Halogens Flashcards
What are the characteristic physical properties of halogens? (5)
- halogens are the most reactive non - metals
- They do not occur in elemental form in nature
- At room temperature they exist as diatomic molecules
- They contain elements in all 3 physical states
What is the trend in properties of halogens
As you go down the halogens, boiling point increases and density increases
Reactivity decreases
Why does the boiling point increase down the halogen group?
- The number of electrons increases which increases the strength of London forces.
- This means more energy is required to break the intermolecular forces in the molecule which increases the boiling point
What is the appearance and state at RTP of fluorine
- It is a pale yellow gas
What is the appearance and state at RTP of chlorine?
Pale green gas
What is the appearance and state of bromine at RTP?
Red - brown liquid
What is the appearance and state of iodine at RTP?
It is a shiny grey black solid
What are the redox reaction of halogens
- halogens have 7 outer electrons and redox reactions are their most common reaction
- Each halogen atom is reduced and gains one electron to have a full outer shell (-1 charge)
- Another species then gains the looses an electron to the group 7 ion, so halogens are oxidising agents
How can we tell that reactivity decreases down a group?
Through displacement reactions
Why does reactivity decrease down a group?
- Atomic radius increases which increases shielding
- more repulsion and less nuclear attraction between the nucleus and outer electron
- this reduces reactivity
- harder to gain an electron
What is the most reactive element in group 7?
Fluorine
What is Disproportionation reaction?
It is a redox reaction in which the same element is both oxidised and reduced
What are common examples of disproportionation reactions
- The reaction of chlorine and water
- ## The reaction of chlorine and dilute NaOH
What is the reaction of water and chlorine
Cl2 (aq)+ H20(L) - HCLO(aq) + HCL(AQ)
What are the products of the reaction of water and chlorine used for?
- The products are chloric acid and hydrochloric acid
- Chloric acid acts as a weak bleach and chlorine can be used as a water disinfectant as it kills bacteria
What is the reaction of chlorine with cold, dilute NaOH?
Cl2 (aq) + 2NaOH (aq) - NaClO(aq) + NaCl(aq) + H2O(l)
What are the products used for?
The chlorate ions ClO- in NaClO are present in household bleach
What are the benefits and risks of chlorine use?
- Useful in disinfecting water
- Kills harmful bacteria
- Without chlorine, water could contain harmful and infectious bacteria that can cause cholera and typhoid
What are the risks of chlorine usage?
- It is an extremely toxic gas
- It is a respiratory irritant in small concentrations and fatal in large
- chlorinated water reacts with organic hydrocarbons which can cause chlorinated hydrocarbons which can cause cancer
Do the benefits outweigh the risks?
yes, the overall risk of contaminated water is more dangerous and risky than chlorinated hydrocarbons
