answers: decreases
context: Period 3 element A period 3 element is one of the chemical elements in the third row (or period) of the periodic table of the chemical elements. The periodic table is laid out in rows to illustrate recurring (periodic) trends in the chemical behaviour of the elements as their atomic number increases: a new row is begun when the periodic table skips a row and a chemical behaviour begins to repeat, meaning that elements with similar behavior fall into the same vertical columns. The third period contains eight elements: sodium, magnesium, aluminium, silicon, phosphorus, sulfur, chlorine, and argon. The first </s> the same. Valency in the periodic table across a period first increases and then decreases. There is no change going down a group. However, this periodic trend is sparsely followed for heavier elements (elements with atomic number greater than 20), especially for lanthanide and actinide series. The greater the number of core electrons, the greater the shielding of electrons from the core charge of the nucleus. For this reason ionization energy is lower for elements lower down in a group, and polarizability of species is higher for elements lower down in a group. The valency does not change going down </s> Periodic Law. Periodic Law also led to the development of the periodic table, which is widely used nowadays. The atomic radius is the distance from the atomic nucleus to the outermost stable electron orbital in an atom that is at equilibrium. The atomic radius tends to decrease across a period from left to right due to the shrinking of the atom because of increasing nuclear force on the electrons. The atomic radius usually increases while going down a group due to the addition of a new energy level (shell which causes shrinkage in the size of the atoms across the
question: in the third period as the atomic number increases from group 1 to group 18 the atomic radius