The Physical and Chemical Properties of the Group 7 elements Fluorine Atomic Number 9 Mass Number 19 Chlorine Atomic Number 17 Mass Number 35 Bromine Atomic Number 35 Mass Number 80 Iodine Atomic Number 53 Mass Number 127 What is the number of protons, electrons and neutrons for each element? What is the electronic configuration for the first two elements? Why are the elements all in group 7?

ANSWERS Element Fluorine 9 10 2,7 Chlorine 17 18 2,8,7 Bromine 35 45 protons neutrons electrons arrangement Fluorine 9 10 2,7 Chlorine 17 18 2,8,7 Bromine 35 45 2,8,18,7 Iodine 53 74 2,8,18,8,7 ALL HAVE 7 electrons in outer shell

Physical Properties Structure Melting/boiling Points Colour See the video on Firefly ‘Group 7 elements’ https://thorntoncollege.fireflycloud.net/Resources/Subjects%20%5BF4%5D/Science%20%5BF5%5D/Chemistry%20%5BF6r%5D/KS4%20Chemistry%20%5BF9j%5D/Revision%20Sheets%20%5BF9l%5D/group%207.mp4

Structure All are diatomic molecules F2, Cl2, Br2, I2 There is a COVALENT BOND between the atoms in the molecule

Melting/boiling points Fluorine -220oC -188oC Chlorine -101oC -34oC Bromine -7oC +58oC Iodine +114oC +184oC State at RT Trend in mp/bp

ANSWERS All have Low melting/boiling points. All are Simple molecular structures Melting/boiling points increases down group. Iodine sublimes on heating. (Turns from solid Gas)

Chemical Properties REACTIVITY Reaction with other halides (displacements)

REACTIVITY I Download the video from Firefly ‘Group 7 for sep’ https://thorntoncollege.fireflycloud.net/science/chemistry/ks4-chemistry/revision-sheets Observe and note trend in reactivity

REACTIVITY II Reactivity decreases down the group as illustrated by Reactions with metals get less violent and slower

REACTIVITY III NB Full outer shell = stable atom NB In reactions atoms lose/gain or share electrons to achieve full outer shell NB Group 7 elements have 7 electron in their outer shell SO to achieve full outer shell they: GAIN ONE ELECTRON during reactions. SHARE ONE ELECTRON during reactions

REACTIVITY IV Further the electron in outer shell is from the nucleus the harder it is to gain/share. Closer the electron in outer shell is to the nucleus the easier it is to gain/share. Inner shells SHIELD (dilute) effect of nucleus.

Displacement reactions of Halogens IDEA Will a more reactive halogen displace a less reactive halogen? How could we test this idea? What problems might there be (considering the elemental state of these elements)? All of the halogens dissolve in petrol. Sodium Chloride, Sodium Bromide and Sodium Iodide are readily available

A more reactive halogen will displace a less reactive halogen from its compound Practical Add a small amount of a halogen to a test tube Add a few drops of hexane Add a small amount of solution containing a Potassium halide. Observe the colour of the petrol at the end of the reaction.

Results Halogen at start Colour of petrol layer at start Potassium halide Colour of petrol layer at the end Halogen at end Has a displacement taken place Chlorine Pale Green Potassium Bromide Orange Bromine Yes, Chlorine has removed Bromine from its compound Potassium Iodide Purple Iodine Chlorine has removed Iodine from its compound Potassium Chloride No Bromine has not removed chlorine from its compound Bromine has removed Iodine from its compound Iodine has not removed chlorine from its compound Iodine has not removed Bromine from its compound

Cl2 + 2KI  2KCl + I2 (if we remove K+ from both sides we get) Cl2 + 2I- 2Cl- + I2 HENCE Cl2  2Cl- 2I-  I2 The more reactive halogen is GAINING electrons going from neutral to negative. It is being REDUCED The general equation would be X2 + 2Y-  2X- + Y2 (where Y is below X in Group)