Review – Chapter 4                                                      Name_______________________________

J. Rodriguez, Chemistry 253                                                     Date__________________________

 

1. (a)  What is the difference between the atomic number and the mass number of an element?

 

The atomic number is the number of protons in an atom while the mass number is the number of protons and neutrons in an atom.

 

 

(b)    Can atoms of two different elements have the same atomic number?  Why or why not?

 

No.  The number of protons is what identifies an element.

 

 

(c)     Could they have the same mass number?  Why or why not?

 

Yes.  Two atoms could have the same mass number because the number of neutrons vary among atoms of the same element.

 

 

2. Carbohydrates, a class of compounds containing the elements carbon, hydrogen, and oxygen, were originally thought to contain one water molecule (H₂O) for each carbon atom present.  The carbohydrate glucose contains six carbon atoms.  Write a general formula showing the relative number of each type of atom present in glucose.

 

C₆(H₂O)₆   =   C₆H₁₂O₆

 

 

3.  Write the atomic symbol (    X) for each of the isotopes described below.

 

(a)     Z = 6, number of neutrons = 7

13

6   C

 

(b)    the isotope of calcium with a mass number of 41

41

20  Ca

 

3. Complete the following table.

 

Symbol	Protons	Neutrons	Mass Number
Ca	20	21	41
55 25   Mn	25	30	55
109 47   Ag	47	62	109

 

4. (a)Draw the atomic structure of Al³⁺ ion.

 

Drawing should contain 13 p+, 14n^o, 2 electrons in the first energy level and 8 electrons in the second energy level.

 

 

 

 

(b)    Does aluminum donate electrons to other atoms or receive electrons from other atoms?

Donate.

 

 

5. For the following pairs of ions, use the concept that a chemical compound must have a net charge of zero to predict the simples compound that the ions are most likely to form.

 

(a)    Co³⁺  and S^2-

 

Co₂S₃

 

(b)    Fe²⁺  and PO₄^3-

 

Fe₃(PO₄)₂

 

(c)    Na⁺  and  P^3-

 

1          Na₃P

 

6. (a)  List five nonmetallic elements that exist as gaseous substances under ordinary conditions.

 

N, O, F, Cl, Ne, He, Ar, Kr, Xe, H

 

 

 

(b)    Do any metallic elements ordinarily occur as gases?

 

No