Metallic bonding ( Desmond)

1) Metallic bonding is the electromagnetic interaction between delocalized electrons, also known as conduction electrons which are gathered in an area with alot of electrons . This also allows for metals to be ductile, strong, have better electric conductivity and also better strength to withstand heat.

2) Examples would be iron and steel but they can be of any combination so as long as they have flexible metallic bonds which allows these to carry the propeties of ductility and mallebility. The process of metallic bonding is also hard as it takes alot of practice to do it and there is still an infinite combinations of metal for anyone to try. This is why I choose this topic because it is fascinating and also very fun as you do not know what kind of result you might get after combining different types of metal.

3) A metallic bond is actually some what similar to a covalent bond except that the electrons are able to circulate between all the atoms. This accounts for metals ability to conduct electricity and other propeties like their ductility.

Electrolysis By Zachary Ang

In chemistry and manufacturing, electrolysis is a method of using an electric current to drive an otherwise non-spontaneous chemical reaction. Electrolysis is commercially highly important as a stage in the separation of elements from naturally-occurring sources such as ores using an electrolytic cell.

The illustration of electrolysis apparatus that is usually used in school's laboratories.

Overview

Electrolysis is the passage of an electric current through an ionic substance that is either molten or dissolved in a suitable solvent, resulting in chemical reactions at the electrodes and separation of materials.

The main components required to achieve electrolysis are:

• A liquid containing mobile ions - an electrolyte
• An external source of direct electric current
• Two solid rods or plates known as electrodes

The components perform the following roles in the electrolysis process:

• The mobile ions are the carriers of electrical current in the liquid (electrolyte). If the ions are not mobile, as in a solid salt then electrolysis cannot occur.
• The externally supplied direct electric current supplies the energy necessary to create or discharge the ions in the liquid or solution. Electric current is carried by electrons in the external circuit.
• The electrodes provide the physical interface between
  • The electrical circuit providing the energy to achieve the electrolysis
  • The electrolyte containing the ionic materials that are to be separated.

The electrodes must be able to conduct electricity. Electrodes of metal, graphite and semiconductor material are widely used. Choice of suitable electrode depends on:

• Chemical reactivity between the electrode and electrolyte
• Cost of manufacture of the electrode

Ancillary practical components to achieve electrolysis include:

• Vessels to supply, contain and remove the reactants and products
• Electrical circuitry

Process of electrolysis

The key process of electrolysis is the interchange of atoms and ions by the removal or addition of electrons from the external circuit. The required products of electrolysis are in some different physical state from the electrolyte and can be removed by some physical process. For example, in the electrolysis of brine to produce hydrogen and chlorine, the products are gaseous. These gaseous products bubble from the electrolyte and are collected.

A liquid containing mobile ions (electrolyte) is produced by

• Solvation or reaction of an ionic compound with a solvent (such as an acid) to produce mobile ions
• An ionic compound is melted (fused) by heating

An electrical potential is applied across a pair of electrodes immersed in the electrolyte.

Each electrode attracts ions that are of the opposite charge. Positively-charged ions (cations) move towards the electron-providing (negative) cathode, whereas negatively-charged ions (anions) move towards the positive anode.

At the electrodes, electrons are absorbed or released by the atoms and ions. Those atoms that gain or lose electrons to become charged ions pass into the electrolyte. Those ions that gain or lose electrons to become uncharged atoms separate from the electrolyte. The formation of uncharged atoms from ions is called discharging.

The energy required to cause the ions to migrate to the electrodes, and the energy to cause the change in ionic state, is provided by the external source of electrical potential.

