Engineering Chemistry and Environmental Studies UNIT I(A) Atomic structure(1). Write about the Fundamental particles in an atom?Ans: They are three fundamental particles present in an atom.They are (1) Electron ()(2) Proton (p)(3) Neutron (n)S.NoParticleDiscoveredMassCharge

KgsAmuCoulombse.s.u

1Electron ()J.J. Thomson9.1 10-310.005486- 1.6 10-19- 4.8 10-10Negative(-)

2Proton (p)Gold stein1.6 10-271.00728+ 1.6 10-19+ 4.8 10-10Positive (+)

3Neutron (n)James Chadwick1.6 10-271.00866500Neutral

(2). What is Atomic Number and explain with an example?Ans: Atomic Number (Z): The number of protons or electrons present in the atom is called atomic number. This is denoted by the letter Z.Atomic Number (Z) = Number of electrons (or) protons.Example: Na = Z =11i.e., sodium atomic number is 11.So, sodium contains 11 electrons (or) 11 protonsMosley proposed the relationship between atomic number and frequency of X-rays = a(Z-b) Where a, b = constants = frequency of X-RaysZ= atomic number(3). what is Mass Number? Ans.Mass Number (A):The sum of protons and neutrons present in an atom is called mass number.It is denoted by AWhere A = No. of Protons + No. of NeutronsA-Z = No. on Neutrons(4). Explain the Bohrs Atomic Theory and write its Merits and Demerits? Ans. Neils Bohr in 1913 proposed atomic model based on the Plancks quantum theory. He retained the Rutherfords concept that the atom contains positively charged nucleus at the centre.Postulates :1. The electron in an atom revolves around the nucleus with high velocity in circular paths. These circular paths are called orbits.2. Each orbit is associated with certain amount of energy.These orbits are called energy levels.The energy levels are named as K, L, M, N . (or) numbered as 1,2,3,43. As long as the electron moves in a orbit, its energy is constant and does not emit any electromagnetic radiation. Hence these orbits are called stationary orbits.4. When electrons jumps from a higher energy level to a lower energy level, the difference in energy is emitted as radiation. When electron jumps from a lower energy level to higher energy level the difference is energy is absorbed as radiation.E2 - E1 =hWhere E1 = Energy of first orbitE2 = Energy of second orbith = Plancks Constant = integer

5. The angular momentum revolving electron in stationary orbit is equal to integral multiplies of mvr = where m = mass of electronv= velocity of electronr= radius of the orbith=Plancks constantn=integer

Merits: 1. Bohrs atomic model successfully explains the spectrum of hydrogen and hydrogen like ions (He+, Li2+) which contains one electron2. This model explains the stability of atom also.3. This model also useful in calculating energy and radii of orbits.Demerits:1. This model fails to explain spectra of multi electron atoms2. It is failed to explain the Zeeman effect.Splitting of spectral lines in the applied magnetic field is called Zeeman effect.3. It is failed to explain the Stark effectSplitting of spectral line in the applied electric field is called Stark effect.4. According Bohrs model electron revolving in definite orbits. It is against to debrogles wave nature. Quantum Numbers:A set of numbers used to describe an electron completely with position and energy in an atom is called quantum numbers.There are four quantum numbersThey are (1) Principle Quantum Number (n)(2) Azimuthal Quantum Number (l)(3) Magnetic Quantum Number (m)(4) Spin Quantum Number (s)(1). Principle Quantum Number (n):(a) It is proposed by NeilsBhor(b) It is denoted by the letter n(c) n represents as 1,2,3,4 (or) K,L,M,N(d) It gives the size and energy of stationary orbit(e) The number of orbitals present in a given orbit as n2.(f) The minimum number of electrons in a given orbit is 2n2.(2). Azimuthal Quantum Number (l):(a) It is proposed by Sommer field.(b) It is also called Angular Momentum Quantum number(c) It is denoted by the letter l(d) It gives the shape of orbital(e) l values are 0,1,2,. (n-1)l = 0 indicates s orbitall = 1 indicates p orbitall = 2 indicates d orbitall = 3 indicates f orbital(3). Magnetic Quantum Number (m):(a) It is proposed by Lande(b) It is denoted by the letter m(c) It gives the orientation of the orbital in space(d) m values are -l.. 0 l(e) Total number of m values for a given l value is (2l+1)(4). Spin Quantum Number (s):(a) It is proposed by Goud smith and ulhen beck(b) It is denoted by the letter s(c) It gives spin of electron(d) The spin may be clockwise S = +1/2 (or) Or Anticlockwise S = -1/2 (or)

