Question: iron forms a bcc lattice with a density of 7870 kg/m^3. In the bcc structure each atom has c1 = 8 nearest neighbours (coordination number) at a distance of dc1 = 2r = √3 2 a ≈ 0. Nearest cities. 6. If a distance between two nearest atoms is 3. To find the nearest neighbour distances from one point pattern to another point pattern, use nncross. Medium. 7 4 P F B C C = 0 . Coordination number (CN) is the number of nearest neighbors of a central atom in the structure. Potassium has a bcc structure with nearest neighbour distance 4. The length of this diagonal in terms of the radius ( r) of particle is 4r. The density of the element is 8. In a crystal lattice, the distance between nearest-neighbor atoms can be expressed in terms of the l. British Columbia (Canada) Driving Distance Calculator, calculates the Distance and Driving Directions between two addresses, places, cities,. T l A l (S O 4 ) 2 . The nearest neighbour distance dis the same as the distance from. 1x of. Calculate its density - ( A s s u m e m a s s o f s o d i u m = 2 3 g / m o l ) MediumThe models can be extended to bcc metal structures and incorporate polarization. So for BCC let's consider the atom at the body centre, for this atom the atom at the corner are nearest. Step 4. Answered by Varsha | 25 Jan, 2019, 11:43: AMPotassium has a bcc structure with nearest neighbour distance of 4. Sodium has bcc structure with nearest neighbour distance 367. The number of nearest neighbors and the next nearest neighbors are, _______ respectively. Its atomic mass is 39 g/mole. Then: Your first neighbours are at the corners of the same cell. 6 8Trick to calculate Nearest neighbour distance and coordination number in Bcc // solid state class 12. Electrical Engineering. 15dc1. 53%. Sodium has a bcc structure with the nearest neighbor distance 3 6 5. 311 ˚ A at 0 K, the nearest neighbour distance in A r at 0. The nearest neighbor atoms in a bcc unit cell are the center atom and any of the corner atoms. Find atoms/cell and nearest neighbor distance for sc, bcc, and fcc lattices. sc: atoms/cell = 8 1 = 1 8 nearest neighbor distance =VIDEO ANSWER: the question is that how is that going to close back lettuce can be represented but figure if C. 47 DC 4 12 1. Find the perpendicular distance between the two planes indicated by the Miller indices (1 2 1) and (2 1 2) in a unit cell of a cubic lattice with a lattice constant parameter ‘a’. a 1, a 2, a 3, a 4 are coefficients of any 4 consecutive terms in the expansion of (1 + x) n, then a 1 a 1 + a 2 + a 3 a 3 + a 4 =Thus, the nearest-neighbor distance is: d = r * sqrt(2) (b) For the BCC crystal along the [111] direction, there are four atoms per unit cell along this direction. calculate the nearest-neighbor distance d_nn, and the length of the conventional crystal unit cell,a. View solution. A recently proposed analytic nearest-neighbour model for fcc metals is criticised and two alternative nearest-neighbour models derived from the separable potential method (SPM) are recommended. centred cubic (BCC) and face-centred cubic (FCC). Therefore, larger k value means. a nearest neighbour distance of 0. 15 linear chain 2 2 2 1. These are the nearest neighbours for the atom at the center. 02:17. Reason: Bcc has greater packing efficiency than fcc. ! The simple cubic has 1 lattice point per unit cell, with a total area of a3! Number of nearest neighbours: 6! Nearest neighbour distance: a! Number of next-nearest neighbours: 12! Next-nearest neighbour distance: √2a (prove this!) Simple cubic lattice (4/3)π(a/2)3 (a3) Packing fraction. 1 Find atoms/cell and nearest neighbor distance for sc, bcc, and fcc lattices. 4824 A°, but is 2. This is the link • Trick to calculate. 0016 g cm^(-3)? by Chemistry experts to help you in doubts & scoring excellent marks in Class 12 exams. That will be the nearest neighbour at the next level. Potassium has BCC structure with nearest neighbour distance (2. The. First of all, the structural characteristics of BCC lattice is examined. g. 10. , 12 nearest neighbor for perfect FCC and HCP crystals, 14 nearest neighbors for perfect BCC crystals). , 6 for the fee, bcc, and sc Bravais lattices. The cutoff distance was selected so that the distance is longer than the second nearest neighbor distance of Ti, an element with the longest nearest neighbor distance among V, Cu, Mo, and Ti. 2 Ao. Let’s just use the distance formula in 3D. The nearest neighbor distance in the FCC structure equals: √2a, 3a, √2/2, √3a/2. 