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Inorganic chemistry AS - Coggle Diagram
Inorganic chemistry AS
2.1: Periodicity
2.1.1: Classification of an element
The Periodic Table: Structure & Classification:
The periodic table is a list of all known elements arranged in order of increasing atomic number, from 1 to 118.
In addition to this, the elements are arranged in such a way that atoms with the same number of shells are placed together, and atoms with similar electronic configurations in the outer shell are also placed together. This is achieved as follows:
The elements are arranged in rows and columns.
Elements with one shell are placed in the first row (i.e. H and He)
Elements with two shells are placed in the second row (Li to Ne) and so on.
A row of elements thus arranged is called a period. The period number, n, is the outer energy level that is occupied by electrons.
In addition, the elements are aligned vertically (in columns) with other elements in different rows, if they share the same outer-shell electronic configuration
The outer electrons are known as the valence electrons.
A column of elements thus arranged is called a group.
Since the electronic configurations of H and He are unusual, they do not fit comfortably into any group. They are thus allocated a group based on similarities in physical and chemical properties with other members of the group.
He is placed in group 0 on this basis, but hydrogen does not behave like any other element and so is placed in a group of its own.
All elements belong to one of four main blocks: the s-block, the p-block, the d-block and the f-block:
The s-block elements are all those with only s electrons in the outer shell
The p-block elements are all those with at least one p-electron in the outer shell
The d-block elements are all those with at least one d-electron and at least one s-electron but no f or p electrons in the outer shell (up to 5d)
The f-block elements are all those with at least one f-electron and at least one s-electron but no d or p electrons in the outer shell
The physical and chemical properties of elements in the periodic table show clear patterns related to the position of each element in the table
Elements in the same group show similar properties, and properties change gradually as you go across a period
As atomic number increases, the properties of the elements show trends which repeat themselves in each period of the periodic table
These trends are known as periodic trends and the study of these trends in known as periodicity
Reactions with oxygen:
The reactions of period 3 elements with oxygen can be summarised as follows:
Element --> chemical equation --> reaction conditions --> reaction --> flame --> product.
Na --> 4Na (s) + O2 (g) --> 2Na2O --> heated --> vigorously --> bright yellow flame --> white solid.
Mg --> 2Mg + O2 (g) --> 2MgO (s) --> heated --> vigorously --> bright white flame --> white solid.
Al --> 4Al (s) + 3O2 (g) --> 2Al2O3 (s) --> powdered Al --> fast --> bright white flame --> white powder.
Si --> Si (s) + O2 (g) --> SiO2 (s) --> powdered Si, heat strongly --> slowly --> bright white sparkles --> white powder.
P --> 4P (s) + 5O2 (g) --> P4O10 (s) --> heated --> vigorously --> yellow or white flame --> white clouds.
S --> S (s) + O2 (g) --> SO2 (g) --> powdered S is heated --> gently --> blue flame --> toxic fumes
Reactions with chlorine:
The reactions of period 3 elements with chlorine can be summarised as follows:
Element --> Chemical equation --> reaction conditions --> reaction
Na --> 2Na (s) + Cl2 (g) --> 2NaCl (s) --> heated --> vigorously
Mg --> Mg (s) + Cl2 (g) --> MgC2 (s) --> heated --> vigorously
Al --> 2Al + 3Cl2 (g) --> Al2Cl6 --> heated --> vigorously
Si --> Si (s) + 2Cl2 (g) --> SiCl4 --> heated --> vigorously
P --> 2P (s) + 5Cl2 (g) --> 2PCl5 (s) --> heated --> vigorously
Reaction of sodium & magnesium with water:
Sodium reacts vigorously with cold water:
2Na (s) + 2H2O (l) → 2NaOH (aq) + H2 (g)
The sodium melts into a ball and moves across the water surface until it disappears
Hydrogen gas is given off
The solution formed is strongly alkaline (pH 14) due to the sodium hydroxide which is formed
Magnesium reacts extremely slowly with cold water:
Mg (s) + 2H2O (l) → Mg(OH)2 (aq) + H2 (g)
The solution formed is weakly alkaline (pH 9-10) as magnesium hydroxide is only slightly soluble
However, when magnesium is heated in steam, it reacts vigorously with steam to make magnesium oxide and hydrogen gas:
Mg (s) + H2O (g) → MgO (s) + H2 (g)
2.1.2: Trends of Period 3 elements: Atomic radius
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2.3: Group 7 (17): The halogens
2.3.1: Physical Properties of Group 7
The group 7 elements are called halogens
The halogens have uses in water purification and as bleaching agents (chlorine), as flame-retardants and fire extinguishers (bromine) and as antiseptic and disinfectant agents (iodine)
Colours:
All halogens have distinct colours which get darker going down the group
F2 --> pale yellow gas
Cl2 --> green / yellow gas
Br2 --> brown / orange liquid
I2 --> grey / black solid, purple vapour
Volatility:
Volatility refers to how easily a substance can evaporate
A volatile substance will have a low boiling point
Going down the group, the boiling point of the elements increases which means that the volatility of the halogens decreases
This means that fluorine is the most volatile and iodine the least volatile
Bond Strength:
Halogens are diatomic molecules in which covalent bonds are formed by overlapping their orbitals.
