Atomic size of the elements in the modern periodic table, What is Atomic size (Atomic radius)?

Atomic radius is used as a measure for the atomic size of the atom, and its measuring unit is picometre (Pm). The picometre is part from million of a million part of metre.

There is a graduation of the atomic size of the elements in the periodic table, where the atomic size for the elements of the same period is inversely proportional to the atomic number.

Atomic size decreases in the periods by increasing the atomic number (from left to right), due to the increase in the attraction force between the positive nucleus and the outermost electrons.

The atomic size for the elements of the same group is directly proportional to the atomic number. The atomic size increases in the groups, by increasing the atomic number (from up to down), due to the increase of the number of energy levels occupied by the electrons.

The nucleus is positively charged as it contains the protons, and the neutral neutrons, In the modern periodic table, You notice that the largest atom of the elements in size is the cesium atom, and the smallest one is fluorine.

FAQs about Atomic Size in the Modern Periodic Table

1. What is atomic size (atomic radius)?

Atomic size (or atomic radius) is the distance from the nucleus to the outermost electron shell of an atom. It indicates how large or small an atom is.

2. How does atomic size change across a period?

Atomic size decreases from left to right across a period.

Why?

• The number of protons increases.
• Nuclear attraction becomes stronger.
• Electrons are pulled closer to the nucleus.

3. How does atomic size change down a group?

Atomic size increases from top to bottom in a group.

Why?

• New energy levels (shells) are added.
• The distance between the nucleus and outer electrons increases.
• Shielding effect reduces nuclear attraction.

4. What is the shielding effect?

The shielding effect is when inner electrons reduce the attraction between the nucleus and outer electrons, making the atom larger.

5. Why are alkali metals the largest atoms in a period?

Elements in Group 1 (alkali metals) have:

• Fewer protons.
• Weaker nuclear attraction.

So, their atomic size is larger compared to others in the same period.

6. Why are noble gases small in size?

Noble gases (Group 18) have:

• High nuclear charge.
• Strong attraction to electrons.

So, they have a smaller atomic size across a period.

7. What factors affect atomic size?

Atomic size depends on:

• Number of electron shells.
• Nuclear charge (number of protons).
• Shielding effect.

8. What is the trend of atomic size in the periodic table?

• Across a period: decreases ⬅️➡️
• Down a group: increases ⬆️⬇️

9. Which element has the largest atomic size?

Elements at the bottom-left of the periodic table (like Francium) have the largest atomic size.

10. Which element has the smallest atomic size?

Elements at the top-right (like Helium) have the smallest atomic size.

11. What is the difference between atomic size and ionic size?

• Atomic size: size of a neutral atom
• Ionic size: size of an atom after losing or gaining electrons

12. Why do cations have smaller size than atoms?

Cations (positive ions): Lose electrons. Experience stronger nuclear attraction. So, their size becomes smaller than the original atom.

13. Why do anions have larger size than atoms?

Anions (negative ions): Gain electrons. Increase electron repulsion. So, their size becomes larger than the original atom.

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Graduation of the properties of the elements in the modern periodic table

The graduation of the metallic and nonmetallic property in the modern periodic table

Atoms components, Rutherford and Bohr’s Atomic Models

Evolution concept of the atomic structure, Atomic theory & Properties of cathode rays

Modern periodic table and classification of Elements

Chemical combination, Types of bonds (Chemical bonds & Physical bonds)