Isotopes and Average Atomic Mass:
* Isotopes: Elements can exist in different forms called isotopes. Isotopes of the same element have the same number of protons (defining the element) but different numbers of neutrons. This means they have slightly different masses.
* Boron's Isotopes: Boron has two main isotopes: boron-10 and boron-11. Boron-10 has 5 protons and 5 neutrons, while boron-11 has 5 protons and 6 neutrons.
* Average Atomic Mass: The atomic mass listed on the periodic table is the *weighted average* of the masses of all the naturally occurring isotopes of an element. The weighting is based on the relative abundance of each isotope.
Example:
Imagine you have 100 boron atoms. Let's say 20 of them are boron-10 (mass ~10 amu) and 80 are boron-11 (mass ~11 amu). To calculate the average atomic mass:
1. Multiply the mass of each isotope by its abundance:
* Boron-10: (20/100) * 10 amu = 2 amu
* Boron-11: (80/100) * 11 amu = 8.8 amu
2. Add the results: 2 amu + 8.8 amu = 10.8 amu
In summary:
* The atomic mass listed on the periodic table represents the average mass of all the boron atoms found in nature.
* No single boron atom has a mass of 10.81 amu because it's a weighted average of the different isotopes' masses.
