Science Olympiad Test: Periodic Classification of Elements- 2 - Class 10 MCQ

Since the element with atomic number 14 i.e., Si forms an acidic oxide and a covalent halide, it must be metalloid.

Eka-aluminium i.e ., gallium lies in group III of the Mendeleev’s periodic table. Therefore, it has a valency of 3 and forms on oxide having molecular formula E₂O₃.

In a group valency of all elements is fixed because of having the same outer shell electronic configuration while all the remaining three properties increase down the group.

Element with atomic number 7 has electron configuration 2, 5 which means it can gain 3 electrons and is an electronegative element. It should be a non-metal and non-metals will form acidic oxide.

The non-metallic character is the tendency of an element to accept electrons and form negative ions or anions. Chlorine and oxygen are the most electronegative elements.

• Li is on the left of in the 2^nd period of the modern periodic table followed by beryllium.
• Fluorine is right next to Neon.
• Fluorine shows maximum non-metallic characters followed by Oxygen, Berrylium, carbon and Lithium.

A, B and C are the elements of a Dobereiner's triad. If the atomic masses of A and C are 7 and 39 respectively, then according to Dobereiner's triad law, the atomic mass of B is the average of the atomic masses of A and C.
So, the average of the atomic masses of A and C 

Therefore, the atomic mass of B is 23.

X and Y are two elements having similar properties which obey Newlands’s Law of Octaves. The minimum and maximum number of elements in between X and Y respectively are 6 and 8.

• Though only 63, elements were known at the time when Mendeleev started his work, he left some places vacant for elements to be discovered later.
• While developing his Periodic Table of the elements,he named aka-Aluminum to the element just below of Aluminium.
• Mendeleev gave the name eka-Aluminium to a compound which contains aluminium, a mixture of aluminium and an unknown element.
• The unknown element he predicted would have properties similar to those of aluminium and which have rare isotope of aluminium.
• It was later discovered as Gallium with an atomic weight of 68 and atomic number of 31.
• Germanium was named as Aka-Silicon first and was later discovered.
• Germanium has atomic number 32 and an atomic weight of 72.

Hence, Mendeleev left the gaps for the elements with predicted atomic weight 68 & 72 respectively are discovered later as Gallium & Germanium.

Elements in the Modern Periodic Table are arranged based on their increasing atomic number hence option (i) is wrong. In the modern periodic table atomic mass is not a criteria hence option (ii) is wrong. Isotopes are given the same position in the periodic table hence option (iii) is wrong.

Let us take a look at the electronic configurations of the given elements, 
A: (2, 7)
B: (2, 8, 1) 
C: (2, 8, 7)
D: (2, 8, 2)
E: (2, 8, 3)
We can see that elements A and C both have 7 valence electrons. Thus, both the elements belong to the same group.
So, the correct option is A.

A tabular arrangement of elements in groups and periods that highlights the regular trends in properties of elements is defined as the periodic table.

• The modern periodic table has 18 groups and 7 periods. Columns are called groups and rows are called periods.
• Modern periodic law states that the properties of elements are dependent on their atomic numbers and elements show similar properties at regular intervals of increasing atomic numbers.

• Electronic configuration of Na, Al, Si and P are 2, 8 1, 2, 8, 3, 2, 8, 4, and 2, 8, 5 respectively. 
• Valence electrons in Na, Al, Si and P are 1,3,4 and 5.
• Hence phosphorus has maximum number of valence electrons.

Atomic radius decreases across a period because nuclear charges increase across a period. When the charge increases, the electrons are pulled towards the nucleus with greater force decreasing the size of the atomic radius. Hence Fluorine has the least radius as its atomic number is larger than oxygen and nitrogen. The same case is with oxygen, it has more number of positive charges than nitrogen. Hence nitrogen has the largest size than oxygen and then fluorine.

Isotopes of an element have same atomic number but different atomic masses. They show same chemical properties but different physical properties.

The metalloids; boron (B), silicon (Si), germanium (Ge), arsenic (As), antimony (Sb), tellurium (Te), polonium (Po) and astatine (At) are the elements found along the step like line between metals and non-metals of the periodic table.