31 graphene 3 6 1. Q3. First closest neighbor is eight (molecules at corner)and The Second closest neighbor is six. The nearest distance is the distance between centre of these atoms. 最近傍探索（英: Nearest neighbor search, NNS ）は、距離空間における最も近い点を探す最適化問題の一種、あるいはその解法。 近接探索（英: proximity search ）、類似探索（英: similarity search ）、最近点探索（英: closest point search ）などとも呼ぶ。 問題はすなわち、距離空間 M における点の集合 S があり. g. Reason Bcc has greater packing efficiency than fcc. Thus, the nearest-neighbor distance is: d = r * sqrt(2) (b) For the BCC crystal along the [111] direction, there are four atoms per unit cell along this direction. View Solution. Nearest neighbour distance in bcc unit cell is greater than that of fcc having same edge length. 29 A. Class 9; Class 10; Class 11; Class 12; CBSE BoardThat will be the nearest neighbour at the next level. Potassium has a bcc structure with nearest neighbour distance 4. Text Solution. 73 Angstrom. Its atomic weight is. 5071 and 4. 248 nm and 0. 543 nm. First three nearest neighbour distance for body centred cubic lattice are respectively:Introduction of edge length and Calculation of coordination no. d O 2a/v3 . Its density would be (1(5. For cubic materials, there are equations in which to calculate nearest neighbor (NN), second nearest neighbor, etc. . Find the number of atoms/unit-cell and nearest neighbor distance for (a) sc, (b) bcc, (c) fcc, (d) diamond, and (e) zinc blende unit-cells. Calculate its density (atomic mass of sodium = 23) A. because Statenemt -2: fcc has greater pack. This is incorrect. View Solution. For cube of length a and atomic radius r, we have. 43a=5ǺǺ. The no. radii of A and B atoms are then 1Ǻ number of A atoms per unit cell = 8 ⋅ 18 = 1 A number of B atoms per unit cell = 1 4Å volume of atoms per unit cell = 1 ⋅ 4π3 ⋅ (1Å)3 + 1 ⋅ 4π3 ⋅ (1Å)3. View Solution. In bcc lattice the corner atoms are called as the nearest neighbours and also a bcc structure has 8 corners atoms, so the pottassium atom will have 8 nearest neighbours. 3. 3r ≈ 1. Since there are two lattice sites per bcc cubic cell, the density should be. Results for copper and aluminium illustrate the utility of the recommended models. This is correct. . What is metal X if its density is 1. And in a 3D packing a unit cell will be sitting on the top of our unit cell. 7 ? A then what is the lattice parameter? Find the reciprocal lattice vectors for the bcc and fcc structures and calculate the primitive volume for each. In body centered cubic packing structure model we have an atom at the center and eight atoms at the 8 corners of the cube. The radius of the sodium atom is approximately :-12. The NaCl structure can be regarded as two interpenetrating FCC lattices. A metal X has a BCC structure with nearest neighbor distance 365. Here a is the lattice constant of the bcc lattice and R is the radius of the sphere. The first three nearest neighbor distance for primitive cubic lattice are respectively (edge length of unit cell = a): A. First closest neighbor is eight (molecules at corner)and The Second closest neighbor is six. Can you help me with hints on how to proceed preferably with a diagram. Numeric vector or matrix containing the nearest neighbour distances for each point. For body-centered cubic (BCC) structures the cutoff radius should be positioned between the second and the. Threfore there are three groups of four lattice points lying in three perpendicular face planes. Make a table of N n and r n for n = 1,. This is incorrect. J K CET 2004: The nearest distance between two atoms in case of a bcc lattice is equal to (A) (a√2/3) (B) (a√3/2) (C) a√3 (D) (a/√2) . 