Periodic Table and Periodicity of Properties
9th chemistry chapter 3 solved exercise short questions
Q#1 : Why noble gases are not-reactive ?
Because their valence shells are completely filled and do not tend to lose or gain electrons from any other atom.
Therefore, they are not reactive .
Q#2 : Why Cesium (at.no.55) requires little energy to release its one electron present in the outermost shell ?
- Cesium releases its valence electrons easily due to following reasons:
✔ Atomic size of cesuim is very large .
✔ Greater shielding effect.
✔ Less nuclear charge.
Q#3 : How is periodicity of properties dependent upon number of protons in an atom ?
- The trend of number of protons in periodic table is :
→ In periodic table , when we move from left to right , proton number increases in nucleus.
→ Hence, nuclear charge will also increase .
- When nuclear charge changes , properties of elements will also change .
Q#4 : Why shielding effect of electron makes cation formation easy ?
With the increase in shielding effect, cation formation becomes easy due to following reasons :
- increase of atomic number results in increase of shielding effect.
- it makes easy to take away electron from the outermost shell.
Q#5 : What is difference between Mendeleev’s periodic law and modern periodic law ?
Q#6 : What do you mean by groups and periods in the periodic table ?
” The vertical columns in the periodic table are called groups .”
- They are numbered from left to right as 1 to 18 .
” The horizontal rows of elements in the periodic table are called periods .”
- There are 7 periods numbered from top to bottom .
Q#7 : Why and how are elements arranged in 4th period ?
→ Fourth period has 18 elements .
→ First 2 elements are put in s-block ;
→ Next 10 elements are in d-block transition metals and
→ Next 6 elements are in p-block.
- These elements are put in 4th period as all they have four number of shells .
Q#8 : Why the size of atom does not decrease regularly in a period ?
- Atomic radius decreases in a periodic table due to reason .
- Because of change in Shielding Effect is not regular .
→ If shielding effect increases, the size will also increase .
→ If shielding effect decreases, the size will also decrease .
Q#9 : Give the trend of ionization energy in a period . Also give reasons .
Trend of Ionization Energy :
The ionization energy of elements increases from left to right in a period .
- Due to following factors :
→ Increase in nuclear charge.
→ Shell number remains same .
→ Decrease in atomic size .