3. (d) S2- ions form fee lattice and Zn2+ ions go into alternate tetrahedral voids of the unit cell. One electron of carbon remains free. (c) super cooled liquids (d) super cooled solids Question 50. For the CF 2 Cl 2 Lewis structure there are a total of 32 valence electrons available. Thus far, we have used two-dimensional Lewis structures to represent molecules. And so if you wanted to represent oxygen with its six valence electrons, you could go ahead and draw in six valence electrons like that. of atoms per unit cell = 4 Tin atoms make covalent bonds. (d) Anisotropic nature A covalent bond is formed between two atoms by sharing electrons. Which of the following is true about the charge acquired by p-type semicon-ductors? Question 5. There are a number of molecules whose total number of valence electrons is an odd number. Question 11. For one dopant atom, one hole is created because the place where fourth electron is missing is called vacancy or hole and is responsible for conduction of germanium doped with gallium. Solution: (b) Anisotropy: Crystalline solids are anisotropic in nature, that is some of their physical properties like electrical resistance or refractive index show different values when measured along different directions in the same crystal. Choose the correct answer out of the following choices. How many covalent bonds does a hydrogen atom typically form? (c) Delocalised electrons increase the conductivity of doped silicon Iron is in group 8, so group 8 - 3+ charge = d 5 (or 3d 5) 8 - 3 = 5. Why are solids incompressible? (b) Assertion and Reason both are correct statements but Reason is not the correct explanation for Assertion. Ans: PF 5 is trigonal bipyramidal, whereas IF 5 is square pyramidal 40. T. he two delocalized electrons make multiple resonance structures possible for the sulfate ion (SO 4-2). Question 41. Solution: (b) In graphite one carbon atom is attached to three other carbon atoms. Now each Cl atom has seven electrons and the Br atom has seven electrons. Figure %: The periodicity of valence electrons This table illustrates a number of interesting, and complicating, features of electron configuration. Solution: (d) Amorphous solids are isotropic because they show thermal and optical properties, same in all directions. Also sodium atom contains one valence electron which is unpaired, then does sodium atom is also considered a radical? The Lewis structure for CF 2 Cl 2 is similar to CF 4 or CCl 4. Solution: (a, d) Ferrimagnetic substances lose ferrimagnetism on heating and become paramagnetic. A covalent bond is formed when two atoms share electrons. In Cl2 molecule, each chlorine atom is surrounded by an octet number of electrons. of particles present in close packing Which of the following represents correct order of conductivity in solids? (iii)In case of BCC atom present at the corner and center of the body touch each other. Which of the following statement is not true about the hexagonal close packing? (a) Graphite (C) (b) Quartz glass (SiO2) Assertion (A): The total number of atoms present in a simple cubic unit cell is one. (c) A and C (d) B and D CaF2(s) dissolves in water to form particles. Why does table salt, NaCl sometimes appear yellow in colour? While SO, Chapter 6 General Principles and Processes of Isolation of Elements, Chapter 12 Aldehydes, Ketones and Carboxylic Acids, NCERT Solutions for Class 10 Science Chapter 1, NCERT Solutions for Class 10 Science Chapter 2, Periodic Classification of Elements Class 10, NCERT Solutions for Class 10 Science Chapter 7, NCERT Solutions for Class 10 Science Chapter 8, NCERT Solutions for Class 10 Science Chapter 9, NCERT Solutions for Class 10 Science Chapter 10, NCERT Solutions for Class 10 Science Chapter 11, NCERT Solutions for Class 10 Science Chapter 12, NCERT Solutions for Class 10 Science Chapter 13, NCERT Solutions for Class 10 Science Chapter 14, NCERT Solutions for Class 10 Science Chapter 15, NCERT Solutions for Class 10 Science Chapter 16, CBSE Previous Year Question Papers Class 12, CBSE Previous Year Question Papers Class 10. (a) conducting solid (b) network solid distance in the crystal lattice . In the HBr molecule, H achieves a full valence of two electrons (duet) while Br achieves an octet. (a) Silicon doped with an electron rich impurity is a p-type semiconductor Question 24. (i) If the crystal lattice consists of SCC, the atom which is present at the comers touch each other Question 77. Question 62. (d) domains are not affected by magnetic field. Question 14. (a) SiC (b) AIN (c) 8 tetrahedral voids each of which is shared by four adjacent unit cells of. A molecule is a discrete combination of atoms; a formula unit is the lowest ratio of ions in a crystal. 9.9 Bond Energy Practice Questions Solution:The conductivity of semiconductors is increased by adding an appropriate amount of suitable impurity or doping. How many bonding electrons and nonbonding electrons are in the molecule? Solution:  (a, b) In p-type semiconductor, the conductivity is due to existence of hole. Why do hydrogen atoms not follow the octet rule when they form covalent bonds? Refer to graph, table and property element trend below for Valence Electrons of all the elements in the periodic table. This gives the formal charge:Br: 7 – 7 = 0Cl: 7 – 7 = 0 All atoms in BrCl 3 have a formal charge of zero, and the sum of the formal charges totals zero, as it must in a neutral molecule. (d) In this arrangement, spheres of the fourth layer are exactly aligned with those of the first layer. Question 42. Question 21. (c) Frenkel defect (d) Schottky defect (b) Holes will appear to be moving towards the negatively charged plate Two separate fluorine atoms have the following electron dot diagrams: Each fluorine atom contributes one valence electron, making a single bond and giving each atom a complete valence shell, which fulfills the octet rule: The circles show that each fluorine atom has eight electrons around it. Question 17. The atoms in group 6A make two covalent bonds. If it is doped with an electron rich impurity, the extra electron becomes