Chlorine has 7 electrons in its valence shell. It needs one more electron to attain a complete octet. When it gets this electron from elements like metals, it becomes a charged ion called the chloride ion, Cl−.
Chlorine is a very versatile element and its uses cut across laboratory and household applications. Chlorine is a product of the hydrolysis of sodium chloride brine into sodium ions (Na+) and chloride ions (Cl−).
The chloride ion is very much like the neutral chlorine atom, except for its charge and a few other differences. The chloride ion is the anion that makes up the negatively charged portion of salts like sodium chloride, potassium chloride, and hydrogen chloride.
Keep reading to learn about the ionic charge, nuclear charge, effective nuclear charge, and the reactions of chlorine. I will also discuss the applications of the chloride ion.
Properties of chlorine
- Chlorine is the 17th element of the periodic table and the second member of the halogen family
- It has an atomic number of 17 and a mass number of 35.45
- Chlorine is located in group 17, period 4, and in the p-block of the periodic table
- It is a pale yellow-green gas at STP with melting and boiling points of – 150.7°F (-101.5°C) and – 29.27°F (-34.04°C), respectively
- At STP, chlorine gas has a density of 3.2 g/L and 1.5625 g/cm3 at its boiling point
- Chlorine has an electronic configuration of 1s22s22p63s23p5 with 2, 8 & 7 electrons in its shells
- Chlorine can exhibit a variety of oxidation states that range from -1 to +7
- Furthermore, chlorine is a unique element. It is the third most electronegative element and the element with the highest electron affinity. This makes it highly reactive and strongly oxidizing
- Because of the above characteristics, chlorine does not occur in its free form. It is usually found in the form of chlorides, such as potassium chloride, calcium chloride, and sodium chloride
- Also, small amounts of chlorine gas are found in volcanic gases
- The trace amounts of chlorine present on the Earth’s crust are made of two chlorine isotopes. They are chlorine-35 which makes up 75.53% and chlorine-37 which makes up 24.47%
- Although chlorine is not abundant on the Earth, it is versatile. The uses of chlorine range from common household bleach to the production of other chemicals. Chlorine in its ionic form also has a lot of biological importance
What is the charge of Cl when it forms an ion?
Chlorine forms an ion, chloride ion (Cl−) when it has gained one electron to complete its octet. The charge on the chloride ion is -1.
An implication of this is an increase in the number of electrons in the atom. A neutral Cl atom has an equal number of protons and electrons. When it gains one electron, the chlorine atom has 17 protons and 18 electrons.
What is the nuclear charge of Cl?
The nuclear charge of the chlorine atom is 17. The nuclear charge of any atom is the number of protons in the nucleus of that atom. It is also equal to the atomic number of the element.
What is the effective nuclear charge of Cl?
Effective nuclear charge, Zeff, = Z – S
Z is the nuclear charge and S is the shielding constant
S can be determined using Slater’s rule as follows:
The electronic configuration of Cl is 1s22s22p63s23p5
The electrons in 1s2 experience a shielding effect of 1, electrons in 2s22p6 experience a shielding effect of 0.85, and the electrons in 3s23p5 experience a shielding effect of 0.35.
However, only electron in 3s23p5 is the focus. Therefore, the number of electrons to be considered will be 6 instead of 7.
S = (0.35 x 6) + (0.85 x 8) + (1 x 2)
= 2.1 + 6.8 + 2
= 10.9
Zeff = Z – S
= 17 – 10.9
Zeff = 6.1
Reactions of chlorine
Reaction with hydrogen
Chlorine gas reacts with hydrogen gas in an exothermic reaction to form hydrogen chloride gas. In the presence of heat or light, the reaction could result in an explosion.
Cl2 + H2 ———> 2HCl
Reaction with metals
Chlorine forms metal chlorides with metals in a vigorous reaction. It is more likely to react with alkali and alkali Earth metals than with other metals.
Cl2 + 2Na ———> 2NaCl
Reaction with water
Chlorine reacts with water in a reversible reaction to form a strong and weak acid, hydrochloric acid (HCl) and hypochlorous acid (HOCl). Hypochlorous acid is a powerful oxidizing agent that is used as a bleach.
It also has strong antibacterial, antifungal, and anti-inflammatory properties, which makes it an important ingredient in many skincare products.
Cl2 + H2O ⇌ HCl + HOCl
Reaction with organic compounds
Organic compounds undergo substitution reactions with chlorine. Chlorine atoms replace the hydrogen atoms in a process known as chlorination. This process is vital to producing plastics, many solvents, and chemicals.
