AP Chapter 5 Structure of the Atom

Review Quiz Chapter 5 Net Ionic Equations

Thermal Emission and Photoelectric Effect Thermal emission is the emission of electrons from very hot substances. The photoelectric effect is the emission of electrons from materials (especially active metals) that are exposed to light.

Radioactivity Radioactivity is the spontaneous breakdown of unstable atoms into more stable atoms with the simultaneous emission of particles and rays.

Radioactivity Different radioactive elements emit different amounts of three kinds of radiation (alpha, beta, and gamma). Alpha rays are helium nuclei (He 2+ ). Beta rays are electrons. Gamma rays are photons having high energy.

Radioactivity and Half - Life The half-life of carbon-14 is 5730 years. How old is a bone that has about 12.5% of the carbon-14 that a living organism would have in it?

Carbon Dating

Nuclear Chemistry a nuclear reaction is the process in which two nuclei, or else a nucleus of an atom and a subatomic particle (such as a proton, or high energy electron) from outside the atom, collide to produce products different from the initial particles.

Particles found in Nuclear Reactions Alpha Beta  - or Positron  + or Proton p + or a hydrogen nucleus ( ) Neutron n 0 ( ) Gamma rays (not truly a particle) 

Electron Capture A proton is converted into a neutron when one of the electrons in an atom is captured by the nucleus.

Electron Capture You may see energy released in this reaction in the form of a neutrino ( or e V ). Energy is always released however sometimes it is not written in the equation

Beta Emission In beta emission a neutron in the nucleus changes to a proton (that remains in the nucleus) and an electron (beta particle) is ejected. Technetium (element 43), a radioactive element that does not occur naturally on the earth was first prepared in It decays by beta emission.

Beta Emission

Positron Emission Beta Positive (β + decay) A proton is converted to a neutron and releases a positron.

Positron Emission (β + decay)  + +

Positron Emission Tomography (PET Scans)

Positron emission tomography (PET) is a nuclear medicine imaging technique that produces a three-dimensional image or picture of functional processes in the body. The system detects pairs of gamma rays emitted indirectly by a positron-emitting radionuclide (tracer), which is introduced into the body on a biologically active molecule. Three- dimensional images of tracer concentration within the body are then constructed by computer analysis. As the radioisotope undergoes positron emission decay (also known as beta positive decay), it emits a positron, an antiparticle of the electron with opposite charge. The emitted positron travels in tissue for a short distance (typically less than 1 mm, but dependent on the isotope ), during which time it loses kinetic energy, until it decelerates to a point where it can interact with an electron. The encounter annihilates both electron and positron, producing a pair of (gamma) photons. These are detected by the PET scanning device.

Alpha Particles in nuclear reactions The first radioactive element that was found, polonium, was found in 1898 by Marie and Pierre Curie. It decays by alpha emission. Alpha emission is the release of an alpha particle. ( ) This causes the nucleus to lose 2 protons and 2 neutrons. Therefore the atomic number is reduced by 2 and the mass number is reduced by 4.

Alpha Emission

Gaining an alpha particle in a nuclear reaction

Alpha Particles in nuclear reactions The first element prepared by artificial means was prepared in 1919 by bombarding nitrogen atoms with alpha particles. This caused the nitrogen nucleus to increase in mass.

Alpha Particles in nuclear reactions The N and He have a total of 9 neutrons and 9 protons. In forming O a proton is lost leaving us with 8 protons and the number of neutrons stays at 9.

Lord Ernest Rutherford (1871 – 1937) Discovered the nucleus of the atom.

Rutherford’s Gold Foil Experiment

Rutherford’s Nuclear Model of the Atom The nucleus is very small, dense, and positively charged. Electrons surround the nucleus which contains the protons and “neutrons”. Most of the atom is empty space

Subatomic Particles PARTICLESYMBOLCHARGEMASS (amu) LOCATION electrone-e- 00 orbit nucleus protonp+p+ +1 11 inside nucleus neutronn0n0 0 11 inside nucleus

Electromagnetic Waves Properties of waves include speed, frequency, wavelength and energy All electromagnetic waves including light travel at a speed of 3 x 10 8 m/s. However the frequency, wavelength and energy of the waves vary.

