CHEM 201: Structure and Bonding Lecture Notes

Flashcards covering atomic models, quantum numbers, and the shapes of s, p, and d orbitals based on the CHEM 201 lecture notes from Fall 2025 by Dr. Farideh Jalilehvand.

In the Bohr model, how does an electron move around the nucleus?

In a fixed path or 'orbit,' similar to planets around the sun.

What does 'n' represent in the Bohr model?

The shell (principal quantum number), which labels each orbit.

What is the relationship between the electron's distance from the nucleus and its energy in the Bohr model?

When the electron is further away from the nucleus (higher n), it has higher energy, E.

What are two key concepts from the Bohr model that were steps forward in understanding electronic structure?

The quantum number 'n' concept and the consideration of fixed energy levels for electrons.

What is a 'wavelength'?

The distance between two successive peaks or the distance from the beginning to the end of a wave cycle.

What is 'frequency'?

The number of wave cycles per second.

What are the common units for wavelength?

Meters (m), centimeters (cm), nanometers (nm), or Angstroms (Å).

What is the symbol and common units for frequency?

Symbol: nu (ν); Units: s⁻¹ or Hz (hertz).

What is the 'amplitude' of a wave?

The maximum height of a wave, related to the intensity of radiation.

What is a 'node' in a wave?

Points with zero amplitude.

When do two waves have 'constructive interference'?

When they are in-phase and their amplitudes add up.

When do two waves have 'destructive interference'?

When they are out-of-phase and their amplitudes cancel each other.

What does Heisenberg's Uncertainty Principle state?

We can either calculate the position of an electron precisely, or its energy; not both at the same time.

What two important things do orbitals define?

Their energy and their shape.

What does 'ψ²' (psi squared) represent?

The probability of finding an electron in a given space (or volume), also known as electron density.

What are the three quantum numbers used to define the probability of finding an electron in 3D space?

Principal quantum number (n), secondary quantum number (l), and magnetic quantum number (ml).

What does the principal quantum number (n) define?

The size and energy of the electron wave/orbital, representing the shell.

What does the secondary quantum number (l) define?

The shape of the orbitals, representing the subshell.

What are the letter designations for 'l' values 0, 1, 2, and 3?

s, p, d, and f, respectively.

What does the magnetic quantum number (ml) define?

The orientation of orbitals relative to each other in space.

What is the shape of all 's' orbitals?

Spherical.

What is a spherical node in an 's' orbital?

A point or region where the probability of finding an electron is zero; the number of nodes is (n-1).

What is the general shape of 'p' orbitals?

They have two lobes.

What is a 'nodal plane' in a 'p' orbital?

A plane between the lobes where electron density at each point is zero.

How many 'p' orbitals are there, and how are they oriented?

There are three p orbitals (px, py, pz) that are perpendicular to each other.

How do 3p orbitals compare to 2p orbitals in size and nodes?

3p orbitals are larger than 2p orbitals and have an additional spherical node besides the nodal plane.

How many 'd' orbitals are there?

There are five d-orbitals.

What is the general shape of four of the five 'd' orbitals (e.g., dxy, dxz, dyz, dx²-y²)?

They have four lobes with two nodal planes.

Which 'd' orbital has two nodal cones?

The dz² orbital.

What is the main difference in electron description between the Bohr model and the Schrödinger model?

The Bohr model describes electrons as particles in fixed orbits (2D), while the Schrödinger model describes electrons as wave functions (orbitals) in 3D space.

In the Bohr model, how does an electron move around the nucleus?

In a fixed path or 'orbit,' similar to planets around the sun.

What does 'n' represent in the Bohr model?

The shell (principal quantum number), which labels each orbit.

What is the relationship between the electron's distance from the nucleus and its energy in the Bohr model?

When the electron is further away from the nucleus (higher n), it has higher energy, E.

What are two key concepts from the Bohr model that were steps forward in understanding electronic structure?

The quantum number 'n' concept and the consideration of fixed energy levels for electrons.

What is a 'wavelength'?

