Final answer:
Periodic trends and properties of elements are primarily determined by their electron configurations, which are derived from the element's atomic number.
Step-by-step explanation:
Periodic trends, chemical properties, and physical properties are ultimately the result of an element's electron configuration, which is determined by the atomic number (the number of protons in the nucleus of an atom). The atomic number is a fundamental property that influences other characteristics; for example, it dictates the number of electrons around an atom and their arrangement in shells or energy levels, leading to patterns in atomic size, ionization energy, and electron affinity. The arrangement of elements in the periodic table, based on increasing atomic numbers, allows the grouping of elements with similar properties and the prediction of various behaviors and trends.