Module 7.1 - Periodicity (3.1.1 - Spec reference)
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Who crated one of the first periodic tables with gaps in it?
Dmitri Mendeleev
What did the gaps in the table represent from Mendeleev?
They represented elements that he predicted would have specific properties These predictions were based on other elements in the same group
How many elements were in Mendeleev’s table?
63
What did Mendeleev call Germanium before it was discovered?
Eka - silicon It was next to silicon in the table
How did Mendeleev arrange his table?
By Relative atomic mass(Mr)
How are elements arranged in the table today?
By increasing atomic number
What is a group? What does it show?
Vertical columns of elements Elements in groups have the same number of outer shell electrons Group number gives the number of outer shell electrons
What is a period? What does it show?
Horizontal rows in the periodic table Number of the period gives the number of the highest energy electron shell of the element’s atom
Periodicity def
A repeating trend in properties of elements
Examples of periodicity in elements
Electron Configuration Ionisation energy Structure Melting points
What is the trend across a period?
For each period, the s - and p - sub shells are filled in the same way A periodic pattern
Trend down a group
All elements in that group have the same number of outer shell electrons
What are the old and new group numbers now for the table? Which groups do they represent?
(Old)1 - 1 - alkali metals (Old)2 - 2 - alkaline earth metals Groups 3-12 are transition metals (Old)7 - 17 - halogens (Old)8- 18 - Noble gases
Definition of first ionisation energy
The energy required to remove one electron from each atom in one mole of gaseous atoms of an element to from one mole of gaseous 1+ ions
Factors affecting ionisation energy
Atomic radius Nuclear Charge Electron Shielding
How atomic radius affects ionisation energy
Greater the distance between nucleus and outer shell electrons the less the nuclear attraction (Force of attraction falls off sharply with increasing distance, so atomic radius has a large effect)
How nuclear charge affects ionisation energy
More protons in nucleus gives greater attraction between nucleus and outer shell electrons
How electron shielding affects ionisation energy
Electrons are negatively charged, so inner shell electrons repel outer shell electrons This reduces attraction between nucleus and outer shell electrons
Difference in first and second ionisation energies
Second ionisation energy is larger than first When one electron is lost, other electrons have a stronger nuclear attraction to unchanged number of protons Therefore electrons pulled closer to nucleus, so atomic radius decreases So more attraction to nucleus so more energy needed to remove the remaining electrons
Def of second ionisation energy
Amount of energy required to remove on electron from each atom of one mole of gaseous 1+ ions to form one mole of gases out 2+ ions
What do large spikes in ionisation energies in successive ionisations show?
Suggest that electron must have been removed from a new electron shell Due to atomic radius being smaller, so nuclear attraction increases
What can successive ionisations show?
Number of electrons in the outer shell Group of the element in the periodic table The identity of an element
Trend in first ionisation energy down a group
Atomic radius increases More inner shells so shielding increases Nuclear attraction on outer shells decreases Therefore first ionisation energy decreases
Trend in first ionisation energy across a period
Nuclear charge increases(same no. of protons whilst electrons increases) Same shell:similar shielding Nuclear attraction increases Atomic radius decreases So first ionisation energy increases