【People's Education Press】High School Chemistry, Compulsory Course Part One: The Mystery of the Atomic Nucleus — Quantitative Relationships Between Mass Number, Protons, and Neutrons

Foundations of the Microscopic World

In the grand narrative of chemistry, atoms are no longer indivisible 'solid spheres.' They are tiny yet orderly systems: at their core lies an atomic nucleus formed by tightly boundprotonsandneutronsclosely bound together. Surrounding it are lightelectrons outside the nucleus.

The Logic of Quantification

Electrical Neutrality: In electrically neutral atoms, the following must hold:Atomic Number = Nuclear Charge = Proton Count = Electron Count Outside Nucleus. This serves as the element's 'identity card'.
Definition of Mass Number: The sum of the approximate integer values of the relative masses of all protons and neutrons within the nucleus is called the mass number. The formula is expressed as: $$A = Z + N$$.
Identity Label: Elements are numbered in order according to their position in the periodic table, yielding the atomic number. By examining the hydrogen cell (p. 96), we can clearly see the relationship between the number in the top-left corner and the relative atomic mass below.

Just as archaeologists use $^{14}_6C$ to date artifacts, this precise quantitative relationship forms the physical foundation for humanity’s understanding of material evolution.

Core Reminder

Electrons always fill inner shells first, then proceed to outer ones. This ordered arrangement determines the chemical properties of elements.

QUESTION 1

Carbon-14 ($^{14}_6C$) is commonly used in archaeology to date artifacts. How many neutrons are in the nucleus of $^{14}_6C$?

QUESTION 2

Which of the following descriptions best defines the 'mass number'?

The actual mass of the atom

The sum of the relative masses of protons and electrons

The sum of the approximate integer values of the relative masses of all protons and neutrons within the nucleus

The relative atomic mass of the atom

QUESTION 3

In electrically neutral atoms, which of the following relationships does NOT necessarily hold equal?

Atomic number and nuclear charge

Proton count and electron count outside the nucleus

Proton count and neutron count

Atomic number and proton count

QUESTION 4

An atom has a nuclear charge of 17 and a mass number of 37. What is its number of electrons outside the nucleus?

QUESTION 5

Given that the atomic number of sodium is 11 and its neutron count is 12, what is its mass number A?