1. mendeleev's periodic table of elements was organized by
a. mass
b. atomic number
c. number of electrons
d. number of protons

2. compared with group 6a elements, group 2a elements have
a. more atoms in the ground state.
b. more valence electrons.
c. more isotopes.
d. fewer valence electrons.

3. which element is found in most of the compounds in your body except for water?
a. iodine
b. potassium
c. iron
d. carbon

4. which of the following group 1a elements is the least reactive?
a. cs (cesium)
b. li (lithium)
c. k (potassium)
d. na (sodium)

5. to keep them from reacting, some highly reactive elements are stored in
a. water.
b. pure oxygen.
c. liquid mercury.
d. argon.

6. the tendency of an element to react is closely related to
a. its atomic mass.
b. attractions between its atoms.
c. the number of valence electrons in atoms of the element.
d. the ratio of protons to neutrons in atoms of the element.

7. the usefulness of mendeleev’s periodic table was confirmed by
a. the discovery of subatomic particles.
b. its immediate acceptance by other scientists.
c. the discovery of elements with predicted properties.
d. the discovery of the nucleus.

8. group 8a of the periodic table contains the
a. least reactive metals.
b. most reactive metals.
c. least reactive nonmetals.
d. most reactive nonmetals.

9. one twelfth the mass of a carbon-12 atom is used to define a(an)
a. atomic mass unit.
b. atomic mass.
c. mass number.
d. atomic number.

10. atoms of the least reactive elements tend to have
a. one or seven valence electrons.
b. eight valence electrons.
c. four or five valence electrons.
d. no valence electrons.

1. Mendeleev's periodic table of elements was organized by,

             Mass

                       Mendeleev was a Russian chemist who worked on periodic table after John Newland. Mandeleev arranged the elements in periodic table in order of their relative atomic masses. It was realized by Mendeleeve that most of the chemical and physical properties of elements were related to their atomic masses. Also, these properties were found to repeat after a specific periodicity hence, he arranged the elements with same properties in a vertical columns now known as groups.

2. Compared with Group 6A elements, Group 2A elements have,

               Fewer valence electrons.

                       Group 6A also known as oxygen family has a general valence shell electronic configuration as shown below,

                                                      ns², np⁴

                       While, Group 2A also known as Alkaline earth metals have a general valence shell electronic configuration as shown below,

                                                      ns²

Therefore, it is concluded that the Group 2A elements have 2 valence electrons while, 6A elements have 6 valence electrons in valence shell respectively.

3. Which element is found in most of the compounds in your body except for water?

               Carbon

                     Our body contains organic compounds. Organic compounds are those compounds which are made up of carbon atoms. Due to peculiar behavior of Carbon it has a property of Catenation (self linkage), isomerism (compounds having same molecular formula but different structural formula) and multiple bond formation (single, double and triple bonds) it results in the formation of numerous organic compounds in our body including proteins, enzymes, lipids, and much more.

4. Which of the following Group 1A elements is the least reactive?

               Lithium

                     Reaction rate of Group 1A depends upon the ionization energy of particular element. Smaller the ionization energy greater is the reactivity of that element. Hence, Lithium having the greatest ionization energy will be the least reactive and Cesium having the least ionization energy will be the most reactive element.

5. To keep them from reacting, some highly reactive elements are stored in,

               Argon

                         In order to keep them away from reacting one should keep the compounds in inert environment. In given Argon is the substance which belongs to Group of inert class of elements called as noble gases. Noble gases are least reactive because they have their valence shell complete. Hence, with complete octet noble gases are the stable elements hence least reactive.

6. The tendency of an element to react is closely related to

               The number of valence electrons in atoms of the element.

                     Atoms react with each other to form a molecule or compounds in order to gain stability. For example,

                                        2 Na  +  Cl₂    →    2 NaCl

In above reaction sodium metal losses one electron and chlorine gains one electron. Also, sodium only looses one electron because it has only one valence electron so by loosing that electron it gains a stable electronic configuration of Neon. On the other hand Chlorine has 7 valence electrons so in order to gain a noble gas configuration of Argon Cl gains one electron. Hence, we can conclude that the valence electrons are responsible for the reactivity of elements.

7. The usefulness of Mendeleev’s periodic table was confirmed by

               The discovery of elements with predicted properties.  

                      As discussed earlier Mendeleev arranged elements with same chemical properties in a vertical columns called as groups. At that time few elements were still not discovered hence their position was reserved in advanced and their properties were predicted bases on the properties of elements present in the same groups.

8. Group 8A of the periodic table contains the

               Least reactive nonmetals.  

                          Already discussed, Group 8 elements also called as noble gases are inert in nature and are least reactive in nature. The reason for least reactive nature is the complete octet. As atoms have reactivities due to loosing or gaining electron in order to gain noble gas configuration, Noble gases don't follow that trend as it already has a complete octet.

Remaining Questions are attached below.

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