How does the size of atoms (atomic size) generally vary in going from left to right in a period of the periodic table? Why does it vary this way
The Correct Answer and Explanation is:
Correct Answer:
As we move from left to right across a period in the periodic table, atomic size (atomic radius) generally decreases.
Detailed Explanation (Textbook Style):
The atomic size, also known as atomic radius, refers to the distance from the nucleus of an atom to the outermost electrons. This size is influenced by two key factors: the number of protons in the nucleus (nuclear charge) and the number of energy levels (electron shells).
When moving from left to right across a period in the periodic table, each successive element has one more proton and one more electron than the previous one. However, all these electrons are added to the same principal energy level (same shell). This means that the electron shielding remains relatively constant because no new inner shells are added.
At the same time, the nuclear charge increases due to the addition of more protons in the nucleus. A higher nuclear charge means a stronger positive pull on the negatively charged electrons. Since the added electrons are not increasing the shielding effect significantly (they are in the same shell), the increased nuclear attraction pulls the electron cloud closer to the nucleus, effectively reducing the atomic radius.
Therefore, the atomic size decreases from left to right across a period because the electrons are pulled in closer to the nucleus due to the increasing nuclear charge, without a corresponding increase in shielding.
For example, consider the elements in Period 2:
- Lithium (Li) has a larger atomic radius than
- Beryllium (Be), which is larger than
- Boron (B), and so on, up to
- Fluorine (F) and Neon (Ne), which have much smaller atomic radii.
This trend continues consistently across all periods in the periodic table.
