Essay PreviewMore ↓
"salt - former" and is based on the fact that the elements combine
with most metals to form salts. (halides)
State at 20oC
Electron affinity is the enthalpy change when gaseous atoms of an
element gain electrons to become negative ions.
The FIRST ELECTRON AFFINITY of an element is the ENTHALPY CHANGE WHEN
ONE MOLE OF GASEOUS ATOMS GAINS ELECTRONS TO FORM ONE MOLE OF GASEOUS
Electron affinity DECREASES as you DESCEND the group VII:
F à 333kJ
Cl à 346kJ of energy is released for every one mole of F/Cl/Br/I
Br à 324kJ atoms changing to a mole of F/Cl/Br/I ions.
I à 295kJ
This trend can be explained by the fact that as you descend the group,
the X- ion becomes less stable and is therefore less likely to form. H
is less stable because electrons are less strongly attracted due to
the fact that the valence electrons are further from the attractive
How to Cite this Page
"Group VII Elements - Halogens." 123HelpMe.com. 29 Feb 2020
Need Writing Help?
Get feedback on grammar, clarity, concision and logic instantly.Check your paper »
- Arranges elements in order of increasing relative atomic mass. Mendeleev realised that the physical and chemical properties of elements were related to their atomic mass, ordering them so that groups of elements with mutual properties fell into vertical columns in his table. Due to the pattern in which the elements have been arranged, the table fails to indicate the element’s atomic number. While Mendeleev is most often regarded as the founder of the Periodic Table, his table was the first to gain credibility in society.... [tags: chemical properties,atomic mass,elements]
1040 words (3 pages)
- The Halogens The word 'halogen' is from the Greek word meaning for 'salt producing'. JÓ§n Jacob Berzelius in the early nineteenth century used it to indicate that chlorine, bromine and iodine all occur in the sea as salts. The halogens all have common characteristics excluding astatine, as it is highly radioactive. These characteristics are: - Element Salt Metal/ Non Metal REDOX Toxicity ======== Oxidation Number Reactivity Colour at room temperature F Fluoride Non Metal F2 Oxidising agent Poisonous -1 Very Reactive Pale yellow Cl Chloride Non Metal Cl2 Oxidising agent Poison... [tags: Papers]
1001 words (2.9 pages)
- Fluorine is a corrosive, pale yellow gas and is the smallest of the Halogen group but also the element with the highest electronegativity in the Periodic Table. With such a high electronegativity it makes fluorine the most reactive of all of the elements. The high electronegativity of fluorine is beneficial in several goods, for example; polymers, toothpastes, pesticides, cancer drugs, and antibiotics. Fluorochloro-hydrocarbons are widely used in air conditioners and refrigerators, and have been associated with the vanishing of the ozone layer (Stillinger, 1988).... [tags: Chlorine, Sodium chloride, Iodine, Halogen]
717 words (2 pages)
- ... Sulfur also has six outer electrons in its electron cloud. The octet rule stats that an element will want eight in its outer shell, so sulfur will go and take two electrons from another element. When it fills its outer shell with eight electrons it will have a negative two charge do to the protons are less than the electrons. Sulfur has many different characteristics. It is a solid at room temperature and 1atm pressure. Sulfur is also odorless (almost), usually yellow, and tasteless. Sulfur is very abundant in the Earth’s crust.... [tags: group, element, electron]
1757 words (5 pages)
- There are many elements of a small group discussion each of which is important and play a key role. One of these elements is small group member roles and leadership which entails each member of the group taking on a specific role to benefit the group as well as gaining some form of leadership to help guide the group. The main roles that exist are; initiator-contributor role, information giver, orienter role, recorder role, and encourager and harmonizer roles. Each of these roles helps to keep the group and the discussion on the right path.... [tags: Leadership, Kurt Lewin, Member of Parliament]
1039 words (3 pages)
- How has the Halogen Bromine, been used to protect swimming pools. The Halogen Bromine (Atomic number: 35, Atomic weight: 79.9) is the only non-metallic element that’s state is liquid at room temperature . Bromine, produced firstly by Carl Lowig, was not associated with him as even though he was believed to have first created the element his student life took priority giving Antoine-Jérôme Balard another chemist, enough time to discover Bromine for himself and publish a paper in 1826 discussing his findings.... [tags: stench, chemical elements, environment]
1006 words (2.9 pages)
