Question: What is the number of protons in the nucleus of an atom called?
About the article "Proton", section "Abstract".

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The atom is the basic unit of chemistry.
It consists of a dense core called the atomic nucleus surrounded by a space called the electron cloud.
The nucleus is made up of positively charged protons and uncharged neutrons (together called nucleons), while the electron cloud consists of negatively-charged electrons which orbit the nucleus.
In a neutral atom, the negatively-charged electrons balance out the positive charge of the protons.
The nucleus is dense; the mass of a nucleon is 1,836 times that of an electron, yet the radius of an atom is about 10,000 times that of its nucleus.
The atom is also the smallest entity that can be envisaged to retain the chemical properties of the element, such as electronegativity, ionization potential, preferred oxidation state(s), coordination number, and preferred types of bonds to form (e.g., metallic, ionic, covalent). 
Isotopes are variants of a particular chemical element such that, while all isotopes of a given element have the same number of protons in each atom, they differ in neutron number.
The term isotope is formed from the Greek roots isos (ἴσος "equal") and topos (τόπος "place"), meaning "the same place".
Thus, different isotopes of a single element occupy the same position on the periodic table.
The number of protons within the atom's nucleus is called atomic number and is equal to the number of electrons in the neutral (un-ionized) atom.
Each atomic number identifies a specific element, but not the isotope; an atom of a given element may have a wide range in its number of neutrons.
The number of nucleons (both protons and neutrons) in the nucleus is the atom's mass number, and each isotope of a given element has a different mass number.
For example, carbon-12, carbon-13 and carbon-14 are three isotopes of the element carbon with mass numbers 12, 13 and 14 respectively.
The atomic number of carbon is 6, which means that every carbon atom has 6 protons, so that the neutron numbers of these isotopes are 6, 7 and 8 respectively. 
The atom is a basic unit of matter that consists of a dense central nucleus surrounded by a cloud of negatively charged electrons.
The atomic nucleus contains a mix of positively charged protons and electrically neutral neutrons (except in the case of hydrogen-1, which is the only stable nuclide with no neutrons).
The electrons of an atom are bound to the nucleus by the electromagnetic force.
Likewise, a group of atoms can remain bound to each other by chemical bonds based on the same force, forming a molecule.
An atom containing an equal number of protons and electrons is electrically neutral, otherwise it is positively or negatively charged and is known as an ion.
An atom is classified according to the number of protons and neutrons in its nucleus: the number of protons determines the chemical element, and the number of neutrons determines the isotope of the element.
Chemical atoms, which in science now carry the simple name of "atom," are minuscule objects with diameters of a few tenths of a nanometer and tiny masses proportional to the volume implied by these dimensions.
Atoms can only be observed individually using special instruments such as the scanning tunneling microscope.
Over 99.94% of an atom's mass is concentrated in the nucleus, with protons and neutrons having roughly equal mass.
Each element has at least one isotope with an unstable nucleus that can undergo radioactive decay.
This can result in a transmutation that changes the number of protons or neutrons in a nucleus.
Electrons that are bound to atoms possess a set of stable energy levels, or orbitals, and can undergo transitions between them by absorbing or emitting photons that match the energy differences between the levels.
The electrons determine the chemical properties of an element, and strongly influence an atom's magnetic properties.
The principles of quantum mechanics have been successfully used to model the observed properties of the atom. 
The mass number (A), also called atomic mass number or nucleon number, is the total number of protons and neutrons (together known as nucleons) in an atomic nucleus.
Because protons and neutrons both are baryons, the mass number A is identical with the baryon number B as of the nucleus as of the whole atom or ion.
The mass number is different for each different isotope of a chemical element.
This is not the same as the atomic number (Z) which denotes the number of protons in a nucleus, and thus uniquely identifies an element.
Hence, the difference between the mass number and the atomic number gives the number of neutrons ("N") in a given nucleus: "N=A−Z".
The mass number is written either after the element name or as a superscript to the left of an element's symbol.
For example, the most common isotope of carbon is carbon-12, or , which has 6 protons and 6 neutrons.
The full isotope symbol would also have the atomic number (Z) as a subscript to the left of the element symbol directly below the mass number: .
This is technically redundant, as each element is defined by its atomic number, so it is often omitted. 
  The atom is the smallest unit of an element that retains the chemical properties of that element.
An atom has an electron cloud consisting of negatively charged electrons surrounding a dense nucleus.
The nucleus contains positively charged protons and electrically neutral neutrons.