The periodic table Module 3 Flashcards
What does the period tell you?
Amount of electron shells
What does the group tell you?
Number of electrons in outer shell
What is the first ionisation energy?
Energy required to remove 1 mole of electrons from 1 mole of a gaseous species
Eg. O(g) = O+(g) + e-
Factors affecting the ionisation energy?
Nuclear charge- the more protons in the nucleus, the more positively charged it is, the stronger the attraction for the nucleus
Atomic radius- Bigger the radius, the bigger the distance, the less the attraction
Electron sheilding- The more sheilding, the weaker the attraction
What does a high ionisation energy mean?
Strong attraction between the electron and the nucleus, so more energy required to overcome these forces and remove the electron
Why does ionisation energy decrease as you go down the group?
More electron shielding
Larger atomic radius
Why as you go across a period the ionisation energies increase?
The amount of protons is increasing, so nuclear charge is becoming stronger and the amount of shells isn’t increasing
However there are 2 exceptions in the rule that ionisation energy increases along a period between group 2 to 3 and group 5 to 6 explain why?
The outer electrons in group 3 elements is a p orbital, rather than an S orbital, which means it’s further away from the nucleus, and has additional shielding from s orbital, theses factors overide the increased nuclear charge
In the group 5 elements, the electron is being removed from a singly-occupied orbital, in group 6 being removed from orbital containing 2 electrons. The repulsion means between 2 electrons in a orbital makes it easy to remove from shared orbitals
What’s the second ionisation of oxygen?
O+(g) = O(2+)(g) + e-
How can successive ionisations show shell structure?
Look at where there are big jumps to identify when a new shell is broken into to
Give 3 examples of giant covalent lattices?
Diamond
Graphite
Graphene
Why is diamond so hard?
Each carbon atom is covalently bonded to 4 other carbon atoms, in a tetrahedral shape
What do it mean for the properties of diamond due to it’s strong covalent bonds?
Very high melting point
Very hard
Vinrations easily travel though it, making it a good thermal conductor
Can’t conduct electricity, all outer electrons held in localised bonds
Won’t dissolve in any solvent
What’s graphites structure?
The carbon atoms are arranged in sheets of flat hexagons, covalently bonded with 3 bonds each
The 4th outer electron of each carbon is delocaslied between the sheets of electrons
Sheets of hexagons bonded together by weak induced dipole-dipole interactions
Explain the features of graphite?
Weak forces between layers, so can easily slide over each other making it a good lubricant
The delocalised electrons can carry charge, so it can conduct electricity
Insoluble and very high melting point due to strong covalent bonds
What is graphene and it’s features?
It’s just one sheet of hexagons on carbons making 3 covalent bonds, with delocalised electrons all around it
Very good conductor due to delocalsied electrons not having to go through layers
Delocaslied electrons also strengthen the covalent bonds making it even stronger
Explain the structure of giant metallic lattice structures?
The electrons in outermost shell of a metal atom are delocalised the electrons are free to move about the metal, leaving a positively charged metal cation
Metal cations are electrostatically atrracted to the delocalsied negative electrons. So they form a lattice of closely packed cations in a sea of delocaslied electrons- this is metallic bonding
How dooes metallic bonding explain features of metals?
Number of delocaslied electrons affects melting point, the more there are the stronger the bonding will be, group 1 metals will only release 1 electron per atom whereas group 2 metals will release 2 per atom
Malleable and ductile because there’s no bonds holding specific ions together so can slide over each other
Good electrical conductors because delocaslised electrons can carry charge
Structure of simple molecular structures?
Very strong covalent bonds, however very weak molecular forces due to weak induced dipole-dipole interactions
So very low melting and boiling points
Why does reactivity increase as you go down group 2?
The ionisation energies decrease due to increased atomic radius and the shielding effect, so electrons lost more easily making it more reactive
What do group 2 metals produce when reacted with water?
Metal hydroxide and hydrogen
What are the oxides and hydroxides of group 2 metals?
Bases, most of them are also soluble in water so also alkalis
As you go down the group the oxides form more strongly alkaline solutions as the OH groups are more soluble
What are group 2 compounds used for?
The alkaline earth metals are used to nuetralise acidity
Agriculture, digestion pills
Colour and state at room temp of fluorine?
pale yellow
gas
Colour and state at room temp of chlorine?
Green
gas
Colour and state at room temp of Bromine?
Red-brown
Liquid
Colour and state at room temp Iodine?
Grey
Solid
Why do group 7 halogens melting point increase as you go down the group?
London forces get stronger as they have more electrons
Why does reactivity decrease as you go down group 7?
Atomic radius increases, and so does the amount of shielding so less attraction from nucleus to outer electrons, so harder for them to attract electrons
What will a more reactive halogen do to a less reactive halide ion in solution?
Displace it in a displacement reaction
they swap positions
How do you test for halogens?
Add silver nitrate solution and then dilute ammonia and then conc ammonia
Chloride ions form AgCl which is a white precipitate, dissolves in dilute NH3
Bromide ions form AgBr which is a cream preicpitate, dissolves only in conc NH3
Iodide ions form AgI which is a yellow precipitate, and doesn’t dissolve in conc NH3
What’s a disproportionation reaction?
Where the same element is oxidised and reduced
What do halogens undergo disproportionation with and what’s the general equation?
Alkalis
X2 + 2NaOH = NaXO + NaX +H2O
What’s a chlorate ion?
ClO-
How do you make bleach?
React chlorine gas with cold dilute aqueous sodium hydroxide in a disproportionation reaction
How is chlorine used to kill bacteria in water?
