Dmitri Mendeleev and the Periodic Table

Background

Dmitri Mendeleev: Russian chemist and inventor from the mid-19th century.
Contribution: Devised the periodic table which organized all known elements.
Notable Achievement: Predicted elements that were not yet discovered.

Reading Order: Left to right, top to bottom.
Atomic Number: Represents the number of protons in the atom.
Box Components:
- Right: Elemental symbol (e.g., Na for Sodium).
- Bottom Left: Atomic number (number of protons).
- Top Left: Mass number (total number of protons and neutrons).

Mendeleev noted a repeating pattern of chemical properties, forming rows called periods.
Elements in a vertical column share similar chemical properties, forming a group.

Group Number: Indicates the number of electrons in the outer shell.
Group 1 (Alkali Metals): One electron in outer shell, e.g., Lithium (3 electrons overall), Sodium (11 electrons).
- React violently with water.
- Reactivity increases down the group.
Group 2: Two electrons in outermost shell.
Group 7 (Halogens): Seven electrons in outer shell.
- Reactivity decreases down the group.
Group 0 (Noble Gases):
- Full outer shells (Helium has 2 of 2, Argon has 8 of 8).
- Very unreactive.

Zigzag Line: Separates metals (left side) from nonmetals (right side).
- More metals than nonmetals.
Transition Metals: A special block of elements within metals.

Different periodic tables might display mass and atomic numbers differently, but the information remains the same.
In exams, tables similar to the one discussed will be provided.

Understanding the periodic table's structure and grouping helps predict chemical properties and reactivity.
Further videos will explore specific groups and differences between metals and nonmetals.

Note: Always ensure to check the atomic number as the smaller value when identifying elements in various table formats.