Periodic Table
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What is the modern periodic table arranged in?
By order of proton number
What are Döbereiner triads?
The groups that were made when, in 1817, Johann Döbereiner attempted to group similar elements
What did the English chemist, John Newlands, notice when her arranged the elements in order of mass?
That elements with similar chemical and physical properties occurred at regular intervals, but every 8th element was different
What did Newlands call his discovery?
The law of octaves
What does the Periodic law state?
If you arrange the elements in order of increasing atomic number then their chemical and physical properties will repeat in a systematic way
What was different about Mendeleev’s table?
He left gaps, so that elements with similar properties were in the same group
Give an example of a case where 2 elements in the periodic table are the wrong way around?
Ar —-> K are not in order of atomic mass
All the elements within the same period have the same number of…
Shells
What is periodicity?
A repeating pattern of physical and chemical properties across a period
Why is the sub-shell 4s before 3d?
The 4s sub-shell has a lower energy level
What is the electron configuration of cobalt (27 electrons)
1s2 2s2 2p6 3s2 3p6 4s2 3d7
What is the first ionisation energy?
The energy needed to remove 1 mole of electrons from 1 mole of gaseous atoms
What type of process is the first ionisation energy?
Endothermic, as you have to put energy in to remove the 1st electron
Write out the 1st ionisation energy equation of oxygen
O —–> O+ + E-
Why do you have to use the gas state symbol when writing out the equation for the first ionisation energy?
Because ionisation energies are measured for gaseous atoms
The lower the ionisation energy…
The easier it is to form an ion
What is an endothermic process?
One that takes in heat
What does a high ionisation energy mean?
There’s a strong electrostatic attraction between the electron and nucleus, so more energy is needed to remove the first electron
What 3 things affect ionisation energy?
Nuclear charge Atomic radius Shielding
How does nuclear charge affect ionisation energy?
The more protons there are in the nucleus, the more positively charged it is and so the stronger the attraction for the electrons
How does atomic radius affect ionisation energy?
Attraction falls off rapidly with distance, so an electron closer to the nucleus will be more strongly attracted than one that’s further away
How does shielding affect ionisation energy?
As the number of electrons between the outer electrons and the nucleus increases, the outer electrons feel less attraction
What is the trend in ionisation energy down a group?
As you go down a group, ionisation energies decrease (as it gets easier to remove an electron)
Why does ionisation energy decreases down a group?
Elements further down a group have extra electron shells, so the atomic radius is larger (reducing attraction to the nucleus). Shielding also increases