Review of Periodic Table and Trends - SS3 Chemistry Lesson Note
The periodic table is a tabular arrangement of chemical elements based on their atomic number, electron configuration, and chemical properties. It is a fundamental tool in chemistry, as it provides a systematic way of organising and understanding the properties of elements. The periodic table is divided into periods (horizontal rows) and groups (vertical columns). Let's review the periodic table and explore some of the key trends observed in the elements:
Periods:
● The periodic table is divided into seven periods, numbered from 1 to 7, representing the principal quantum number (n) of the outermost electron shell of the elements.
● As you move from left to right across a period, the atomic number increases, and so does the number of protons and electrons in the elements.
● The elements in a period generally have similar outer electron configurations, but as you move across the period, the chemical properties change gradually.
Groups:
● The periodic table is divided into 18 groups (1 to 18), each containing elements with similar electron configurations and chemical properties.
● Groups are often referred to by their common names, such as alkali metals (Group 1), alkaline earth metals (Group 2), halogens (Group 17), and noble gases (Group 18).
Key Trends in the Periodic Table:
1. Atomic Radius: Atomic radius refers to the size of an atom, typically measured as the distance from the nucleus to the outermost electron cloud. Within a period, as you move from left to right, the atomic radius generally decreases. This is due to an increase in effective nuclear charge (the attraction between protons and electrons) across the period, causing the electrons to be pulled closer to the nucleus. Within a group, as you move down the group, the atomic radius increases. This is because new electron shells are added as you move down, resulting in larger electron clouds.
2. Ionization Energy: Ionisation energy is the energy required to remove an electron from an atom, forming a positively charged ion (cation). Within a period, as you move from left to right, the ionisation energy generally increases. This is because the effective nuclear charge increases, making it more difficult to remove electrons from the atoms. Within a group, as you move down the group, the ionisation energy generally decreases. This is because the outermost electrons are farther from the nucleus and are shielded by inner electron shells, making them easier to remove.
3. Electronegativity: Electronegativity is the tendency of an atom to attract electrons when it is chemically bonded to another atom. Within a period, as you move from left to right, electronegativity generally increases. This is because the effective nuclear charge increases, leading to a stronger attraction for electrons. Within a group, as you move down the group, electronegativity generally decreases. This is because the larger atomic size and increased electron shielding reduce the attraction for electrons.
4. Metallic Character: Metallic character refers to the tendency of an element to exhibit metallic properties, such as high electrical conductivity, lustre, and malleability. Within a period, as you move from left to right, metallic character generally decreases. Nonmetals are located on the right side of the periodic table and have a low metallic character. Within a group, as you move down the group, a metallic character generally increases. Metals are located on the left side of the periodic table and have a high metallic character.
Overall, the periodic table and its trends provide a valuable framework for understanding the properties and behaviours of elements. The periodic table has been instrumental in predicting the existence of new elements, guiding the synthesis of compounds, and advancing our understanding of chemical reactions and materials.