Which pattern is used to arrange elements in the modern periodic table?
a
The atoms are arranged by atomic mass, and elements with similar properties are aligned vertically in groups or columns.
b
The atoms are arranged by atomic mass, and elements with similar properties are aligned horizontally in periods or rows.
c
The atoms are arranged by atomic number, and elements with similar properties are aligned vertically in groups or columns.
d
The atoms are arranged by atomic number, and elements with similar properties are aligned horizontally in periods or rows.