In this blog post, we’ll cover
- Electronegativity in a Periodic Table
- Electronegativity trend across a period
- Contributing Factors
- Why does electronegativity increase?
- How does electronegativity varies along a period and why?
Electronegativity increases across a period because as you move from left to right on the periodic table, there is an increase in the number of protons and electrons. This pull on the valence electrons equals a higher attraction towards a more electronegative atom.
Electronegativity in a Periodic Table
Electronegativity is a term used in organic chemistry to describe the tendency of an atom to attract electrons to itself. The higher the electronegativity of an atom, the more it will pull electrons away from other atoms. The electronegativity of an atom is determined by its position on the periodic table. The further to the left and down on the table an atom is, the higher its electronegativity.
The elements with the highest electronegativities are fluorine, oxygen, and chlorine. These elements are all highly reactive and are often found in compounds with other elements. The elements with the lowest electronegativities are sodium and potassium.
These elements are not very reactive and are often found in compounds with other non-reactive elements such as metals. Electronegativity is an important concept in Chemistry because it helps to explain why certain chemical reactions occur.
Electronegativity trend across a period
The trend of electronegativity across a period can be explained by the number of valence electrons in the atoms. As you move across a period from left to right, the number of valence electrons increases. Atoms with more valence electrons are more electronegative because they are better able to attract electrons from other atoms. This trend is also affected by the size of the atom.
As atoms get larger, their valence electrons are less tightly held, making them low electronegative. The trend of electronegativity across a period can be used to predict which elements will form covalent bonds and which will form ionic bonds. Covalent bonds occur between atoms with similar electronegativities, while ionic bonds occur between atoms with very different electronegativities. For example- NaCl
You may think this makes no sense without knowing what electronegativities are, so let me go into that first. Electronegativity is a measure of the ability of an atom to attract valence electrons to itself. This property is used to determine how many bonds an atom will form. Two things contribute to electronegativity:
- Atomic number (the number of protons), and
- Shielding effect.
The shielding effect is the “protection” of the electrons in the core from being pulled too much by an approaching atom’s nucleus. In other words, it’s how far away from an atom’s nucleus its valence electrons are. As you can see, both factors contribute to a higher value for electronegativity going across a period.
How does electronegativity varies along a period and why?
The periodic table is a way of organizing different elements according to their properties. Electronegativity is one of these properties, and it increases as you move from left to right across the periodic table. This is because the atoms on the right side of the table have more protons in their nucleus, which makes them more positively charged. This increased positive charge makes it easier for these atoms to attract electrons.
As a result, elements on the right side of the periodic table are generally more electronegative than those on the left side. Fluorine is the most electronegative element, while cesium is the least electronegative.
Electronegativity is an important property because it affects how atoms interact with each other. Atoms with high electronegativity will tend to form bonds with atoms that have low electronegativity. This is why water molecules (H2O) are held together by hydrogen bonds: the oxygen atoms are more electronegative than the hydrogen atoms, so they pull the electrons away from
Why does electronegativity increase?
The electronegativity of an atom increases as the atomic number increases. This is because the further away from the nucleus an electron is, the less attracted it is to the nucleus. As a result, atoms with more electrons tend to be more electronegative than those with fewer electrons.
Additionally, atoms with smaller nuclei are generally more electronegative than those with larger nuclei. This is because the smaller nuclei have a greater ratio of protons to electrons, making the electrons more attracted to the nucleus. In general, electronegativity increases as the distance between an electron and the nucleus increases, and as the ratio of protons to electrons decreases.
If an atom has the same number of protons and electrons, we say that it is uncharged. For example, helium has 2 protons and 2 electrons, so it’s electrically neutral. Neon on the other hand has 10 protons and 10 electrons so it also carries no charge. Fluorine as another example has 9 protons and 10 electrons meaning it also carries no charge. In each of these cases, the number of protons is equal to the number of electrons so one would expect an equal affinity for both elements to share their valence electrons.
In fluorine’s case, however, its electronegativity is higher than that of neon because its electrons are further from the nucleus. This is because the extra electron that fluorine has pulls those electrons even further away from fluorine’s core, making it more electronegative than neon. This increase in the value of electronegativity going across a period happens at every step with a new electron being added to a noble gas configuration.
Consider the case with helium below
You can see that both neon (10) and fluorine (9) have the same number of valence electrons, but fluorine’s are more “protected” or shielded by the core of nuclei. Remember that electronegativity is a measure of the ability of an atom to attract valence electrons to itself. If an atom has more protons, it is easier to attract the valence electrons because there are more protons pulling on them.
Another case that would help is to think of this in terms of “distance”.
Neon and fluorine both have 10 electrons but they’re very spread out (the first 2 are in the 1s orbital, the next 8 are in an eight-shell configuration (2s^2 2p^6)). Fluorine’s valence electrons are much closer to it’s nucleus because of this, meaning that its core is more polarized towards the nuclei. This means that fluorine is more likely to attract another atom’s electrons than neon.
So going back to the question, electronegativity increases across a period because as you move from left to right on the periodic table, there is an increase in the number of protons and electrons causing the valence electrons to be attracted more strongly toward a more electronegative atom.