AtomicNumber and Mass Atoms of each element contain a characteristic number of protons and electrons, which are equal.
The number of protons determines an element’s atomicnumber (Z) and distinguishes one element from another.
Isotopes of the same element will have the same atomicnumber but different mass numbers.
For example, the atomic mass of chlorine (Cl) is 35.45 because chlorine is composed of several isotopes, some (the majority) with an atomic mass of 35 (17 protons and 18 neutrons) and some with an atomic mass of 37 (17 protons and 20 neutrons).
Given an atomicnumber (Z) and mass number (A), you can find the number of protons, neutrons, and electrons in a neutral atom.
The atomicnumber is the number of protons in an element while the number of protons plus the number of neutrons determines the mass number.
In the periodic table the elements are organized and displayed according to their atomicnumber and are arranged in a series of rows (periods) and columns (groups) based on shared chemical and physical properties.
In addition to providing the atomicnumber for each element, the periodic table also displays the element’s atomic mass.
Looking at carbon, for example, its symbol (C) and name appear, as well as its atomicnumber of six (in the upper left-hand corner) and its atomic mass of 12.11.
Electron Shells and the Bohr Model As previously discussed, there is a connection between the number of protons in an element, the atomicnumber that distinguishes one element from another, and the number of electrons it has.
In all electrically-neutral atoms, the number of electrons is the same as the number of protons.
Each element, when electrically neutral, has a number of electrons equal to its atomicnumber.
These orbits form electron shells or energy levels, which are a way of visualizing the number of electrons in the various shells.
These energy levels are designated by a number and the symbol “n.” For example, 1n represents the first energy level located closest to the nucleus.