Chemistry · Class 9

Structure of the Atom

Atoms are the building blocks of all matter. Understanding atomic structure, including the nucleus and electron shells, explains chemical behavior and

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Why does atomic mass differ from atomic number?

Atomic number counts only protons. Atomic mass includes both protons and neutrons. Most atoms have more neutrons than protons, so atomic mass is always greater than atomic number.

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What makes isotopes of the same element behave differently?

Chemical properties depend mainly on electrons, which are the same in isotopes. However, isotopes differ in neutron number, affecting nuclear properties like radioactivity and nuclear mass, which can influence some chemical properties slightly.

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Why do electrons not fall into the nucleus?

In quantum mechanics, electrons have a certain probability distribution around the nucleus defined by orbitals. They do not actually orbit like planets but exist in energy states that prevent them from collapsing into the nucleus due to the uncertainty principle.

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