(6) What is orbital ?Ans:Orbital:The probability of finding electron maximum around the nucleus is called orbital.The probability of finding electron 2) at that point can be calculated by Schrodinger wave equation

Where E = Total Energy of electron V = potential energy = Wave function of electron7) Define and explain the Shapes of orbitals?Ans:Shapes of orbitals:S orbital:S - orbital has spherical shape is equal to all directions.l value for s orbital is zero.

p orbital:p orbital has dumb bell shape.l value for p orbitals is one.m values are -1,0,+1There are three orientations are possible to p orbitalThere are represented as px, py, and pz.Three p orbitals are mutually perpendicular to each otherThese three orbitals have same energy called degenerate orbitals.Each p orbital contains one nodel plane.

d orbital:d orbital has double dumb bell shapel value for d orbital is twom values are -2,-1,0,+1,+2.There are five orientations are possible to d orbitalThese are represented as dxy, dyz, dzx, dx2-y2, dz2dxy, dyz, dzx, dx2-y2 has four labelsdz2 has two labelsall d orbitals have same energy called degenerate orbitals each d orbital contains two nodel planes

8) What is Electronic Configuration ?Ans: Electronic Configuration:The arrangement of electrons in various orbitals in an atom is called electronic configuration.(a) Aufbau Principle:Afbau means building upAfbau principle states that electrons enter into the orbitals in the increasing order of their energy This means electron occupy the lowest energy orbital first.The energy of orbital is given by (n+l)n = Principle quantum numberl = Azimuthal quantum number Energy orbitals shown by Moeller diagram

9) Write the Hunds Principle?Ans:(b) Hunds principle: Hunds rule states that pairing of takes place in the degenerate orbital is filled with one electronEg: Carbon electronic configuration = 6 = 1S2 2S2 2P2

1S2 2S210) Write Paulis exclusion principle?Ans:(c) Paulis Exclusion principle:Paulis Exclusion principle states that No two can have the same set of 4 quantum numbers in an atom.Eg: Helium =2 = 1S2

1S21st electron 2nd electronn = 1n = 1l = 0l = 0m = 0m = 0s = +1/2s = -1/2

11) Write the Electronic Configuration of Cr and Cu?Ans:Electronic Configurations: Chromium (Cr)= Z =24 = 1S2 2S2 2P6 3S2 3P6 3d5 4S1Copper (Cu) = Z =29 = 1S2 2S2 2P6 3S2 3P6 3d10 4S1(12) Write the differences between orbit and orbital?Ans:OrbitOrbital

(1). Orbit is a circular path around the nucleus(1). Probability of finding is maximum around the nucleus

(2). Orbits are circular in shape(2). Orbitals have different shapes

(3). The distance of the orbit from nucleus to an is fixed(3). It is impossible to know the exact position of electron in an orbital

(4). It is represented by two dimensional way(4). It is represented by three dimensional way.

13) What is Chemical bonding ?Ans: Chemical bonding: The attraction force between two atoms (or) ions (or) molecules is known as chemical bond.Electronic Theory of Valency:Kossel and Lewis proposed a theory to explain chemical bond.Postulates:(1) The electron in the outermost orbit is called Valency electron. This orbit is called Valency orbit.(2) Valency electrons are participate in bond formation.(3) Noble gas elements are stable and chemically inert due to octet (ns2 np6) configuration.(4) Atoms of other elements tend to attain 8 electrons in their Valency orbit to get stability.(5) The chemical bond is formed by losing electrons from Valency orbit to another atom (or) gaining of electrons from other atom (or) sharing the electrons of the Valency orbit with other atom.(6) Valency electrons causes for chemical relativity.

Representation of Valency electrons by Lewis method?