The distance between two successive peaks or the distance from the beginning to the end of a wave cycle.

What is 'frequency'?

The number of wave cycles per second.

What are the common units for wavelength?

Meters (m), centimeters (cm), nanometers (nm), or Angstroms (Å).

What is the symbol and common units for frequency?

Symbol: nu (ν); Units: s⁻¹ or Hz (hertz).

What is the 'amplitude' of a wave?

The maximum height of a wave, related to the intensity of radiation.

What is a 'node' in a wave?

Points with zero amplitude.

When do two waves have 'constructive interference'?

When they are in-phase and their amplitudes add up.

When do two waves have 'destructive interference'?

When they are out-of-phase and their amplitudes cancel each other.

What does Heisenberg's Uncertainty Principle state?

We can either calculate the position of an electron precisely, or its energy; not both at the same time.

What two important things do orbitals define?

Their energy and their shape.

What does 'ψ²' (psi squared) represent?

The probability of finding an electron in a given space (or volume), also known as electron density.

What are the three quantum numbers used to define the probability of finding an electron in 3D space?

Principal quantum number (n), secondary quantum number (l), and magnetic quantum number (ml).

What does the principal quantum number (n) define?

The size and energy of the electron wave/orbital, representing the shell.

What does the secondary quantum number (l) define?

The shape of the orbitals, representing the subshell.

What are the letter designations for 'l' values 0, 1, 2, and 3?

s, p, d, and f, respectively.

What does the magnetic quantum number (ml) define?

The orientation of orbitals relative to each other in space.

What is the shape of all 's' orbitals?

Spherical.

Sketch a diagram of a 1s orbital and indicate any nodes.

The diagram should show a sphere representing the 1s orbital with no internal nodes.

Sketch a diagram of a 2s orbital and indicate any nodes.

The diagram should show a sphere with an inner label for the 1s orbital and an outer label for the 2s orbital. A spherical node should be indicated between these two regions. The general rule is: for an s-orbital, the number of spherical nodes is (n-1). Thus, a 2s orbital has (2-1 = 1) spherical node.

What is a spherical node in an 's' orbital?

A point or region where the probability of finding an electron is zero; the number of nodes is (n-1).

What is the general shape of 'p' orbitals?

They have two lobes.

Sketch a diagram of a $p_x$ orbital, showing its orientation and nodal plane.

The diagram should show two lobes aligned along the x-axis, with a nodal plane perpendicular to the x-axis passing through the nucleus.

What is a 'nodal plane' in a 'p' orbital?

A plane between the lobes where electron density at each point is zero.

How many 'p' orbitals are there, and how are they oriented?

There are three p orbitals (px, py, pz) that are perpendicular to each other.

Sketch diagrams of all three 'p' orbitals (px, py, pz) illustrating their spatial orientation.

The diagram should show three dumbbell-shaped orbitals: one aligned along the x-axis, one along the y-axis, and one along the z-axis, all perpendicular to each other.

How do 3p orbitals compare to 2p orbitals in size and nodes?

3p orbitals are larger than 2p orbitals and have an additional spherical node besides the nodal plane.

How many 'd' orbitals are there?

There are five d-orbitals.

Sketch a diagram of a $d_{xy}$ orbital, highlighting its lobes and nodal planes.

The diagram should show four lobes lying in the xy-plane, between the x and y axes, with two nodal planes being the xz and yz planes.

What is the general shape of four of the five 'd' orbitals (e.g., dxy, dxz, dyz, dx²-y²)?

They have four lobes with two nodal planes.

Sketch a diagram of a $d_{z^2}$ orbital, indicating its unique shape and nodal cones.

The diagram should show two main lobes along the z-axis and a donut-shaped ring around the middle (in the xy-plane), with two conical nodes.

Which 'd' orbital has two nodal cones?

The $d_{z^2}$ orbital.

What is the main difference in electron description between the Bohr model and the Schrödinger model?

The Bohr model describes electrons as particles in fixed orbits (2D), while the Schrödinger model describes electrons as wave functions (orbitals) in 3D space.