Four statements about the arrangement of particles are given. 1 Particles are packed in a regular arrangement.
2 Particles are randomly arranged.
3 Particles move over each other.
4 Particles vibrate about fixed points.
Which statements describe the particles in a solid?
A 1 and 3
1 and 4 C 2 and 3 D
B
2 and 4

atomic mass = 39

number of neutrons = 20

number of protons= 19

electronic configuration = 1s2 2s2 2p6 3s2 3p6 4s1

the number of electron in first shell = 2

number of electrons in n=3 shell = 8

answer: atomic mass was originally used to arrange elements on the periodic table, but is no longer used to organize the modern version.

explanation:

originally atomic mass was used to arrange elements on the periodic table from left to right in a row. each column then shows similar properties of elements of a group.

in modern periodic table, the atoms are arranged in increasing atomic number. as atomic number represents the number of protons in an atom which is unique for every atom.