What determines the chemical properties of an element?
1. the number and arrangement of the electrons in an atom?
2. the number of neutrons and protons in an element
3. the arrangement of all the neutron, protons, and electrons
4. the atomic mass of an atom

the answer is 1.  the number and arrangement of the electrons in an atom

Explanation:

periodic trends is an atom that gets larger as the number of electronic shells increase, the radius of atoms increases as you go down a certain group in the periodic table of elements. in general, the size of an atom will decrease as you move from left to right of a certain period.