Subatomic Particles and
Isotopes
Subatomic Particles

Protons- Positively Charged




Located in the nucleus
Have the same mass as a neutron
Have same but positive charge of an electron
Atomic number tells number of protons in an
atom of that element

Atomic Number = # protons


Example- Carbon atomic number= 6
 Has 6 Protons
Neon- Atomic Number ?
# protons ?
Electrons





Negative charge
In the electron cloud
Smaller than protons and neutrons
Has the same charge as protons, but it is
negative
In a neutral atom, # protons= #electrons
Electrons


In a neutral atom, # protons= #electrons
If electrons ≠ protons, the atom has a charge




Known as an ion
If more protons- atom has a positive charge
If more electrons- atom has a negative charge
To find the charge:

charge= protons - electrons
Neutrons





Neutrally charged
Located in nucleus
Have the same mass of protons
For most atoms, # protons=#neutrons
However, for some atoms
#protons ≠ #neutrons

These are called isotopes
Isotopes



#protons ≠ #neutrons
Mass number= #protons + #neutrons
What is the mass number of carbon with 8
neutrons?

Answer: 14

Written: carbon- 14
Isotopes
How many neutrons does hydrogen-3 have?
Answer: 2
mass #= #protons + #neutrons
3
=
1
+
# neutrons
3–1
=
#Neutrons
Why are isotopes important?

They contribute to the mass of the atom.

Why?
Most of the mass of the atom is from protons and
neutrons
 If there is an additional neutron the mass
increases


Also, they have properties different from
other isotopes

Carbon-14
The Average Atomic Mass

The average of the masses of all the
isotopes of an atom

That’s why the average atomic mass is a
decimal!
Average Atomic Mass


Tells you the most abundant isotope of an
atom.
Example- Iron (Fe)


Average atomic Mass: 55.845
Round the mass to the nearest whole number


55.845 round to 56
Iron- 56 is the most abundant isotope of iron
Determine the Most Abundant
Isotopes for the Following
Elements
1.
2.
3.
4.
5.
6.
Lithium (Li)
Carbon
Oxygen
Hydrogen
Neon
Chlorine
•Lithium- 7
•Carbon- 12
•Oxygen- 16
•Hydrogen- 1
•Neon- 20
•Chlorine- 35 and Chlorine36