# 18.11 Occurrence, preparation, and properties of halogens

 Page 1 / 5
By the end of this section, you will be able to:
• Describe the preparation, properties, and uses of halogens
• Describe the properties, preparation, and uses of halogen compounds

The elements in group 17 are the halogens. These are the elements fluorine, chlorine, bromine, iodine, and astatine. These elements are too reactive to occur freely in nature, but their compounds are widely distributed. Chlorides are the most abundant; although fluorides, bromides, and iodides are less common, they are reasonably available. In this section, we will examine the occurrence, preparation, and properties of halogens. Next, we will examine halogen compounds with the representative metals followed by an examination of the interhalogens. This section will conclude with some applications of halogens.

## Occurrence and preparation

All of the halogens occur in seawater as halide ions. The concentration of the chloride ion is 0.54 M ; that of the other halides is less than 10 –4 M . Fluoride also occurs in minerals such as CaF 2 , Ca(PO 4 ) 3 F, and Na 3 AlF 6 . Chloride also occurs in the Great Salt Lake and the Dead Sea, and in extensive salt beds that contain NaCl, KCl, or MgCl 2 . Part of the chlorine in your body is present as hydrochloric acid, which is a component of stomach acid. Bromine compounds occur in the Dead Sea and underground brines. Iodine compounds are found in small quantities in Chile saltpeter, underground brines, and sea kelp. Iodine is essential to the function of the thyroid gland.

The best sources of halogens (except iodine) are halide salts. It is possible to oxidize the halide ions to free diatomic halogen molecules by various methods, depending on the ease of oxidation of the halide ion. Fluoride is the most difficult to oxidize, whereas iodide is the easiest.

The major method for preparing fluorine is electrolytic oxidation. The most common electrolysis procedure is to use a molten mixture of potassium hydrogen fluoride, KHF 2 , and anhydrous hydrogen fluoride. Electrolysis causes HF to decompose, forming fluorine gas at the anode and hydrogen at the cathode. It is necessary to keep the two gases separated to prevent their explosive recombination to reform hydrogen fluoride.

Most commercial chlorine comes from the electrolysis of the chloride ion in aqueous solutions of sodium chloride; this is the chlor-alkali process discussed previously. Chlorine is also a product of the electrolytic production of metals such as sodium, calcium, and magnesium from their fused chlorides. It is also possible to prepare chlorine by the chemical oxidation of the chloride ion in acid solution with strong oxidizing agents such as manganese dioxide (MnO 2 ) or sodium dichromate (Na 2 Cr 2 O 7 ). The reaction with manganese dioxide is:

${\text{MnO}}_{2}\left(s\right)+2{\text{Cl}}^{\text{−}}\left(aq\right)+4{\text{H}}_{3}{\text{O}}^{\text{+}}\left(aq\right)\phantom{\rule{0.2em}{0ex}}⟶\phantom{\rule{0.2em}{0ex}}{\text{Mn}}^{2+}\left(aq\right)+{\text{Cl}}_{2}\left(g\right)+6{\text{H}}_{2}\text{O}\left(l\right)$

The commercial preparation of bromine involves the oxidation of bromide ion by chlorine:

$2{\text{Br}}^{\text{−}}\left(aq\right)+{\text{Cl}}_{2}\left(g\right)\phantom{\rule{0.2em}{0ex}}⟶\phantom{\rule{0.2em}{0ex}}{\text{Br}}_{2}\left(l\right)+2{\text{Cl}}^{\text{−}}\left(aq\right)$

Chlorine is a stronger oxidizing agent than bromine. This method is important for the production of essentially all domestic bromine.

