Atomic radius generally decreases from left to right across a period because the effective nuclear charge while electrons are being added to the same outer level. These additional electrons are shielded by inner electrons and are therefore attracted strongly by the nucleus

At 20∘c, the hole in an aluminum ring is 2.800 cm in diameter. you need to slip this ring over a steel shaft that has a room-temperature diameter of 2.804 cm . 1. to what common temperature should the ring and the shaft be heated so that the ring will just fit onto the shaft? coefficients of linear thermal expansion of steel and aluminum are 12×10−6 k−1 and23×10−6 k−1 respectively.