In this post, I am sharing the Class 12 Chemistry Notes Chapter 1 Short Questions PDF for the students of Intermediate Part 2. The name of this chapter is Periodic Classification of Elements and Periodicity. Students can download the Class 12 Chemistry Chapter 1 Short Questions Notes PDF on their laptops or mobile. These Chemistry Notes are for all the boards working under the Punjab Board like Gujranwala Board, Lahore Board, Faisalabad Board, Multan Board, Rawalpindi Board, Sargodha Board, DG Kahn Board, and Sahiwal Board. Here are the complete FSC 2nd Year Biology Notes PDF chapters.
FSc 2nd year Chemistry Chapter 1 – Periodic Classification of Elements and Periodicity
Why melting and boiling points of elements belonging to groups VA to VllA are lower? Discuss the trend of ionization energy in periodic table.
when we move from left to right in a period the number of electrons go on increasing in the outermost shell. The tendency to un-pair the electron increases up to group lVA. In this way, the binding froces increase, hence melting and boiling points increase up to group lVA. After that, the pairing of electrons starts and binding force become less. That’s why, the melting and boiling points of elements belonging to groups VA to VllA are lower.
Trend in Period:
Ionization energy increases form left to right in a period.
Reasons:
- Due to increase in proton number effective nuclear charge increases.
- Shielding effect remains the same.
- Number of shells remain the same.
- Atomic size decreases.
Trend in Group:
Ionization energy decreases from top to down in a group.
Reasons:
- Due to a decrease in proton number effective nuclear charge decreases.
- Sheilding effect increases.
- Number of shells increases down the group.
- Atomic size increases.
Why diamond is a non-conductor and graphite fairly a good conductor of electricity? Diamond is a non-conductor:
In a diamond, unit cell is tetrahedral. Each carbon atom is sp3 hybridized and forms 4 sigma bonds with 4 other carbon atoms and this trends throughout the crystal. All the four electrons of each barbon atom are tightly bound in these cobalent bonds. As a result, no free electron are available in diamond so it is a nonconductor of heat and electricity.
Graphite is agood conductor:
In Graphite, each carbon atom is sp2 hybridized and bonded to 3 neighbor atoms so one of its four valance electrons is relatively free to move along the layers. Hence, graphite is a conductor parallel to the layers and non-conductor perpendicular to the layer.
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