The Periodic table - SS1 Chemistry Lesson Note
The periodic table is a tabular arrangement of chemical elements based on their atomic numbers, electron configurations, and chemical properties. The Russian Chemist, Dmitri Mendeleev formulated the first periodic table to be generally accepted in 1869. It provides a systematic way of organising and understanding the elements, showcasing their relationships and trends. Here are some key aspects and features of the periodic table:
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Organization of Elements: The periodic table arranges elements in order of increasing atomic number, which represents the number of protons in an atom's nucleus. Elements with similar properties are grouped in the same column, known as a group or family. There are 18 groups in the periodic table.
Periods: The periodic table is divided into periods, which are rows that represent the energy levels or electron shells of the elements. The period number corresponds to the highest occupied energy level in an element's electron configuration.
Groups and Families: Elements in the same group or family have similar chemical properties because they share the same number of valence electrons, which are the outermost electrons involved in bonding. Some common groups include alkali metals, alkaline earth metals, halogens, and noble gases.
Blocks: The periodic table is divided into blocks based on the type of subshell being filled with electrons. These blocks include s-block, p-block, d-block, and f-block. The elements in each block have similar electron configurations and exhibit similar properties.
Atomic Symbol and Atomic Mass: Each element in the periodic table is represented by its atomic symbol, which is a one- or two-letter abbreviation derived from its English or Latin name. The atomic mass of an element is usually listed beneath its symbol and represents the weighted average of the masses of its naturally occurring isotopes.
Periodic Trends: The periodic table provides valuable information about periodic trends, which are consistent patterns in the properties of elements across a period or down a group. Some important trends include atomic radius, ionisation energy, electronegativity, and metallic character.
Metals, Nonmetals, and Metalloids: Elements in the periodic table can be broadly categorised into metals, nonmetals, and metalloids. Metals are typically found on the left side of the periodic table and tend to be good conductors of heat and electricity. Nonmetals are located on the right side and often have poor conductivity. Metalloids, also known as semimetals, have properties that lie between metals and nonmetals.
Periodic Table Trends: The periodic table reveals trends in atomic size, ionisation energy, electronegativity, and metallic character. Atomic size generally increases from right to left and from top to bottom. Ionisation energy, the energy required to remove an electron from an atom, generally increases from left to right and from bottom to top. Electronegativity, the tendency of an atom to attract electrons in a chemical bond, generally increases from left to right and from bottom to top. Metallic character tends to decrease from left to right and from top to bottom.
Discoveries and Predictions: The periodic table has played a significant role in predicting the existence and properties of new elements. Gaps in the periodic table led to the discovery of elements that filled those gaps, such as gallium and germanium. Additionally, the periodic table provides a framework for understanding and predicting the chemical behaviour of elements and their compounds.
The periodic table is an essential tool for chemists and scientists in various fields. It provides a systematic and organised way of classifying elements, understanding their properties, and predicting their behaviour. It's development and ongoing updates have significantly contributed to the advancement of chemistry and our understanding of the building blocks of matter.