Periodicity of elements
Francine Taylor-Campbell, Contributor

Dr. Claude Packer, principal, welcomes the new students to The Mico University College's dedication ceremony at St. Matthews Anglican Church, Weeville Gordon Road, on Sunday, September 24. - Nathaniel Stewart/Freelance Photographer

SYLLABUS REQUIREMENTS

Students should be able to:

• Identify trends in Group II
  
  
• Identify trends in Group VII
  
  
• Identify trends in period three using gradation from metallic to non-metallic properties
  
  
• Predict properties of unknown elements based on group trends.

Consider the following questions.

1. Which statement is true about the elements in Group II of the periodic table?

A. They occur uncombined in nature.

B. They are equally reactive chemically.

C. They form chlorides of similar formulas.

D. They become less metallic as the relative proton (atomic) number increases.

E. The proton (atomic) number of an element is one greater than that of the element above it.

Ans: C. The elements of group II are very reactive (not uncombined in nature) and this reactivity increases as you go down the group. This is because as electrons move further away from the nucleus they are held less strongly and are more easily lost. The two electrons in the outer shell of group II elements combine to form chlorides of the formula; BeCl 2 , MgCl 2 , CaCl 2 , etc.

2. Which statement about the elements in the periodic table is correct?

A. Group O elements are unreactive metals.

B. Group I elements form covalent chlorides.

C. Group VII elements form negative ions.

D. The elements become more metallic from left to right across a period.

E. The number of electrons in the outer shell decreases from left to right across a period.

Ans: C. The elements of group VII, the halogens have seven electrons in their outer shell and so gain an electron to form the halide ion, X -1 to become stable. Group O is the noble gases which are very unreactive because of their filled shells while Group I elements are metals which form ionic chlorides. Statements D and E are also false since as you move from left to right of the Periodic Table the number of outer electrons increases and the elements become less metallic.

3. Many properties of an element and its compounds can be predicted from the position of the element in the Periodic Table. Which property could not be predicted in this way?

A. The acidic or basic nature of its oxide.

B. The charge on its ion

C. The formula of its oxide.

D. tThe number of isotopes it has.

E. Its metallic or non-metallic properties.

Ans: D. All other properties of an element can be predicted by their position in the periodic table except the number of isotopes that the element has. This is not related to the number of electrons in the outer shell or that is available for bonding hence it cannot be predicted based solely on position in the table.

4. Astatine (At) is in Group VII of the periodic table. Which of the following is a property of astatine?

A. It forms basic oxides

B. It is a good conductor of electricity

C. It is displaced by chlorine from aqueous potassium astatide

D. It displaces iodine from aqueous potassium iodide.

Ans: C. Astatine is a non-metal hence does not form basic oxides and is a poor conductor of electricity. It is below chlorine and iodine in the group hence it can be displaced by both chlorine and iodine from solution. It is not reactive enough to displace iodine.