What is collision theory
why would you not make potassium chloride from potassium and hydro caloric acids
what is the hardest substance
with what scale one would be 💎
coland
diamond a 10
coland
1-10
coland
there is actually other elements that can cut diamonds and also withstand greater hear and temperature than diamonds.
Jallal
I wish someone had more questions for me to answer. I like helping others and I love knowledge. Please everyone ask away no matter how trivial. Any question is always a good question. it's much better to be inquisitive than silent.
Gibbs free energy continued
when ∆G>0, the process is endergonic and not spontaneous in the forward direction. instead it will proceed spontaneously in the reverse direction to make more starting materials
Jallal
when ∆G=0, the system is in equilibrium and the concentrations of the products and reactants will remain constant
Jallal
when the system is in equilibrium that means the forward reaction and the reverse reaction are occurring at the same rate
Jallal
Although ∆G is temperature dependent, it's generally okay to assume that the ∆H and ∆S values are independent of temperature as long as the reaction does not involve a phase change. that means that if we know ∆H and ∆S we can use those values to calculate ∆G at any temperature.
Jallal
calculating ∆H and ∆S can be done using tables of standard values among other methods
Jallal
when the process occurs under standard conditions (all gases at 1 bar pressure, all concentrations are 1 M, and T=25°C), we can also calculate ∆G using the standard free energy of formation, ∆fG°
Jallal
be sure to pay close attention two units when ∆G from ∆H and ∆S because ∆H is given in kJ/mol-reaction while ∆S is given as J/mol-reaction • K, which is a difference factor of 1000
Jallal
when is ∆G negative? the equation of ∆Gsystem depends on 3 values. using ∆Gsystem=∆Hsystem-T∆Ssystem, the temperature in this equation is always positive or zero because it has units of K there for the second term in our equation T∆Ssystem will always have the same sign as ∆Ssystem
Jallal
now we can make the following conclusions about when processes will have a negative ∆Gsystem
Jallal
when the process is exothermic (∆Hsystem < 0), and the entropy of the system increases (∆Ssystem > 0), the sign of ∆Gsystem is negative at all temperatures. thus the process is always spontaneous
Jallal
when the process is endothermic, ∆Hsystem > 0, and the entropy of the system decreases, ∆Ssystem < 0, the sign of ∆G is positive at all temperatures. thus the process is never spontaneous
Jallal
for other combinations of ∆Hsystem and ∆Ssystem, the spontaneity of a process depends on the temperature
Jallal
exothermic reactions (∆Hsystem < 0) that decrease the entropy of the system (∆Ssystem < 0) are spontaneous at low temperatures
Jallal
endothermic reactions (∆Hsystem > 0) The increased entropy of the system (∆Ssystem > 0) or spontaneous at high temperatures
Jallal
thermodynamics is also connected to concepts in other areas of chemistry for example, in chemical equilibrium we can relate ∆G with the equilibrium constant, K
Jallal
in electrochemistry, ∆G is related to the cell voltage, Ecell
Jallal
lastly depending on the signs of ∆H and ∆S, the spontaneity of a process can change at different temperatures
Jallal
if any part of this explanation of the concept of Gibbs free energy is not clear please let me know so I may clarify
Jallal
Why's Ph not good for consumption?
A given amount of gas occupies 10.0dm5 at 4atm and 273°C. The number of moles of the gas present is? [ Molar volume of gas at s.t.p= 22.4dm3]
you must use the Ideal Gas Law equation: pV=nRT, where p is the pressure, V is the volume, n is the number of moles, R is the gas constant, and T is the temperature. You have everything you need to calculate the answer you just need to do some algebra first to rearrange the equation to find n
Jallal
Jallal
for the future always remember that the pressure must be pascals. the volume must be converted to cubic meters, the gas constant R is 8.31441 J K^-1 mol^-1, the temperature must always be in Kelvin so if you are given degrees in Celsius make sure to add 273 to it
Jallal
solubility
Shehu
solubility
Abubakkar
yes tell me more on solubility
Shehu
solubility is the property of a solid, liquid, or a gaseous chemical substance called solute to dissolve in a solid, liquid or gaseous solvent. the solubility of a substance fundamentally depends on the physical and chemical properties of the solute and solvent as well as temperature, pressure and
Jallal
presence of other chemicals (including changes in pH) of the solution.
Jallal
the extent of the solubility of a substance in a specific solvent is measured as the saturation concentration, we're adding more solute does not increase the concentration of the solution and begins to precipitate the exorcism out of solute.
Jallal
precipitate of the excess amount of solute collects at the bottom in solid form
Jallal
