Problem 4 - Chemistry The Molecular Science

Question

Atoms of elements can have varying numbers of neutrons in their nuclei. (a) What are species called that have varying numbers of neutrons for the same element? (b) How do the mass numbers vary for these species? (c) What are two common elements that exemplify this property?

Step-by-Step Solution

Answer

(a) Isotopes. (b) Mass numbers vary due to different neutron counts. (c) Hydrogen and Carbon.

Step 1: Identify species with varying neutrons

The species that have the same number of protons (hence, the same element) but different numbers of neutrons are known as isotopes. Isotopes have nearly identical chemical properties but different physical properties due to the change in mass.

Step 2: Determine mass number differences

Isotopes of an element vary in their mass numbers because the mass number is the sum of protons and neutrons in the nucleus. With varying numbers of neutrons, the mass number also changes even though the number of protons remains the same.

Step 3: Identify examples of common isotopic elements

Common elements that have isotopes include Hydrogen and Carbon. Hydrogen has isotopes like deuterium and tritium, while Carbon has carbon-12 and carbon-14 as isotopes.

Key Concepts

Neutrons

Neutrons are subatomic particles found in the nucleus of an atom, along with protons. They do not carry any electric charge, which makes them neutral. Neutrons are crucial as they contribute to the mass of an atom and influence its stability.
Atoms of the same element can have different numbers of neutrons. These variations do not affect the chemical behavior of the element but do affect its mass. Understanding the role of neutrons is important in studying isotopes, where atoms have the same number of protons but different numbers of neutrons.
Key points about neutrons:

• Located in the nucleus of an atom
• No charge; thus, electrically neutral
• Contribute to the atomic mass
• Affect the stability of the atom

Mass Number

The mass number of an atom is a simple but very important concept. It is the sum of the number of protons and neutrons in an atom's nucleus. While all atoms of a given element have the same number of protons, they can have different mass numbers due to varying numbers of neutrons.
The mass number is used to distinguish between different isotopes of an element. For example, a carbon isotope with 6 protons and 6 neutrons has a mass number of 12 ( 6 + 6 = 12 ), while a carbon isotope with 6 protons and 8 neutrons has a mass number of 14 ( 6 + 8 = 14 ).
Important aspects of mass number include:

• It represents the total number of protons and neutrons
• Helps identify isotopes
• Differs between isotopes of the same element

Common Elements with Isotopes

Many elements exist as isotopes. While they are chemically similar, these isotopes differ in mass and sometimes in stability. Understanding common elements with isotopes helps in various fields, including chemistry, physics, and even medicine.
Two well-known elements that have isotopes include hydrogen and carbon.

• Hydrogen: The most abundant element in the universe, with three isotopes: protium (no neutrons, mass number 1), deuterium (one neutron, mass number 2), and tritium (two neutrons, mass number 3).
• Carbon: An essential element for life, with isotopes such as carbon-12 (6 neutrons, mass number 12) and carbon-14 (8 neutrons, mass number 14). Carbon-14 is particularly interesting due to its use in radiocarbon dating.

These examples highlight how isotopes can have the same chemical properties but vary significantly in terms of physical characteristics and applications.