623. Reason Bcc has greater packing efficiency than fcc. For bcc metals, as well known, the second nearest–neighbor distance is larger than the first nearest–neighbor distance by only about 15% and the number of the second nearest–neighbor atoms (Z 2 = 6) is very near to that of the first nearest–neighbor atoms (Z 1 = 8). The atoms behave as hard spheres and touch along the < 1 1 1 > directions. Third neighbours: centers of the next adjacent cells. I have also discussed how to find out first,second and third nea. ALL ABOUT CUBE :- WITH US ON CHEMISTRY UNTOLD HINDI :- equal to -Z1/2 and the scaled equilibrium nearest-neighbour distance is unity. Assertion :Nearest neighbour distance in bcc unit cell is greater than that of fcc having same edge length. A simple cubic crystal has only. Note that the nearest-neighbor distance corresponds to the atomic bond length Calculate the density (in units of g/cm3) of Si and GaAs from the lattice constants, atomic weights, and Avogadro's number. More From. 200 pm. e. $ dfrac{{asqrt 3 }}{2} $ = $ 4. Now put all the given values in this formula, we get :What is the nearest neighbour distance and what is the radius of the xenon atom? N earest neighbour distance = 2r (in FCC) ⇒ = 4r. If the nearest neighbour distance is x then calculate the volumes of the unit cells in bcc, fcc, & sc structures in terms of x. Answer: For a body centered cubic (BCC) lattice, the nearest neighbor distance is half of. Then: Your first neighbours are at the corners of the same cell. Thus, the number of unsaturated bonds in particular layers. 86 g/cm3. Prove that : a + 1 a + 2 a + 2 1 a + 2 a + 3 a + 3 1 a + 3 a + 4 a + 4 1 = - 2. Therefore, for a simple cubic lattice there are six (6) nearest neighbors for. This problem has been solved! You'll get a detailed solution from a subject matter expert that helps you learn core concepts. One way one can get this is as follows. Get Distance & Directions. Sodium has a BCC structure with nearest neighbour distance of 365. And there are $8$ such atoms, at a distance $(a√2)/2 = 0. 9 pm. 0 ˚ A respectively. That is not the maximum (which is 12, found in close-packed structures), but BCC has such high stability because of its next-nearest neighbors. CsCl has the bcc arrangement and its unit cell edge length is 400 pm. The density of the element is 7. This is the nearest distance in fcc. Its density will be. The density of the element is 8. It can also be imagined as stacking 3 close-packed hexagonal layers such that the top layer and bottom layer line up. Silicon Crystal Structure Last updated 2/26/22 These concepts have been greatly simplifiedatoms/cell = 8 ⋅ 18 = 1 sc sc: lattice a 2 nearest neighbor distance = a bcc: atoms/cell = 8 ⋅ 18 + 1 = 2 bcc lattice a⋅ 3 a 2 √3 nearest neighbor distance = a 2 2 a 2 √2 fcc: atoms/cell = 8 ⋅ 18 + 6 ⋅ 12 = 4 fcc lattice a⋅ 2 a a 2 √2 nearest neighbor distance = 2 2 a 2 Prob. Its atomic mass is 39 g/mole. The nearest neighbour distance (in pm) is : Medium. Continue reading. So for BCC let's consider the atom at the body centre, for this atom the atom at the. READ SOMETHING ELSE. How many nearest neighbors does each particle in the face-centered cubic structure have? The coordination number of atoms in fcc lattice 12 and hence the number of nearest neighbours is 12 around each particle in face centered cubic lattice. Say you are sitting in the center of a cell. Formally, the nearest-neighbor (NN) search problem is. . ∴ Distance between two atoms. This is consistent with the packing density calculations reported in lecture that give FCC as being 74% dense and BCC 68% dense. If k = 1 (the default), the return value is a numeric vector v such that v[i] is the nearest neighbour distance for the ith data point. Bihar Board. 52 Å. View solution > An element crystallizes in a bcc lattice. 4. Check A. 0 g cm −3 . H. In a bcc structure, for any atom at the corner of the lattice, nearest neighbour is at the centre of the lattice which is at a distance ofThe second nearest neighbour isat the adjacent corners of the lattice at a distance of a. The number of nearest neighbors and the next nearest neighbors are, _______ respectively. In this video I have discussed the effective number of atoms in the simple cubic unit cell . (1), one can find the nearest neighbour distance at pressure P and temperature T. The correct option is C a √2. All calculations were done with the LAMMPS [18] and an in-house MD code, KISSMD [19]. 0 g cm −3 . Sodium has a bcc structure with nearest neighbour distance of 365. e. The values are written as messages at the bottom of the Geoprocessing pane during tool execution and passed as derived output values for potential use in models or scripts. Nearest neighbors and next-nearest neighbors of the elements are respectively : Q. 43 °A, calculate: (a) the distance from the center of one silicon atom to the center of its nearest neighbor, (b) the number density. 