this is because the solvent it's completely saturated you cannot dissolve any more solute
Jallal
the solvent most commonly used is water which is why it is also called the universal solvent as it can most readily mix with mostly anything
Jallal
excuse the few typos
Jallal
hi
Affum
welcome affum
Shehu
how do u derive this fundamental constants
am not sure how
Shehu
do you have an idea
Shehu
no
Mugala
Bertram
could you elaborate a little more on your question?
Jallal
or reword it perhaps. I think I understand what you're trying to ask but the wording of the question makes it confusing
Jallal
what fundamental constants?
Ruth
you see Bertran. if you can do a little more explaining on what you are trying to have answered there wouldn't be so much confusion and you'd most likely get your answer your searching for
Jallal
Bertram*
Jallal
this value would be a little hard to understand so I thought you should know how it is derived
Bertram
I need a deeper explanation to this value
Bertram
you're still being very ambiguous. please tell me what fundamental constant you are referring to.
Jallal
am asking this question under fundamental physical constant
Bertram
ok how do u derive the value of Avogadro's number without cramming
Bertram
fundamental physical constants are dimensionless and cannot be derived and have to be measured.
Jallal
dimensionless quantities are obtained as ratios of quantities that are not dimensionless
Jallal
if you want to understand better then I suggest you read up on "dimensional analysis", "dimensionless quantity", and "dimensionless physical constant"
Jallal
what is an atom
An atom is the smallest indivisible particle of an element that is capable of independent existence
akinboboye
That's conventional thinking since the Greeks and our current teaching, but it's been discovered that atoms are made up of even smaller subatomic particles called "quarks". Until fully understood let's stick with the current knowledge that an atom is the smallest unit of mass being indivisible
Jallal
definition of ions
Salman
an ion is an atom or molecule that has a net electrical charge. the charge of the electron atom as negative and is equal and opposite to that of the proton that item which is positive. the net charge of an ion is non-zero.
Jallal
this is due to the total number of electrons being on equal to its total number of protons. a cation is a positively charged ion with fewer electrons than protons while an anion is negatively charged with more electrons and protons.
Jallal
because of their opposite electric charges cations and anions attract each other and readily form ionic compounds.
Jallal
thanks
Salman
so please who can throw more light on acids and base for me
Shehu
an acid is a molecule or ion capable of donating a proton (hydrogen ion H+) it is a substance that increases the concentration of hydronium ions (H3O+) when added to water or decreases the hydroxide concentration water.
Jallal
how separating acid to gas
Abubakkar
a base is a proton acceptor and it's a substance that dissociates in water to form hydroxide ions (OH-). thus the base decreases the aqueous hydronium concentration in water and increases aqueous hydroxide concentration in water.
Jallal
also a reaction between an acid with a base is called a neutralization reaction and the products of the reaction are salt and water and not an acid or base
Jallal
is the smallest particle of elements
Abubakkar
separating acid to gas is there a process called amine gas treating also called acid gas removal. since many different amines can be used in the process each process is slightly different depending on which amine to use.
Jallal
can I get some example of concentrated acid
Shehu
hydrochloric acid (HCl) it can come in diluted forms which you can apply on your hands (obviously not recommended) but that's to show it's concentration then there's highly concentrated HCl which will instantly burn/melt your skin
Jallal
If you want the strongest most concentrated acid there is then that's hydrogen fluoride (HF) now that is some very nasty stuff. even with proper equipment it can still be extremely dangerous to handle
Jallal
thank you jallal
Shehu
anytime
Jallal
jallal am going to be writing an exam on chemistry can you tell me some important stuff in chemistry
Shehu
I need a little more information than that. you see there's general chemistry, organic chemistry, nonorganic chemistry, analytical chemistry, biochemistry. which subject is it and what exactly will be your topic?
Jallal
I'm not really sure what you mean by important stuff so I give general ideas and principals. ranging from basic fundamentals to more in depth knowledge
Jallal
chemistry is a branch of science that studies matter and change. first chemistry deals with the study of the composition and the properties of matter then chemistry deals with change or how these substances evolve when submitted to certain conditions or how one substance changes or reacts while
Jallal
interacting with a different substance
