There are four naturally occurring isotopes of strontium:...

There are four naturally occurring isotopes of strontium: $(4.4,4.5)$ ${ }_{38}^{84} \mathrm{Sr},{ }_{38}^{86} \mathrm{Sr},{ }_{38}^{87} \mathrm{Sr}$, and ${ }_{38}^{88} \mathrm{Sr}$ a. How many protons, neutrons, and electrons are in Sr-87? b. What is the most abundant isotope in a strontium sample? c. How many neutrons are in Sr-84? d. Why don't any of the isotopes of strontium have the atomic mass of $87.62 \mathrm{amu}$ listed on the periodic table?

There are four naturally occurring isotopes of strontium: $(4.4,4.5)$
${ }_{38}^{84} \mathrm{Sr},{ }_{38}^{86} \mathrm{Sr},{ }_{38}^{87} \mathrm{Sr}$, and ${ }_{38}^{88} \mathrm{Sr}$
a. How many protons, neutrons, and electrons are in Sr-87?
b. What is the most abundant isotope in a strontium sample?
c. How many neutrons are in Sr-84?
d. Why don't any of the isotopes of strontium have the atomic mass of $87.62 \mathrm{amu}$ listed on the periodic table?

Key Concepts

Nuclear Composition (Protons, Neutrons, and Electrons)

In any atom, the number of protons is fixed by its atomic number, and in a neutral atom, the number of electrons equals the number of protons. The number of neutrons can be calculated by subtracting the atomic number (protons) from the mass number. This concept is fundamental when analyzing the structure of an atom and understanding its isotopic form.

Isotopes

Isotopes are variants of a particular chemical element that have the same number of protons but different numbers of neutrons in their nuclei. This difference in neutron number affects the mass of the isotope but generally does not change the chemical properties of the element. Understanding isotopes is essential in nuclear chemistry and physics, as they can influence atomic mass and nuclear stability.

Atomic Number and Mass Number

The atomic number of an element represents the number of protons in its nucleus and defines the element, while the mass number is the sum of the protons and neutrons present in the nucleus. The mass number provides an approximation of an isotope's atomic mass in atomic mass units (amu). Recognizing the difference between these two numbers is crucial in determining the nuclear composition of atoms.

Isotopic Abundance and Average Atomic Mass

The average atomic mass of an element listed on the periodic table is a weighted average of the masses of all its naturally occurring isotopes, based on their relative abundances. This average does not necessarily correspond to the mass of any single isotope. Instead, it represents a composite value that reflects the contributions of all isotopes present in nature.

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