Chemistry
How does the number of (i) valence electrons (ii) valency; vary on moving from left to right:
(a) in the second period of a periodic table?
(b) in the third period of a periodic table?
Answer
(a) In the second period, the number of valence electrons increases from 1 to 8 as we move from left to right. The valency changes as follows:
| Element | Li | Be | B | C | N | O | F | Ne |
|---|---|---|---|---|---|---|---|---|
| Valency | 1 | 2 | 3 | 4 | 3 | 2 | 1 | 0 |
(b) In the third period, the number of valence electrons increases from 1 to 8 as we move from left to right. The valency changes as follows:
| Element | Na | Mg | Al | Si | P | S | Cl | Ar |
|---|---|---|---|---|---|---|---|---|
| Valency | 1 | 2 | 3 | 4 | 3 | 2 | 1 | 0 |
Related Questions
(a) What are the following groups known as?
- Group 1
- Group 17
- Group 18
(b) Name two elements of each group.
What is the number of elements in the :
(a) 1st period, and
(b) 3rd period, of the modern periodic table?
How do atomic structures (electron arrangements) change in a period with an increase in atomic numbers, moving from left to right?
State the criteria used by Mendeleev in proposing his periodic table?