Jallal
everything is chemistry from the chemicals in our foods to the air we breathe even to the medicine we use. everyday modern life all involves mixture of chemistry
Jallal
chemistry is also known as the central science without chemistry you wouldn't have the physical sciences or life sciences such as biology or applied sciences like engineering. in essence all sciences are glued together by chemistry
Jallal
an atom is defined as the basic unit of a chemical element however we now know that atoms are made of smaller particles called subatomic particles known as protons electrons and neutrons. protons and neutrons are not fundamental particles they're made of quarks. electrons are fundamental particles
Jallal
and they are not made of anything smaller
Jallal
a molecule is a group of atoms bound together which is the next step of chemical complexity. molecules represent the basic unit of a chemical compound
Jallal
there are three basic types of chemical compounds which have different bonding properties the difference is the force that holds together the atoms
Jallal
neutral molecules or compounds in nature or held together by covalent bonds. covalent bonds generally occur between two nonmetal atoms with share pairs of electrons or bonding pairs
Jallal
then there are ionic compounds where atoms are in ionic form which is to say charged and are held together by ionic forces which give rise to large networks of oppositely charged ions. ionic bonds occur between metals and nonmetals. one ionic compound example is sodium chloride also known as salt
Jallal
then there are extended networks of atoms formed between one or more types of metal atoms which are called metallic bonds
Jallal
chemistry studies changes in matter thus a chemical reaction is a process in which one set of chemical compounds are transformed into another. this occurs when there is an interaction between the compounds in which some initial bonds are broken and some new bonds are formed.
Jallal
this happens because the energy holding the new bonds together is higher than the energy that held the initial bonds. this is what is known as a thermodynamically favored process. favorable thermodynamics is the most fundamental step that leads to compounds to react with each other
Jallal
another important factor that allows compounds to react with each other is known as reaction kinetics
Jallal
there is also something known as chirality which is a geometric property of certain molecules. molecule is said to be chiral when its mirror image is not superimposable to the molecule itself.
Jallal
essentially chirality is symmetrical mirror image of a molecule. this can also be explained through enantiomers. however the origin of chirality is still unknown and debatable as to why it came to exist in the first place but they do serve important biological functions. many medicines use chirality
Jallal
then there acids and bases. an acid is a compound such as hydrochloric acid (HCl) that is able to release a hydrogen cation or proton (H+). basis such as sodium hydroxide (NaOH) can catch protons water given rise to hydroxide anions.
Jallal
basically an acid is a substance that accepts alone pair of electrons and a base is a substance that donates a lone pair of electrons. relative acidity or basicity of solutions are mixtures is measured using a logarithmic scale called the pH scale which goes from 0 to 14. 7 is considered neutral
Jallal
anyting below 7 is considered acidic with 0 being the most acidic. anything above 7 is considered basic with 14 being the most basic.
Jallal
stoichiometry is a way of measuring or determining the amount of each substance that is involved in a reaction (reactants), and the amount of products that are generated. basically this is just making both sides of the reaction, the reactants and the products equal to each other so the reaction to
Jallal
proceed
Jallal
next comes oxidation and reduction. redox processes are a type of chemical reaction in which one of the reacting compounds gets oxidized and the other gets reduced. a redox reaction involves the transfer of electrons. when a compound or atom loses electrons it is oxidized.
Jallal
when a compound or atom gains electrons it is reduced
Jallal
the most common example of a redox process is the rusting of iron. when oxygen reacts with iron it produces iron oxide. the new oxidation state of iron is + 3 iron has lost three electrons therefore it is oxidized.
Jallal
on the other hand the new oxidation state of oxygen is -2 therefore each oxygen atom has gained two electrons becoming reduced
Jallal
then there is also radioactive decay or radioactivity. this a the process in which an unstable nucleus loses energy by the emission of radiation in the form of a particle. not all atoms that exist or stable. one of these unstable atoms decay they release energy in the form of particles
Jallal
