The Nuclear atom

Question 1

What is an atom?

Answer 1

Atoms are the smallest particle that has the properties of an element.

Question 2

What sub-atomic particles are present in an atom and where can they be found?

Answer 2

The nucleus contains protons (positive) and neutrons (no charge). This makes the nucleus positive. Electrons (negative) are found in energy levels that surround the nucleus.

Question 3

What is the atomic number and the mass number?

Answer 3

The atomic number (Z) is the number of protons and the mass number (A) is the combined number of neutrons and protons in the nucleus (A above Z)

Question 4

How do you find the number of electrons and protons in an ion?

Answer 4

When the ion is positive, the number of electrons is less than the number of protons. When the ion is negative the number of electrons is more than the number of protons. The number of protons stays the same.

Question 5

What is an isotope and when do the properties alter?

Answer 5

• Atoms of the same element that have the same number of protons but a different number of neutrons (nucleon number)
• Isotopes have the same chemical properties (same number of electrons)
• Have different physical properties

Question 6

What is a mass spectrometer and how does it link to the relative abundance and mass to charge ratio?

Answer 6

It is a tool used to determine the relative atomic mass (Ar) of elements from their isotopic composition. The mass spectrum shows the relative abundance (% occurrence of the isotope in nature, adds up to 100%) and the mass to charge ratio (m/z)

Question 7

What is the formula for the relative atomic mass?

Answer 7

Ar= (isotopic mass x % abundance) / 100

• each % abundance is multiplied by the isotopic mass separately and then added together
• give to 2 decimal places
• The isotopic mass is the number written next to the isotope

Question 8

How do you calculate the percentage abundance?

Answer 8

One of the isotopes has a higher % abundance called ‘predominant’. It is always the isotope with the lower value e.g. bromine-79 has a higher % than bromine-81.

e.g. 79x + 81(100-x)
= 79x +8100 -81x
2x=8100 this is the total mass of 100 atoms (we only want one)
Ar = 79.90
79.90= (8100-2x) / 100
7990=8100 -2x
x= 55 bromine-79 has a 55% abundance and bromine-81 a 45% abundance