Key Information & Overview
Key points which are covered in this article:
- Key definition of what Coulombic attraction is
- Factors which affect the coulombic attraction
- Coulombic Attraction along the Period
Coulombic Attraction is the attraction between oppositely charged particles.
Factors which affect the coulombic attraction
Like, the South Pole of a magnet and the North Pole of another magnet attract. Similarly, oppositely charged particles are also attracted to each other. This could either be:
- protons (which are positively charged) and electrons ( which are negatively charged) attracted to each
- positively charged ions and negatively charged ions being attracted to each
(The electrons are attracted to the nucleus because the nucleus has positively charged protons in it. This coulombic attraction causes electrons to orbit around the nucleus.)
The strength of the coulombic attraction depends on two things:
- The size of the atom
- The total charge of the atom
The bigger the size of the atom, the electrons, especially the valence electrons are further away from the nucleus. The nucleus is not able to pull the electrons, that are in orbitals further away from the nucleus, towards itself and the coulombic attraction decreases.
In a charged atom, the bigger the atom, the less is the coulombic attraction. Taking Li1+ and Na1+, both have the same charge, but the number of electrons and occupied shells is different. Na1 has a bigger atom and more electrons, but the charge is the same as Li1+. The charge gets distributed over a larger surface area in Na compared to Li. That is why Li has a larger coulombic attraction compared to Na. This is also a reason why Li is more reactive than Na.
(Lithium only has 1s2 2s1 subshells occupied. Sodium has 1s2 2s2 2p6 3s1 subshells occupied.)
The size of the charge also affects the coulombic attraction. When there is a high number of protons, the positive charge increases. The increase in positive charge improves the strength of the nucleus and is able to pull the electrons which are even further away.
Carbon has more protons than Lithium. Carbon has 6 protons whereas Lithium only has 3 protons. Carbon attracts more electrons towards its nucleus compared to Lithium. Thus, we can
say that Carbon has higher coulombic attraction compared to Lithium. The coulombic attraction is so high that Carbon is able to attract the electrons of other atoms giving it a -4 charge
(Lithium has electrons in the 1s2 and 2s1 subshells. Carbon, on the other hand, has electrons in the 1s2, 2s2 and 2p2 subshells.)
In ions, there is a coulombic attraction between the positively charged ions and negatively charged ion. The size of the charges on the ions makes a difference in the coulombic attraction. The ions with a larger charge will attract more opposite charged ions towards itself compared to ions with a smaller charge. This is because the ion with a larger charge has more charge spread over a certain surface area and the ion with a lower charge has lower charge spread over a certain surface area. Ions with a larger charge make stronger bonds compare to ions with a smaller charge.
The sodium ion has a charge of +1 and the magnesium ion has a charge of +2. However, both of them have the same number of electrons. In magnesium, a larger charge is spread over the surface area compared to in sodium, where a smaller charge is spread over the surface area. Magnesium ion has a higher coulombic attraction compared to the coulombic attraction of Sodium. This is why Magnesium ion is more reactive than Sodium Ion.
(Sodium has a +1 charge and Magnesium has a +2 charge. Magnesium has a higher coulombic attraction than sodium.)
Coulombic Attraction along the Period
Due to the coulombic attraction, the electrons are attracted towards the positively charged nucleus which contains protons. The strengths of the nuclei differ from atom to atom. Some atoms have a strong coulombic attraction compared to others due to the number of protons in the nucleus.
Atoms increase in coulombic attraction along the period. This is because the number of protons in the nucleus increases and thus the strength of the nucleus increases. Due to this, the size of the atom decreases along the period
Coulombic Attraction in Bonding
When two atoms come close with different coulombic attractions, the atom with the larger coulombic attraction has the tendency to attract the electrons of the other atom which has a smaller coulombic attraction between its nucleus and electrons.
Coulombic Attraction in Ionic Bonding
When the two atoms come close and the coulombic attractions have a big difference (due to them being further away in the periodic table), the atom with the larger coulombic value steals
the electrons of the atom with the smaller coulombic value. The atom with the larger coulombic value develops a negative charge due to having an excess of electrons. The atom with a smaller
coulombic value develops a positive charge because it is electron deficient.
As one atom is positively charged and the other atom is negatively charged, a coulombic attractions forms between the charged atoms and they get pulled towards each other. This is how they form an ionic bond.
Coulombic Attraction in Covalent Bonding
When the two atoms come close and the coulombic attractions have a smaller difference (due to them being closer together in the periodic table), the atoms form a covalent bond. The pull towards the electrons gets cancelled out because they are of almost equal strengths and the electron stays in the middle. Both the atoms share the electrons and they form a covalent bond.
- Coulombic attraction is the attraction of oppositely charged ions and
- The smaller the size, the bigger the coulombic
- The bigger the charge, the bigger the coulombic
- Bonding occurs due to the difference in coulombic
- If the difference is high, an ionic bond is
- If the difference is low, a covalent bond is