Homework #15

13. a. A horizontal row is also a period, with elements listed in order of increasing atomic numbers.
    b. A vertical column is a group, that contains elements with similar properties.

14. Sodium (Na) and Potassium (K).

15. a. The noble gases are located on the far right side of the periodic table.

    b. Noble gases are unreactive. 
    c. Noble gases are chemically inert. 

16. a. MgF2
    b. GaP

17. 

Potassium is right between sodium and rubidium on the periodic table:

98+39=137
137/2=68.5

18. I would expect the boiling point of chlorine to be lower than that of iodine. From what I have observed, I believe that elements with higher atomic weights have higher boiling points than those with lower atomic weights. Chlorine has a lower atomic weight (35.45) than iodine (126.90), so, chlorine must have a lower boiling point. 

19. 

Completed chart:

20. 

a. 4 protons, 4 or 5 neutrons, 4 electrons.
b. 7 protons, 7 or 8 neutrons, 7 electrons.
c. 10 protons, 10 or 11 neutrons, 10 electrons. 

21. Although protons are positive, when an atom forms an ion, it either loses or gains electrons. Since a lead ion with a 2+ charge was formed, the atom must have lost two electrons.

22. 

a.
Carbon: 6+6=12, or 6+7=13; 12 or 13
Calcium: 20+21=41; 41
Platinum: 78+117=195; 195
Uranium: 92+146=238; 238

b. Carbon has two isotopes in the table. 

23. No, the discovery of a new element would not be justified by only its mass number. It would be more helpful to know either the atomic weight or atomic number in order to be able estimate physical and chemical properties of the element and its probable spot on the periodic table. An element's mass number does not provide enough information to justify its existence. 

24. The mass of an electron is about 1/2000 the mass of a proton or a neutron. Because of its minuscule weight, it is insignificant, and not used to calculate the mass number of an atom.

25. 

Completed Chart: