1. ISOTOPES

2. What does this Symbol Mean?
Symbol for lithium.
Second letter is always lower case.
What does this Symbol Mean? 7 L
Therefore
A Lithium atom contains
3 protons
4 neutrons (3+4=7) i
Mass Number
protons + neutrons 3
Atomic Number
Number of protons

3. But something is different!
Both these symbols represent carbon atoms.
But something is different! 14 12 12
Different mass number

4. 12 p e 6 n 6 p e 6 n 6 6 8

5. Isotopes are atoms with the
same number of protons
but a different number of neutrons.
Most elements have several different isotopes but only one or two of which are stable.

6. Past Questions B B e e 9 11 4 4 What is the an isotope?
Atoms of an element that contain the same number of protons but a different number of neutrons.
2. Calculate the number of protons and neutrons in these two atoms of beryllium. 9 B 11 B e e 4 4 p 4 e n 7 p 4 e n 5