In a covalent bond, the bonding pair of electrons is attracted to the nuclei on either side and it is this attraction that holds the molecule together
Going down the group, the atomic size of the halogens increases
The bonding pair of electrons get further away from the halogen nucleus and are therefore less strongly attracted towards it
Bond enthalpy data:
The bond strength of the halogen molecules decreases going down the group.
Bond enthalpy is the energy needed to break one mole of covalent bonds
The higher the bond enthalpy, the stronger the bond
An exception to this is fluorine which has a smaller bond enthalpy than chlorine and bromine
Fluorine is so small that when two atoms of fluorine get together their lone pairs get so close that they cause significant repulsion counteracting the attraction between the bonding pair of electrons and two nuclei
2.2: Group 2: the Alkaline Earth metals
2.2.1: Trends in group 2: the Alkaline Earth metals
Chemical trends:
All elements in Group 2 (also called alkali earth metals) have two electrons in their outermost principal quantum shell.
All Group 2 metals can form ionic compounds in which they donate these two outermost electrons (so they act as reducing agents) to become an ion with +2 charge (so they themselves become oxidised)
Going down the group, the metals become more reactive
This can be explained by looking at the Group 2 ionisation energies
The first ionisation energy is the energy needed to remove the first outer electron of an atom
The second ionisation energy is the energy needed to remove the second outer electron of an atom
The graph above shows that going down the group, it becomes easier to remove the outer two electrons of the metals
Though the nuclear charge increases going down the group (because there are more protons), factors such as an increased shielding effect and a larger distance between the outermost electrons and nucleus outweigh the attraction of the higher nuclear charge
As a result of this, the elements become more reactive going down the group as it gets easier for the atoms to lose two electrons and become 2+ ions
This trend is shown by looking at reactions of the Group 2 metals:
With dilute hydrochloric acid: bubbles of hydrogen gas are given off much faster indicating that the reactions become more vigorous
With oxygen: the metals get more reactive with oxygen down the group (Ba is so reactive, that it must be stored in oil to prevent it from reacting with oxygen in air)
Physical trends:
Going down the group, the elements become larger as the outer two electrons occupy a new principal quantum shell which is further away from the nucleus
The melting point of the elements decreases going down the group as the outer electrons get further away from the nucleus
This means that the attraction between the nucleus and the bonding electrons decreases causing a decrease in melting point
As you go down the group, the density of the alkali earth metals drops and then increases
Density is also affected by the packing structure of the metals, not just the atomic radius - no trend is perfect!
2.2.2: Solubility of Group 2 Compounds: Hydroxides & Sulfates
Group 2 hydroxides:
Going down the group, the solutions formed from the reaction of group 2 oxides with water become more alkaline.
When the oxides are dissolved in water, the following ionic reaction takes place:
O2- (aq) + H2O (l) → 2OH- (aq)
The higher the concentration of OH- ions formed, the more alkaline the solution
The alkalinity of the solution formed can therefore be explained by the solubility of the Group 2 hydroxides
The hydroxides dissolve in water as follows:
X(OH)2 (aq) → X2+ (aq) + 2OH- (aq)
Where X is the Group 2 element
When the metal oxides react with water, a group 2 hydroxide is formed
Going down the group, the solubility of these hydroxides increases
This means that the concentration of OH- ions increases, increasing the pH of the solution
As a result, going down the group, the alkalinity of the solution formed increases when Group 2 oxides react with water
Going down the group, the solubility of the hydroxides increases which means that the solutions formed from the reactions of the group 2 metal oxides and water become more alkaline going down the group
Group 2 sulfates:
The solubility of the group 2 sulfates decreasing going down the group.
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