Oxidation and reduction at the electrodes

Oxidation of ions or neutral molecules occurs at the anode, and the reduction of ions or neutral molecules occurs at the cathode. For example, it is possible to oxidize ferrous ions to ferric ions at the anode:

Fe2+aq → Fe3+aq + e^–

It is also possible to reduce ferricyanide ions to ferrocyanide ions at the cathode:

Fe(CN)3-6 + e^– → Fe(CN)4-6

Neutral molecules can also react at either electrode. For example: p-Benzoquinone can be reduced to hydroquinone at the cathode:

+ 2 e^– 2 H⁺ →

In the last example, H⁺ ions (hydrogen ions) also take part in the reaction, and are provided by an acid in the solution, or the solvent itself (water, methanol etc). Electrolysis reactions involving H⁺ ions are fairly common in acidic solutions. In alkaline solutions, reactions involving OH^- (hydroxide ions) are common.

The substances oxidised or reduced can also be the solvent (usually water) or the electrodes. It is possible to have electrolysis involving gases.

Energy changes during electrolysis

The amount of electrical energy that must be added equals the change in Gibbs free energy of the reaction plus the losses in the system. The losses can (in theory) be arbitrarily close to zero, so the maximum thermodynamic efficiency equals the enthalpy change divided by the free energy change of the reaction. In most cases, the electric input is larger than the enthalpy change of the reaction, so some energy is released in the form of heat. In some cases, for instance, in the electrolysis of steam into hydrogen and oxygen at high temperature, the opposite is true. Heat is absorbed from the surroundings, and the heating value of the produced hydrogen is higher than the electric input.

Related techniques

The following techniques are related to electrolysis:

• Gel electrophoresis is an electrolysis using a gel solvent. It is used to separate substances, such as DNA strands, based on their electrical charge.
• Electrochemical cells, including the hydrogen fuel cell, utilise differences in Standard electrode potential in order to generate an electrical potential from which useful power can be extracted. Although related via the interaction of ions and electrodes, electrolysis and the operation of electrochemical cells are quite distinct. A chemical cell should not be thought of as performing "electrolysis in reverse".

Faraday's laws of electrolysis

First law of electrolysis

In 1832, Michael Faraday reported that the quantity of elements separated by passing an electrical current through a molten or dissolved salt is proportional to the quantity of electric charge passed through the circuit. This became the basis of the first law of electrolysis:

Second law of electrolysis

Faraday also discovered that the mass of the resulting separated elements is directly proportional to the atomic masses of the elements when an appropriate integral divisor is applied. This provided strong evidence that discrete particles of matter exist as parts of the atoms of elements.

Industrial uses

Hall-Heroult process for producingaluminium

• Production of aluminum, lithium, sodium, potassium, magnesium
• Coulometric techniques can be used to determine the amount of matter transformed during electrolysis by measuring the amount of electricity required to perform the electrolysis
• Production of chlorine and sodium hydroxide
• Production of sodium chlorate and potassium chlorate
• Production of perfluorinated organic compounds such as trifluoroacetic acid
• Production of electrolytic copper as a cathode, from refined copper of lower purity as an anode.

Electrolysis has many other uses:

• Electrometallurgy is the process of reduction of metals from metallic compounds to obtain the pure form of metal using electrolysis. For example, sodium hydroxide in its molten form is separated by electrolysis into sodium and oxygen, both of which have important chemical uses. (Water is produced at the same time.)
• Anodization is an electrolytic process that makes the surface of metals resistant to corrosion. For example, ships are saved from being corroded by oxygen in the water by this process. The process is also used to decorate surfaces.
• A battery works by the reverse process to electrolysis. Humphry Davy found that lithium acts as an electrolyte and provides electrical energy.^{[citation needed]}
• Production of oxygen for spacecraft and nuclear submarines.
• Electroplating is used in layering metals to fortify them. Electroplating is used in many industries for functional or decorative purposes, as in vehicle bodies and nickel coins.
• Production of hydrogen for fuel, using a cheap source of electrical energy.
• Electrolytic Etching of metal surfaces like tools or knives with a permanent mark or logo.

Electrolysis is also used in the cleaning and preservation of old artifacts. Because the process separates the non-metallic particles from the metallic ones, it is very useful for cleaning old coins and even larger objects.

