An atomic nucleus possesses a definitive positive charge. The atom is composed of a dense, central core, the nucleus, surrounded by a much larger, diffuse electron cloud. This nucleus is the source of all positive charge within the atom. Although the atom as a whole is typically electrically neutral, the concentrated charge at its center plays a fundamental role in atomic structure and chemical properties.
The Constituents of the Atomic Nucleus
The nucleus of an atom is a compact region containing two primary types of subatomic particles: protons and neutrons. These particles are collectively referred to as nucleons and account for more than 99.9% of the atom’s total mass.
Protons and neutrons are significantly heavier than the electron, which orbits the nucleus. This mass difference explains why the nucleus is dense, with the atom’s bulk concentrated in a minute volume at its center.
The combination of protons and neutrons creates the stable core of the atom. The presence of these particles is constant across all elements, except for the most common isotope of hydrogen, which contains a single proton and no neutrons.
Defining Nuclear Charge by Atomic Number
The positive charge of the nucleus is entirely attributed to protons. Every proton carries a single unit of positive electrical charge (+1). Neutrons possess no electrical charge, meaning they are electrically neutral.
The total positive charge of any nucleus is the sum of the charges of all its constituent protons. This count of protons is a fundamental property of the atom and is known as the Atomic Number, symbolized by Z.
The Atomic Number determines the magnitude of the positive nuclear charge. For instance, an atom with five protons has a nuclear charge of +5.
The Atomic Number is the defining feature of an element, dictating its identity. Changing the number of protons changes the nuclear charge, which in turn changes the element itself.
Every atom with Z=6 is carbon, and every atom with Z=8 is oxygen, regardless of the number of neutrons present. This relationship means the nuclear charge determines an atom’s place on the periodic table and its chemical behavior.
How the Atom Achieves Electrical Neutrality
While the nucleus is positively charged, an atom in its standard state is electrically neutral, possessing a net charge of zero. This neutrality is achieved by the presence of negatively charged electrons surrounding the nucleus in the electron cloud.
Each electron carries a charge equal in magnitude but opposite in sign to that of a proton (-1). In a neutral atom, the number of electrons orbiting the nucleus must exactly match the number of protons within the nucleus.
This precise balance ensures the total negative charge from the electrons cancels out the total positive charge from the protons. Therefore, the number of electrons in a neutral atom is also equal to the Atomic Number, Z.
If an atom gains or loses one or more electrons, this balance is disrupted, creating a charged particle called an ion. If an atom gains an electron, it becomes negatively charged (an anion), and if it loses an electron, it becomes positively charged (a cation).