- This essay explores the research question “In what ways does the use of supernatural elements in literature serve to reflect the nature of humanity?” and focuses on fairy tales, Hamlet, and Macbeth. It begins by outlining and examining the role of supernatural elements in promoting struggles between both the characters and groups within the plot. It then proceeds to showcase how using these elements to create struggles within the plot helps the author to outline the societal struggles of his or her time period within the work of literature.... [tags: supernatural elements]
3356 words (9.6 pages)
- The VII of the Civil Rights Act of 1964 is a federal law that prohibits most harassments and discriminations within the workplace (Roscigno, Mong, Byron, & Tester, 2007). It applies to all private companies, local and state government, as well as institutions of education which employ 20 and more employees. Discriminations prohibited by Title VII include discrimination based on color, sex, race, religion, national origin, and pregnancy. However, the Age Discrimination in Employment Act (ADEA) passed in 1967, as a federal law, that governs age discrimination within workplaces (Neumark, 2008).... [tags: Employment, Discrimination]
782 words (2.2 pages)
- The Importance of Group Work in Education When I was in high school, and one of my teachers would ask us to form groups in order to do something, I would usually roll my eyes. Ironically enough, some of the best work that I put forth and learned from was done in a group work setting. By working with my peers towards a common end, I got things done much quicker and thorough than I ever did on my own. I chose to research group work for this essay, because in my limited experience as a teacher, youth worker, and student, group work proves to be a most effective teaching method; when it is done successfully.... [tags: Group Work Education Essays]
2449 words (7 pages)
- An interest group is a group that seeks a collective good, the achievement of which will not selectively and materially benefit the membership or activists of the organization. These organizations try to achieve at least some of their goals with government assistance. The difference between interest groups and political parties is that political parties seek to constitute the government, whereas interest groups try only to influence it. Some of the things that interests groups seek from government are information that affects the interests of the interest group, influence of the government policy, goodwill of the administrators who carry out the policy, and symbolic status.... [tags: Political Special Interest Group Politics]
1029 words (2.9 pages)
inner shells which, in turn, increases the shielding effect.
HALOGENS AS OXIDISING AGENTS
Since their atoms accept electrons, the halogens are oxidising agents
(OIL), and in a reaction they are reduced (RIG). Of the halogens,
fluorine is the most powerful oxidising agent, and astatine, the
least. This can be explained by the relative size of their atoms. The
fluorine atom is the smallest (i.e., the outer electrons are closer to
the nucleus), with fewer inner - shell shielding electrons, so it's
nucleus can have a greater attraction for an extra electron.
EXPLAINING THE CHANGE IN STATE FROM F2 TO I2
F2 [IMAGE] Cl2 [IMAGE] Br2 [IMAGE] I2
Pale Yellow Pale Green Red-Brown Black
Gas Gas Liquid Solid
This can be explained by instantaneous dipole-induced dipole forces.
The likelihood is that, at any instant, the charge distribution of an
atom will not be symmetrical. If electrons are thought of as " charge
clouds", wherein the electrons are in constant motion, then it is
entirely plausible that, at any instant, there will be more electrons
in one area than in another. Therefore, at that instant, the atom is
This INSTANTANEOUS DIPOLE can affect the electron distribution in
nearby atoms, so that they too are distorted. The result of this is to
INDUCE DIPOLES in nearby atoms ( the area of instantaneous high
electron density in the electron cloud will repel the electrons in
nearby atoms and so polarize these atoms too ). These atoms will then
be attracted to the original dipoles.
The instantaneous dipole - induced dipole forces are the forces that
hold halogen atoms together whether as gases, liquids or solids. The
forces increase as you go down the group.
As the atomic number of an element increases, the element becomes more
POLARIZABLE and the instantaneous dipole - induced dipole forces
become stronger. This is because, as the number of electrons
increases, so too does the likelihood that the charge distribution of
an atom will not be symmetrical. It also follows that, with more
electrons, the forces will be stronger. Therefore, as you descend
Group VII the elements change from being gases to being solid at room
THE HALOGEN DISPLACEMENT REACTION
A halide ion can be displaced from it's compound by any halogen higher
in Group VII. Since fluorine is the most reactive halogen, it can
react with the halide ion of any of the other halogens. Fluorine
becomes the fluoride ion, and the free halogen (chlorine, bromine or
iodine ) is formed from the halide ion.
