Arrange these elements in order of decreasing atomic radius: Cs, Pb, Sb, Se, S.

Atomic radius is a measure of the size of an atom, typically defined as the distance from the nucleus to the outermost electron shell. It generally increases down a group in the periodic table due to the addition of electron shells, while it decreases across a period from left to right due to increased nuclear charge, which pulls electrons closer to the nucleus.

Periodic trends refer to predictable patterns in the properties of elements as you move across or down the periodic table. Key trends include atomic radius, ionization energy, and electronegativity. Understanding these trends helps in predicting the behavior of elements, including their size and reactivity.

Elements are organized in groups (columns) and periods (rows) in the periodic table. Elements in the same group share similar properties and have the same number of valence electrons, while elements in the same period have the same number of electron shells. This organization is crucial for understanding atomic size, as elements in lower periods generally have larger atomic radii.