) Wavelength ( ) Measured in units of length: m, nm, A º

) Frequency ( ) Measured in cycles/second = hertz (Hz)

Visible Light

For all waves = cFor all waves = c c = the speed of light = 3.00 x 10 8 m/s Electromagnetic Radiation

A photon of red light has a wavelength of 665 nm. What is the frequency of this light?

665 nm = 665 x m

A photon of red light has a wavelength of 665 nm. What is the frequency of this light? 665 nm = 665 x m c =

A photon of red light has a wavelength of 665 nm. What is the frequency of this light? 665 nm = 665 x m c = = c ÷ = 3.00 x 10 8 m/s ÷ 665 x m

A photon of red light has a wavelength of 665 nm. What is the frequency of this light? 665 nm = 665 x m c = = c ÷ = 3.00 x 10 8 m/s ÷ 665 x m = x /s or Hz

A photon of red light has a wavelength of 665 nm. What is the frequency of this light? 665 nm = 665 x m c = = c ÷ = 3.00 x 10 8 m/s ÷ 665 x m = x /s or Hz = 4.51 x /s or Hz

An x-ray has a frequency of 7.25 x Hz. What is the wavelength?

7.25 x Hz = 7.25 x /s

An x-ray has a frequency of 7.25 x Hz. What is the wavelength? 7.25 x Hz = 7.25 x /s c =

An x-ray has a frequency of 7.25 x Hz. What is the wavelength? 7.25 x Hz = 7.25 x /s c = = c ÷ = 3.00 x 10 8 m/s ÷ 7.25 x /s

An x-ray has a frequency of 7.25 x Hz. What is the wavelength? 7.25 x Hz = 7.25 x /s c = = c ÷ = 3.00 x 10 8 m/s ÷ 7.25 x /s = x m

An x-ray has a frequency of 7.25 x Hz. What is the wavelength? 7.25 x Hz = 7.25 x /s c = = c ÷ = 3.00 x 10 8 m/s ÷ 7.25 x /s = x m = 4.14 x m

For all waves: E = hFor all waves: E = h h = 6.63 x J s or J/Hz Energy of Electromagnetic Radiation

A photon of red light has a wavelength of 665 nm. What is the energy of this light?

665 nm = 665 x m c = = c ÷ = 3.00 x 10 8 m/s ÷ 665 x m = x /s or Hz = 4.51 x /s or Hz

A photon of red light has a wavelength of 665 nm. What is the energy of this light? 665 nm = 665 x m c = = c ÷ = 3.00 x 10 8 m/s ÷ 665 x m = x /s or Hz = 4.51 x /s or Hz E = h = (6.63 x J s)(4.51 x /s)

A photon of red light has a wavelength of 665 nm. What is the energy of this light? 665 nm = 665 x m c = = c ÷ = 3.00 x 10 8 m/s ÷ 665 x m = x /s or Hz = 4.51 x /s or Hz E = h = (6.63 x J s)(4.51 x /s) E = x J

A photon of red light has a wavelength of 665 nm. What is the energy of this light? 665 nm = 665 x m c = = c ÷ = 3.00 x 10 8 m/s ÷ 665 x m = x /s or Hz = 4.51 x /s or Hz E = h = (6.63 x J s)(4.51 x /s) E = x J = 2.99 x J

An x-ray has a frequency of 7.25 x Hz. What is it’s energy?

E = h = (6.63 x J/Hz)(7.25 x Hz)

An x-ray has a frequency of 7.25 x Hz. What is it’s energy? E = h = (6.63 x J/Hz)(7.25 x Hz) E = x J

An x-ray has a frequency of 7.25 x Hz. What is it’s energy? E = h = (6.63 x J/Hz)(7.25 x Hz) E = x J E = 4.81 x J

wavelength, frequency and energy = 665 x m = 4.51 x Hz E = 2.99 x J = 4.14 x m = 7.25 x Hz E = 4.81 x J Red Light X-ray

Wavelength, frequency and energy Wavelength and frequency have an indirect relationship. Energy and frequency have a direct relationship. Electromagnetic radiation of short wavelength will have high frequency and high energy. Electromagnetic radiation of long wavelength will have low frequency and low energy.

Bohr Model of the Atom The Bohr atomElectrons orbit the nucleus in orbits that represent specific quantities of energy. The energies of the electrons in the atom are quantized. Only certain electron orbits (energy levels) are allowed. The Bohr Atom

Ground State The lowest energy state of an atom.

