1. How many atoms are in 1.00g of tungsten? How many moles is this? 2. How many

Question

1. How many atoms are in 1.00g of tungsten?  How many moles is this?

2. How many atoms are in 1.00 cm3 of lead?  In 1.00 m3 of silicon?

3. A cube of aluminum contains 1.0x1021 atoms. How long is its edge (in mm)?

4. How many electrons are in the outer shell of the following neutral atoms?

(a) krypton (b) oxygen (c) magnesium (d) potassium

5. What kind of bonding is present in (a) methane (gas)  (b) sodium bromide

(c) aluminum oxide, (d) aluminum metal, (e) frozen (solid) argon.

6. Sketch a cube.  How many vertices does it have?  How many edges?  How many faces?  Mark four vertices of the cube that are also vertices of a regular tetrahedron.

7. In a methane molecule CH4 the four hydrogen atoms are arranged as if at the vertices of a regular tetrahedron centered on the carbon atom. Sketch it. What is the angle between the C-H bonds in methane?  Prove it by calculation.

8. Three spheres, A, B and C, each 1 inch in diameter, are arranged on a horizontal flat surface so that they touch each other and their centers form an equilateral triangle. A fourth sphere D, also 1 inch in diameter, is placed on top of the other three so as to form a regular tetrahedral configuration (it touches each of the other three spheres).

(a) Make a sketch of the four spheres arranged as described above.

(b) What is the distance between the centers of the spheres?

(c) How far above the flat surface is the center of  sphere A?

(d) How far (vertical distance) above the center of sphere A is the center of sphere D?

(Hint: if you can't visualize this, use pool balls or ping-pong balls to help you. This problem may be solved using only the Pythagorean theorem if you are good at geometry, but it is much easier with trig.).

Explanation / Answer

1) atomic mass of tungusten = 184 so no of moles = 1/184 = 0.0054

2) density of lead = 11.34 g/cm^3 density of silicon= 2.3290 g/cm^3

weight of lead = 11.34*1 = 11.34g no of moles = 11.34/207 = 0.054

no of atoms = 0.054*6.023*10^23 = 3.25*10^22

weight of silicon = 2.3290*10^6g no of moles = 2.3290*10^6/28 = 8.31*10^4 moles

no of atoms = 8.31*10^4*6.023*10^23 = 5.005*10^28

3)no of moles = 1.0*10^21/(6.023*10^23) = 0.00166

weight of Al = 0.00166*27 = 0.04482 g

desnity of Al = 2.70 g/cm^3

volume = 0.04482/2.7 = 0.0166 cm^3

edge length = cube root ( 0.0166 cm^3) = 0.255 cm or, 2.55 mm

4)a)Krypton = 8 b) oxygen = 6 c)magnesium = 2 d)potassium = 1

5)a) methane (gas) --> covalent

b) sodium bromide--> ionic

c) aluminum oxide--> ionic

d) aluminum metal--> metal bonding

e)frozen (solid) argon--->none

6)

vertices = 8, edges= 12, faces=6

start from any vertex draw a vertical line to the next vertex from there draw two lines two the next two vertices these are the vertices of a tetrahedron

7)

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