Ocr Chemistry F321, Groups 2&7
Topic 11a – Group 7, the Halogens
Revision Notes
1) Trends in physical properties of the elements
• At room temperature, Cl2 is a pale green gas, Br2 is a brown liquid, I2 is a blue-black solid. • In Group 7, boiling point increases down the group because the molecules have more electrons and, therefore, stronger van der Waal’s forces which require more energy to overcome them • Electronegativity is the ability of an atom to attract the electrons in a covalent bond • Down Group 7, the shared electrons are further from the nucleus and more shielded. There is a weaker attraction for the bonding electrons down the Group
2) Trends in chemical properties of the elements
• The Group 7 elements are oxidising agents which gain an electron when they react • The ability to oxidise decreases down Group 7 • This can be shown by halogen displacement reactions where elements higher up the group will displace elements further down the group • This can be done with chlorine dissolved in water or by bubbling chlorine gas through NaBr(aq) or NaI(aq)
Cl2 + 2NaBr ( 2NaCl + Br2 Pale green solution Yellow solution/orange in hexane
Cl2 + 2NaI ( 2NaCl + I2 Pale green solution Brown solution/purple in hexane
Br2 + 2NaI ( 2NaBr + I2 Orange solution Brown solution/purple in hexane
• These equations can also be written in ionic form
Cl2 + 2Br- ( 2Cl- + Br2
Cl2 + 2I- ( 2Cl- + I2
Br2 + 2I- ( 2Br- + I2
• Down the group the outer electron is further from nucleus and more shielded so gained less easily
3) Trends in properties of the halides
• The halides (chlorides, bromides and iodides) are reducing agents which lose an electron when they react • The ability to act as a reducing agent increases down the Group • Down the group the outer electron is further from nucleus and
Revision Notes
1) Trends in physical properties of the elements
• At room temperature, Cl2 is a pale green gas, Br2 is a brown liquid, I2 is a blue-black solid. • In Group 7, boiling point increases down the group because the molecules have more electrons and, therefore, stronger van der Waal’s forces which require more energy to overcome them • Electronegativity is the ability of an atom to attract the electrons in a covalent bond • Down Group 7, the shared electrons are further from the nucleus and more shielded. There is a weaker attraction for the bonding electrons down the Group
2) Trends in chemical properties of the elements
• The Group 7 elements are oxidising agents which gain an electron when they react • The ability to oxidise decreases down Group 7 • This can be shown by halogen displacement reactions where elements higher up the group will displace elements further down the group • This can be done with chlorine dissolved in water or by bubbling chlorine gas through NaBr(aq) or NaI(aq)
Cl2 + 2NaBr ( 2NaCl + Br2 Pale green solution Yellow solution/orange in hexane
Cl2 + 2NaI ( 2NaCl + I2 Pale green solution Brown solution/purple in hexane
Br2 + 2NaI ( 2NaBr + I2 Orange solution Brown solution/purple in hexane
• These equations can also be written in ionic form
Cl2 + 2Br- ( 2Cl- + Br2
Cl2 + 2I- ( 2Cl- + I2
Br2 + 2I- ( 2Br- + I2
• Down the group the outer electron is further from nucleus and more shielded so gained less easily
3) Trends in properties of the halides
• The halides (chlorides, bromides and iodides) are reducing agents which lose an electron when they react • The ability to act as a reducing agent increases down the Group • Down the group the outer electron is further from nucleus and