Competing half-reactions in solution electrolysis

Using a cell containing inert platinum electrodes, electrolysis of aqueous solutions of some salts leads to reduction of the cations (e.g. metal deposition with e.g. zinc salts) and oxidation of the anions (e.g. evolution of bromine with bromides). However with salts of some metals (e.g. sodium) hydrogen is evolved at the cathode and for salts containing some anions (e.g. sulfate (SO₄²⁻)) oxygen is evolved at the anode, and in both cases this is due to water being reduced to form hydrogen or oxidised to form oxygen. In principle the voltage required to electrolyse a salt solution can be derived from the standard electrode potential for the reactions at the anode and cathode. The standard electrode potential is directly related to the Gibb's free energy, ΔG, for the reactions at each electrode and refers to an electrode with no current flowing. An extract from the table of standard electrode potentials is shown below.

Half-reaction	E° (V)	Ref.
Na+ + e− Na(s)	-2.71
Zn2+ + 2e− Zn(s)	-0.7618
2H+ + 2e− H2(g)	≡ 0
Br2(aq) + 2e− 2Br−	+1.0873
O2(g) + 4H+ + 4e− 2H2O	+1.23
Cl2(g) + 2e− 2Cl−	+1.36
S2O82– + 2e− 2SO2−4	+2.07

In terms of electrolysis, this table should be interpreted as follows

• oxidised species (often a cation) nearer the top of the table are more difficult to reduce than oxidised species further down. For example it is more difficult to reduce sodium ion to sodium metal than it is to reduce zinc ion to zinc metal.
• reduced species (often an anion) near the bottom of the table are more difficult to oxidise than reduced species higher up. For example it is more difficult to oxidise sulfate anions than it is to oxidise bromide anions.

Using the Nernst equation the electrode potential can be calculated for a specific concentration of ions, temperature and the number of electrons involved. For pure water (pH 7):

• the electrode potential for the reduction producing hydrogen is −0.41 V
• the electrode potential for the oxidation producing oxygen is +0.82 V.

Comparable figures calculated in a similar way, for 1M zinc bromide, ZnBr₂, are −0.76 V for the reduction to Zn metal and +1.10 V for the oxidation producing bromine. The conclusion from these figures is that hydrogen should be produced at the cathode and oxygen at the anode from the electrolysis of water which is at variance with the experimental observation that zinc metal is deposited and bromine is produced. The explanation is that these calculated potentials only indicate the thermodynamically preferred reaction. In practice many other factors have to be taken into account such as the kinetics of some of the reaction steps involved. These factors together mean that a higher potential is required for the reduction and oxidation of water than predicted, and these are termed overpotentials. Experimentally it is known that overpotentials depend on the design of the cell and the nature of the electrodes.

For the electrolysis of neutral (pH 7) sodium chloride, the reduction of sodium ion is thermodynamically very difficult and water is reduced evolving hydrogen leaving hydroxide ions in solution. At the anode the oxidation of chlorine is observed rather than the oxidation of water since the overpotential for the oxidation of chloride to chlorine is lower than the overpotential for the oxidation of water to oxygen. The hydroxide ions and dissolved chlorine gas react further to form hypochlorous acid. The aqueous solutions resulting from this process is calledelectrolyzed water and is used as a disinfectant and cleaning agent.

Electrolysis of water

One important use of electrolysis of water is to produce hydrogen.