delocalised and increases the conductivity. Why is FeO(s) not formed in stoichiometric composition? (d) A true solid CF 4 ∆E = 4.0 - 2.5 = 1.5 for F-C strongly polar covalent -150°C Why does CF 4 have a similar mp to CH 4 when the bond polarities are very different? Question 9. (d) different arrangement of constituent particles in different directions The value of magnetic moment is zero in the case of antiferromagnetic substances because the domains … (d) They are anisotropic in nature Under the influence of electric field, which of the following statements are true about the movement of electrons and holes in a p-type semiconductor? Reason (R): Intermediate, conductivity in semiconductor is due to partially filled valence band. For doing so K atom loses electrons form K ions. Solution: (c, d) Statements (c) and (d) can be correctly written as (c) Impurity defect This concept can be illustrated by using two hydrogen atoms, each of which has a single electron in its valence shell. (b) Ferrimagnetic’substances do not lose ferrimagnetism on heating and remain ferrimagnetic Draw the Lewis diagram for the covalent bond in the Br2 molecule. (b) Brittle nature This structure satisfies the octet rule. Since, packing efficiency for hep or ccp is calculated to be 74% which is maximum among all type of crystals. Hence, existence of free electrons are not possible, it is possible on in case of imperfection in solid. Astatine is a synthetic element, made one atom at a time in huge “atom-smasher” machines. Show that in a cubic close packed structure, eight tetrahedral voids are present per unit cell. 6. (a) 74 (b) 68 (c) 32 (d) 26 z How many valence electrons does an oxygen atom have A 2 B 6 C 8 D 16 03 08z from CHM 204 at Bradley University This oxide is always non-stoichiometric i.e., the composition of Fe2+ and O2 ions is not 1 : 1. Fluorine is another element whose atoms bond together in pairs to form diatomic (two-atom) molecules. Example: FeO, FeS, NiO. This is summarized in the table below. Reason (R): Simple cubic unit cell has atoms at its comers, each of which is shared between eight adjacent unit cells. (a) all the domains get oriented in the direction of magnetic field Solution: (b, c) NaCl has fee arrangement of CF ions. H forms only one bond because it needs only two electrons. However, there is another way an atom can achieve a full valence shell: atoms can share electrons. For doing so sodium atom loses electrons form Na+ ions. Consider a molecule composed of one hydrogen atom and one fluorine atom: Each atom needs one additional electron to complete its valence shell. (c) Amorphous solids can be moulded by heating Reason (R): Graphite is soft in nature on the other hand diamond is very hard and brittle. This is known as thermodynamic conduction in intrinsic semiconductors. However, diamond is hard due to compact three-dimensional network of bonding. An atom of an element in the carbon family can lose or gain electrons. So in this case, the N atoms involved in the dative bond have the valence of 3 that we expect from bipy, while the Cu has a valence of 4: >>> How does the number of valence electrons in atoms of metalloids explain why metalloids are semiconductors? Solution: (b). An electron moved from shell n = 2 to shell n = 1. what most likely happened during the transition? Solution: (a, c) Solution: (a) Conductivity of metal, insulator and semiconductors can be represented in the term of k (Kappa) which depends upon energy gap between valence band and conduction band. Question 61. The central atom N (group 5A) has 3 bonds and one lone pair.  When Ge is doped with group 13 elements, for example, gallium, the structure of crystal lattice does not change. Figure \(\PageIndex{1}\): How Many Covalent Bonds Are Formed? (b) 4 tetrahedral voids within the unit cell Question.13. Thus, (a) Vacancy defect results in a decrease in the density of the substance Adopted a LibreTexts for your class? The transition elements and inner transition elements also do not follow the octet rule since they have d and f electrons involved in their valence shells. Since filled d or f subshells are seldom disturbed in a chemical reaction, we can define valence electrons as follows: The electrons on an atom that are not present in the previous rare gas, ignoring filled d or f subshells. (a) A tetrahedral void is formed when a sphere of the second layer is present above triangular void in the first layer They have one or two valence electrons, so they can lose or gain electrons. For example, methane (\(\ce{CH4}\)), the central carbon atom bonded to four hydrogen atoms, can be represented using either of the Lewis structures below. (a) hep (b) bcc (c) simple cubic (d) fee (c) electron (d) atom Total number of octahedral voids = 12 x 1/4 +1 = 4. The transition elements and inner transition elements also do not follow the octet rule since they have d and f electrons involved in their valence … Solution: The intemuclear distance between the constituent particles (atoms, molecules or ions) in solids are very less. (b) Smaller ions occupy either the tetrahedral or the octahedral voids depending upon their size Reason (R): Besides the body centre, there is one octahedral void present at the centre of each ofthe six faces of the unit cell and each of which is shared between two adjacent unit cells. (c) The gap between valence band and conduction band cannot be determined (c) same arrangement of constituent particles in different directions The number of electrons required to obtain an octet determines the number of covalent bonds an atom can form. These four electrons can be gained by forming four covalent bonds, as illustrated here for carbon in CH4 (methane). Figure \(\PageIndex{1}\) shows the number of covalent bonds various atoms typically form. Within each column, or group, of the table, all the elements have the same number of valence electrons. Solution: (d) The fraction of octahedral or tetrahedral voids occupied depends upon the radii of the ions present at the lattice points. 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