For instance, the chlorination of methane starts with the formation of chloromethane (CH3Cl) and finishes as carbon tetrachloride (CCl4).
- CH4 + Cl ———> CH3Cl + HCl
- CH3Cl + Cl ———> CH2Cl2 + HCl
- CH2Cl2 + Cl ———> CHCl3 + HCl
- CHCl3 + Cl ———> CCl4 + HCl
Combustion reaction
Chlorine gas is not a combustible gas. However, it supports combustion when there is a flame or spark. It will react with flammable substances, such as hydrogen or hydrocarbons, to enhance the burning process.
Reaction with ammonia
Chlorine replaces all the hydrogen atoms in ammonia (NH3) to form nitrogen trichloride (NCl3), a highly explosive compound, and hydrogen chloride gas.
3Cl2 + 4NH3 ———> 3NCl3 + 6HCl
Reaction with sodium hydroxide
The bleaching potential of chlorine is seen when it reacts with sodium hydroxide (NaOH) to form sodium hypochlorite (NaClO), a common household bleach.
Cl2 + 2NaOH ———> NaClO + NaCl + H2O
What reactions does chloride ion undergo?
Precipitation reactions
Chloride ions react with silver ions (Ag+) to form an insoluble white precipitate of silver chloride (AgCl)
Ag+ + Cl− ——–> AgCl
Acid-base reactions
Chloride ion is a weak base and will be protonated by a strong acid like sulphuric acid, H2SO4. This process is sometimes used to prepare hydrochloric acid in some laboratories.
NaCl + H2SO4 ———> NaHSO4 + HCl
Electrolysis
Electrolysis of sodium chloride (NaCl) in water will produce chlorine gas at the anode and hydrogen gas and NaOH at the cathode.
Displacement reactions
Reactivity decreases down the group in the halogen family. When chlorine ion reacts with compounds that contain less reactive halogens like bromine, it displaces bromine and forms a chloride compound.
For instance, chlorine will displace bromine in sodium bromide or potassium bromide to form sodium chloride or potassium chloride.
Cl2 + 2KBr ———> 2KCl + Br2
Reaction with oxygen
Chloride ions will only react with oxygen at very high temperatures. Oxygen reacts with chlorine to form chlorates or perchlorates.
Complex formation
Chloride ions form complexes with various metal ions in aqueous solutions. These complexes have applications in coordination chemistry.
Applications of chloride ion
- Chloride ions are useful for water treatment through the process of chlorination
- They participate in the ion exchange process used in water softening and purification
- They find application in the production of plastic and polymers like polyvinyl chloride (PVC) which is used in the production of pipes and cables
- Chloride ions are also used in the synthesis of various chemicals
- Chloride ions are key indicators in titration and complexometric reactions
- Chloride compounds are important components of dyes and pigments
- Chloride ions are components of many electrolyte solutions, such as sodium chloride
- These ions are present in many food preservatives and flavorings
- Biologically, chloride ions are important to the body. They help to maintain pH balance, electrolyte balance, and proper hydration. They are also used in the treatment of cystic fibrosis
FAQs
Can chlorine form cations?
Under certain conditions, chlorine may lose electrons to form cations. For instance, when dichlorine oxidizes, it forms Cl2+, an unstable cation. However, chlorine would rather form anions than cations.
What are dichlorine dioxides?
Dichlorine dioxides are compounds made of two chlorine atoms and two oxygen atoms. Chlorine forms three dichlorine dioxides, namely; ClO dimer (Cl2O2), chloryl chloride (ClO2Cl), and chlorine chlorite (ClOClO).
Which compound has chlorine in its highest oxidation state?
Chlorine is in its highest oxidation state in perchloric acid, HClO4, where it has an oxidation state of +7.
In this compound, the oxidation states of O and H are -2 and +1 respectively. And, the overall sum of all atoms in this compound is 0.
Therefore,
1 + Cl + 4(-2) = 0
1 + Cl – 8 = 0
Cl – 7 = 0
Cl = +7
Conclusion
The ability of chlorine to form ions significantly influences its chemical behavior. It is also responsible for many applications in human health, medicine, and various industries.
Chloride ion finds application in water treatment, the production of disinfectants, plastic, bleach, and many chemicals. Biologically, it is useful in maintaining electrolyte balance, pH balance, and overall hydration.
Also, learn about the charge of fluorine, the preceding halogen for chlorine.
Thanks for reading.