2 H₂O(l) → 2 H₂(g) + O₂(g); E₀ = +1.229 V

Hydrogen can be used as a fuel for powering internal combustion engines by combustion or electric motors via hydrogen fuel cells . This has been suggested as one approach to shift economies of the world from the current state of almost complete dependence upon hydrocarbons for energy

The energy efficiency of water electrolysis varies widely. The efficiency is a measure of what fraction of electrical energy used is actually contained within the hydrogen. Some of the electrical energy is converted to heat, a useless byproduct. Some reports quote efficiencies between 50% and 70% This efficiency is based on the Lower Heating Value of Hydrogen. The Lower Heating Value of Hydrogen is total thermal energy released when hydrogen is combusted minus the latent heat of vaporisation of the water. This does not represent the total amount of energy within the hydrogen, hence the efficiency is lower than a more strict definition. Other reports quote the theoretical maximum efficiency of electrolysis as being between 80% and 94%.. The theoretical maximum considers the total amount of energy absorbed by both the hydrogen and oxygen. These values refer only to the efficiency of converting electrical energy into hydrogen's chemical energy. The energy lost in generating the electricity is not included. For instance, when considering a power plant that converts the heat of nuclear reactions into hydrogen via electrolysis, the total efficiency is more likely to be between 25% and 40%.

NREL found that a kilogram of hydrogen (roughly equivalent to a gallon of gasoline) could be produced by wind powered electrolysis for between $5.55 in the near term and $2.27 in the long term.

About four percent of hydrogen gas produced worldwide is created by electrolysis, and normally used onsite. Hydrogen is used for the creation of ammonia for fertilizer via the Haber process, and converting heavy petroleum sources to lighter fractions via hydrocracking.

Chapter 3.1 - Why Compounds Form (Ionic Compounds) - by Nicholas 3y

What is an ionic compound?

A compound is a group of ions held together by ionic bonds. The positively charged portion of the compound usually consists of metal cations or positively charged ions, while the negatively charged portion is usually an anion or a negatively charged ion. The ions are held together by the electrostatic forces between the oppositely charged bodies. The ions in the compounds can be single atoms, such as a sodium atom, or complex groups, such as carbonate. Note: Group 0 elements do not usually form compounds. Their atoms are therefore described as unreactive or stable as their valence shells are full.

How and Why do ionic compounds form?

Ionic Compounds are formed when atoms of 2 different elements react with one another to form a stable ionic compound. The atoms become ions and chemically bond together, such as a Sodium ion and a Chloride ion which bond together to form Sodium Chloride, or NaCl.

What are some differences between an ionic compound an a molecular compound?

There are some differences in the physical properties between ionic compounds and molecular compounds. For example, at room temperature, ionic compounds are in the solid state while molecular compounds can exist in any state (solid, liquid or gas). Another difference is that ionic compounds consist of a positively charged ion, or a cation which is usually a metal, and a negatively charged ion, or an anion. Whereas a molecular compound is a covalent compound which means it is formed with 2 non-metals which are usually anions.

Ionic compounds are also often soluble in water. They also have high melting and boiling points as they have strong electrostatic bonds between particles.

Thanks for your attention! :)

Complete Chemistry for IGCSE,Page 230-231,Chapter 16,Lesson 16.5:Chlorine by Nguyen Ngoc Tri

CHLORINE

Chlorine [Cl]
CAS-ID: 7782-50-5
An:17 N: 18
Am: 35.453 g/mol
Group No: 7
Group Name: Halogen
Block: p-block Period: 3
State: gas at 298 K
Colour: yellowish green Classification: Non-metallic
Boiling Point 239.11K (-34.04°C)
Melting Point: 171.6K (-101.5°C)
Critical Temperature 417K (144°C)
Density: 3.2g/l

-Discovery Information

-Who:Karl Wilhelm Scheele

-When: 1774

-Where: Sweden

-Name Origin Greek :khloros (green),

"Chlorine" in different language

-Sources

Never found in free form in nature. Salt (sodium chloride, NaCl) is its most common compound. Chlorides make up much of the salt dissolved in the Earth's oceans - about 1.9% of the mass of seawater is chloride ions.

-Abundance

Universe: 1 ppm (by weight)

Sun: 8 ppm (by weight)

Carbonaceous meteorite: 380 ppm

Earth's Crust: 130 ppm

Seawater: 18000 ppm

-Human:

1.2 x 106 ppb by weight

2.1 x 105 ppb by atoms

-History

Chlorine was discovered in 1774 by Swedish chemist Karl Wilhelm Scheele, who called it dephlogisticated muriatic acid and mistakenly thought it contained oxygen. Chlorine was given its current name in 1810 by Sir Humphry Davy, who insisted that it was in fact an element.

