Module 1: Electronic Structure of an Atom

particulate

concentration of energy

wave

vibrating disturbance by which energy is transmitted

Max Planc

light is not continuous; light absorbed in discrete packets (quanta)

excitation

depends on supplied energy

wave

have distinguishable properties and are periodic; repeat regularly both in space and time; characterized by their length and height and by the number of wares that pass through a certain point in one second

wavelength

distance between two successive troughs or crests; ses units of length (eg. nanometer, nm); inversely proportional to the frequency

frequency

number of complete waves passing through a given time; cycles/sec or Hertz, Hz

amplitude

vertical distance from the midline of a wave to a crest or trough

light

consists of electromagnetic radiation that carries energy through space in the form of waves

Electromagnetic Radiation

consists of electromagnetic radiation that carries energy through space in the form of waves; energy is emitted through space

Matter

particulate in nature

Particles

had mass; position in space can be specified

Waves

massless and delocalized

Max Planc

proposes the quantum theory

Albert Einstein

explains the photoelectric effect

Blackbody Radiation

Emission of light from hot objects; electromaghetic radiation whose wavelength and color depends on the temperature of the object; Max Planc

low

low energy, ____ frequency based on Blackbody Radiation

Blackbody Radiation

all radiation absorbed emit specific emission wavelength; continues to absorb of energy

Photoelectric effect

emission of electrons from metal surfaces on which light shines; light has both waves and particle nature

incident radiation

ejection of electrons happens immediately after _______ reaches the surface

Kinetic Energy

Another feature of Photoelectric effect is the ____ does not depend on intensity of light.

threshold frequency

below this, no electrons were ejected no matter how intense the light; above, electrons are proportional

electrons

held metal by attractive forces; removing them requires light of a sufficiently high-frequency

Emission Spectra

emission of light from electronically excited gas atoms

Quantum Theory

quantization of energy; energy can be released or absorbed by atoms only in discrete chunks

Quantum

smallest quantity of energy that can be emitted or absorbed as electromagnetic radiation

Photon

single packet of light; quantum of radiant energy › particles of light / energy

inversely proportional

Energy _________ to wavelength

Photoelectric Effect

phenomenon in which electrons are ejected from the surface of certain metals exposed to light

directly proportional

No. of ejected electrons is ________ to intensity of the light but the energies of the ejected electrons are not.

E = hv

formula for light consists of photon

minimum frequency

In order to break the electron free from the attraction of the atomic nuclei, a ________ (corresponding to min. energy) is required.

No

Is there an ejection of electron if the frequency (for energy) is not sufficient.

Dualistic Nature of Light

Depending on the circumstances being considered, light behaves either as a wave or a stream of particles.

Niels Bohr

applied the new quantum theory to the Rutherford model; provided a theoretical explanation of the emission spectrum of hydrogen atom

Continuous Spectrum

spectrum exhibited by light (eg. sunlight) passing through a prism; shows all colors

Line Spectrum

each line corresponds to a light of specific energy; the fingerprint of the elements; a spectrum in which light of only a certain wavelength is emitted or absorbed, rather than continuous

definite energy

light corresponds to light of particular wavelength

Continuous spectrum

contains all light colors

Atomic Spectra

spectrum of frequencies emitted or absorbed transitions); atom supplied by energy (ground state to high energy unstable

quantized

Energy levels of a hydrogen atom had to be _______

• certain values are allowed

• if it has any value of energy , continuous spectrum is observed.

Bohr Model

each line corresponds to a light of specific energy; the fingerprint of the elements; absorption (higher A)

Bohr orbit

defines both the energy level and the position of the electron; represents angular momentum

constant

As long as the electron remains in a given orbit, it is non-radiating – it’s energy remains _______.

Absorption

electrons can go to an orbit of higher energy

emitted

When an electron drops from a higher-energy orbit to a lower one, energy is ________.

