Using the periodic table determine the atomic mass of na2c2o4

Masses of atoms are the sum of neutrons and protons. Atomic mass given for the element is the weighted atomic masses of the isotopes depending on the abundance of the isotopes.
Atomic masses of the elements making up Na₂C₂O₄ are as follows;
Na - 22.98 a.m.u
2 atoms of Na - 22.98 x 2 = 45.96
C - 12.01 a.m.u
2 atoms of C - 12.01 x 2 = 24.02
O - 15.99 a.m.u
4 atoms of O - 15.99 x 4 = 63.96
Sum of the atomic masses = 45.96 + 24.02 + 63.96 = 133.94 
Mass is 133.94 g/mol

☆ionisation energy increases across a period from na -> ar☆ionisation energy decreases down a group from li -> fr☆ionic radius decreases across a period from na -> cl☆ionic radius increases down a groupfrom f -> ii hope it clarifies your doubts

Answercreating graphs and performing calculations;