In chemistry, the periodic table is designed to organize elements based on characteristics and similarities. The atomic number of an element serves as a primary organization factor in the table, with elements being arranged according to increasing atomic number. An additional elemental characteristic, melting point, directly relates to atomic number. Across the periodic table, relationships between the two result based on the placement of elements.
The atomic number of an element, as listed on the periodic table, refers to the number of protons present in a single atom of the element. For completely undisturbed atoms, which are neutral of electric charge, the number of electrons will be identical. Barring rare exceptions, the atomic weight of an element is considered to increase with higher atomic numbers.
The melting point of an element describes the temperature in which the transition between solid and liquid occurs. The melting point of an element can be an extremely small variation of temperature, with melting point measurements of 0.1 degrees Celsius capable for an element. While a liquid element can potentially be supercooled to a temperature below its individual freezing point, it is considered extremely difficult to heat a solid element above melting point, due to the energy converting the solid to a liquid as it enters the element.
Relationships occur between the atomic number and melting point of elements on the periodic table. Beyond the first period on the table, the melting point of elements will increase until the midpoint of period, in which the melting points will begin to drop. In single rows of elements, the melting point generally increases as the atomic number increases in a set of elements.
The relationship between atomic number and melting point features exceptions both across periods and in single rows. Transition metals do not follow melting point trends, will individual temperatures varying wildly. Hydrogen does not feature a melting point. In single columns, alkali metals and groups located around metalloids, the melting point decreases as the atomic number increases.