52 ∘A . Q 5. r = 43a. atoms crystal-structure solid-state-chemistry. 23 26 Metallic is explained by Diffusion of ions (O Excitation of free electrons Oscillation of positive ions Existence of bcc al I attic. Interplanar cystal spacing of cubic crystal families is defined as. Number of atom per unit cell = 8 x 1/8 + 1 x 1 = 2 Number of atoms in - 8ghto4gg. View Solution. Not yet answered Marked out of 1 2 سؤال 2 The nearest neighbor distance in case of bcc structure of side a is: . 9 pm. >> Number of Atoms in a Unit Cell. 52 Å`its atomic weight is `39` its density (in kg `m^(-3)`) will be asked Mar 31, 2020 in Chemistry by Chithrajain ( 84. for the bcc lattice. The analysis algorithms [acna,baa,cspfcc,cspbcc,voro,nda] sort the neighbor. type and ε 0 the energy at the equilibrium distance. Its relative atomic mass is 39. View solution > Answer the following questions . There are no spare bonds. The red rectangles indicate primary cell in each structure and the circles indicate the ranges over which an atom interacts with its neighbors. 1 answer. Therefore, the distance between nearest-neighbor atoms in a BCC lattice is v3 times the lattice constant "a. Crystal structures: If the nearest neighbor distance is 2 A then calculate the volume of the unit cells in bcc, fcc and sc structures. 8; 3 4 3 3 / 8 3 2 4. 03 dimer 1 3. Who are the experts?Bihar Board. For a simple cubic lattice, the nearest neighbor distance is the lattice constant. Question One: Find the number of third nearest neighbors and its distance for the: SC, BCC and FCC structures. Sodium has a bcc structure with nearest neighbour distance of 365. In the fcc crytsal lattice, the atoms are present at corners of the cube and at the face-centres of the cube. These formulas can be used to obtain a good cutoff distance: The units of the cohesive energy E c, equilibrium nearest-neighbor distance r e, and the bulk modulus B are eV/atom, Å, and 10 12 dyne/cm 2, respectively. Hence, it will have 6 nearest atom to it in simple cubic. 47. In crystallography, the cubic (or isometric) crystal system is a. Question 2 1 pts The 4th nearest neighbor distance in a BCC lattice that has a lattice parameter equal to a is Q v3 w/2 O 2a Question 3 1 pts The number of atoms per unit area on the closest packed plane in a BCC lattice that has a lattice parameter equal to a is O 1/8*2 O V2 /2a*2 Q 2/ 2 a*2 O v3/2a^2In the present video I have discussed details of Face centered Cubic Structure. ALL ABOUT CUBE :- WITH US ON CHEMISTRY UNTOLD HINDI :- In the N a C l type structure shortest distance between two nearest neighbours is 100 pm, then the distance between two next nearest neighbours in the same unit cell will be: Q. View solution. 286 nm, respectively. 9 p m Calculate its density. If the index is less than 1, the pattern exhibits clustering; if the index is greater than 1, the trend is toward. . 9 pm. And there are $8$ such atoms, at a distance $(a√2)/2 = 0. As a result, the nearest neighbours are 12 atoms. Q. The four corners of this face are nearest neighbours to the central lattice point. = 23a. as in this crystal structure the first-nearest-neighbour distance is only slightly smaller than the second-nearest-neighbour distance and. This value is expected to increase further with the increased dumbbell. 25330 Note: • expect sum of 1/rn to converge rapidly for large n • A12 is dominated by the nearest neighbours (10 in FCC, HCP, 8 in BCC), but more distant neighbours affect A6 4. -The number of atoms present per unit cell in a bcc lattice is 2. 036, N A = 6 × 10 23, K = 39) View Solution SolveThe total number of atoms in a bcc unit cell is 1/8 * 8 (corner atoms) + 1 (center atom) = 2 atoms. In FCC, the nearest atom from one corner is at the face center at a distance of √(2a/2). function of the interatomic distance, (a) Using the Lennard-Jones potential, calculate the lattice constants of the fcc, hcp, and bcc crystals at zero pressure and temperature. Similarly, in the the figure for 4th nearest neighbors, there are more than 18 atoms linked by the black lines. The displacement of atom A is approximately equals to half of the neighbor distance along <111> direction in bcc lattice, so A′ is the split interstitial site. In terms of the lattice constant a, what is the distance between nearest neighbor atoms in (a) a simple cubic lattice (b) a bcc lattice, and (c) a foc lattice? 