Write the number of periods the Modern Periodic Table has. State the changes in valency and metallic character of elements as we move from left to right in a period. Also state the changes, if any, in the valency and atomic size of elements as we move down a group.

Explanation

### Step-by-Step Solution

1. **Number of Periods in the Modern Periodic Table**:
The Modern Periodic Table consists of **7 periods**. These periods are the horizontal rows in the table.

2. **Changes in Valency and Metallic Character from Left to Right in a Period**:
- **Valency**: As we move from left to right across a period, the valency of elements generally increases from 1 to 4 and then decreases from 4 to 0. This is because the number of valence electrons increases, affecting how many electrons an atom can gain or lose to achieve stability.
- **Metallic Character**: The metallic character decreases as we move from left to right in a period. This is due to the increasing nuclear charge (Z-effective), which holds the outer electrons more tightly, making it harder for the elements to lose electrons and exhibit metallic properties.
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