Atomic size

Definition

Atomic size refers to the measure of the radius of an atom, which indicates how large or small an atom is. This size is influenced by the number of electrons and protons in an atom, as well as the arrangement of these particles within the electron shells. Understanding atomic size is crucial when examining multi-electron atoms and their placement in the periodic table, as it helps explain trends in atomic properties across different elements.

5 Must Know Facts For Your Next Test

1. Atomic size generally increases down a group in the periodic table due to the addition of electron shells.
2. Across a period, atomic size decreases from left to right because of the increasing effective nuclear charge that pulls electrons closer to the nucleus.
3. The concept of electron shielding explains why atoms with many inner-shell electrons tend to have larger radii than expected based solely on their number of protons.
4. Metals typically have larger atomic sizes compared to nonmetals within the same period due to their lower effective nuclear charge.
5. Atomic size can influence chemical reactivity, as larger atoms tend to lose or gain electrons more easily compared to smaller atoms.

Review Questions

• How does atomic size vary across a period in the periodic table, and what factors contribute to this trend?
  • Atomic size decreases across a period in the periodic table due to increasing effective nuclear charge. As protons are added to the nucleus while electrons are added to the same energy level, the increased positive charge attracts the electrons more strongly, pulling them closer to the nucleus and resulting in a smaller atomic radius.
• Discuss how electron shielding affects atomic size and its implications for multi-electron atoms.
  • Electron shielding occurs when inner shell electrons repel outer shell electrons, effectively reducing the attraction between these outer electrons and the nucleus. This reduction in attraction leads to larger atomic sizes, especially in multi-electron atoms where more inner-shell electrons are present. As a result, understanding electron shielding is essential for predicting atomic sizes in complex elements and their chemical behavior.
• Evaluate how changes in atomic size impact chemical reactivity and element classification within the periodic table.
  • Changes in atomic size significantly influence chemical reactivity, as larger atoms with greater distances between their outermost electrons and nucleus tend to lose or gain electrons more readily. This impacts element classification; for example, metals with larger atomic sizes are often more reactive than nonmetals with smaller sizes. As such, understanding atomic size trends allows for better predictions about an element's behavior during chemical reactions and its placement on the periodic table.

Related terms

ionic radius: The ionic radius is the measure of the size of an ion in a crystal lattice, which can differ from the atomic radius depending on whether the atom has gained or lost electrons.

electron shielding: Electron shielding refers to the phenomenon where inner shell electrons reduce the effective nuclear charge felt by outer shell electrons, affecting atomic size.

effective nuclear charge: Effective nuclear charge is the net positive charge experienced by electrons in an atom, which plays a significant role in determining atomic size and electron configurations.