What is Atomic Size?, Atomic size refers to the atomic radius, which is the distance between the centre of the nucleus and the outermost shell of an isolated atom.Unit: It is measured in picometres ({pm}): 1 { pm} = 10-12 m;Example: The atomic radius of Hydrogen is 37 { pm}., Give reasons: Atomic radius decreases as we move from left to right across a period., Scientific Reason: ✮As we move across a period, electrons are added to the same valence shell (the number of shells remains constant).✭As we move across a period, electrons are added to the same valence shell (the number of shells remains constant).✭At the same time, the nuclear charge (number of protons in the nucleus) increases by one unit at each step.This increased positive charge exerts a stronger electrostatic pull on the electrons, drawing them closer to the nucleus and shrinking the atomic radius., Atomic radius increases as we move down a group., Moving down a group, a new electron shell is added at each successive step.✮This increases the physical distance between the outermost electrons and the nucleus.✭This increases the physical distance between the outermost electrons and the nucleus.✭Even though nuclear charge increases, the addition of extra inner electron shells shields the outer electrons, overriding the nuclear pull and causing the overall atomic size to increase., Why does atomic radius decrease as we move from left to right across a period?, Because electrons are added to the same valence shell while the nuclear charge increases. This stronger positive nuclear charge pulls the electrons closer to the nucleus, reducing atomic size., Arrange the following elements in decreasing order of their atomic size: {Na (11), Cl (17), Mg (12), P (15)}., All four elements belong to Period 3. Since atomic size decreases across a period from left to right:{Na} > {Mg} > {P} > {Cl} ✭Sodium ({Na}) is the largest, and Chlorine ({Cl}) is the smallest., Between Lithium ({Li}, Z=3) and Potassium ({K}, Z=19):✭Which atom has a larger atomic radius?✭Give a scientific reason for your answer.✭What is the unit used to express atomic radius?, ✮Potassium ({K}) has a larger atomic radius.✭Both belong to Group 1. Moving down from Lithium (2 shells: K, L) to Potassium (4shells: K, L, M, N), extra shells are added, increasing the distance between the nucleus and the outermost electrons.✭It is expressed in picometres ({pm}).

Atomic Size

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