Question

What are periods in a periodic table? What is meant by period number? What does it signify?

Answer 1

To solve this question, we must first understand some basic concepts about our Modern Periodic Table. Then we need to assess its properties and information related to Periods and write them in a very clear and precise manner and then only we can conclude the correct answer.

Complete step by step answer:
Before we move forward with the solution of this given question, let us first understand some basic information about Periodic Table:
The periodic table is a Tabular form of arrangement of the chemical elements ordered by atomic number so that periodic properties of the elements (chemical periodicity) are made clear.
Period: A period in the periodic table is a row of chemical elements. Arranged this way, groups of elements in the same column have similar chemical and physical properties, reflecting the periodic law. All elements in a row have the same number of electron shells. There are seven periods in the periodic table, with each one beginning at the far left.
Periodic Number: also known as the atomic number or proton number (symbol $Z$ ) of a chemical element is the number of protons found in the nucleus of every atom of that element.
The atomic number uniquely identifies a chemical element. It is identical to the charge number of the nucleus. In an uncharged atom, the atomic number is also equal to the number of electrons. Atoms with the same atomic number but different neutron numbers, and hence different mass numbers, are known as isotopes.

Note: Modern quantum mechanics explains these periodic trends in properties in terms of electron shells. As atomic number increases, shells fill with electrons in approximately the order shown in the ordering rule diagram. The filling of each shell corresponds to a row in the table.