What is the position of the element Z = 20 in the modern periodic table?

Options

A. `4^(th)` period
B. `3^(rd)` period
C. `2^(nd)` period
D. `1^(st)` period

Answer

To determine the position of the element with atomic number Z = 20 in the modern periodic table, we can follow these steps:

### Step-by-Step Solution:

1. **Identify the Atomic Number**:
The atomic number (Z) of the element is given as 20. This means the element has 20 protons and, in a neutral atom, also 20 electrons.

2. **Determine the Electronic Configuration**:
The electronic configuration of an element describes how the electrons are distributed in the atomic orbitals. For Z = 20, the electronic configuration can be determined as follows:
- The first shell (K) can hold a maximum of 2 electrons.
- The second shell (L) can hold a maximum of 8 electrons.
- The third shell (M) can hold a maximum of 18 electrons, but for Z = 20, we only need 10 more electrons after filling the first two shells.
- Therefore, the electronic configuration is:
- K: 2 electrons
- L: 8 electrons
- M: 8 electrons
- N: 2 electrons
- This gives us the configuration: 2, 8, 8, 2.

3. **Determine the Period**:
The period number in the periodic table corresponds to the highest principal energy level that contains electrons. In our case, the highest principal energy level is 4 (from the 2 electrons in shell N). Therefore, the element is in the **fourth period**.

4. **Determine the Group**:
The group number can be determined by the number of valence electrons, which are the electrons in the outermost shell. For Z = 20, the outermost shell (N shell) has 2 electrons. Therefore, the element belongs to **Group 2** (the alkaline earth metals).

5. **Identify the Element**:
The element with atomic number 20 is **Calcium (Ca)**, which is known to be an alkaline earth metal.

6. **Conclusion**:
Based on the above analysis, the position of the element with atomic number Z = 20 in the modern periodic table is in the **fourth period and second group**.

### Final Answer:
The element Z = 20 is located in the **fourth period** of the modern periodic table.