The Periodic Table Notes for TLT, ECT, PST, JEST Exam | General Science

The Periodic Table

Subject: Science (Chemistry)  |  Topic: The Periodic Table

For TLT, ECT, PST, JEST & All Competitive Exams

In our last topic, we learned about atomic structure — protons, neutrons, electrons, and the atomic number that defines each element. Now we'll see how scientists used exactly that information — the atomic number — to organize all known elements into one giant, logical chart: the Periodic Table. This topic is frequently tested in TLT, ECT, PST, JEST, and other competitive exams.

What is the Periodic Table?

The Periodic Table is a systematic arrangement of all known chemical elements, organized in order of increasing atomic number, in a way that elements with similar chemical properties fall into the same column. It allows scientists — and students — to predict how an element will behave just by looking at its position on the table.

History: Who Made the Periodic Table?

The modern periodic table is credited to the Russian chemist Dmitri Mendeleev, who in 1869 arranged the known elements by increasing atomic mass and noticed that their properties repeated in a periodic pattern. He was so confident in this pattern that he left gaps for elements not yet discovered — and correctly predicted their properties. Later, the table was refined to be arranged by atomic number instead of atomic mass, which is the version we use today.

Remember: Mendeleev arranged elements by atomic mass. The modern periodic table arranges them by atomic number (number of protons) — this is called the Modern Periodic Law.

Periods & Groups in the Periodic Table

Periods and Groups

The periodic table is arranged into rows and columns, each with its own meaning:

• Periods — the horizontal rows of the periodic table. There are 7 periods. Moving across a period from left to right, the atomic number increases by one each time.
• Groups — the vertical columns of the periodic table. There are 18 groups. Elements in the same group have similar chemical properties because they have the same number of valence electrons.

Easy Way to Remember: Periods = Pass across (left to right, horizontal). Groups = Go down (top to bottom, vertical).

Metals, Non-Metals, and Metalloids

The periodic table is also divided based on the general properties of elements:

Category	Position	Key Properties
Metals	Left side and center of the table	Shiny, good conductors of heat & electricity, malleable (can be hammered into shape), lose electrons easily
Non-Metals	Right side of the table	Dull, poor conductors, brittle in solid form, tend to gain electrons
Metalloids	Zig-zag line between metals and non-metals	Show properties of both metals and non-metals (e.g., Silicon, Boron)

Basic Periodic Trends

As you move across the periodic table, certain properties change in a predictable pattern:

• Atomic Size: Generally decreases as you move left to right across a period (more protons pull electrons in tighter), and increases as you move down a group (more electron shells are added).
• Reactivity: Metals become more reactive as you move down a group (electrons are lost more easily), while non-metals become more reactive as you move up a group and across toward the right.

Note: These trends are studied in more depth later on — for now, just remember the basic direction: atomic size shrinks left-to-right, and grows top-to-bottom.

Why This Topic Matters

The periodic table is the roadmap of chemistry. Once you understand how it's organized, you can predict an element's number of valence electrons, whether it's a metal or non-metal, and how it's likely to bond and react — all just from its position on the table. This directly builds on Atomic Structure and prepares you for the next topics: Chemical Bonding and Chemical Reactions. It is also a frequent source of MCQs in TLT, ECT, PST, and JEST exams.

Practice MCQs

1. Who is credited with creating the modern periodic table?
a) Isaac Newton b) Dmitri Mendeleev c) John Dalton d) Albert Einstein

2. The modern periodic table arranges elements in order of increasing:
a) Atomic mass b) Atomic number c) Number of neutrons d) Number of shells

3. What are the horizontal rows of the periodic table called?
a) Groups b) Periods c) Blocks d) Series

4. What are the vertical columns of the periodic table called?
a) Periods b) Rows c) Groups d) Levels

5. Elements that show properties of both metals and non-metals are called:
a) Isotopes b) Metalloids c) Compounds d) Alloys

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