this is what we call radiation. when this process takes place a new nucleus is formed and therefore also a new atom. the new atom can also be unstable and it can keep releasing radiation until it turns into a stable atom which no longer emits energy as radiation.
Jallal
if you would like me to discuss and explain other areas of chemistry please let me know I will be more than happy to
Jallal
thank you jallal
Shehu
any more important things to know
Shehu
there are lots of important things. I can write them up for hours and still have more to say which I don't mind. how much more or detail do you require? in the meantime I'll just keep typing up other important areas of chemistry.
Jallal
balancing equation,Gibbs free energy
Shehu
sure thing. I just need to type protocol development on a clinical trial and send it to my employer. please give me a few moments to finish the study design and guidelines
Jallal
in what other form do we extract zinc apart from blende?
miriam
a chemical equation is the symbolic representation of a chemical reaction. the reactant entities are on the left hand side while the product entities are on the right hand side.
Jallal
because of the law of conservation of mass dictates that the quantity of each element does not change in a chemical reaction and the law of conservation of charge also states that the charge is conserved in a chemical reaction therefore each side of the chemical equation must represent the same
Jallal
quantity of any particular element also the same charge must be present on both sides of the balanced equation. this is where stoichiometric comes into play which is the calculation of reactants and products in chemical reactions
Jallal
balancing a chemical formula for a simple chemical reaction can be easily done by trial-and-error however more complex chemical equations can be solved using a system of linear equations.
Jallal
when balancing equations one should use the smallest whole-number coefficient. if a fractional coefficient exists then multiply every coefficient with the smallest number required to make them whole which is typically the denominator of the fractional coefficient
Jallal
an example of one balanced equation is: 2 HCl + 2 Na --> 2 NaCl + H^2. the 2 on the last hydrogen is supposed to be a subscript but I don't have that symbol on my phone
Jallal
an example of one balanced equation is: 2 HCl + 2 Na --> 2 NaCl + H^2.
Jallal
if if there is no coefficient in front of the chemical formula then the coefficient is automatically 1
Jallal
another example of a balanced equation is CH4 + 2O2 --> CO2 + 2H2O
Jallal
the 2 after the first oxygen on the left side it's supposed to be a subscript also the 2 after the oxygen on the right side is also a subscript same goes for the 2 in H2O
Jallal
the stoichiometric ratio free agent is the optimum amount when all of the reagent consumed, there is no deficiency of the reagent, and there is no excess of their reagent
Jallal
regardless of whether or not all the atoms are actually involved in a reaction both sides of the formula, the reactant side and the product side must be equal
Jallal
also different elements have different atomic mass so as a collection of single atoms molecules have a definite molar mass measured with the unit mole also known as Avogadro's constant. thus to calculate the stokke allometry by mass the number of molecules required for each reactant is expressed
Jallal
in moles and multiplied by the molar mass of each to give the mass of each reactant per mole of reaction. the mass ratios can be calculated by dividing each why the total in the whole reaction.
Jallal
stoichiometric is not only used to balance equations but also used in conversions such as converting from grams to moles using molar mass as a conversion factor or from grams to milliliters using density. for example to find the amount of NaCl (sodium chloride) in 2.00 g, you would do the following.
Jallal
2.00 g NaCl/58.44 g NaCl mol^-1= 0.034 mol
Jallal
stokke allometry is also used to balance chemical equations known as reaction stoichiometry to determine molar proportion. for example 2 diatomic gases, hydrogen oxygen, can combine to form a liquid, water, in an exothermic reaction shown by the following 2 H^2 + O^2 --> 2 H2O
Jallal
stoichiometry can also be used to find the quantity of a product yielded by a reaction. if a piece of solid copper (Cu) or added to an aqueous solution of silver nitrate (AgNO3), the silver (AG) would be replaced in a single displacement reaction forming aqueous copper (II) nitrate (Cu(NO3)2) and
Jallal
solid silver. how much silver is produced if 16.00 grams of Cu is added to the solution of excess silver nitrate?
Jallal
the following steps would be used: 1. write and balance the equation. 2. Mass to moles: convert grams of Cu 2 moles of Cu. 3. Mole ratio: convert moles of Cu to moles of Ag produced. 4. Mole to mass: convert moles of Ag to grams of Ag produced
Jallal
the complete balanced equation would be: Cu + 2 AgNO3 ---> Cu(NO3)2 + 2 Ag
Jallal
I think I went into more depth than you wanted. let me give a simplified version of balancing equations
