Periodic Classification and Elements

Mendeleev classified the elements according to their increasing atomic masses in horizontal rows in such a way that the elements with similar chemical properties (i.e. elements with similar formulae of oxides and hydrides) fell in the same vertical column. He preferred only oxygen and hydrogen because oxygen and hydrogen form bond with almost all elements.

Mendeleev's periodic law states that poperties  of elements are periodic functions of their atomic masses. Therefore the elements are arranged in the increasing order of their atomic masses.  However Mendeleev placed cobalt before nickel eventhough it has a slightly higher mass than nickel. 

According to the modern periodic table, elements belonging to group 17 are designated as halogens because they form salts with metals.

Element X, having atomic number 9, contains 9 protons and its valence shell contains 7 electrons. To acquire noble gas configuration, it can accept one electron.

H, F, Cl and Br have some similar properties as they all have valency 1 and exist in nature as diatomic molecules (i.e. in the form of H₂, F₂, Cl₂, Br₂). Cobalt is a transition metal and its properties are different from those of H, F, Cl and Br.

In a group, all the elements have the same valency.

The number of shells tells the period and the number of electrons in the last valence shell tells the group.

Elements belonging to the 18^th group of the periodic table have fully filled last valence shell. So, they have zero valency.

Newlands found that the properties of the eighth element were similar to the properties of the first element. He compared this with the octaves found in the musical scale. Therefore, this method of classification of elements is called Newlands’ Law of Octaves.

In Mendeleev’s periodic table, there are 8 groups, which are further subdivided into 2 parts (e.g. I A, I B) and 7 periods.

this option is correct because , p subshell has 3 orbital each can accommodate 2 electrons hence ' p '  orbital can accommodate 6 electrons . in this case p has 7 electrons . hence this statement is wrong and therefore  this option is correct .

This option is correct becausI radial node = n - l -1 . planar node =  l . total nodes = n - 1 . in this case n = 4, hence, total number nodes = 3 .

In 1817, Johann Wolfgang Dobereiner, a German chemist, tried to arrange elements with similar properties into groups called triads having 3 elements each.

Copper is placed along with potassium in group I of Mendeleev’s periodic table.

Mendeleev classified elements on the basis of their atomic mass and chemical properties.