Understanding Atomic Weight and Isotopes

The video tutorial explains the difference between mass number and atomic weight. Mass number is the sum of protons and neutrons in an atom, indicating its weight in atomic mass units (AMU). Atomic weight, however, is the average mass of an element's isotopes, considering their abundance. Using boron as an example, the video illustrates how to calculate atomic weight by factoring in the percentage of each isotope. The tutorial concludes by clarifying that mass number applies to individual atoms, while atomic weight considers isotopic distribution.

What is the mass number of an atom with 5 protons and 6 neutrons?

• 10

• 11

• 13

• 12

Which of the following is true about mass number?

• It is the number of electrons in an atom

• It is the average mass of all isotopes

• It is the sum of protons and neutrons in an atom

• It is the same as atomic weight

Which of the following best describes isotopes?

• Atoms with the same number of protons but different neutrons

• Atoms with the same number of neutrons but different protons

• Atoms with different numbers of protons and neutrons

• Atoms with the same mass number

What determines the element of an atom?

• The atomic weight

• The number of protons

• The number of electrons

• The number of neutrons

What percentage of boron atoms are Boron-11?

• 50%

• 80%

• 20%

• 100%

How do you calculate the average atomic weight of an element with isotopes?

• Average the number of protons and neutrons

• Use the mass number of the most common isotope

• Multiply the mass of each isotope by its percentage and sum the results

• Add the mass numbers of isotopes and divide by two

Why is the average atomic weight of boron closer to 11 AMU?

• Because Boron-11 has fewer neutrons

• Because Boron-10 is more abundant

• Because Boron-11 is more abundant

• Because both isotopes are equally abundant

What is the significance of isotopes in determining atomic weight?

• Atomic weight is determined by the heaviest isotope

• The distribution of isotopes affects atomic weight

• Only the most common isotope affects atomic weight

• Isotopes do not affect atomic weight

What does the number 10.8 represent on the periodic table for boron?

• The atomic weight of boron

• The mass number of Boron-11

• The mass number of Boron-10

• The number of protons in boron

How does the atomic weight differ from the mass number?

• Atomic weight is for individual isotopes, mass number is an average

• Mass number is for individual isotopes, atomic weight is an average

• Both are averages of isotopes

• Both are for individual isotopes