Question

Determine the number of neutrons, protons, and electrons for a bromide ion that has a mass number of 76, and a charge of -1. 

number of neutrons: 

number of protons: 

number of electrons:

Determine the element symbol, number of protons, and number of electrons for an ion that has a mass number of 56, 30 neutrons, and a charge of +3. 

element symbol: 

number of protons: 

number of electrons:

Determine the element symbol, m number, and charge for an atom or ion that has a 49 neutrons, 38 protons, and ass 36 electrons. 

element symbol: 

mass number charge:

Answer 1

An element is identified by its atomic number (Z) which is equal to the number of protons in the nucleus of that element and also equal to the number of electrons in the neutral atom of the element. Thus,

........1

The mass number (A) of an element gives the sum of protons (p) and neutrons (n) in the element. That is,

.........2

The complete atomic symbol of an element includes the symbol of the element along with its atomic number as subscript and mass number as superscript.

1. We have a bromide ion with charge = -1 and mass number = 76.

The atomic number of Bromine (Br) is 35. So , using equation 1 we have

Number of protons = 35

By using equation 2 we can calculate number of neutrons as :

Number of neutrons = Mass number - Number of protons

So, we get

Number of neutrons = 76 - 35 = 41

Now, by using equation 1 we have ,

Number of electrons in neutral Br atom = 35

But here we have Bromide ion with a -1 charge which means it has an extra electron in it. So total electrons in bromide ion = 35 + 1 extra electron. Thus,

Number of electrons = 36

2. We have, mass number = 56 , number of neutrons = 30 and charge = +3.

Using equation 2 we get,

Number of protons = Mass number - Number of neutrons

So, Number of protons = 56 - 30 = 26

Thus atomic number of the element is 26 and the element with atomic number 26 is Iron (Fe).

So Element symbol = Fe

Also, number of electrons in neutral Fe atom = 26

Since the ion has +3 charge which means the ion has 3 electrons less in it due to the positive charge on it , so number of electrons in the ion = 26 - 3 electrons.

Number of electrons in the ion = 23

3. Here, number of neutrons = 49, number of protons = 38 and number of electrons = 36.

Since number of protons = 38 so atomic number of the element is 38 and the element with atomic number 38 is strontium (Sr).

So, Element symbol = Sr

By using equation 2 we get ,

Mass number = 38 + 49 = 87

Since number of electrons = 36 which are 2 less than the atomic number of the element so the species in not neutral atom but is an ion with two less electrons. So,

Charge = +2

( When electrons are less there is a positive charge on ion and when electrons are extra there is a negative charge on the ion.)