Question

What is the trend in atomic radius as you go across a period?

Answer 1

A row of chemical elements in the periodic chart is called a period. The number of electron shells in each element in a row is the same. Each subsequent element in a period has one more proton than its predecessor and is less metallic. The periodic rule is reflected in this arrangement, as groupings of elements in the same column have comparable chemical and physical characteristics.

Complete answer:
The arrangement of electrons in fixed-capacity shells explains how the atomic radius changes with increasing atomic number. Because negatively charged electrons are attracted to positively charged protons in the nucleus, the shells are typically filled in order of increasing radius. The extra electrons go into the same outermost shell as the atomic number grows along each row of the periodic table, whose radius gradually decreases owing to the rising nuclear charge. The outermost shell of a noble gas is entirely occupied, therefore the additional electron of the following alkali metal will move into the next outer shell, accounting for the rapid rise in atomic radius.
Shielding is a phenomenon in which the growing nuclear charge is somewhat counterbalanced by the increasing number of electrons, which explains why the size of atoms generally rises along each column. There is one significant exception, known as the lanthanide contraction: due to the weak shielding of the 4f electrons, the 5d block of elements is substantially smaller than one would anticipate. Essentially, as the number of protons increases, the atomic radius shrinks with time. As a result, the protons and electrons have a stronger attraction because opposing charges attract, and more protons produce a stronger charge.
The stronger attraction pulls the electrons closer to the protons, shrinking the particle's size. As a result, the atomic radius shrinks. The atomic radius grows as you progress through the groupings. Because there are more energy levels, the distance between protons and electrons is larger. Furthermore, electron shielding reduces attraction, allowing leftover electrons to move further away from the positively charged nucleus. As a result, the size, or atomic radius, grows.
So across a period the atomic radius decreases.

Note:
Electrons lack fixed orbits and well defined ranges. Instead, their locations must be represented as probability distributions that taper off gradually as one travels out from the nucleus, with no sudden cutoff; these are known as atomic orbitals or electron clouds. Furthermore, in condensed matter and molecules, atoms' electron clouds frequently overlap, and some electrons may travel across a broad range covering two or more atoms.