ElectronicStructureof Atoms

Chapter 4Electronic Structure

of Atoms

ElectronicStructureof Atoms

Waves

• The distance between corresponding points on adjacent waves is the wavelength ().

ElectronicStructureof Atoms

Waves• The number of waves

passing a given point per unit of time is the frequency.

• For waves traveling at the same velocity, the longer the wavelength, the smaller the frequency.

ElectronicStructureof Atoms

Electromagnetic Radiation

• All electromagnetic radiation travels at the same velocity: the speed of light (c), 3.00 x 108 m/s.

• Only Frequency and Wavelength change.

ElectronicStructureof Atoms

The Nature of Energy• The wave nature of light

does not explain how an object can glow when its temperature increases.

• Max Planck explained it by assuming that energy comes in packets called quanta.

ElectronicStructureof Atoms

Quantum

• A quantum of energy is the minimum quantity of energy that can be lost or gained by an atom.

• Planck suggested that objects emit energy in small packets called quanta.

ElectronicStructureof Atoms

The Nature of Energy

• A photon is a particle of electromagnetic radiation having zero mass and carrying a quantum of energy

ElectronicStructureof Atoms

The Nature of Energy

Another mystery involved the emission spectra observed from energy emitted by atoms and molecules.

ElectronicStructureof Atoms

Emission Spectrum• The lowest energy state of an atom is its

ground state.

• A state in which an atom has a higher potential energy than it has in its ground state is an excited state.

• When a narrow beam of light is shined through a prism, it is separated into 4 specific colors. The 4 bands are known as hydrogen’s line-emission spectrum.

ElectronicStructureof Atoms

Emission Spectrum• When 1st experimented with, scientists

expected to get a continuous range of frequencies of electromagnetic radiation and not 4 frequencies. This was known as a continuous spectrum.

• Disproving the continuous spectrum led to an entirely new atomic theory known as quantum theory.

ElectronicStructureof Atoms

Quantum Theory• Whenever an excited atom falls to its ground

state or to a lower-energy excited state, it emits a photon of radiation.

• Excited neon atoms emit light when electrons in higher energy levels fall back to the ground state or lower levels. This is what produces the neon glow.

ElectronicStructureof Atoms

The Nature of Energy• Niels Bohr adopted

Planck’s assumption and explained these phenomena in this way:

1. Electrons in an atom can only occupy certain orbits (corresponding to certain energies).

ElectronicStructureof Atoms

The Nature of Energy

2. Electrons in permitted orbits have specific, “allowed” energies; these energies will not be radiated from the atom.

ElectronicStructureof Atoms

The Nature of Energy3. Energy is only

absorbed or emitted in such a way as to move an electron from one “allowed” energy state to another.

ElectronicStructureof Atoms

Quantum Numbers• Electrons do not travel around the nucleus in

neat orbits as Bohr thought but instead in certain regions called orbitals.

• An orbital is a 3-dimensional region around the nucleus that indicates the probable location of an electron.

• Orbitals have different shapes and sizes.

ElectronicStructureof Atoms

Value of l 0 1 2 3

Type of orbital s p d f

ElectronicStructureof Atoms

• 1s = 2 electrons

• 2s = 2 electrons

• 2p = 6 electrons

• 3s = 2 electrons

• 3p = 6 electrons

• 3d = 10 electrons

• 4s = 2 electrons

• 4p = 6 electrons

• 4d = 10 electrons

• 4f = 14 electrons

ElectronicStructureof Atoms

Hund’s Rule

ElectronicStructureof Atoms

Orbital Diagrams

• Each box represents one orbital.

• Half-arrows represent the electrons.

• The direction of the arrow represents the spin of the electron.

ElectronicStructureof Atoms

ElectronicStructureof Atoms

Lithium – atomic number 11Draw the orbital notation

ElectronicStructureof Atoms

Boron’s electron configurationAtomic number = 5

ElectronicStructureof Atoms

The electron configuration of boron is 1s22s22p1. How many electrons are present in an atom of boron? What is the atomic number for boron?

Write the orbital notation for boron.

• The number of electrons is equal to the sum of the superscripts = ______

• The number of protons = electrons so the atomic number = _____

ElectronicStructureof Atoms

Write both the complete electron configuration for iron, Fe.