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Tendency of Atoms to Attract Electrons each of the atoms to attract electrons from the other. A positively charged ion The type of bond formed between a pair of atoms is decided by using the capability of (called a cation) types when an atom loses one or greater electrons, and a negatively charged ion (called an anion) forms when an atom provides electrons. For a free, iso- lated atom, the potential to lose an electron is measured by way of its ionization energy, whereas the ability to acquire an electron is measured by the electron affinity. The av- erage between these two houses of remoted atoms defines a new quantity referred to as the electronegativity, which measures the internet tendency of one atom to entice elec- trons from any other atom to which it is bonded. Comparing the electronegativity values for two atoms shows whether or not they will structure an ionic, covalent, or polar covalent bond.

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In this part we outline electron affinity and combine it to define electronegativity. A key point will be the relationship of electronegativity for each atom to its position in the periodic table. In the final sections of this chapter, we will use this background to describe systematically ionic, covalent, and polar covalent bonds and to introduce the properties of the resulting structures when these bonds are formed.

Changing the electron arrangement round an atom by using attain or loss of electrons additionally changes the energy of the atom, as evidenced by using the fact that ionization power and electron affinity have bodily dimensions of energy. You need to evaluate Section 1.7, which describes the electricity concept, in coaching for studying these proper- ties of atoms.

Electron Afinity

we described the ionization energy, which measures the ease with which an offers up an electron to shape a cation. The opposite reaction, in which an atom accepts an more electron to shape an anion, is described by means of the electron affin- ity of the atem.

An anion is shaped via the electron attachment reaction

X(g)+eX¯(g)

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for which the energy exchange AE, described as in Section 3.2, is known as the electron at- tachment energy. If AE is negative, energy is launched in the response and the anion is stable. If AE is positive, power ought to be expended in order to preserve the electron at- esmic tached to the atom, and the anion is unstable. For historic reasons, the electron affinity is described as the power released when an electron is attached to a impartial atom and is given as a tremendous number. This is a ordinary if demanding excep-

tion to the in any other case regularly occurring convention that electricity liberated in a technique is as- signed a negative number. You must hold this “reverse convention” in thinking to the keep away from confusion when dealing with electron affinity, which is a simple concept.

It is difficult to measure the electron attachment electricity directly, and to reap Hethe electron affinity from EA = – ΔΕ (electron attachment). It is less difficult to gain EA from every other size that determines the balance of the gaseous anion and is

Factors that have an effect on electron affinity
Nuclear charge
More protons capability a superior pull on the incoming electron. Across a period, nuclear cost increases, so electron affinity commonly will become more exothermic.
Atomic radius and shielding:
A large atom places the outer location farther from the nucleus. Add protecting from extra shells, and the superb appeal drops. Down a group, electron affinity tends to emerge as less exothermic.
Electron–electron repulsion in subshells:
If the introduced electron enters a crowded subshell, repulsion will increase and the method will become much less favourable. This is where the pleasant IB Chemistry explanations pick out up marks: you’re now not just stating the trend, you’re giving the mechanism.
Periodic trends: across a period vs down a group
Across a period: electron affinity becomes more exothermic
In IB Chemistry, the fashionable rationalization is:
Nuclear cost increases
Atomic radius decreases
Shielding adjustments littl:
Attraction for the incoming electron increases
So elements on the right (especially non-metals) are greater probable to acquire electrons.
Down a group: electron affinity will become less exothermic
Down a group:
Atomic radius increases
Shielding increases
The incoming electron feels less attraction
This trend is also tied to reactivity arguments, particularly for Group 17, and you can revise that link directly in Reactivity of factors based on periodic trends.
The halogen story (and the fluorine vs chlorine twist)
Halogens are one electron short of a full outer shell. In IB Chemistry, that’s why their first electron affinities are amongst the most exothermic.

Conclusion: the exam-ready way to bear in mind electron affinity Electron affinity in IB Chemistry is the energy alternate when a gaseous atom gains an electron to form a gaseous 1– ion. The first electron affinity is commonly exothermic because of nuclear attraction, while the 2nd is continually endothermic because of repulsion. Across a period, electron affinity commonly will become extra exothermic; down a group it will become much less exothermic. And if you keep in mind only one exception, bear in mind why chlorine beats fluorine.