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Q1. Did Dobereiner’s triads also exist in the columns of Newlands’ Octaves ? Compare and find out.
Answer:
Yes, Dobereiner’s triads also existed in the columns of Newland’s Octaves.
For example, Li, Na, K.
If we consider lithium as the first element, then sodium is eighth element. If we consider sodium as the first element, then potassium is the eighth element.

Q2. What were the limitations of Dobereiner’s classification ?
Answer:

The limitations of Dobereiner’s classification are:

1. It could be applied to three triads.

2. Many elements could not be grouped into triads.

3. The atomic mass of the middle element was not the exact average of the other two in some cases.

Q3. What were the limitations of Newlands’ law of octaves ?
Answer:

The limitations of Newlands’ Law of Octaves are:

1. It worked well only for lighter elements upto calcium

2. Elements with different properties were sometimes placed in the same group.

3. Newlands forced the pattern even when it did not fit well, leading to incorrect grouping. For example, cobalt (Co) and nickel (Ni)

4. Newlands assumed that only 56 elements existed in nature and no more elements would be discovered in the future. But later oon several new elements were discovered

5.  Iron (Fe) element which resemble elements like cobalt and nickel in properties, was placed far away from these elements.

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Q1. Use Mendeleev’s Periodic Table to predict the formulae for the oxides of the following elements : K, C, Al, Si, Ba
Answer:
K₂O,  CO₂,  Al₂O₃,  SiO₂,  BaO.

Q2. Besides gallium, which other elements have since been discovered that were left by Mendeleev in his periodic table ? (any two)
Answer:
Scandium and Germanium.

Q3. What were the criteria used by Mendeleev in creating his Periodic Table ?
Answer:
Mendeleev used the relationship between the atomic masses of the elements and their physical and chemical properties. He used similarity in physical properties, similarity in the formation of hydrides and oxides of element.

Q4. Why do you think the noble gases are placed in a separate group ?
Answer:
Noble gases are placed in a separate group because they have very different properties from other elements. They are inert or chemically unreactive due to their complete outer electron shells. Unlike other elements, noble gases do not easily form compounds because their atoms are stable on their own. This unique behavior sets them apart, so they are grouped separately in the periodic table.

Q1. How could the modern periodic table remove various anomalies of Mendeleev’s periodic Table ?
Answer:

The modern periodic table is based on the atomic number of elements, unlike Mendeleev’s table which was arranged by atomic mass. This change solved many anomalies because the atomic number reflects the number of protons, which determines an element’s properties. For example, Mendeleev placed some elements out of order based on atomic mass, but in the modern table, these elements are correctly arranged according to their atomic numbers. The modern table also includes the noble gases, which were missing in Mendeleev’s table, and groups elements more accurately based on their chemical behavior.

Q2. Name two elements you would expect to show chemical reactions similar to magnesium. What is the basis for your choice ?
Answer:
Beryllium (Be) and Calcium (Ca).
Both Be and Ca  have similar electronic configuration, i.e. two electrons in outermost shells.
Be =   2,2
Ca =2, 8, 8, 2
Both Be and Ca react with oxygen to give basic oxides, BeO and MgO.

Q3. Name :
(a) three elements that have a single electron in their outermost shells.
(b) two elements that have two electrons in their outermost shells.
(c) three elements with filled outer most shells.
Answer:
(a) Lithium : Atomic number = 3(2, 1); Sodium : Atomic number =11(2, 8, 1); Potassium : Atomic number  = 19(2, 8, 8, 1).
(b) Beryllium : Atomic number = 4(2, 2); Calcium : Atomic number = 20(2, 8, 8, 2)
(c) Helium : Atomic number     =2(2); Neon : Atomic number – 10(2, 8); Argon : Atomic number – 18(2, 8, 8).

Q4.(a) Lithium, sodium, potassium are all metals that react with water to liberate hydrogen gas. Is there any similarity in the atoms of these elements ?
(b) Helium is an unreactive gas and neon is a gas of extremely low reactivity. What, if anything, do their atoms have in common ?
Answer

(a) Lithium, sodium, and potassium all belong to the same group in the periodic table (alkali metals). Their atoms each have one electron in their outermost shell, which makes them highly reactive and able to react with water to release hydrogen gas.

(b) Helium and neon are noble gases, meaning their atoms have completely filled outer electron shells. This makes them very stable and unreactive because they do not easily lose, gain, or share electrons with other elements.

Q5. In the modern periodic table, which are the metals among the first ten elements ?
Answer:The first ten elements in modern periodic table are hydrogen, helium, lithium, beryllium, boron, carbon, nitrogen, oxygen, fluorine and neon. Out of these, lithium, beryllium and boron are metals, because they have 1, 2 and 3 electrons respectively in their outermost shells.

Q6. By considering their position in the Periodic Table, which one of the following elements would you expect to have maximum metallic characteristics ?
Ga, Ge, As, Se, Be
Answer:
Beryllium (Be). In the periodic table, the elements placed on the left show maximum metallic characteristics. Since beryllium occupies the most left position in comparison to other elements, hence it shows maximum metallic characteristics.