F2 + 2NaCl à 2NaF + Cl2
F2 + 2Cl- à 2F- + Cl2
Cl2 + 2NaBr à Br2 + 2NaCl
Cl2 + 2Br - à Br2 + 2Cl -
IDENTIFYING HALIDE IONS
The presence of Cl -, Br -, and I- in aqueous solution can be
confirmed by the formation of a precipitate with silver nitrate
AgNO3(aq) + X- (aq) à AgX (s) + NO3- (aq)
Silver nitrate Halide ion Silver halide Nitrate ion
SILVER CHLORINE --- WHITE WHY
SILVER BROMIDE --- CREAM CAN'T
SILVER IODIDE --- YELLOW YOU
Silver Bromide (cream) and Silver Iodide (yellow) can be difficult to
distinguish by eye. This situation is remedied by the fact that these
silver halides have different solubilities in ammonia solution.
THE VARIATION IN SOLUBILITY OF THE SILVER HALIDES IN WATER AND IN
DILUTE AND CONCENTRATED AMMONIA
White precipitate in water
Soluble in dilute NH3
Soluble in concentrated NH3
Cream precipitate in water
Slightly soluble in dilute NH3
Soluble in concentrated NH3
Yellow precipitate in water
Insoluble in dilute NH3
Insoluble in concentrated NH3
OXIDISING NATURE OF THE HALOGENS
The following is a brief description of an experiment that can be
carried out to demonstrate the different oxidizing abilities of the
halogens Cl2 to I2.
The oxidising ability of the halogens decreases s you descend the
group. If chlorine water is added to a salt of bromine, eg.NaB. (aq)
or Iodine, eg.KI. (aq), then the chlorine will displace the halogen
from it's compound. The colourless Solution will turn brown as bromine
is formed, or red as iodine is formed.
Cl2 (aq) + 2NaBr (aq) à 2NaCl (aq) + Br2 (aq)
Cl2 (aq) + 2KI (aq) à 2KCl (aq) + I2 (actually KI3 (aq) as I2 does not
dissolve In water.)
Bromine water could be used to displace iodine from an iodide salt,
such as KI, but it could not displace chlorine from a chloride salt
such as KCl.
Br2 (aq) + 2KI (aq) à 2KBr (aq) + I2 (aq)
Brown Colourless Colourless Red
Halogens form diatomic molecules.
[IMAGE]They form HOMO - NUCLEAR DIATOMIC MOLECULES :
Br - Br
I -- I
i.e., they have no permanent dipole and are therefore non - polar.
They therefore dissolve better in non - polar solvents. Having said
this, the halogens DO dissolve in water, a polar solvent, because of
instantaneous dipoles. They dissolve much more readily and easily,
however, in non - polar solvents.
Hexane is a non - polar solvent. In this experiment, hexane is put in
a test tube with the aqueous solution of a halide ion:
Hexane (non - polar)
The test tube is shaken and the hexane is physically mixed through the
aqueous solution. As it is mixed through the solution, the halide ions
move from the aqueous solution to the hexane, because they dissolve
much more readily in the non - polar solvent.Hexane is less dense than
water and, when the shaking stops, the hexane floats to the surface
with the dissolved halide ions in it. The initially colourless hexane
now takes on the colour of the ions dissolved in it, and so
facilitates observations to be made.
PREPARATION OF THE HYDROGEN HALIDES
Preparations of ALLthe hydrogen halides needto be carried Out in a
FUME CUPBOARD. (Mosthydrogen halides can be produced by reacting the
metal halide with concentratedH2SO4)
HF (g) is acolourless acidic gas with a pungent odour.
NaF(s) + H2SO4(l) = NaHSO4(aq) + HF (g)
Thisis prepared by a similar process - reacting NaCl with H2SO4(l)
NaCl(s) + H2SO4(l) = NaHSO4(aq) + HCl (g)
HCl(g) is a colourless acidic gas that has an acid odour. It fumes in
moist airgiving droplets of hydrochloric acid. (Same apparatus as for
Ametal bromide is reacted with concentrated H2SO4using the apparatus
shownfor the preparation of HF.
KBr(s) + H2SO4(l) = KHSO4(aq) + HBr (g)
HydrogenBromide has a similar appearance to Hydrogen Chlorine.
