Isotopes
Isotopes
- Isotopes are atoms of the same element with a different number of neutrons.
- Same protons ($Z$), different nucleon number ($A$).
- They behave the same chemically — but differ slightly physically.
Practice
Isotopes of an element have:
Isotopes share the proton number Z but differ in neutron number, so they have different nucleon numbers A.
What makes an isotope
- Isotopes have the same proton number $Z$ but a different nucleon number $A$.
- We write one as $^{A}_{Z}\text{X}$ — e.g. chlorine has $^{35}_{17}\text{Cl}$ and $^{37}_{17}\text{Cl}$.
Same chemistry, different physics
- Chemical properties depend on the electrons — isotopes have the same electron arrangement, so they react identically.
- Some physical properties depend on mass — a heavier isotope (more neutrons) has a higher density.
Practice
Isotopes of one element have the same chemical properties because:
Chemistry depends on the electrons; isotopes have identical electron arrangements, so they react the same.
Practice
Which property can differ between two isotopes?
A heavier isotope (more neutrons) has more mass and so a higher density; chemistry is unchanged.
You've got it
Key idea
- isotopes = same element, same $Z$, different $A$ (different neutrons)
- written $^{A}_{Z}\text{X}$ (e.g. $^{35}_{17}\text{Cl}$ and $^{37}_{17}\text{Cl}$)
- same chemical properties (same electrons); different physical (mass → density)