Question

write the symbol for every chemical element that has atomic number less than 13 and atomic mass greater than 12.8 u.

Explanation:

Step1: Recall elements with atomic number < 13

Elements with atomic number less than 13 are hydrogen (H, atomic - number = 1), helium (He, atomic - number = 2), lithium (Li, atomic - number = 3), beryllium (Be, atomic - number = 4), boron (B, atomic - number = 5), carbon (C, atomic - number = 6), nitrogen (N, atomic - number = 7), oxygen (O, atomic - number = 8), fluorine (F, atomic - number = 9), neon (Ne, atomic - number = 10), sodium (Na, atomic - number = 11), magnesium (Mg, atomic - number = 12).

Step2: Check atomic mass

The atomic masses of these elements are: H (1.008 u), He (4.003 u), Li (6.941 u), Be (9.012 u), B (10.811 u), C (12.011 u), N (14.007 u), O (15.999 u), F (18.998 u), Ne (20.180 u), Na (22.990 u), Mg (24.305 u).

Step3: Select elements meeting criteria

The elements with atomic number less than 13 and atomic mass greater than 12.8 u are nitrogen (N), oxygen (O), fluorine (F), neon (Ne), sodium (Na), magnesium (Mg).

Answer:

N, O, F, Ne, Na, Mg