N.B. The concentrated sulphuric acid will oxidise some of the HBr as
2HBr + H2SO4 à Br2 + SO2 + 2H2O
Therefore,one will observe aReddish Vapourdue to some brominebeing
Metal iodides give a complex series of reactions with concentrated
sulphuric acid. In addition to HI, one also obtains some :-
The reactions may be summarised thus:
· KI(s) + H2SO4(l) à KHSO4 + HI (g)
· H2SO4(l) + 2HI (g) à SO2 + I2 + 2H20
· H2SO4(l) + 6HI (g) à S + 3I2 + 4 H20
· H2SO4(l) + 8HI (g) à H2S + 4I2 + 4 H20
Duringthe reaction one will observe :
¨ VioletIodine Vapourbeing evolved,
¨ Theviolet vapour cooling and subliming to formdarksolidiodine,
¨ Asmell ofrotten eggs(H2S)
¨ Somefree sulphur
¨ SomeHI (g). (it is similar in appearance toHCl (g))
THERMALSTABILITY OF THE HYDROGEN HALIDES
Thethermal stability of the hydrogen halides DECREASES as you DESCEND
The decomposition of hydrogen halides is an endothermic process.
LeChatelier's Principle states: - If a system inequilibrium is
subjected to a change,processes will occur which tend to counteract
the change imposed.
H2(g) + I2(g) H is positive
[IMAGE][IMAGE]Text Box: 2HI (g)Take, for example, the reaction
When the temperatureis increased the equilibrium shifts to the right
because the forward reaction isendothermic. An increase in
temperature, by Le Chatelier's Principle, promotesthe reaction which
will use up this extra energy, i.e., the forward endothermicprocess.
Now we haveestablished how an increase in temperature causes the
decomposition of HI, wemust explain the trend of decreasing thermal
stability as relative molecularmass increases, (i.e., as you go down
the group). This is accountedfor by the decrease in the bond energy
from H - F toH - I.
EXAMININGTHE EASE OF OXIDISATION OF THE HYDROGEN HALIDES
q CONCENTRATED SULPHURIC ACID AS THE OXIDISINGAGENT
· HF } + H2SO4(l) à NO REACTION
· HCl } NOT OXIDISED
Oxidation No. increases
Bromine is oxidised
-1 +6 0 +4
· 2HBr + H2SO4(l) à Br2 + SO2 + 2H2O
Oxidisation No. decreases Sulphur is reduced
Text Box: Oxidation No. increases Bromine is oxidised -1 +6 0 +4 · 2HBr + H2SO4 (l) à Br2 + SO2 + 2H2O Oxidisation No. decreases Sulphur is reduced
8HI + H2SO4(l) à H2S + 4I2 + 4H20
· 2HI + H2SO4(l) à SO2 + I2 + 2H20
· 6HI + H2SO4(l) à S + 3I2 + 4H20
CONCENTRATED SULPHURIC ACID ALONG WITHMANGANESE (IV) OXIDE AS THE
This is an even stronger oxidising solution and it is capable of
oxidising HCl as well as HBr and HI. Concentrated sulphuric acid alone
is not a sufficiently strong oxidising agent to oxidise HCl(g) to Cl2(g).
This isdue to the relatively strong H - Cl bond. In combination with
MnO2it can oxidise HClto Cl2.
2HCl + H2SO4(l) MnO2 CL2 + SO2 + 2H2O
Text Box: 2HCl + H2SO4 (l) MnO2 CL2 + SO2 + 2H2O A COMBINATION OF
HYDROGEN PEROXIDE ANDDILUTE SULPHURIC ACID AS AN OXIDISING SOLUTION.
This oxidisingsolution is only sufficiently strong to oxidise iodide
to iodine. Itcannotoxidise solutions of theother halide ions.
REACTIONWITH WATER OF THE HYDROGEN
All the hydrogenhalides dissolve in water to form acid solutions:
HX (g) + H2O à H3O+(aq) + X-(aq)
(Where X = Cl, Br or I)
The hydrogen halides are covalently bonded, whereas, their
corresponding acids are ionically bonded. Hydroiodic acid is a
stronger acid than Hydrobromic acid, which, in turn, is stronger than
hydrochloric acid. In other words, acid strength increases from HCl
(aq) to HI(aq). This can be explained by virtue of the fact that the H
- I bond is weaker than the H - Cl bond. Therefore, HI dissociates
more fully in water. All three acids are STRONG ACIDS and display the
typical reactions of strong acids. Dilute Hydrofluoric Acid is a WEAK
ACID. Only about 10% of the HF molecules are dissociated in a 0.1 mol
dm-3solution. This is because the H - F bond is very strong and the
presence of strong intermolecular hydrogen bonds hinders dissociation.