Jallal
chemical equations are used to describe the rearrangement of atoms and electrons during a chemical reaction.
Jallal
the atoms can be neither created nor destroyed and always react in fixed proportions each side of the equation must contain the same number of each kind of atom. this is called a balanced equation
Jallal
example: for the reaction of hydrogen and oxygen to give water, H2 + O2 ---> H2O
Jallal
equation is unbalanced. there are two oxygens on the reactant side, only one on the product side. to balance it, the number of product water molecules must be increased to 2, and then the number of reactant H2 molecules must also be increased to 2.
Jallal
this provides the balanced equation: 2H2 + O2 ---> 2H2O
Jallal
you can also visually draw these two equations to show you the unbalanced equation and the balanced equation.
Jallal
that concludes balanced equations. now on to Gibbs free energy
Jallal
Gibbs free energy is part of thermodynamics it is also known as free enthalpy which is also a thermodynamic potential that can be used to calculate the maximum of reversible work that may be performed by thermodynamic system at a constant temperature and pressure.
Jallal
the Gibbs free energy equation is: (∆G°=∆H-T∆S°), and is measured in joules
Jallal
∆G° is Gibbs free energy. ∆H° is change in enthalpy. ∆S° is the change in entropy. T is the temperature always in Kelvin at 298.15 K. the second law of thermodynamics helps us determine whether a process will be spontaneous and using changes in Gibbs free energy to predict whether a reaction will be
Jallal
genius in the forward or reverse direction or whether it is at equilibrium
Jallal
the second law of thermodynamics says that entropy of the universe always increases for a spontaneous process: ∆Suniverse=∆Ssystem + ∆Ssurroundings > 0
Jallal
at constant temperature and pressure the change in Gibbs free energy is defined as ∆G=∆H-T∆S
Jallal
when ∆G is negative a process will proceed spontaneously and is referred to as exergonic
Jallal
the spontaneity other process can depend on the temperature
Jallal
in chemistry a spontaneous process is one that occurs without that diction of external energy. spontaneous process may take place slowly or quickly because spontaneity is not related to kinetics or reaction rate.
Jallal
a spontaneous processes can be exothermic or endothermic. which is to say that spontaneity is not necessarily related to the enthalpy change of a process, ∆H
Jallal
we can determine if a process will occur spontaneously by using the second law of thermodynamics which states any spontaneous process must increase the entropy in the universe. this can be expressed mathematically as follows: ∆Suniverse=∆Ssystem + ∆Ssurroundings > 0 for a spontaneous process
Jallal
to determine the change in entropy and spontaneity we use Gibbs free energy equation shown before. the symbol G has typically units of kJ/mol-rxn also known as kilojoules over mole of reaction
Jallal
when using Gibbs free energy to determine the spontaneity of a process we are only concerned with the changes in G rather than its absolute value. the change in Gibbs free energy for a process is thus written as ∆G, which is the difference between Gfinal, the Gibbs free energy of the products
Jallal
and Ginitial, the Gibbs free energy of the reactants. ∆G=Gfinal-Ginitial
Jallal
the equation ∆G=∆H-T∆S allows us to determine the change in Gibbs free energy using the enthalpy change ∆H and the entropy change ∆S. we can use ∆G to determine whether a reaction is spontaneous in the forward direction backward direction or if the reaction is at equilibrium
Jallal
when ∆G<0, the process is exergonic and will proceed spontaneously in the forward direction to form more products
Jallal
What is rightful definition of element
an element is the group of (vertical columns) of the periodic table exhibit similar chemical behaviour.
Barnabas
okay
angela
any other information
Salman
a chemical element is a species of atom having the same number of protons and it's atomic nuclei
Jallal
for example let's use oxygen the atomic number of oxygen is 8 so the element oxygen describes all atoms which have 8 protons
Jallal
Jallal
in*
Jallal
is alkanes a saturated hydrocarbon?
yup
it's saturated cos it has single bonds
yh....because they don't undergo additional reactions which hydrogen and other atoms can add across the carbon-carbon or triple bond
patience
and me...I'm I wrong?
patience
how does metal looses electron
By oxidation and reduction
hamidat
by oxidation loss
Official
An acid is a proton donor.
what is an acid
an acid is a substance when dissolved in water produces hydrogen ion or hydroxonium ion
hamidat
good
Mudassir
thanks
hamidat
is a substance which dissolves in water to produce hydrogen ions as the only positively charged ions
Kwagala
what is ionic bonding
It involves the transferring of electron from a metal to a non mental
hamidat
that's right
Edward
bonding between a metal and a non metal
miriam