Atomic Structure: The Orbitals In chemistry, we learn that electrons in an atom don't just move around randomly. Instead, their behavior is described by a math formula called a wave equation. When scientists solve this equation, they get a wave function, also called an orbital (written as the Greek letter psi, or ψ). If you square this wave function (ψ²) and plot it in 3D, it shows the area around the nucleus where the electron is most likely to be. You can think of an orbital like a blurry photo of the electron taken with a slow camera—it shows a fuzzy cloud where the electron spends most of its time. This cloud doesn’t have a clear edge, but scientists usually say it covers the space where the electron is found about 90% to 95% of the time. There are four main types of orbitals: s, p, d, and f. They all have different shapes: s orbitals are round like a ball, with the nucleus in the center. p orbitals look like a dumbbell or a figure-eight. d orbitals have more complex shapes (Fig-1.3) —four look like clover leaves, and one looks like a long dumbbell with a ring around it. In organic and biological chemistry, we mostly deal with s and p orbitals. The orbitals in an atom are grouped into different energy levels, or shells, around the nucleus. Each shell is bigger and has more energy than the one before it. Every shell has a certain number and type of orbitals, and each orbital can hold up to two electrons. The first shell has only one - s orbital (called 1s) and can hold 2 electrons. The second shell has one 2s orbital and three 2p orbitals, so it can hold a total of 8 electrons. The third shell has one 3s orbital, three 3p orbitals, and five 3d orbitals, which adds up to a total of 18 electrons. These groups of orbitals and their energy levels are usually shown in a diagram for better understanding (Fig-1.4). Each set of p orbitals in a shell has three orbitals, named px, py, and pz, because they point in different directions—along the x, y, and z axes (Fig-1.5) in space. Each p orbital has two lobes, and in between them is a node, which is a region where there is no electron. The two lobes of a p orbital have opposite signs in the wave function, often shown in different colors in diagrams. These signs (+ and −) are not about charge, but are important when it comes to how atoms bond and how chemicals react, which we’ll learn about later. #Organic_Chemistry #Pharmacy_Education # # # # # # # # # # # # # # # # # # # #

1. In chemistry, we learn that electrons in an atom don't just move around randomly. Instead, their
behavior is described by a math formula called a wave equation. When scientists solve this
equation, they get a wave function, also called an orbital (written as the Greek letter psi, or ψ).
If you square this wave function (ψ²) and plot it in 3D, it shows the area around the nucleus where
the electron is most likely to be. You can think of an orbital like a blurry photo of the electron
taken with a slow camera—it shows a fuzzy cloud where the electron spends most of its time. This
cloud doesn’t have a clear edge, but scientists usually say it covers the space where the electron is
found about 90% to 95% of the time. There are four main types of orbitals: s, p, d, and f. They all
have different shapes: s orbitals are round like a ball, with the nucleus in the center. p orbitals look
like a dumbbell or a figure-eight. d orbitals have more complex shapes (Fig-1.3) —four look like
clover leaves, and one looks like a long dumbbell with a ring around it. In organic and biological
chemistry, we mostly deal with s and p orbitals.
The orbitals in an atom are grouped into different energy levels, or shells, around the nucleus. Each
shell is bigger and has more energy than the one before it. Every shell has a certain number and
type of orbitals, and each orbital can hold up to two
electrons.
The first shell has only one - s orbital (called 1s) and can hold 2 electrons. The second shell has
one 2s orbital and three 2p orbitals, so it can hold a total of 8 electrons. The third shell has one 3s
orbital, three 3p orbitals, and five 3d orbitals, which adds up to a total of 18 electrons.
These groups of orbitals and their energy levels are usually shown in a diagram for better
understanding (Fig-1.4).
Fig-1.4: The first shell has one
1s orbital and can hold 2
electrons. The second shell has
one 2s orbital and three 2p
orbitals, so it can hold 8
electrons. The third shell has one
3s orbital, three 3p orbitals, and
five 3d orbitals, for a total of 18
electrons. Higher shells continue
this pattern. Each orbital can hold 2 electrons, which are often shown as up and down arrows to represent
their opposite spins. Also, even though it's not always shown in diagrams, the 4s orbital actually has a
slightly lower energy than the 3d orbital, so it fills first.
Fig-1.3: Shapes of s, p, and d orbitals:
An s orbital is shaped like a ball (a
sphere). A p orbital looks like a dumbbell
with two connected lobes. Most d
orbitals look like a cloverleaf with four
lobes. Sometimes, the lobes of p and d
orbitals are drawn as teardrop shapes to
make them easier to see, but in reality,
their shape is more like a doorknob.

2. Each set of p orbitals in a shell has three orbitals, named px, py, and pz, because they point in
different directions—along the x, y, and z axes (Fig-1.5) in space. Each p orbital has two lobes,
and in between them is a node, which is a region where there is no electron. The two lobes of a p
orbital have opposite signs in the wave function, often shown in different colors in diagrams. These
signs (+ and −) are not about charge, but are important when it comes to how atoms bond and how
chemicals react, which we’ll learn about later.
Fig-1.5: Shapes of
the 2p orbitals:
There are three 2p
orbitals, and each
one is shaped like a
dumbbell with two
lobes. The three
orbitals point in
different
directions—x, y,
and z—and are
perpendicular to
each other. Each orbital has a node in the middle where there's no electron. The two lobes have opposite
signs in the wave function, which are usually shown using different colors in pictures.