=a (Z-b) a → Proportionality constant b screening constant. Moseley stated that it is the atomic number and not the atomic mass which describes the properties of an atom. He formulated the modern periodic table.

802- e = 8+2 = 10 p= 8 n = 16-8 = 8 (ii) Explain why the 4s subshell is filled before the 3d subshell, according to the Aufbau principle. Ans. According to Aufbau principle the energy of 4s is less than the energy of 3d orbital so, it is filled first. The values for 4s of nt C rule is 4+0 = 4 while for 3d is 3+2 = 5, that's why it is filled before 3d.

Atoms having same atomic masses but different atomic numbers are called isobars. Examples "N & 40, "C & "N

Atoms having same atomic numbers but different mass numbers are called isotopes. Examples: |н 3н, 3н 3cе 3,cе

Positive rays consist of protons and cathode rays consist of electrons. Mass of proton is 1836 times greater than that of electron. So e/m value for positive rays will be 1836 times less as compared to cathode rays.

When the spectral lines are split up into a number of thin lines in the presence of electric field then that is called as Stark effect.

When emission spectrum is studied in the presence of magnetic field. The spectral lines are split up into thinner lines it is called as Zeeman effect.

Neutrons have following properties. (i) They have high penetrating power. (ii) They cannot ionize gases. (wii) They can expel high speed protons from paraffin water, paper and cellulose. (iv) They have no effect of electric and magnetic field. Electronic configuration

The formula is 2(2l+1) For s-orbital 2(2X0+1) = 2 electrons For p-orbital 2(2 × 1+1) = 6 electrons For d-orbital 2(2×2+1) = 10 electrons For f-orbital 2(2×3+1) = 14 electrons

The orbitals are arranged in the increasing order of (n+l) if any two orbitals have the same (n+l) values, then that orbital should be placed first whose 'n' value is smaller. For example: (n+l) Is (1+0) = 1 2s (2+0) = 2 and so on. Spectrum

after being absorbed by the absorbing substance is called as atomic absorption spectrum. It is represented by dark lines separated by bright spaces. It appears as dark lines against the bright background. The spectrum of light when passed through unexcited hydrogen atom is the atomic absorption spectrum. are

"A spectrum formed by the radiations emitted by the heated substance is called as atomic emission spectrum" It is represented by bright lines separated by dark spaces. It appears as bright lines on a dark background. Example: The spectrum of light emitted by the excited hydrogen atom us atomic emission spectrum Energy levels

We can calculate the energy of an electron experimentally by measuring the ionization energy of an electron. electron of Example: The energy of hydrogen atom is actually its 1st ionization energy. → He 4H, = +1313.315kJ/ mol H(g) → Nag) te AH, = +496kJ/mol Na(g) ionization

Amount of energies required to remove all the electrons one by one until the nucleus is left. For example: An element "X" has three electrons, its successive ionization energies are: x →*+ +e x+ → X2+ +ē ΔH12 x?+ → X3++è

All the ionization energies strongly endothermic because they require energy to separate the electrons atom. Due to attractive forces of nucleus. Shapes of Atomic Orbitals

2pz orbital 2px orbital 2py orbital n=2, l= 1, m = 0, -1, +1 can electrons How many 032. accommodate K, L, M and N shells with their subshells? Ans. The total number of electrons in a shell can be calculated by "2n?" K shell (n=1); 2 electrons (1s orbital) L shell (n=2); 8 electrons (2s and 2p orbitals) M shell (n=3); 18 electrons (3s, 3p and 3d orbitals) N shell (n=4); 32 electrons (4s, 4p, 4d and 4f orbitals Identification of Position o Element

element based on its valence shell electron ended up in the particular subshell. If the valence electron presents in s-subshell, then the element present in s-block. Similarly, p, d and f block elements have their valence electrons in their respective subshells. Examples: Na is s-block element & O is p- block element.

configuration as: X = 15, 25, 2p', 35, 3p° as per valence shell configuration, the valence electron present in 4s. So, it is s- block element. And 4s' shows it is of 1st group of s-block, means it is an alkali metal period as of 4s end of present in 4th configuration and the element is K-19. Distribution of Electrons in Shells and Sub-shells

The number of electrons in a subshell can be calculated by 2(2l+1) formula. For s, l = 0 s: 2(2l+1) = 2(2(0)+1) = 2(1) = 2 electrons For p, l = 1 p: 2(2l + 1) = 2(2(1) + 1) = 2(3) = 6 electrons For d, l= 2 d: 2(2l + 1) = 2(2(2)+1) = 2(5) = 10 electrons For t, l = 3 f: 2(2l + 1) = 2(2(3) +1) = 2(7) = 14 electrons

Mg has two electrons in its valence s- subshell, so due to the full filled rule, Mg requires more energy than Al because it has one electron in its valence p subshell that makes Al unstable as compared to Mg, although Mg has bigger size than Al.

outermost shell are called valence electrons. These are such electron that are primarily involved in chemical reactions. The similarities among the configurations of valence electrons account for similarities of DESCRIPTIVE QUESTIONS (EXERCISE)

Semi-conductors are the materials that can conduct electricity under some conditions. They conduct electricity more than insulator and less than conductors. Some examples are Si, Ge, As, Sb, etc.

Impurity atoms with three valence electrons (like Al) are added to the pure semiconductor. Some of the trivalent atoms take place of the Si atoms in the crystals. The silicon atoms cannot make four bonds due to the lack of electrons. For this reason, there are created holes in the crystal lattice, which act as positive charge carriers. This creates a positive-type process semiconductor or P-type semiconductor.

When impurity atoms with five valence electrons (like phosphorus) are added to the pure semiconductor, some of Si atoms are replaced with the pentavalent phosphorus atoms. The Si atoms in the vicinity of these atoms can make four bonds and the fifth electron is an extra electron. These impurity atoms contribute extra electrons to the crystal lattice, which become free to move and act as negative charge carries. This process creates N-type semiconductor.