Question

Beryllium (Be) has an atomic number of 4 and an atomic mass of 9. Beryllium has _____.

9 electrons
4 electrons
5 electrons
13 electrons

Answer 1

2nd option

Step-by-step explanation:

The number of neutrons is the atomic mass (9) - the atomic number (4) = 5 neutrons. For every positive proton there needs to be a negative electron in order for the atom to be neutral, which means beryllium must have 4 electrons to be neutral.

Answer 2

`\huge\boxed{\sf No.\ of\ electrons = 4}`

Step-by-step explanation:

Given that,

Atomic mass = 9

Atomic number = 4

Atomic number:

• The number of protons in an atom.

Atomic mass:

• The sum of protons and neutrons in an atom.

So,

No. of protons = 4

In an atom,

No. of electrons = No. of protons

So,

No. of electrons = 4

`\rule[225]{225}{2}`