Write the correct symbols for the atoms that contain: (a) 25 protons, 25 electrons, and 27 neutrons; (b) 10 protons, 10 electrons, and 12 neutrons; (c) 47 protons, 47 electrons, and 60 neutrons; (d) 53 protons, 53 electrons, and 74 neutrons; (e) 94 protons, 94 electrons, and 145 neutrons.

Understanding atomic mass is crucial when studying the composition of atoms. Atomic mass, also known as atomic weight, is the total mass of protons and neutrons in an atom's nucleus. Electrons also contribute to the atomic mass, but their mass is so small compared to protons and neutrons that it is often negligible in calculations.

Take, for example, an atom of manganese (Mn) with 25 protons and 27 neutrons. The atomic mass is calculated by simply adding the number of protons to the number of neutrons: \( 25 + 27 = 52 \) — making the atomic mass 52 atomic mass units (amu). It is essential to differentiate between atomic mass and mass number; the latter only includes the total number of protons and neutrons and is always a whole number, whereas atomic mass is averaged over all isotopes and may be a decimal.

The atomic number is designated as the number of protons found in the nucleus of an atom and is fundamental to the identity of an element. It is represented by the 'Z' symbol and defines the chemical properties of the element because it determines the element's position on the periodic table.

For instance, iodine (I) always has an atomic number of 53 because it has 53 protons. No other element shares this atomic number, making it unique to iodine. Furthermore, since the number of protons equals the number of electrons in a neutral atom, the atomic number also tells us the number of electrons orbiting the nucleus.

What Are Isotopes?

Isotopes are variants of a particular chemical element that have the same number of protons (and thus the same atomic number) but different numbers of neutrons. This variation leads to different atomic masses.

Isotopes can be stable or unstable (radioactive). For instance, carbon has three naturally occurring isotopes: Carbon-12, Carbon-13, which are stable, and Carbon-14, which is radioactive and used in radiocarbon dating. Silver (Ag), with an atomic number of 47, has numerous isotopes, such as Ag-107 and Ag-109, which have 60 and 62 neutrons respectively.

Element symbols serve as a shorthand to represent chemical elements in scientific writing. These one or two-letter abbreviations are derived from their English or Latin names and provide a universal language for chemists and scientists across the world.

For example, 'Ne' represents Neon, and 'Pu' stands for Plutonium. When denoting isotopes, the element symbol is often followed by a hyphen and the mass number, such as Ne-22 for an isotope of Neon or Pu-239 for an isotope of Plutonium. It's important to note that the element symbol alone does not provide information about the isotope; the hyphen and mass number must also be included to convey this.