All matter in the universe is constructed from fundamental building blocks called atoms. These tiny structures are composed of three primary subatomic particles: protons and neutrons, which reside in the dense central nucleus, and electrons, which orbit the nucleus. The unique combination of these particles defines every element found on the periodic table. To understand the element Thorium, or any element, it is necessary to examine the specific count of these particles, beginning with the foundational number of protons.
The Definitive Answer
Thorium (Th) possesses exactly 90 protons within the nucleus of every one of its atoms. This specific count of 90 is known as the element’s Atomic Number, which is represented by the symbol \(Z\). The periodic table organizes all known elements based on this increasing atomic number, placing Thorium as the 90th element. This number is a fundamental identifier for the element. The atomic number is typically displayed directly above the element’s chemical symbol on a standard periodic table. For Thorium, the symbol Th is accompanied by the number 90 to signify its unchangeable proton count.
Protons Define the Element
The number of protons an atom contains is the single characteristic that determines which element it is. Changing the number of protons transforms the atom into an entirely different element. This concept is fundamental to the organization of the periodic table. If a Thorium atom were to gain one proton, its atomic number would increase from 90 to 91, instantly changing the element into Protactinium (Pa). Conversely, if the atom lost a proton, it would become Actinium (Ac), the element with 89 protons. This rule is absolute in chemistry and physics. It is important to distinguish the proton count from the number of neutrons or electrons. Atoms can gain or lose electrons to become electrically charged ions, or they can have differing numbers of neutrons to form isotopes, but they remain the same element as long as the proton count remains fixed at 90. The chemical properties of the element are largely dictated by the number of electrons, which in turn is equal to the number of protons in a neutral atom.
Thorium’s Identity and Atomic Structure
Beyond the 90 protons, the full identity of a Thorium atom is completed by its neutrons and electrons. Thorium is classified as an actinide, a series of metallic elements typically found at the bottom of the periodic table. This classification helps define its chemical behavior.
Isotope Thorium-232
The most common form of the element found in nature is the isotope Thorium-232 (Th-232), which accounts for nearly 99.98% of all naturally occurring Thorium. The number 232 is the mass number (A), representing the total count of protons and neutrons combined in the nucleus.
To determine the number of neutrons in Th-232, one subtracts the atomic number (90 protons) from the mass number (232 total particles). This calculation reveals that Th-232 contains 142 neutrons (232 – 90 = 142). While Thorium has other isotopes with different neutron counts, the 90 protons are present in all of them.
Electron Count and Radioactivity
As a neutral atom, Thorium must have an equal number of electrons orbiting the nucleus to balance the positive charge of the 90 protons. Therefore, a neutral Thorium atom contains 90 electrons. All isotopes of Thorium are radioactive, but Th-232 is considered weakly radioactive because it decays extremely slowly. It has a half-life of 1.4 x 10^10 years, which is longer than the age of the Earth. This prolonged decay rate is a characteristic property of this atomic structure.