4. 18 16 : 57. `=2xxsqrt3/4a=sqrt3/2a`. View solution > Sodium metal crystallizes in a body-centered cubic lattice with a unit cell edge of 4. A metal crystallize in a body centered cubic lattice (bcc) with the edge of the unit cell 5. Consider the lattice point at the centre of the top face of an FCC unit cell. 10. Solution. The distance between nearest neighbour is: Q. The definition of the distance function is central for obtaining a good accuracy on a given data set and differ-ent distance functions have been proposed to increase the performance. 414 * a So, for bcc, d = 1. Q 5. Therefore, for a BCC lattice there are eight (8) nearest neighbors for any given lattice point. Check A. 9 pm. In the bcc structure, two types of. The number of nearest neighbours for that element is the number of atoms that are at this distance from your starting atom. 2) 2 = 0. Since each fluoride ion has four nearest-neighbor calcium ions, the coordination in this structure is described as (8:4). Step by step video, text & image solution for First three nearest neighbour distance for body centred cubic lattice are respectively: by Chemistry experts to help you in doubts & scoring excellent marks in Class 11 exams. Each radial cutoff distance was set to a value larger than the second nearest neighbor distance in each system. (8) For the fccmetal the. For instance, for fcc and hcp it should be larger than then nearest neighbor distance, while for bcc, it should be larger than the second nearest neighbor distance. a. Statement 1: Distance between nearest lattice points in BCC is greater than the same in FCC having same edge length. 414). 9 p m. 12. The number of next nearest neighbors in the BCC structure equals: 4, 8, 12. Solution (a) The answer can be found by looking at a unit cell of Cu (FCC). A metal X has a BCC structure with nearest neighbor distance 365. Number of atom in unit cell of BCC (Z) = 2 Nearest neighbor distance, r = Atomic mass (M) = 39 g/mole Avogadro's number . The next neighbors are in the center of the cube, and there are $8$ such atoms, at a distance $(a√3)/2 = 0. Second nearest neighbors are the neighbors of the first neighbors. The distance of the nearest lattice points in terms of the lattice parameter (i. Caleulate its density 13. In Potassium (bcc crystal lattice); a) Distance between the nearest neighbours: Taking the center atom in consideration; as we know in a bcc lattice each center atom is attached to eight corner atoms which are the nearest neighbour atoms. The nearest distance is the distance between centre of these atoms. We must know that in BCC lattice, the packing efficiency is 68%. View solution. If k = 1 (the default), the return value is a numeric vector v such that v[i] is the nearest neighbour distance for the ith data point. For face centred cubic lattice nearest neighbour distance is half of the face diagonal distance, a√2/2. In a bee lattice, the atoms touch one another along the body diagonal. 0 Å, respectively. 27, has a distorted close-packed structure. The nearest neighbor distance is 0. Sodium has a bcc structure with nearest neighbour distance of 365. of atom touching a particular atom in the given unit cell is known as coordination number and that atoms are known as nearest neighbour. BCC unit cells: (a) atomic-site unit cell, (b) hard-sphere unit cell, and(c) isolated unit cell. Sodium has a bcc structure with the nearest neighbor distance 365. Who are the experts?Nearest neighbour distance in bcc unit cell is greater than that of fcc having same edge length. Crystal structures: If the nearest neighbor distance is 2 A then calculate the volume of the unit cells in bcc, fcc and sc structures. Aluminum: 286. There is one at the center of the adjacent cube to our cube. 414). There are eight first nearest neighbors, six second nearest. r = nearest neighbor distance. Like. Interplanar distance in FCC and BCC. It is given by : AF= (AD) 2+(FD) 2= (a) 2+(a2) 2=a3. We would like to show you a description here but the site won’t allow us. 91 kg m-3 b)0. Here a a is the length of a side of the unit cell and R R is the radius of the atom the cell consists of. So for BCC let's consider the atom at the body centre, for this atom the atom at the. Closeness is typically expressed in terms of a dissimilarity function: the less similar the objects, the larger