What is the atomic number of hydrogen and the number of its electrons in the outer shell?

The Atomic No. of hydrogen is '1' .

Often indicated by ' Z = 1 '.

It is the first and least massive element in the Periodic Table.

Hydrogen's atomic structure is ;- 1 proton and 1 electron.

However, Hydrogen exhibits three ISOTOPES.

They are : -

protium ; 1 proton , 1 electron , 0 neutrons ; Atomic Mass = 1

deuterium ; 1 proton , 1 electron , 1 neutron ; Atomic mass = 2

tritium ; 1 proton , 1 electron , 2 neutrons ; Atomic mass = 3

Hydrogen's symbol is 'H'.

protium isotope is the most common isotope of hydrogen and generally referred to as hydrogen .

Atomic Mass is 1 proton + 0 neutrons = 1

Symbolically, [1/1]H

deuterium isotope(D) is far less common isotope of hydrogen and generally referred to as 'heavy hydrogen' and makes ' heavy water'.

Atomic Mass is 1 proton + 1 neutrons = 2

Symbolically [2/1]H

tritium isotope (T) is very rare isotope of hydrogen and generally referred to as 'super-heavy hydrogen' and is radio - active

Atomic Mass is 1 proton + 2 neutrons = 3

Symbolically as [3/1]H

NB The next element in Periodic Table is Helium (He)

Its atomic structure is 2 protons, 2 neutrons, and 2 electrons. Helium's symbol is 'He'.

It is the most inert element of all.

Atomic Mass is 2 proton + 2 neutrons = 4

Symbolically, [4/2]He

Note the differences between hydrogen and helium atomic structures.