Line Spectrum of Hydrogen

each line in the emission spectrum corresponds to a particular allowed transition in a hydrogen atom; all possible transitions are shown; brightness of the line depends on how many photons of the same wavelength are emitted

emission spectrum

came from emission of electrons (excited state to ground state); emit any wavelength (continuous)

refract

the emitted radiation _____

absorption spectrum

incident light passes to electron; not absorbed: seeen in this spectrum

Balmer Series

Frequencies of lines observed in the visible region of the spectrum of hydrogen fit sample equation; produced form excitations of hydrogen electron from n=2

Rydberg Equation

Wavelengths of visible (emission) lines and other series of lines that would be observed

Lyman Spectral Series

produced from the excitations of the hydrogen electron from n=1

Limitations of Bohr Model

1. doesn't work if more than one electron

2. can 't explain spitting

Hydrogenic atoms

atoms contain only a single elctron

small

In wave nature of particles, the momentum of such particles have to be very _____ to have an observable de Broglie wavelength.

momentum values

heavy object moving slow; light object moving fact

De Broglie’s Matter Waves

basis: dual nature of light; matter can also have dual nature

De Broglie wavelength

λ = h/mv

Schrondinger Equation

describes behavior and energies of particles (mass: particulate properties; wave function: wave properties)

definite radius

Electrons move in 3D space around the nucleus but not in an orbit of _______.

probability

The exact position of the electron at a given time cannot be exactly pinpointed; only the _______ of the electron’s location can be defined.

Heisenberg’s Uncertainty Principle

It is impossible to determine accurately both the momentum and the position of the electron (or any other small particle) simultaneously.

orbital

region of space where the electron can most likely be found

allowed energy states

Atoms and molecules exist only in certain ________

quantum numbers

allowed energy states of atoms can be described by a set of numbers

Similarities of Bohr and Wave Model

• The atom is nuclear

• The energy of the electron is quantized

• Electrons can transfer from one energy state to another by absorption of energy (quantized)

Bohr Model

Electron is treated as a particle in fixed orbits around the nucleus

Wave Model

Electron is treated mathematically as a wave and possesses both particulate and wave nature

Bohr Model

Both energy and location of the electron are defined

Wave Model

Energy of the electron can be precisely defined but it’s location cannot be exactly determined; only the probability

diffraction

redistribution of a wave when it encounters an obstancle interference

constructive interference

waves add up (+ amplitude)

destructive interference

waves disappear (- amplitude)

2 Fundamental properties that separate waves from particles

when wave is quantized, restrict to certain position and multiple momenta

Quantum Numbers

Mathematical solutions of the Schrödinger equation

atomic orbitals

first three QNs (PAM) describe _______

Spin quantum number

describes electron that reside in orbital

Principal Quantum Number

main energy level (n) ; related to the average distance of the electron from the nucleus

Higher n value

• Generally, higher energy of the orbital

• Larger size of the orbital

• Greater average distance of the electron from the nucleus

Angular Momentum Quantum Number

l; defines the shape of the orbital; divides the main levels (shells) into sublevels (subshells)

Magnetic Quantum Number

describes the orientation of an orbital in space relative to other orbitals with the same l QN

Spin Quantum Number

differentiates how electrons in the same orbital will interact with an external magnetic field

Two possible motions: Clockwise and counterclockwise

Pauli’s Exclusion Principle

• No two electrons in an atom can have the same set of four quantum numbers

• Unique set of QN for each electron in an atom

• Limits the number of electrons in any orbital to two

1 and 2

maximum no of orbitals and electrons of sublevel s

3 and 6

maximum no of orbitals and electrons of sublevel p

5 and 10

maximum no of orbitals and electrons of sublevel d

7 and 14

maximum no of orbitals and electrons of sublevel f

1 and 2

maximum no of orbitals and electrons of main level 1

4 and 8

maximum no of orbitals and electrons of main level 2

9 and 18

maximum no of orbitals and electrons of main level 3

16 and 32

maximum no of orbitals and electrons of main level 4

2n2

max electron population of a main level

Electronic Configuration

Describes the distribution of the electrons among the various atomic orbitals in an atom in the ground state

Ground state

lowest energy arrangement of the electrons around the atom

Aufbau Principle

• “Building-up” principle

• As protons are added one by one to the nucleus to build up the elements, electrons are similarly added to the atomic orbitals

• Electrons occupy the available orbitals in order of increasing energy

lower

Lower (n + l) value → _____ energy of the orbital

Hund’s Rule of Multiplicity

electrons occupy all the orbitals in given subshell singly before pairing begins; unpaired electrons have parallel spins

Diamagnetic Atoms

• weakly repelled by magnets

• all electrons are paired (magnetic effects are cancelled)

Paramagnetic Atoms

• attracted by a magnet

• have unpaired electrons (magnetic effects are reinforced)