Types of chemical bondsMainly there are three types of chemical bondsThey are:(1) Ionic bond(2) Covalent bond(3) Metallic bond14) Define Ionic bond. Explain with examples NaCl, MgO?Ans:(1) Ionic bond:The electrostatic attraction force between two opposite charged ions is called ionic bond.The ionic bond is formed by transfer of electrons from one atom to the other atom.The ionic bond is formed between two atoms which one atom is high electron affinity and other atom is low ionization potential values.Electro negativity difference is more than 1.9Eg:NaCl Sodium chloride.MgO Magnesium oxide.(1) Sodium Chloride formation (NaCl):Sodium metal reacts with chlorine gas to form a crystalline sodium chloride solid.Na = 11 = 1S2 2S2 2P6 3S1Na loses 3S1 electrons and gets nearest noble gas configuration i.e., Na+ ion is formed.Na Na+ + 2,8,1 2,8Chlorine = 17 = 1S2 2S2 2P6 3S2 3P5Cl one electron is required to get Argon electron configuration.Cl + 2,8,7 2,8,8The oppositely charged Na+ and ions are held together by electrostatic force of attraction formed NaCl.Na+ + NaCl(2) Magnesium oxide formation (MgO):Magnesium metal reacted with oxygen gas to form magnesium oxide.Magnesium atomic number = 12.Electronic Configuration of Magnesium= 1S2 2S2 2P6 3S2Mg loses 3S2 electrons and gets nearest noble gas configuration formed Mg2+ ionMg Mg2+ + 22,8,22,8Oxygen atomic number = 8.Electronic Configuration of oxygen = 1S2 2S2 2P4Oxygen required two electrons to get nearest noble gas configuration.O + 2O-22,6 2,8The oppositely charged Mg2+ and O-2 ions are held together by electrostatic force of attraction.2Mg2+ + 2O-2 2MgO.15) Write the Properties of Ionic Compounds?Ans:Properties of Ionic Compounds:(1) Ionic compounds are crystalline solids due to strong electrostatic force of attraction between two opposite charged ions.(2) Ionic compounds are hard and brittle.(3) Ionic compounds have high M.P and B.P values due to strong electrostatic attraction.(4) Ionic compounds soluble in polar solvents Eg: water.(5) Ionic compounds acts as electric conductors in the form of solution and fused state.(6) The reactions between two ionic compounds in solution are very fast.(7) Ionic compounds do not exhibit isomerism due to ionic bond is non - directional.16) Define Covalent bond. Explain with examples H2, O2, N2 ?Ans:Covalent bond:The attraction force is due to equal contribution and mutual sharing of electrons between two atoms is called covalent bond.Eg: H2, O2, N2(1) Formation of H2Atomic number of Hydrogen = 1.Electronic Configuration of Hydrogen = 1S1Hydrogen contains one Valency electronHydrogen is required one electron to get the configuration.So two Hydrogen atoms contribute one electron each other to form bond pair. This bond is shared by two Hydrogen atoms and two hydrogen atoms get the configuration.

(2) Formation of Oxygen:Oxygen atomic number = 8.Electronic configuration of oxygen = 1S2 2S2 2P4.Oxygen contains six Valency electrons.Oxygen requires two electrons to get noble gas configuration.So two Oxygen atoms contribute two electrons each to form two bond pairs.These two bond pairs shared by two Oxygen atoms and double bond is formed between two Oxygen atoms.

(3) Formation of Nitrogen:Oxygen atomic number = 7.Electronic configuration of oxygen = 1S2 2S2 2P3.Nitrogen contains five Valency electrons.Nitrogen required three electrons to get noble gas configuration.So two nitrogen atoms contribute three electrons each to form three bond pairs.These three bond pairs shared by two Nitrogen atoms and triple bond is formed between two Nitrogen atoms

