Module 3: The Periodic Table
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The periodic table What were the only ways to categorise elements in the 1800s
By their physical and chemical properties or their relative atomic mass
The periodic table In 1817 what did dobereiner attempt to do and what were they called
Group similar elements and the groups were called dobereiners triads
The periodic table What groups did dobereiner create
Saw bromine chlorine and iodine had similar characteristic Realises properties of bromine fell halfway between chlorine and iodine Found groups of three eg lithium sodium and potassium
The periodic table What did john newlands do
Tried to make a table of elements in 1863and noticed if her arranged elements in order of mass similar elements appeared regularly
The periodic table What was the law of octaves
John newlands found every eighth elements was similar but this pattern broke down on third row
The periodic table What did dmitri Mendeleev do
In 1869 produced a better table which wasn’t far off current table
The periodic table How did Mendeleev arrange elements
By atomic mass and left gaps in the table where the next element didn’t seem to fit so could keep elements with similar chemical properties in same groups
The periodic table What did Mendeleev predict
Properties of undiscovered elements
The periodic table How is the modern periodic table arranged
By increasing proton number
The periodic table How is the periodic table laid out
Into periods (rows) and groups (columns)
The periodic table What do all elements in same period have and what does this mean
Same number of electron shells and means there are repeating trends in physical and chemical properties across periods
The periodic table What are trends in properties called
Periodicity
The periodic table What do all elements within one groups have and what does this mean
All have same number of electrons in outer shell and have similar chemical properties
Ionisation energies What does it mean if and atom or molecule has been ionised
Electrons have been removed
Ionisation energies Definition for the first ionisation energy
Energy needed to remove 1 mole of electrons from 1 mole of gaseous atoms
Ionisation energies What type of process is it to ionise an atom or molecule and why
Have to put energy in so and endothermic process
Ionisation energies Equation for first ionisation energies
X (g) —> X+ (g) + e-
Ionisation energies Important to rember when writing ionisation energy equations
Must use gas symbol (g) because ionisation energies are measured for gaseous atoms
Ionisation energies What does the lower ionisation energy mean
Easier to form an ion
Ionisation energies What factors affect ionisation energies
Nuclear charge Atomic radius Shielding
Ionisation energies How does nuclear charge affect ionisation energy
More protons in the nucleus, more positively charged the nucleus is and the stronger attraction for the electrons
Ionisation energies How does atomic radius affect ionisation energy
Attraction decreases rapidly with distance, an electron close to the nucleus will be much more strongly attracted than one further away therefore require more energy to remove
Ionisation energies How does shielding affect ionisation energy
As number of electrons increases, there’s more shells therefore shielding from inner shells and less attraction between nucleus and outer electron
Ionisation energies What does a high ionisation energy mean
Strong attraction between the electron and the nucleus so more energy is ended to overcome the attraction and removed the electron