Chlorine gas, also known as bertholite, was first used as a weapon in World War I by Germany on April 22, 1915 in the Second Battle of Ypres. As described by the soldiers it had a distinctive smell of a mixture between pepper and pineapple. It also tasted metallic and stung the back of the throat and chest. It was pioneered by a German scientist later to be a Nobel laureate, Fritz Haber. It is alleged that his role in the use of chlorine as a deadly weapon drove his wife to suicide. After its first use, it was utilized by both sides as a chemical weapon

-Notes

The pure chemical element has the physical form of a diatomic yellow-green gas, Cl2. Chlorine combines readily with nearly all other elements. Chlorine is about two and a half times as heavy as air.

-Hazards

Chlorine irritates respiratory systems especially in children and the elderly. In its gaseous state it irritates mucous membranes and in its liquid state it burns skin. As little as 3.5 ppm (parts per million) can be detected as an odour, and 1000 ppm is likely to be fatal after a few deep breaths.

Toxic fumes may be produced when bleach is mixed with urine, ammonia (NH3), hydrochloric acid (HCl), or another cleaning product. These fumes consist of a mixture of chlorine gas, chloramine and nitrogen trichloride; therefore these combinations should be avoided.

Over 2000 naturally-occurring organic chlorine compounds are known.

Chlorine is very toxic to aquatic organisms. Chlorine Electrons per shell 2,8,7 Electron Configuration [Ne] 3s2 3p5 Ground state 2P°3/2 Atomic Volume 22.7 cm3 mol-1 Electronegativity 3.16 Magnetic ordering Non-magnetic Mas magnetic susceptibility -7.2 x 10-9 Molar magnetic susceptibility -2.55 x 10-10 Speed of Sound 206 m s-1 Flammability Non-flammable gas (strong oxidizer) Vapour Pressure P (Pa) 1 10 100 1K 10K 100K T (K) 128 139 153 170 197 239 Crystal Structure Structure Orthorhombic a = 622.35 pm b = 445.61 pm c = 817.85 pm α = 90° β = 90° γ = 90°

I/Physical properties

-Chlorine is a green-yellow, poisonous with choking smell gas

-Chlorine is not found on Earth as the free element.

-It occurs mainly as the compound rock salt,or sodium chloride

-Usually exist in gas state

-Mass of molecule is equal to 71

-Heavier than air (71>29)

-Soluble in water (the solution is called chlorine water)

II/Chemical properties

-Chlorine is acidic because chlorine reacts with wate to form two acids

Cl₂ (g)+ H₂O (aq) --> HCl (aq) + HOCl (aq)

-Chlorine water act as a bleach because the hypochlorous acid can lose its oxygen to other substances(it oxidises them.Many colored substances lose their colour when oxidised

2HOCl (aq) -> 2HCl (aq) + O_{2 (g)}

Hydrogen burn in chlorine to form hydrogen chloride:

H₂ (g) + Cl₂ (g) --> 2HCl (g)

+Reaction with base:

Chlorine can react with bases to form salts

+Reaction with acid:

+ Reaction with metal:

Chlorine combines with most metals ,forming metal chlorides.For emxample,it combines with burned iron to form iron (III) chloride

Apparatus:

-A ball of iron wool

-a flask containing chlorine gas

A ball of iron wool is heated and placed in a flask containing chlorine gas. The iron reacts vigorously with the chlorine to form a cloud of iron(III) chloride. After several minutes the iron(III) chloride formed by the reaction settles to the bottom of the flask. When the flask is rinsed with water the iron(III) chloride dissolves forming an orange solution.