17) Write the Properties of Covalent Compounds: Ans:Properties of Covalent Compounds: (1) Covalent Compounds are gases (or) volatile liquids (or) solids.(2) Covalent Compounds have low M.P and B.P values due to weak vanderwaals forces.(3) Covalent Compounds soluble in non polar solvents Eg: C6H6, CCl4, Ether.(4) Covalent Compounds are non conductors in fused state and also in solution state due to absence of ions.(5) The reactions between covalent compounds are slow due to participation of molecules.(6) Covalent Compounds show isomerism due to covalent bond is directional.18) Define Metallic Bond ?Ans:Metallic Bond:The electrostatic attraction between positively charged metal ions and negatively charged sea of electrons is called metallic bond.Eg: Na metal, Fe metal etc.,The nature of metallic bond can be explained by following theories.(1). Free Electron Theory (or) Electron Sea Theory(2). Valence Bond Theory (or) Resonance Theory19) Write the Fee electron theory of metallic bond?Ans:(1). Free Electron Theory (or) Electron Sea Theory:This theory was proposed by Prude and Lorentz.According to this theory metal atoms lose their Valency electrons into crystal lattice to give positive metal ions.These ions are called kernels.The Valency electrons freely move in the crystal lattice. These electrons are called sea of electrons.The electrostatic attraction arises between positive metal ions and sea of electrons. Metallic properties depend upon valence electrons.

20) Write the valence bond theory of metallic bond?Ans:(2). Valence Bond Theory (or) Resonance Theory:Valence bond theory proposed by Linus Pauling Every atom in the metal lattice shares valence electrons with neighboring metal atoms.The result is formation of bond pairs.These bond pairs moves freely in vacant orbitals of metals equal structures are formed.The equal structures are called resonance forms.They are in ionic form as well as covalent form.

21) Write Difference between Covalent bond and Metallic bond?Ans:Covalent BondMetallic Bond

(1). Directional because valence electrons are localized (1). Non - Directional because valence electrons are delocalized

(2). Valence electrons strongly attracted towards nucleus (2). Valence electrons weekly attracted towards nucleus

22) Write the Difference between Covalent bond and Ionic bond?Ans:Ionic BondCovalent Bond

1). The Electrostatic attraction force between two opposite charged is called Ionic Bond1). The attraction force is due to equal contribution and sharing of electrons between two atoms is called Covalent Bond

2). Ionic Bond is strong2). Covalent Bond is weak

3). Electronegativity difference between two atoms is more than 1.9Eg:NaCl, KCl3). Electronegativity difference between two atoms is less than 1.9Eg: H2, O2, N2

23) Write the Difference between Ionic Compound and Covalent Compound?Ans:Ionic CompoundsCovalent Compounds

1). These are Crystalline solids1). These are gases (or) volatile liquids (or) solids

2). These are hard and brittle2). These are weak

3). These are having high MP & BP3). These are having low MP & BP

4). These are solute in polar solventsEg: Water4). These are soluble in non-polar solventsEg: Benzene

5). These do not exhibit Isomerism5). These are exhibit Isomerism

24) Define Oxidation and Reduction?Ans:Oxidation and Reduction:Oxidation:1) Removal of electron from an atom (or) ion (or) molecule Na Na+ + 2) removal of H from a molecule or an ion H2S + Cl2 2HCl + S3) addition of oxygen to an atom (or) molecule (or) ionC + O2 CO24) Increase in oxidation state of an atomFe+2SO4 Fe+32 (SO4)3Reduction:1) Gain of electronsNa+ + Na 2) Addition of Hydrogen H2 + Cl2 2HCl 3) Removal of oxygenCuO + H2 Cu + H2O4) Decrease in oxidation state of an atomCu+2I2 Cu2+1 I225) Define Oxidant ? Ans:Oxidant: The substrate which acts as electron acceptorEg: MnO4, K2Cr2O7, OSO4, O, F, Cl26) Define Reductant ?Ans:Reductant: which acts as electron donorEg: Li, Na, K, Mg27) Define Redox reaction?Ans:Redox reaction: A reaction which involves simultaneous oxidation and reduction is called redox reactionZn + Cu+2 Cu + Zn+2Oxidation: Zn Zn + Reduction: Cu+2 + CuUses:1) Important in biological process.2) Important in electrochemical process.28) Write the Difference between Oxidation State and Valency?Ans:Oxidation StateValency

(1). The residual charge present on the atom or ion is called Oxidation Number.(1). The strength of an element to combine with other elements is called Valency.

(2). It may be integral or fractional.(2). It is always integral only.

(3). It may be negative or positive.(3). No position or negative sign for Valency.

(4). An atom may have zero oxidation number in the compounds.(4). An atom has never zero Valency in the compounds.

Prepared by V Naga Surendra Reddy16Fundamentals of chemistryLecturer in Chemistry