This lesson introduces why element properties change regularly across the periodic table and explains trends in covalent radius.
Elements in the same group (vertical column) often behave similarly because they have the same number and general distribution of valence electrons. Moving across a period adds protons to the nucleus and electrons to the valence shell. Moving down a group adds electrons to higher principal energy levels while the number of valence electrons remains similar for representative elements.
All flashcards
What is covalent radius?
One-half the distance between the nuclei of two identical atoms joined by a covalent bond; it is a practical measure of atomic size.
What is effective nuclear charge?
The net positive attraction an electron experiences from the nucleus after the shielding effects of other electrons are considered. A simplified expression is Zeff=Z−S.
Why does atomic radius grow down a group?
Each step down generally adds an occupied principal energy level, placing valence electrons farther from the nucleus.
Why does atomic radius shrink across a period?
Proton number increases across a period while same-shell electrons provide relatively little additional shielding, so greater effective nuclear charge pulls electrons closer.
How does metallic character vary across the periodic table?
It generally increases down a group and decreases from left to right across a period.
Quiz questions
Why do elements in the same group often have similar chemical behavior?Answer: They have similar valence-electron arrangements, including the same number of valence electrons for representative elements.
How is covalent radius defined?Answer: It is one-half the distance between the nuclei of two identical atoms joined by a covalent bond.
What generally happens to covalent radius as one moves down a group?Answer: It increases because valence electrons occupy higher principal energy levels farther from the nucleus.
Why does covalent radius generally decrease from left to right across a period?Answer: Nuclear charge increases while shielding by electrons in the same shell changes only slightly, increasing effective nuclear charge.
Which sequence lists the elements in increasing covalent radius: Kr, Br, Ge, and Fl?Answer: Kr < Br < Ge < Fl
Based on Chemistry 2e by Paul Flowers, Klaus Theopold, Richard Langley, William R. Robinson, PhD (OpenStax), licensed CC BY 4.0. Adapted into a summary, flashcards and quizzes.