Isotope

atoms of the same element have the same proton number, but they can have different nucleon numbers.

That’s because not all atoms of an element have the same number of neutrons.

Atoms of the same element with different numbers of neutrons are called isotopes.

Chemical properties

• Isotopes of the same element have the same number of electrons, so they have the same chemical properties.
• Chemical properties are all about how the electrons interact with other atoms (e.g. in chemical reactions), so isotopes of the same element behave the same way chemically.

Physical properties

• Isotopes of the same element can have different physical properties, such as density, melting point, and boiling point.
• This is because physical properties depend on the mass of the atom, and isotopes have different masses due to their different numbers of neutrons.

Nuclear properties

• They have different nuclear properties, such as radioactivity and half life.
• For example, carbon 12 is perfectly stable, while carbon 14 is radioactive and has a half-life of about 5,730 years, so will eventually radioactively decay.