6. Give one important difference between the following (based on the word in brackets).
(i) Period and group (shell)
(ii) Atomic mass and atomic number (neutrons)
(iii) Period and group (atomic size)
(iv) Metals and non-metals (reducing properties)
(v) Modern periodic table and Mendeleev periodic table (atomic number)
Answers
(i) Periods are rows (go across horizontally).
Groups are columns (up and down vertically).
Periods identify electron “shells” by number vertically.
Groups identify the number of outer “shell” electrons ( ignore numbers 3–12 and instead of 13, call it 3. group 1 and 2 are ok. groups 3–12 are all mislabelled and are actually all 2. What you probably see labelled as 18 is actually group zero ).
You probably don't need to know, but… period numbers identify the number of electrons per “shell” in ordered (growing) sequence left to right…..
Why were the actinoids and lanthanoids moved? They didn't fit :)
(ii) The major difference between atomic number and mass number is that the atomic number states the number of protons present in an atom whereas, the mass number indicates the total of the number of protons and the number neutrons present in an atom.
(iv) Metals ionize by loss of electrons and hence are reducing agents whereas non-metals ionize by gain of electrons and hence are oxidizing agents
(v)MENDELEEV VS MODERN PERIODIC TABLE
Mendeleev’s periodic table is, based on the relation of elements’ properties as dependent on the atomic weight of the element. But the Modern periodic table considers atomic number as the fundamental property that decides the properties of elements.
The modern periodic table does correct the defects of Mendeleev’s periodic table. For example, in Mendeleev’s periodic table, in the element pairs, Argon-potassium, cobalt-nickel, tellurium-iodine and thorium and protactinium, elements with higher atomic mass precede the element with lower atomic weight. However, it is the right places for them but is against Mendeleev’s periodic law.
These elements atomic number shows the reverse order compared to atomic mass. The supposed to be wrong positions in Mendeleev’s table has the right explanation justifying their positions.
Uneven grouping of elements:
In Mendeleev’s periodic table, coinage metals of copper, silver, and gold are, grouped with very active alkali metals. Manganese metal was grouped with halogens in the seventh group. The defects are rectified in the Modern periodic table.
Position of isotopes:
Isotopes with higher atomic weights could not be accommodated in Mendeleev’s table. As isotopes have the same atomic number as the stale atom, they do not need any separate location in the modern periodic table.
No reasons were offered for the triad elements of the viii group. No such special grouping is given in the modern table.
Mendeleev’s periodic table was for the arrangement of sixty-three elements known at that time.
The modern table accommodates all the 118- natural and synthetic elements.
The atomic number is much fundamental property distinguishing each element and hence a better basic nature to decide the physical and chemical properties of elemental atoms than atomic weights.