Introduction to the Building Blocks of the Universe:
Here we will break down the simplest structures of matter in understandable terms.
These basics should be just enough to get you started on a chemical journey.
What are Atoms:
Atoms are the fundamental building blocks of matter in the universe. Just like you see bricks to build a house, atoms make everything in the universe. And these atoms are so small that they cannot be visible to the naked eye or a regular microscope.
Atoms comprise protons, neutrons, nuclei, shells, and electrons. In the centermost is the nucleus, which hosts protons and neutrons. Protons carry a positive charge whereas neutrons carry no charge, they are neutral.
The nucleus is surrounded by shells that host electrons. These electrons are negatively charged and their number always equals that of the protons. The most common shells are K, M, L, and N.
What are Shells:
Shells are the regions surrounding the nucleus in an atom. These shells host electrons and they are commonly classified as K, L, M, and N, starting with the K shell, the closest to the nucleus.
An atom needs some circumstances to be fulfilled to achieve stability and one of these is the stability of shells. Stability in terms of shells means that each shell hosts, either the minimum or the maximum number of electrons it requires for stability.
K Shell:
Stability Rule: The “duplet rule” suggests that the K shell is stable when it has 2 electrons.
Maximum: The K shell can hold a maximum of 2 electrons.
L Shell:
Stability Rule: The “octet rule” applies here, meaning the L shell is stable when it has 8 electrons.
Maximum: The L shell can indeed hold a maximum of 8 electrons.
M Shell:
Stability Rule: Like the L shell, the M shell is also stable when it has 8 electrons.
Maximum: The M shell can hold a maximum of 18 electrons.
N Shell:
Stability Rule: Similarly, the N shell is considered stable with 8 electrons.
Maximum: The N shell can hold a maximum of 32 electrons.
What is an Atomic Number:
An atomic number is evident of the number of protons found in the nucleus of an atom. For example, the oxygen atom has an atomic number of 8 which means it has 8 protons in its nucleus. And since the number of protons always equals the number of electrons, in a neutral atom, the atomic number also tells us the number of electrons in that atom.
It is important to note here that isolated atoms exist in a neutral state, before engaging in chemical reactions or forming bonds with other atoms.
What is an Atomic Mass?
Simply put, atomic mass is the sum of protons and neutrons in the nucleus of an atom. For instance, the oxygen atom has an atomic mass of approximately 16. Since, it contains 8 protons and 8 neutrons. Bear in mind that the number of protons does not necessarily need to be equal to the number of neutrons.
What is a Molecule?
A molecule is a stable group of atoms that are chemically bonded together. For example, the water molecule i.e. H20 is a group of one hydrogen and two oxygen atoms that attained stability by bonding together. To better understand molecules, let’s dive into the water molecule.
Above is an illustration of the water molecule which is comprised of one oxygen atom and two hydrogen atoms.
The oxygen atom has an atomic number of 8, so its electron configuration is 2 electrons in the K shell and 6 in the L shell. Bear in mind that the L shell can host 8 electrons, whereas it has hosted 6, so that leaves it with a capacity to host 2 more electrons.
The hydrogen atom has an atomic number of 1, which means its electron configuration is 1 electron in the K shell. Bear in mind that the K shell can host 2 electrons.
So when 2 hydrogen atoms and 1 oxygen atom come together in the form of a molecule, the hydrogen atoms share their 1 electron each, with the oxygen atom. And the oxygen atom also shares its one electron each with the hydrogen atoms. Consequently, the oxygen atom’s L shell then hosts its maximum capacity of 8 electrons, and both hydrogen atoms K shells also host their maximum capacity of 2 electrons each. With the final shells of all atoms hosting their maximum number of electrons i.e. 8 and 2, the molecule is now stable, hence giving birth to what we call, Water.
The type of bonding between these two atoms is called the covalent bond. In the next section we will discuss the types of bonds but first, let’s take this opportunity to understand the concept of charges.
What is a Charge?
Charges are like invisible force fields around tiny particles. There are mainly two kinds of charges. A positive charge and a negative charge. They are both like the positive and negative ends of a battery. A positive charge attracts the negative and repels the positive. And vice versa.
Positive Charge: If an atom loses one or more electrons, it becomes positively charged because it now has more protons than electrons. This creates an imbalance, with the positive charge outnumbering the negative charge, resulting in a net positive charge.
Negative Charge: Conversely, if an atom gains one or more electrons, it becomes negatively charged because it now has more electrons than protons. This creates an excess of negative charge compared to a positive charge, resulting in a net negative charge.
Now, let’s deepen our understanding of the concept of ‘charge’ by extending the discussion to the context of the H2O molecule previously explored.
Initial State: Before bonding, the oxygen atom is indeed neutral, with 8 protons and 8 electrons. Each hydrogen atom is also neutral, with 1 proton and 1 electron.
Formation of Water Molecule: When the oxygen atom forms covalent bonds with two hydrogen atoms to create a water molecule, it shares electrons with each hydrogen atom. This results in the oxygen atom gaining two additional electrons, bringing its total number of electrons to 10, and the hydrogen atom gaining one additional atom, bringing its total number of electrons to 2.