Cl2 + H2O =(reversible reaction) HCl + HClO
HClO + H2O = (reversible reaction) ClO- + H3O+
Chlorate ions kill bacteria
Pros of using chlorine to treat water?
Kills pathogens
Some chlorine remains in water and prevents reinfection
Prevents growth of algae
Cons of using chlorine to treat water?
Very harmful if breathed in, irritating the respiratory system
Can cause chemical burns
Forms chlorinated hydrocarbons which are carcigenic
Alternatives to treat water?
Ozone strong oxidising agent for killing bacteria, but expensive and short half life
UV light- Kills bacteria by damaging their DNA but inefective in cloudy water
How do you detect carbonates?
Add HCl and if carbon Dioxide is produced then it’s a carbonate
Test for CO2 as limewater goes cloudy
How do you test for sufates?
With HCl and Barium Chloride
White precipitate formed if it’s present
How do you test for halides?
Add silver Nitrate solution
Silver chloride is white (dissolves in dilute NH3)
Silver bromide is cream (dissolves in conc NH3)
Silver Iodide is yellow (doesn’t dissolve in conc NH3)
How do you test for ammonia?
Turns damp red litmus paper blue because it’s alkali
How do you test for ammonium ions?
Add NaOH and warm mixture, if ammonia is given off then ammonium ions were present
What order should you do tests to avoid false negatives?
Test for carbonates - no CO2, so no barium carbonate precipitate can form
Test for sulphates - no sulphate to react with silver nitrate to form silver sulphate
Test for halides
What happens to KCl (colourless) when in aqueous or organic solution and Chlorine water, Bromine water, and Iodine solution are added?
In aqueous solution:
Chlorine water added: no reaction
Bromine water added: no reaction
Iodine solution added: no reaction
In organic solution:
Chlorine water added: no reaction
Bromine water added: no reaction
Iodine solution added: no reaction
What happens to KBr (colourless) when in aqueous or organic solution and Chlorine water, Bromine water, and Iodine solution are added?
In aqueous solution:
Chlorine water added: Goes yellow from Br2
Bromine water added: no reaction
Iodine solution added: no reaction
In organic solution:
Chlorine water added: Goes orange from Br2
Bromine water added: no reaction
Iodine solution added: no reaction
What happens to KI (colourless) when in aqueous or organic solution and Chlorine water, Bromine water, and Iodine solution are added?
In aqueous solution:
Chlorine water added: Goes orange/brown as I2 displaced
Bromine water added: Goes orange/brown as I2 displaced
Iodine solution added: no reaction
In organic solution:
Chlorine water added: Goes purple as I2 displaced
Bromine water added: Goes purple as I2 displaced
Iodine solution added: no reaction
Features of a dynamic equilibrium?
The concentrations of the products and reactants stay the same
Must occur in a closed system
What do you get more of if the position of equilibrium shifts left?
You’ll get more reactants
What do you get if the position of equilibrium shifts right?
You’ll get more products
What does le Chatelier’s principle state?
If there’s a change in concentration, pressure or temperature the equilibrium will move to help counteract the change
What happens if the concentration of a reactant increases in the equilibrium?
The equilibrium will shift right, producing more products
What happens if you reduce the amount of product in an equilibrium?
The equilibrium will shift right and increase the amount of products
What happens if you increase the pressure in a gaseous equilibrium?
It will shift the equilibrium to the side with the fewer moles of gas
What happens if you increase the temperature in a dynamic equilibrium?
The equilibrium shifts in the endothermic (positive enthalpy change) direction
So if the forward reaction is exothermic it will shift left
If the forward reaction is endothermic it will shift to the right
What do catalysts do to the position of equilibrium?
They have no effect on the position of equilibrium, but they do speed up the forward and reverse reactions
Describe the reaction ethene reacting with steam to produce ethanol?
Reversible reaction and the forward reaction is, exothermic
Carried out a pressure of 60-70 atm and at a temperature of 300 degrees, and with a phophoric acid catalyst
It’s a compromise as the forward reaction is exothermic, so for a better yield it would prefer lower temperatures
However at lower temperatures the rate of reaction would be too slow, so 300 degrees is a compromise
High pressure is used as it favours the forward reaction, as there is 2 moles of gas on reactant side, and only one on product side
However even higher pressures are more expensive to produce and can be dangerous so the pressure is a compromise
Formula for Kc the equilibrium constant if the reaction is aA + bB (reversible reaction) = cC + dD and how you work Kc out?
Kc = ({C}^c x {D}^d ) / ({A}^a x {B}^b)
Just put in concentrations to find Kc
To find units use that each concentration has the units moldm^-3 and then use indices rules to find the units
What does the value of Kc tell us?
If Kc is greater than 1 then there are more products that reactants, and the equilibrium lies to the right
If Kc is less than 1 then there are more reactants than products and the position of equilibrium lies to the left
Describe an experiment to investigate the equilibrium position with changing temperature?
In a closed system, the brown gas NO2 exists in equilibrium with the colourless gas N2O4
NO2 to N2O4 has an exothermic forward reaction
So place them in water baths, when you reduce temperature will go colourless as equilibrium shifts to the right, when you increase the temperature will go brown as equilibrium shifts to the left
Describe an investigation to investigate how equilibrium changes with changing concentration?
Have a dynamic equilibrium in which they are different colours on each side
Then add more reactants, equilibrium will shift to right there will be a colour change
Then add more products, equilibrium will shift to the left and a colour change will occur
