Question

Which of the following symbols provides more information about the atom: \({ }^{23}\) Na or \({ }_{11} \mathrm{Na}\) ? Explain.

Short answer

\(_{11} \text{Na}\) provides more information as it directly indicates the element's identity.

Step-by-step solution

Understand Atomic Notation

In atomic notation, \(^{A}_{Z}X \), \( A \) is the mass number (total number of protons and neutrons), \( Z \) is the atomic number (number of protons), and \( X \) is the chemical symbol. These notations help to identify the specifics of an atom's properties.

Compare the Provided Notations

The first notation is \( ^{23} \text{Na} \), where 23 could represent the mass number. The second notation is \( _{11} \text{Na} \), where 11 represents the atomic number.

Define the Information Copies

The atomic number, \(Z\), reveals the number of protons, which defines the element and provides information about its chemical properties. It also indirectly tells about the electron count in a neutral atom. The mass number, \(A\), informs about the atom's isotopic variant, indicating the number of neutrons when subtracted by \(Z\).

Determine Which Symbol Provides More Information

While the atomic number reveals the elemental identity, the mass number indicates the isotopic variant by accounting for neutron count. Since the mass number also requires knowing the atomic number to compute neutron count, directly seeing \(Z\) as in \( _{11} \text{Na} \) provides the definitive identification of both chemical behavior and potential isotopic forms.

Key concepts

Atomic Number

The atomic number, represented as \( Z \), is the number of protons in an atom's nucleus. It is a fundamental property because it defines the element.
For example, hydrogen has an atomic number of 1, which means every hydrogen atom has one proton. In the atomic notation \( _{11} \text{Na} \), 11 is the atomic number.

This tells us the atom is sodium, as sodium is the element with 11 protons.

• Determines the identity of the element.
• Gives the number of electrons in a neutral atom.
• The periodic table is arranged by atomic number.

Mass Number

The mass number, represented as \( A \), is the total count of protons and neutrons in an atom's nucleus. This provides crucial information on isotopic variation.
For \( ^{23} \text{Na} \), the mass number is 23. To find the number of neutrons, subtract the atomic number from the mass number. For sodium:

• Mass number, \( A = 23 \).
• Atomic number, \( Z = 11 \).
• Neutrons = \( A - Z = 23 - 11 = 12 \).

The mass number helps us understand the isotope of the element, distinguishing isotopes that vary by neutron count.

Isotopic Variant

Isotopic variants, or isotopes, are atoms of the same element with different numbers of neutrons. This results in different mass numbers.
All isotopes of an element have the same number of protons, but varying neutrons. For example, chlorine has isotopes with mass numbers 35 and 37. Isotopes can influence atomic mass and are often used in scientific research and medical applications.

• Defined by mass number differences.
• Important for nuclear and chemical reactions.

Protons and Neutrons

Protons are positively charged particles, while neutrons carry no charge. Together, they form the nucleus of an atom and contribute to the atomic mass.
The number of protons (atomic number) defines the element. Neutrons, however, can vary without altering the chemical properties, influencing the mass and forming isotopes.

• Protons impact chemical identity.
• Neutrons determine isotopic variations.
• Both contribute to the mass number.

Chemical Symbol

The chemical symbol is a one- or two-letter abbreviation representing an element. These symbols provide a quick way to communicate chemical identities and are universally recognized.
In sodium's case, "Na" is its chemical symbol. These symbols are standardized by IUPAC and used throughout chemistry to specify elements succinctly.

• Derived from Latin or English names.
• Unique to each element.
• Used globally in scientific notation.