Electric Charge: Since the oxygen atom now has 10 electrons but still has 8 protons, it carries a net negative charge. Specifically, it has two more electrons than protons, giving it a charge of -2. The hydrogen atom, however, becomes slightly positive because it still has 1 proton, and the 2 electrons it now has are more on the side of the oxygen atom. To understand this, we will first need to understand Covalent Bonds.
Covalent Bonds:
A covalent bond is a type of chemical bond that involves the sharing of electron pairs between atoms. There are two main types of covalent bonds:
Polar Covalent Bonds: A polar covalent bond is a type of chemical bond between atoms where the electrons are not shared equally. Instead, one atom has a stronger pull on the shared electrons than the other, resulting in an unequally shared electron/s between the atoms.
Water (H2O) exhibits polar covalent bonds. In a water molecule, each hydrogen atom forms a polar covalent bond with the oxygen atom by sharing one electron. However, due to the higher electronegativity of oxygen compared to hydrogen, the shared electrons are pulled closer to the oxygen atom. This results in an unequal distribution of electron density, with the oxygen atom acquiring a partial negative charge (δ-), because the ratio will be more in favour of the electrons, and since the electrons are negatively charged, the whole atom will be considered as partially negatively charged.
And the hydrogen atoms acquire partial positive charges (δ+) because the oxygen atom attracts the shared electrons more strongly than the hydrogen atoms, which results in the hydrogen atoms having less electron density than proton density.
Non-Polar Covalent Bonds: Unlike the polar covalent bond, a non-polar bond involves the equal sharing of electrons. This happens because the atoms have a similar or equal electronegativity.
O2 exhibits a non-polar covalent bond, where both the oxygen atoms have equal electronegativity so both pull the electrons towards themselves with equal force resulting in an equal sharing of electrons
What is a Partial Charge:
When electrons are shared unequally among atoms, it results in a partial positive or a partial negative charge on the atoms. When electrons are shared equally among atoms, it results in no net change in the charge in the charge
Take the example of the H2O molecule. Before bonding, both; the hydrogen atoms and the oxygen atoms are neutrally charged. But when they come together in a bond, the oxygen atom shares one electron each, with the two hydrogen atoms. The hydrogen atoms also share one electron each with the oxygen atom. Thus allowing both the atoms to achieve stability. The oxygen atom, with its higher electronegativity, pulls towards itself more of the shared electrons. This creates an imbalance of the electrons to protons ratio in both atoms. The number of electrons in the oxygen atoms increases as compared to the protons, leading to a partially negative charge on the oxygen atom.
Similarly, the hydrogen atom, due to its weaker electronegativity, is not able to attract the electrons more towards itself. Because the shared electron pair spends more time around the oxygen atom, the region around the hydrogen atom becomes depleted of electron density, resulting in a partial positive charge on the hydrogen atom. This is because the hydrogen atom effectively experiences a net loss of electron density towards the oxygen atom, hence leading to a net positive charge over the hydrogen atom, since the ratio of protons to electrons is now more in favour of the protons.
What is Polarity:
Polarity refers to the distribution of electric charge in a polar molecule. For instance, in a polar bond where one atom is more electronegative, it will pull towards itself more of an electron resulting in a negative charge on that atom and the opposite on the other atom. Hence, the polarity of one atom is positive and that of the other is negative.
What is a Polar Molecule:
A polar molecule is a molecule comprising polar bonds, and polar bonds, as discussed above are a type of bond which have an uneven distribution of electrons.
What is Electronegativity:
Electronegativity is the ability of an atom to attract electrons towards itself. The higher the electronegativity, the more electrons it can attract. Take the example of the oxygen atom in the H2O molecule. It has higher electronegativity, hence it can attract the shared electrons more towards itself.
What is an Ionic Bond:
An ionic bond is a type of chemical bond which involves the complete transfer of electrons, unlike a covalent bond which is formed by the sharing of electrons.
The atom that loses electrons becomes positively charged because it now has more protons than electrons. This positively charged ion is called a cation. The atom that gains electrons becomes negatively charged because it now has more electrons than protons. This negatively charged ion is called an anion.
Above is an illustration of the Sodium Chloride Molecule (NaCl). The valence shell of the chlorine atom is unstable. It needs one more electron to achieve stability, which it does by attracting one electron from the valence shell of the sodium atom. And the sodium atom achieves stability by getting rid of the valence electrons, hence getting rid of the entire valence shell. Resultantly, the Sodium Chloride Molecule is formed, which is an Ionic Bond involving the complete sharing of electrons.
Bear in mind that the sodium atom cannot attract 7 electrons from the chlorine atom to achieve stability. That is because this is a very energy-intensive process. Additionally, sodium is not chemically predisposed to gain electrons, as it is a metal with a tendency to lose electrons to achieve stability.
Hasham Baig’s perspectives have been significantly shaped by his mentor, Komal Naimat, a master in chemistry, whose guidance is evident in the depth of her analysis.