The structure of atoms and isotopes

What tool is used to determine the relative atomic masses of elements ?

A mass spectrometer is used to determine the masses and relative abundances of isotopes.

What is an isotope ?

• Isotopes are atoms of the same element with the same number of protons but different numbers of neutrons.

• They have the same chemical properties but different physical properties (e.g., melting and boiling points).

What happens when an atom gains or loses electrons ?

• Loss of electrons: Forms a positive ion (cation).

• Gain of electrons: Forms a negative ion (anion).

What are the properties of protons, neutrons, and electrons ?

• Proton (p): Positive charge (+1), relative mass ≈ 1.

• Neutron (n): No charge (0), relative mass ≈ 1.

• Electron (e): Negative charge (-1), relative mass ≈ 0.0005 (5x10⁻⁴).

What are the key features of Dalton's, Thomson's, Rutherford's, and Bohr's models of the atom ?

• Dalton: Atoms are tiny, indivisible particles (1808).

• Thomson: Electrons scattered in a positively charged substance ("plum pudding" model, 1900).

• Rutherford: Atoms have a small, dense nucleus surrounded by electrons (gold foil experiment, 1911).

• Bohr: Electrons are arranged in energy levels or shells around the nucleus (1913).

What are examples of isotopes of hydrogen, and how do they differ ?

• Hydrogen-1 (Protium): 1 proton, 0 neutrons.

• Hydrogen-2 (Deuterium, D): 1 proton, 1 neutron.

• Hydrogen-3 (Tritium, T): 1 proton, 2 neutrons.

Iridium has a relative atomic mass of 192.22 and consists of Ir-191 and Ir-193 isotopes. Calculate the percentage composition of iridium 

How is the relative atomic mass of potassium calculated with its natural abundances ?
Potassium’s isotopes: 93.11% 39K, 0.12% 40K, 6.77% 41K

How is the relative atomic mass of chlorine calculated if it has two isotopes, 35Cl (75%) and 37Cl (25%) ?

How does a mass spectrometer determine the relative atomic masses of elements ?

• A mass spectrometer measures the relative abundance and mass of different isotopes, which allows for the calculation of the relative atomic mass of elements.

How do you determine the atomic number and mass number of an element ?

• Atomic Number (Z): The number of protons in an atom.

• Mass Number (A): The total number of protons and neutrons.

How do you calculate the relative atomic mass (Ar) of an element with isotopes ?

• Relative atomic mass (Ar) is the weighted average of the masses of the isotopes compared to 1/12 of the mass of a carbon-12 atom.

• Formula: ​

  

How do you calculate the number of neutrons in an atom ?

Number of neutrons = Mass number (A) - Atomic number (Z)

Gallium has two naturally occurring isotopes: gallium-69 and gallium-71. The relative atomic mass of gallium is 69.723. Calculate the natural abundance of each isotope