the function values. I am trying to verify this lattice constant a a. Modified 3 years, 8 months ago. 255 nm. HCP has 6 atoms per unit cell, lattice constant. The nearest neighbor of corner atom is at a distance √3a/2 where a is the length of side of unit cell. Now, for a bcc unit cell, the relationship between r and a (edge-length) is: r = √ 3 4 a. The third next neighbors are the 6 next apexes, with a distance a. Sodium has a bcc structure with the nearest neighbor distance 3 6 5. Nearest neighbour to an atom (say at origin) is the atom present is the centre of theat point P and the position of P can be =The correct answer is: = The positions of number of nearest neighbours in a unit cell of bcc structure is given by:a)b)c)d)None of theseCorrect answer is. Copper Oxide Layers The common building blocks for most high temperature (high Tc) su-perconductors are copper oxide layers as shown in the figure below. What is the nearest neighbor distance for a bcc lattice? For a body centered cubic (BCC) lattice, the nearest neighbor distance is half of the body diagonal. g. IIT JEE & NEET video lectures by nucleon KotaDownload app to watch videos prepared in Kota classrooms by IITian educators with. - wherein. Fourth, neighbors are the far corners of the most approaching adjacent cells. Step 2. 5k points) class-12A nearest neighbour in general terms is literally that: Find the closest atom of any given element, that is your nearest neighbour distance for that element in the lattice. Option 1) 12, 6. 50 SC 6 12 1. other (distance = 0. D. If its density (in g cm–3) would be X , then the value of ( 100 X − 1 10 ) is Potassium has a bcc structure with nearest neighour distance `4. Consequently for the middle particle (It will apply for the wide range of various too). dhkl = a h2 +k2 +l2− −−−−−−−−−√. What is the nearest neighbor distance for a fcc lattice? For a face centered cubic (FCC) lattice, the nearest neighbor distance is half of the face diagonal distance, a 2 2. The lattice constant of silicon is 5. In BCC, the nearest atom from one corner is at the body center, at a distance of √(3a/2). •each sphere touches 12 equidistant nearest neighbors (CN = 12). neighbours and the nearest neighbour distance for either a BCC or FCC structure. 11 Å) Body-centered with Edges and Faces. How close-packed structures of spheres can be constructed: In a first layer the spheres are arranged in a hexagonal pattern, each sphere being surrounded by six others (A). View solution > View more. The calculated lattice constants of bcc V-Mo, bcc V-Ti, and hcp V-Ti solid solution phases are presented in Fig. Note that the nearest-neighbor distance corresponds to the atomic bond length. 6. 2 Equilibrium SeparationA 4Å A B A B A A B A 4Å A B Note: The atoms are the same size and touch each other by the hard sphere approximation. Second nearest neighbors are the neighbors of the first neighbors. From our MD simulations,. • Give the average number of atoms in a unit cell for BCC structure and explain why • Given atoms radius of R for the BCC structure, do the followings: • Calculate distance between the centers of one atom to the center of its nearest neighbor • BCC cubic unit cell edge length • Label [100] direction and (001) planePotassium has a bcc structure with nearest neighbour distance 4. So for BCC let's consider the atom at the body centre, for this atom the atom at the. First three nearest neighbour distances for body centred cubic lattices are respectively: A. Question: a) How many atoms are there in a simple cubic unit cell? in a bcc unit cell? in a fcc unit cell? in the unit cell characterizing the diamond lattice? b) In terms of the lattice constant a, what is the distance. 60 0. Viewed 13k times. 9 pm. g. Q. 3. For a simple cubic lattice, it is clear that the nearest neighbor distance is just the lattice parameter, a. In this video I discussed Trick to calculate Nearest neighbour distance & coordination number for simple cubic structure. Since each fluoride ion has four nearest-neighbor calcium ions, the coordination in this structure is described as (8:4). The distance between two nearest neighbour in a bcc cell = `1/2xx` the length of body diagonal = `1/2xx4r=2r` `=2xxsqrt3/4a=sqrt3/2a`. Number of atom in unit cell of BCC (Z) = 2 Nearest neighbor distance, r = Atomic mass (M) = 39 g/mole Avogadro's number .