You could do something like
Map[ElementData[#, "AtomicWeight"] &, Table[n, {n, 118}]]
with output
{Quantity[1.00794, "AtomicMassUnit"],
Quantity[4.002602, "AtomicMassUnit"],
Quantity[6.941, "AtomicMassUnit"],
Quantity[9.012182, "AtomicMassUnit"],
Quantity[10.811, "AtomicMassUnit"],
Quantity[12.0107, "AtomicMassUnit"],
Quantity[14.0067, "AtomicMassUnit"],
Quantity[15.9994, "AtomicMassUnit"],
Quantity[18.9984032, "AtomicMassUnit"],
Quantity[20.1791, "AtomicMassUnit"],
Quantity[22.98976928, "AtomicMassUnit"],
Quantity[24.3050, "AtomicMassUnit"],
Quantity[26.9815386, "AtomicMassUnit"],
Quantity[28.0855, "AtomicMassUnit"],
Quantity[30.973762, "AtomicMassUnit"],
Quantity[32.065, "AtomicMassUnit"],
Quantity[35.453, "AtomicMassUnit"],
Quantity[39.948, "AtomicMassUnit"],
Quantity[39.0983, "AtomicMassUnit"],
Quantity[40.078, "AtomicMassUnit"],
Quantity[44.955912, "AtomicMassUnit"],
Quantity[47.867, "AtomicMassUnit"],
Quantity[50.9415, "AtomicMassUnit"],
Quantity[51.9961, "AtomicMassUnit"],
Quantity[54.938045, "AtomicMassUnit"],
Quantity[55.845, "AtomicMassUnit"],
Quantity[58.933195, "AtomicMassUnit"],
Quantity[58.6934, "AtomicMassUnit"],
Quantity[63.546, "AtomicMassUnit"],
Quantity[65.38, "AtomicMassUnit"],
Quantity[69.723, "AtomicMassUnit"],
Quantity[72.63, "AtomicMassUnit"],
Quantity[74.92160, "AtomicMassUnit"],
Quantity[78.96, "AtomicMassUnit"],
Quantity[79.904, "AtomicMassUnit"],
Quantity[83.798, "AtomicMassUnit"],
Quantity[85.4678, "AtomicMassUnit"],
Quantity[87.62, "AtomicMassUnit"],
Quantity[88.90585, "AtomicMassUnit"],
Quantity[91.224, "AtomicMassUnit"],
Quantity[92.90638, "AtomicMassUnit"],
Quantity[95.96, "AtomicMassUnit"], Quantity[98., "AtomicMassUnit"],
Quantity[101.07, "AtomicMassUnit"],
Quantity[102.90550, "AtomicMassUnit"],
Quantity[106.42, "AtomicMassUnit"],
Quantity[107.8682, "AtomicMassUnit"],
Quantity[112.411, "AtomicMassUnit"],
Quantity[114.818, "AtomicMassUnit"],
Quantity[118.710, "AtomicMassUnit"],
Quantity[121.760, "AtomicMassUnit"],
Quantity[127.60, "AtomicMassUnit"],
Quantity[126.90447, "AtomicMassUnit"],
Quantity[131.293, "AtomicMassUnit"],
Quantity[132.9054519, "AtomicMassUnit"],
Quantity[137.327, "AtomicMassUnit"],
Quantity[138.90547, "AtomicMassUnit"],
Quantity[140.116, "AtomicMassUnit"],
Quantity[140.90765, "AtomicMassUnit"],
Quantity[144.242, "AtomicMassUnit"],
Quantity[145., "AtomicMassUnit"], Quantity[150.36, "AtomicMassUnit"],
Quantity[151.964, "AtomicMassUnit"],
Quantity[157.25, "AtomicMassUnit"],
Quantity[158.92535, "AtomicMassUnit"],
Quantity[162.500, "AtomicMassUnit"],
Quantity[164.93032, "AtomicMassUnit"],
Quantity[167.259, "AtomicMassUnit"],
Quantity[168.93421, "AtomicMassUnit"],
Quantity[173.054, "AtomicMassUnit"],
Quantity[174.9668, "AtomicMassUnit"],
Quantity[178.49, "AtomicMassUnit"],
Quantity[180.94788, "AtomicMassUnit"],
Quantity[183.84, "AtomicMassUnit"],
Quantity[186.207, "AtomicMassUnit"],
Quantity[190.23, "AtomicMassUnit"],
Quantity[192.217, "AtomicMassUnit"],
Quantity[195.084, "AtomicMassUnit"],
Quantity[196.966569, "AtomicMassUnit"],
Quantity[200.59, "AtomicMassUnit"],
Quantity[204.3833, "AtomicMassUnit"],
Quantity[207.2, "AtomicMassUnit"],
Quantity[208.98040, "AtomicMassUnit"],
Quantity[209., "AtomicMassUnit"], Quantity[210., "AtomicMassUnit"],
Quantity[222., "AtomicMassUnit"], Quantity[223., "AtomicMassUnit"],
Quantity[226., "AtomicMassUnit"], Quantity[227., "AtomicMassUnit"],
Quantity[232.03806, "AtomicMassUnit"],
Quantity[231.03586, "AtomicMassUnit"],
Quantity[238.02891, "AtomicMassUnit"],
Quantity[237., "AtomicMassUnit"], Quantity[244., "AtomicMassUnit"],
Quantity[243., "AtomicMassUnit"], Quantity[247., "AtomicMassUnit"],
Quantity[247., "AtomicMassUnit"], Quantity[251., "AtomicMassUnit"],
Quantity[252., "AtomicMassUnit"], Quantity[257., "AtomicMassUnit"],
Quantity[258., "AtomicMassUnit"], Quantity[259., "AtomicMassUnit"],
Quantity[262., "AtomicMassUnit"], Quantity[265., "AtomicMassUnit"],
Quantity[268., "AtomicMassUnit"], Quantity[271., "AtomicMassUnit"],
Quantity[272., "AtomicMassUnit"], Quantity[270., "AtomicMassUnit"],
Quantity[276., "AtomicMassUnit"], Quantity[281., "AtomicMassUnit"],
Quantity[280., "AtomicMassUnit"], Quantity[285., "AtomicMassUnit"],
Quantity[284., "AtomicMassUnit"], Quantity[289., "AtomicMassUnit"],
Quantity[288., "AtomicMassUnit"], Quantity[293., "AtomicMassUnit"],
Quantity[294., "AtomicMassUnit"], Quantity[294., "AtomicMassUnit"]}