The atom is the smallest particle of a substance which can have its own characteristic properties
Atoms are made up of different particles known as "sub-atomic particles"
There are 3 sub-atomic particles that you need to know about:
Protons
Neutrons
Electrons
Protons and Neutrons are known as nucleons as they reside in the nucleus
Electrons exist in energy level "shells" orbiting around the nucleus
Slide 4
Properties of Sub-Atomic Particles
Protons and neutrons are compatible in size (neutrons are slightly larger) and therefore are assigned a relative mass of 1
The mass number of an atom is the sum of the number of the number of protons and neutrons
Protons have a relative charge of +1 and neutrons have a relative charge of 0 therefore nuclei are positively charged overall
Electrons have a relative charge of -1 and orbit the nucleus
Atoms have an overall neutral charge therefore the number of electrons and protons in an atom are equal
The number of protons in an atoms nucleus is known as its atomic number
Atoms with the same atomic number are said to be the same element
Caption: : Most of the atom's mass is in the nucleus however, the size of the nucleus compared to the rest of the atom is very small. The rest of the almost "empty" space of an atom is occupied by electrons in their energy level "shells".
Caption: : Here are some common isotopes of various elements
Relative isotopic mass: the mass of of one atom of an isotope compared to one twelfth of the mass of one atom of carbon-12
Relative atomic mass: the ratio of the average mass of one atom of an element to one twelfth of the mass of an atom of carbon-12.
The number of neutrons in an atom can vary which means that elements can have various isotopes
Isotopes are defined as atoms with the same number of protons but different numbers of neutrons
Relative molecular mass: The ratio of the average mass of one molecule of an element or compound to one twelfth of the mass of an atom of carbon-12
Relative formula mass: The ratio of the average mass of the formula units of a compound relative to one twelfth of the mass of an atom of carbon-12
The definitions of these terms will not be expected but please make sure you understand them.
Slide 6
Mass Spectrometry
The mass spectrometer is a device that can be used to analyse samples and separate them according to mass to charge ratio
One use of mass spectrometry (MS) is to analyse samples of a particular element and identify all the isotopes present
To calculate the relative atomic mass of a particular element from it's mass spectrum, we take the weighted average of all the isotopes
Sometimes 2 electrons can be removed from a particle in the mass spectrometer forming an ion with a 2+ charge
Calculate this ion's mass to charge ratio
Caption: : The mass spectra of chlorine and bromine
Some elements exist as diatomic molecules in their elemental state
Chlorine and bromine are two such elements
Chlorine exists in two isotopes with the ratio 3:1
Bromine exists in two isotopes with the ratio 1:1
It is important for you to be able to predict the mass spectra of diatomic molecules, including relative peak heights
Try to rationalise the following mass spectra by assigning each of the peaks
Tip: the relative intensity often corresponds to the abundance
