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Chapter 7 - Periodicity I - Coggle Diagram
Chapter 7 - Periodicity I
Periodic table
Then
Ordered by atomic mass
Left gaps for missing elements
Go elements
Now
Aranging elements
Atomic number
Arranged in order of increasing atomic number
Each successive elements has atoms with one extra proton
Groups
Each vertical column is called a group
Each element in a group has atoms with the same number of outer-shell electrons
Periods
Each horizontal row is called a period
Number of the period is the number of the highest energy electron shell in an element's atoms
Periodic trend in electron configuration
Trend across a period
Across period 2, 2s sub-shell fills with two electrons followed by the sp sub-shell with six electrons
Each period starts with an electron in a new highest energy shell
Acrpss period 4, although the 3d subshell is involved, highest shell number is still 4
For each period, s- and p- sub-shells are filled in the same way
Trend down a group
Atoms with the same group have the same number of electrons in each sub-shell
Blocks
Elements in the table can be dividied into blocks corresponding to their highest energy sub-shell
s p d f block
Names and numbers for groups
1 - alkali metals
2 - alkaline earth metals
3-12 - transition elements
15 - pnictogens
16 - chalcogens
17 - halogens
18 - noble gases
Ionisation energy
Measusres how easily an atom loses electrons for form positive ions
First ionisation energy is energy required to remove one electron from each atom in one mole of gaseous atoms
Factors
First electron lost will be in the highest energy level and experiences the least attraction from the nucleus
Atomic radius
Greater the distance between the nucleus and outer electrons, the less nuclear attraction
Force of attraction falls of sharply with increasing distance, so ionisation energy decrease as atomic radius increases
Nuclear charge
More protons - greater attraction between the nucleus and outer electrons
Ionisation energy increases as nuclear change increase
Electron shielding
Inner-shell electrons repel outer-shell electrons
Shielding reduces the attraction between the nucelus and outer electrons, so more shielding means lower ionisation energy
Successive ionisation energies
An elements has as many ionisation energies as there are electrons
Helium has two ionisation energies
Second ionisation energy = energy requried to remove one electron from each ion in one mole of gaseous 1+ ions of an element to form one moles of gases 2+
Large increase in ionisation energies marks a change from one shell to another
Predictions
Number of electrons in the outer shell
Group of the element in the periodic table
Identity of an element
Trends in first ionisation energies
Provide important evidence for sub shells
General increase in first ionisation energy acrosos each period
Sharp decrease in first ionisation energy between the end of one period and the start of the next period
Down a group
Atomic radius increases
Shielding increases
Nuclear attraction decreases
First ionisation energy increases
Increase in atomic radius and shielding are the most important factors
Across a period
Nuclear charge increase
Nuclear attraction increase
Atomic radius decreases
First ionisation enegry increases
Increased nuclear change is the most important factor
Sub-shells trends
Although first ionisation energy shows a general increase across period 2 and 3, it does fall in two places
Drops occur at same place each period
Beryllium to Boron
Fall in first ionisation energy from beryllium to boron marks that start of filling the 2p sub-shell
2p sub-shell in boron has a higher enegry than 2s sub shell
In boron the 2p electron is easier to remove than one of the 2s electrons in beryllium
First ionisation energy of boron is less than the first ionisation energy of beryllium
Rise from lithium to beryllium
Fall to boron followed by a rise to carbon and nitrogen
Fall to oxygen followed by a rise to fluorine and neon
Nitrogen and oxygen
Fall in first ionisation energy from nitrogen to oxygen mark the start of electron pairing in the p-orbitals of the 2p sub-shell
In nitrogen and oxygen, highest energy electrons are in 2p sub-shell
In oxygen, paired electrons in one of the 2p orbtials repel one another, making it easier to remove and electron
First ionisation energy of oxygen is less than the first ionisation energy of nitrogen