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This article covers all the following topics in detail:
Ionization Enthalpy: – First ionisation enthalpy is the enthalpy change that occurs when the first electron is removed from an isolated gaseous atom in its ground state.
Born-Haber cycle: – The Born-Haber cycle is a technique for observing and analysing reaction energy. It’s most useful for explaining how different elements combine to generate ionic compounds. Through a series of steps, the technique helps us better comprehend the response process as a whole.
Lattice Enthalpy: – Solid forms of ionic compounds are common due to their strong molecular attraction. A lattice structure is used to describe the arrangement of molecules in these ionic solids. Lattice enthalpy is the amount of energy needed to break down one mole of the solid ionic complex into its constituent gaseous ions.
Enthalpy of Ionization
A gaseous atom or ion can be ionized by taking an electron away from it. It takes a lot of energy to get one mole of electrons out of one mole of separated gaseous atoms or ions. This is called the first or original ionizing force, and it’s called Ei. This is how you measure the enthalpy of ionization: kilocalorie per mole, electron volt (eV) per atom, and kilojoule per mole are all units of it. Enthalpy changes when an electron is removed from a gaseous atom in its ground state. This change in enthalpy is called first ionisation enthalpy.
Periodic table ionization energy trend:
An ionization energy trend may be seen on today’s periodic table of elements, along with atomic radius, electron affinity, electronegativity, and metallicity.
During the time, ionization energy increases from left to right as the atomic radii shrink. Since the electrons are more negatively charged than the nucleus, they have a stronger effective attraction.
The alkali metal on the left side of the chart has the lowest ionization, while the noble gas to the far right has the highest average ionization. The valence shell of the noble gas is tightly packed, preventing the loss of electrons.
The ionization energy diminishes from the top to the bottom of a group. A group’s primary quantum number (PQN) is reduced as the outermost electron’s PQN drops. While the atoms that travel down a group have more protons in them (higher positive charge), their electron shells are reduced in size and the nucleus’s attracting force is filtered out of the outer electrons. The outermost electron is getting further and further away from the nucleus as more electron shells are supplied.
Born-Haber Cycle
The Born–Haber cycle is a way to look at reaction energies. When Max Born and Fritz Haber came up with it in 1919, they called it that. It was also written by Kasimir Fajans and published in the same issue of the same journal at the same time. Ionic compounds are formed when two non-metallic elements react with a metal, such as a metal from Group I or Group II.
Born–Haber cycles are mostly used to figure out how much energy is in a lattice, which can’t be measured directly. Some people say the lattice enthalpy is the enthalpy change that comes with making an ionic compound out of gaseous ions. This is called an exothermic process (an endothermic process). In a Born–Haber cycle, you use Hess’s law to figure out the lattice enthalpy. You compare the standard enthalpy change needed to make an ionic compound (from the elements) to the enthalpy needed to make gaseous ions (from the elements).
To make gaseous ions from elements, you first have to turn each one into a gaseous atom. Then, you have to ionize the atoms. You have to think about how much energy it takes to break apart the bonds in the element first (see also bond energy). It takes a lot of energy to remove one or more electrons from an atom or molecule to make a cation. Electron affinity is the amount of energy released when an electron is added to a neutral atom or molecule in a gaseous state to make a negative Ion.
The Born–Haber cycle only works with fully ionic solids, like some alkali halides. It doesn’t work with other types of solids. Almost all compounds have covalent and ionic contributions to chemical bonding and the energy of the lattice, which is shown by a longer Born–Haber thermodynamic cycle. Using the extended Born–Haber cycle, you can figure out which direction the compound is in and how many of its atoms have different polarities and atomic charges.
Lattice Enthalpy
An ionic solid’s lattice enthalpy measures the strength of the forces that bind its ions together. The stronger the forces become as the lattice enthalpy increases. When the ions are present as gaseous ions, the attraction between them is low, hence the forces are entirely severed.
When it comes to the solid state of sodium chloride, it is more stable than the gaseous state by 787 kg mol-1, which measures how strongly ions are attracted to each other. Keep in mind that the formation of bonds releases energy (thermal energy in this example), and the breaking of bonds releases energy as well.
As a result, the enthalpy of a lattice can be expressed in two ways.
When 1 mole of sodium chloride (or whatever) is created from its scattered gaseous ions, the enthalpy changes. In other words, the diagram’s arrow points downward.
The enthalpy change that occurs when one mole of sodium chloride (or whatever) is split up into its distributed gaseous ions can be expressed as the enthalpy change. As a result, you’re looking at the diagram with an arrow pointing upward.
Factors affecting Lattice Enthalpy:
Charge on ion:
They are attracted to each other because they have a charge on them. The more charge there is, the more force there is. This means that the lattice will be stronger with more charge.
When Potassium Chloride and Calcium Chloride both have the same crystal lattice arrangement, they both have a higher lattice enthalpy than the other one, but they both have the same crystal structure. The reason for this is that calcium ions have two+ charges, while potassium ions only have one+ charge. As we know, the electrostatic force of attraction is directly related to charge, so in this case, the force is stronger.
Size of atoms:
Atoms that are smaller have shorter interatomic distances, which means that they have a stronger bonding force than bigger atoms. This means that the lattice enthalpy is higher. In group 16, for example, the lattice energy for sodium salts of iodides and fluorides keeps going down as we move down the table.
Conclusion
Ionization energy, Ionization enthalpy, Born-haber cycle and lattice enthalpy are 4 terms that we learnt about in this article. We looked at the patterns in ionization enthalpy across the course of the periodic table. When a group moves down, the ionization enthalpy decreases, whereas when a period moves left to right, the ionization energy increases. We also have some exceptions to the rule, in which case the rules are not followed.
