Periodic Table Overview and History

Study Notes

The Periodic Table

The Periodic Table of Elements organizes all discovered elements.
Each element is composed of identical atoms, unique to that element.
Elements cannot be broken down into simpler substances.
The Periodic Table provides information on element properties.

Periodic Table History

Johann Dobereiner (1829) proposed "triads" grouping elements with similar properties.
- For example, chlorine, bromine, and iodine form salt.
- His theory lacked sufficient evidence and was dismissed.
John Newlands (1864) discovered that elements with similar chemical properties have similar atomic structures.
- He organized elements by increasing atomic weight, observing similar elements every eighth element.
- This led to the "Law of Octaves."
Dmitri Mendeleev is considered the "Father of the Periodic Table."
- He arranged elements by increasing atomic weight, identifying patterns.
- Elements in the same column had similar properties.
- Reactivity increased across a row.
- Some inconsistencies arose due to arranging by atomic mass, leading to elements being out of order.
Henry Moseley refined the Periodic Table based on atomic number.
- He measured the wavelengths of electrons emitted from different elements.
- This revealed a consistent increase in the number of protons per element.
- Proposed that the number of protons defines an atom, leading to arranging elements by atomic number.

Periodic Table Organization

The Periodic Table has columns called groups and rows called periods.
- Groups represent periodic families with similar chemical properties.
- Periods signify the number of electron shells in an atom.
There are 18 groups and 7 periods on the Periodic Table.
- The bottom two rows are part of the sixth and seventh periods.

Periodic Table Sections

The Periodic Table is divided into metals, metalloids, and nonmetals.
- A staircase separates the sections, with elements to the left (except hydrogen) being metals.
- Metals share common properties: malleability, ductility, good conductors of heat and electricity.
- Elements above and to the right of the staircase (including hydrogen) are nonmetals.
- Nonmetals share common properties: brittle solids, poor conductors of heat and electricity.

Period vs. Group

Periods are horizontal rows.
- They signify the number of electron orbitals an atom has.
- Reactivity increases across a period.
Groups are vertical columns.
- They signify the number of valence electrons an atom has.
- Reactivity decreases down a group.

Periodic Table Properties

Valence Electrons:
- The outermost electrons in an atom.
- Increase across a period.
- Elements in the same group have the same number of valence electrons.
Atomic Radii:
- Larger in the lower left corner of the Periodic Table.
- Increase down a group.
- Decrease across a period.
Ionization Energy:
- High in the upper right corner.
- Increases across a period.
- Decreases down a group.
Electronegativity:
- High in the upper right corner.
- Increases across a period.
- Decreases down a group.
Electron Affinity:
- High in the upper right corner.
- Increases across a period.
- Decreases down a group.
Oxidizing Nature:
- Higher in elements with large ionization energy, small atomic radii, and more valence electrons.
- Found in the upper right corner (e.g., oxygen, fluorine, chlorine).
Metallic Character:
- Strong in the bottom left corner.
- Increases down a group.
- Decreases across a period.

Description

Explore the fascinating world of the periodic table, where elements are organized based on their properties. Discover the contributions of key figures like Johann Dobereiner, John Newlands, and Dmitri Mendeleev in shaping our understanding of these essential building blocks of matter.