Fe(s) + Cl₂(g) à FeCl₃ (s)

+Reaction with non-metal

Chlorine can reacts with another non-metal to form a compound which has covalent bond.

Apparatus:

-1 Beaker with chlorine inside

-1 capillary with hydrogen inside

-Aqueous of ammonia

Hydrogen gas flowing from a capillary is ignited. The watch glass covering a glass cylinder of chlorine is removed and the hydrogen flame lowered into the chlorine. The reaction between hydrogen and air is replaced by the reaction between hydrogen and chlorine, which produces hydrogen chloride. As the flame burns the level of chlorine gas in the container decreases. When a stopper from a bottle of aqueous ammonia is brought near the flame, white fumes of ammonium chloride are produced indicating the presence of hydrogen chloride.

H₂ (g) + Cl₂ (g) --> 2HCl (g)

+Reaction with another halogen

Chlorine can react with another halogen to form a compound which has covalent bonds.

Apparatus:

-1 test tube with iodine crystal inside

-1 capillary tube with chlorine inside.

Iodine crystals are placed at the bottom of a capillary tube. Chlorine gas is passed through the iodine crystals. The initial reaction between the chlorine and iodine forms iodine monochloride. The brown vapor of iodine monochloride can be seen flowing from the capillary. Dark brown iodine monochloride liquid is collected at the bottom of the test tube. As more chlorine is added, the brown iodine monochloride forms crystals of yellow iodine trichloride.

I₂(s ) + Cl₂(g ) --> 2 ICl(l )

2 ICl(l ) + 2 Cl₂(g ) --> I₂Cl₆(s )

+Displacement reaction

Chlorine can react with a compound that has another halogen which is less reactive than chlorine to displace the halide and form a new compound.

Apparatus:

-An aqueous solution of chlorine

-An aqueous solution of idoide(I^-)

-A test tube

-An aqueous solution of hexane

Iodide ion is added to chlorine water. By observing the color of the hexane layer, we see that the reaction has produced iodine.

(Note that the hexane layer is above the aqueous layer.)

2I^-(aq ) + Cl₂(aq ) --> 2Cl^-(aq ) + I₂(aq )

Chlorine and halogen are very reactive because their atoms are just one electron short of a full shell (in order to gain a stable form)-so they have a strong drive to gain an electron.However,chlorine is more reactive than iodine because its atom are smaller than iodine atoms-so the nucleus can attract an electron more strongly

III/How chlorine is made in industry

In nature, chlorine is found mainly as the chloride ion, a component of the salt that is deposited in the earth or dissolved in the oceans - about 1.9% of the mass of seawater is chloride ions. Even higher concentrations of chloride are found in the Dead Sea and in underground brine deposits. Most chloride salts are soluble in water, thus, chloride-containing minerals are usually only found in abundance in dry climates or deep underground. Common chloride minerals include halite (sodium chloride), sylvite (potassium chloride), and carnallite (potassium magnesium chloride hexahydrate).

Industrially, elemental chlorine is usually produced by the electrolysis of sodium chloride dissolved in water. Along with chlorine, this chloralkali process yields hydrogen gas and sodium hydroxide, according to the chemical equation;

2NaCl + 2H2O -->Cl2 + H2 + 2NaOH

Chlorine can also be made by using brine,which is a concentrated solution of sodium chloride

IV/USES

Used widely in paper product production, antiseptic, dyestuffs, food, insecticides, paints, petroleum products, plastics, medicines, textiles, solvents, and many other consumer products.

Chlorine is an important chemical in some processes of water purification, disinfectants and in bleaches and chlorofluorocarbons (CFC).

To make plastic polyvinyl chloride (PVC)

To male hydrochloric acid

To make solvents such as tetrachloroethane (for dry cleaning)

In making medical drugs,bleaches,disinfectants,and insecticides.(Ex:C₆H₆Cl₆)

To sterilize drinking water and water in swimming pools

To be used as a chemical weapon

THANK YOU FOR YOUR ATTENTION