The Halogens Flashcards
What are group 7 elements called and what are their features?
- their atoms have 7 electrons in their outer shells
- halogens are the most reactive group of non-metals
- non of them are found in nature as the uncombined element
- many halogens form compounds with metals such as those in groups 1 and 2 (metal halides)
What are the physical properties of the halogens?
- F - pale yellow gas consisting of fluorine molecules F2
- Cl - yellow-green gas consisting of chlorine molecules Cl2
- Br - dark red liquid consisting of bromine molecules Br2
- I - shiny grey-black crystalline solid consisting of iodine molecules I2
- As - astatine is very radioactive and very rare
What is the electronegativity of an atom?
A measure of its power to attract the bonding pair of electrons in a covalent bond
What is the trend in electronegativity in the halogens and why?
- it is quite high
- decreases down group 7
- decreases because as the atomic radius of the atom increases, so does the number of shells of electrons that shield the charge on the nucleus. Both size and number of shells reduce the power of the nucleus to attract the bonding pair of electrons.
- when the atomic radius is smaller then it has a stronger nuclear force so can attract the bonding pair more strongly
How do halogen elements exist naturally?
As diatomic molecules made from two halogen atoms covalently bonded and sharing one electron from each atom. This may be shown using dot - and - cross diagrams
Why do the boiling points increase as you go down the halogens?
- the attractions between halogen molecules are intermolecular van der waal forces
- the more electrons an atom or molecule has, the larger the van der waal forces. This is because the electron cloud is more easily distorted the bigger it is and the further it extends from the nucleus
- therefore the boiling point increases down the halogens as the number of electrons increases down the halogens
What are halides?
Compounds made from halogen atoms and atoms of another element
When halogens react what do they form?
- covalent molecules
* negative ions in an ionic compound
Why are halogens good oxidising agents?
Because they accept electrons readily
What is the order of oxidising power of the halogens?
• F2>Cl2>Br2>I2
Why should fluorine not be used inthhe laboratory unless suitable apparatus is available?
Because it is the most reactive element known and is extremely hazardous
What happens when aqueous chlorine is added to potassium bromide solution?
• a yellow orange solution of bromine is formed:
Cl2 + 2KBr -> 2KCl + Br2
Cl2 + 2Br- -> 2Cl- + Br2
• bromine is formed because chlorine is a stronger oxidising agent that bromine and so withdraws an electron from each bromide atom to leave bromine atoms and negatively charged chlorine atoms. the bromine atoms then combine to form molecules of bromine which gives the solution its new colour
• the reaction is also know as a displacement reaction
• the oxidation state of chlorine changes from 0 in Cl2 to -1 in Cl-
• the oxidation state of bromine changes from -1 in Br- to 0 in Br2
What are the redox half equations for adding chlorine to potassium bromine?
- 2Br- -> Br2 + 2e-
* Cl2 + 2e- -> 2Cl-
What electron configuartion do halide ions have?
Noble gas electronic configurations
Are halide ions oxidising or reducing agents?
Reducing agents as they transfer electrons and are oxidised to halogens
