Chapter U1.13, Problem 1TAI

Interpretation Introduction

Interpretation:

Atoms of same element can be different. This has is to be explained.

Concept introduction:

Atoms of one element are different from atoms of another element because they have different number of protons. The number of protons in the nucleus of an element is called atomic number. The atomic number of a neutral atom is equal to the number of electrons. It is unique for each element.

Answer to Problem 1TAI

Atoms of same element can also be different. Although all atoms of an element have many similarities, they may have some differences too. Atoms of an element may differ from each other in their mass numbers and atomic masses.

Explanation of Solution

From the periodic table, following information about elements can be obtained:

Element name, symbol, atomic number and average atomic mass

All atoms of an element are not exact replicas of one another. They are similar to each other in their atomic numbers as all atoms have same number of protons. Therefore, all atoms of an element will have same number of electrons. Some atoms however have different number of neutrons in their nuclei. This makes them differ in their masses. Since, mass number is the sum of number of protons and number of neutrons. If number of neutrons is not same in all atoms of an element, they will have different mass numbers.

Such atoms with different number of neutrons are called isotopes.

For example, carbon has three isotopes; ¹²C, ¹³C and ¹⁴C. All three isotopes have same properties but they have different mass numbers. Since, the mass numbers are different; they will have different atomic masses.

Average atomic mass is calculated by taking average of masses of isotopes of an element in a sample. It is expressed in amu. It is often written in decimal number.

Conclusion

Atoms of same element can be different in their atomic masses as they may have different number of neutrons in their nuclei. Atomic mass is the average of the masses of the isotopes of an element.