Elements in the modern periodic table are arranged by increasing what?

Question

Quizplus · Accepted Answer

Elements are arranged from left to right and top to bottom in order of increasing atomic number, which is the number of protons in an atom of that element.
Atomic mass is the mass of an atom, which is calculated by adding the number of protons and the number of neutrons. 
Although the periodic table is not organized by atomic radius, there are predictable trends on the radius (size) of an atom based on its location on the periodic table. In general, the atomic radius increases as you go up and to the right of the periodic table. Other predictable trends include:
ionization energy:  how much energy it takes for an element to lose an electron/ how much energy it takes to become a positive ion
electron affinity: how easy it is for an element to gain an electron/ how easy it is to become a negative ion
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Elements in the Modern Periodic Table Are Arranged by Increasing