Periodic Table and Properties of Elements

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Periodic Table and Properties of Elements

This lesson aligns with NGSS PS1.A

Introduction

Mendeleev designed his periodic table by arranging elements according to ascending atomic mass, while the modern periodic law is based on the increasing order of atomic numbers. The modern periodic law states that the physical and chemical properties of the elements exhibit periodic functions of their atomic numbers. The nucleus is situated deeply within an atom, while the electrons, particularly those in the outermost shell, are free to move around and participate in chemical reactions. As a result, the properties of an element are influenced more by the atomic number than by the atomic mass. In this article, we will learn about periodicity, transition and inner transition metals.

Periodicity in the Modern Periodic Table

The reason behind periodicity in properties lies in the repetition of similar outer electronic configuration after certain regular intervals.

For instance, elements within group 1, known as alkali metals, share a common outer electronic configuration, ns1, where 'n' denotes the Principal Quantum Number of the outermost shell.
Similarly, elements in group 17 have a similar outer electronic configuration, ns2 np5, leading to similar properties to one another. This group is identified as the halogens.
In contrast, elements in group 18 showcase an outer electronic configuration of ns2 np6, resulting in fully filled orbitals. These elements, known as inert gases, are non-reactive. Helium and Argon share an electron configuration similar to the elements in this group, leading to their classification as inert gases.
The pattern extends to other elements within a group, as they share similar properties with other members of the same group.

Metallic and Non-metallic Character

Elements can either be metals or non-metals. For instance, Steel, which is an alloy of iron, is more metallic than iron. The reason behind this behavior is because of the metallic and non-metallic character of the elements.

Metallic Character of Metal:

The term "metallic character" refers to the reactivity level of a metal. Metals exhibit a tendency to lose electrons during chemical reactions, a characteristic reflected in their low ionization energies. Within a compound, metal atoms show relatively weak attraction for electrons, indicated by their low electronegativities.

Notably, cesium identifies as the most reactive metal, existing rarely in its free elemental form in nature. Cesium's reactivity is demonstrated by its explosive reaction with water and spontaneous ignition in air.

Francium, positioned below cesium in the alkali metal group, is even rarer, with most of its properties remaining unobserved due to its scarcity.

Non-metallic character of a Metal:

Nonmetals tend to gain electrons during chemical reactions and possess a high attraction for electrons within a compound. Notably, the upper right section of the periodic table hosts the most reactive nonmetals. A unique group among nonmetals is the noble gases, distinguished by their inert, non-reactive nature. Remarkably, fluorine is not naturally found in its free elemental state. Its reactivity is demonstrated through explosive reactions with various elements and compounds, positioning it as one of the most hazardous substances known.

Transition Metals and Inner Transition Metals

Transition Metal:

In the midst of the periodic table lies the transition metals, occupying groups 3 to 12. These elements exhibit a variety of oxidation states and are known for their malleability, conductivity, and diverse chemical properties. Transition metals often form colorful compounds due to the presence of different oxidation states.

Inner transition Metals:

Below the main body of the periodic table, we find the inner transition metals, which consist of the lanthanides and actinides. These elements are positioned separately at the bottom to avoid expanding the width of the periodic table excessively. The lanthanides and actinides share similar properties and are often referred to as the rare earth elements.

Importance of Electron Configuration

Understanding the distribution of electrons in different energy levels and sublevels helps explain trends in the periodic table.The Aufbau principle, Pauli exclusion principle, and Hund's rule govern the filling of electron orbitals.

Aufbau Principle:

The Aufbau principle dictates that electrons fill the lowest energy orbitals first, followed by higher energy levels.

Pauli Exclusion Principle

The Pauli exclusion principle states that no two electrons in an atom can have the same set of four quantum numbers, and Hund's rule emphasizes that electrons occupy orbitals singly before pairing up.

These principles ensure that elements are arranged according to their electron configurations.

Summary

The modern periodic law states that the physical and chemical properties of the elements exhibit periodic functions of their atomic numbers.
Metals exhibit a tendency to lose electrons during chemical reactions, a characteristic reflected in their low ionization energies.
Nonmetals tend to gain electrons during chemical reactions and possess a high attraction for electrons within a compound.
The Aufbau principle dictates that electrons fill the lowest energy orbitals first, followed by higher energy levels.

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