The elements of the Periodic Table's second and third rows show gradual property changes across the table as expected from left to right. Due to the addition of protons in the nucleus, electrons in the outer shells of the atoms of these elements have little shielding effects leading to an increase in effective nuclear charge. The effects on atomic properties are therefore: smaller atomic radius, increased energy for first ionization, increased electronegativity, and more non-metallic character. This trend continues until calcium (Z=20) is reached. At this point, there's an abrupt break. In their physical and chemical properties, the next ten elements called the first transition series are remarkably similar. In terms of their relatively small difference in effective nuclear charge over the series, this general similarity in properties has been explained. This happens as each additional electron enters the penultimate 3d shell that provides an effective shield between the nucleus and the shell of the outer 4s.