The modern periodic table consists of 18 groups and 7 periods. What is the atomic number of the element placed in the 3rd group and the 4th period?
- A23
- B21
- C19
- D11
Solution & Step-by-step Explanation
The element placed in the 3rd group and 4th period of the modern periodic table is Scandium (Sc).
Period 1 contains elements with atomic numbers 1–2.
Period 2 contains elements with atomic numbers 3–10.
Period 3 contains elements with atomic numbers 11–18.
Period 4 begins with Potassium (Z=19, Group 1), Calcium (Z=20, Group 2), and Scandium (Z=21, Group 3).
Therefore, the atomic number is 21.
Period 1 contains elements with atomic numbers 1–2.
Period 2 contains elements with atomic numbers 3–10.
Period 3 contains elements with atomic numbers 11–18.
Period 4 begins with Potassium (Z=19, Group 1), Calcium (Z=20, Group 2), and Scandium (Z=21, Group 3).
Therefore, the atomic number is 21.