The missing components in the table to the right are indicated with orange letters. Complete the
table by filling in the corresponding number(s) or
symbol(s) below.
A
B
1111
С
D
E
F
G

The Atomic Number (Z) indicates the number of protons in an atom of an element. If the atom is neutral then the number of protons will be equal to the number of electrons. So the atomic number can also indicate the number of electrons.

Mass Number (A) = Number of protons + Number of Neutrons

Atomic Number (Z) = Mass Number (A) - Number of Neutrons

Atomic number = number of protons = number of electrons  ⇒ neutral atoms

Atomic number - positive charge = number of electrons ⇒ cation

Atomic number + negative charge = number of electrons ⇒ anion

You can also see the periodic system

A. Indium (In)

B. proton = electron = 27

C. proton = electron = 73

D. proton = electron = 49

E=F. atomic mass - neutron = 137 - 81 = 56

G. atomic mass-proton = 115- 49 = 66

H. 181-73 = 108

the number of valence electrons for each molecule or ion is shown beneath the structure. remember hydrogen will not have more than two electrons. this hydrogen is part of a covalent bond (sharing two electrons). a double bond here would cause hydrogen to share four electrons with phosphorus.

a. energy is absorbed in the reaction.

if in a given reaction the energy of products is greater than the energy of reactants it means that reaction is endothermic and during the reaction, the energy is absorbed by reactants. in an endothermic reaction, the products have more stored chemical energy than the reactants. and in this reaction the reactants are more stable than products before the compounds with less energy are always more stable.