Excited State Any energy state of an atom that is of higher in energy than the ground state.

Energy Absorbed

Absorption (Dark – Line) Spectra

Energy Emitted Electron jumps to a lower orbit

Emission (Bright – Line) Spectra

Emission Spectra

The lines present in an emission spectrum are the lines missing in an absorption spectrum.

Star Finder Video Electromagnetic Spectrum

Star Finder Video Fingerprints of Light

Heisenberg’s Uncertainty Principle It is impossible to accurately determine the momentum (velocity) and location of a particle simultaneously. Introduced probability to atomic structure which lead to the development of the quantum – mechanical (electron cloud) model of the atom.

Quantum – Mechanical Model (Electron Cloud) The electron cloud is a visual representation of the most probable locations for an electron within an atom. “Clarity through fuzziness”

Energy Levels – Sublevels - Orbitals Electrons in an atom are within atomic orbitals which are within sublevels which are within energy levels. Chemistry uses quantum numbers to describe these electrons.

The Principal Quantum Number (n) n = 1, 2, 3, 4... Electrons with the same value of “n” within an atom are in the same energy level or shell. The principal quantum number n represents the relative overall energy of an electron and the energy of each electron increases as the distance from the nucleus increases. Example: An electron with n = 2 is further from the nucleus and therefore has more energy than an electron with n = 1.

l) The Azimuthal Quantum Number ( l) l = 0…(n – 1).l = 0…(n – 1). Orbitals with the same value of “n”Orbitals with the same value of “n” may have different shapes. The “ l ” value indicates the shape of the orbitals. may have different shapes. The “ l ” value indicates the shape of the orbitals. lElectrons with the same value of “ l ” within an atom are in the same sublevel or subshell. Example: In the fourth energy level (n = 4) there are four different orbital shapes possible designated l = 0, 1, 2 or 3.Example: In the fourth energy level (n = 4) there are four different orbital shapes possible designated l = 0, 1, 2 or 3.

l) The Azimuthal Quantum Number ( l) Orbital Shapes Page 143

Magnetic Quantum Number (m) llm = - l …0…+ l. Orbitals within an energy level with the l same value of l have the same shape and energy (degenerate) but differ in their orientation. Each possible orientation of the orbital has a specific value of “m”. Electrons with the same value of “m” are in the same atomic orbital (the region of space that an electron is most likely to be found within an atom).

Magnetic Quantum Number (m) l = 1 then m has three possible orientations designated:Example: If l = 1 then m has three possible orientations designated: m = -1, 0 or +1.

Possible Orientations of a “p” atomic orbital Page 143

Possible Orientations of a “d” atomic orbital Page 144

Possible Orientations of a “f” atomic orbital Page 144

Pauli Exclusion Principle No two electrons in the same atom can have the same set of four quantum numbers.

Spin Quantum Number (s) S = +1/2 or -1/2 Specifies the direction of spin of the electron on its axis. Spins are designated up or down.

Electron Spin Opposite spins produce opposite magnetic fields. +1/2-1/2

The Maximum Number of Electrons Possible in an Energy Level 2n 2

Electron Configuration 4d 7 7 electrons are in the d sublevel in the 4 th energy level

Arrow Diagrams s 3p 3d s 2p s 4p 4d 4f s 5p 5d 5f s 6p 6d s 7p

Write the electron configuration for lead (Z = 82).

The periodic table and electron configuration.

© 1998 by Harcourt Brace & Company s p d (period-1) f (period-2) 6767 Periodic Table and Electron Configuration

[Ar]4s 2 3d 10 4p 2 C. Periodic Patterns Example - Germanium

© 1998 by Harcourt Brace & Company 6767 Write the abbreviated electron configuration for lead (Z = 82) using the periodic table. O

Orbital Filling Diagrams

A. General Rules Pauli Exclusion Principle –Each orbital can hold TWO electrons with opposite spins.

Correct Incorrect A. General Rules Hund’s Rule –Within a sublevel, place one e - per orbital before pairing them. –All electrons in singly filled orbitals have the same direction of spin.

O 8e - Orbital Diagram Electron Configuration 1s 2 2s 2 2p 4 B. Notation 1s 2s 2p

Write the quantum numbers that represent each of the electrons within an oxygen atom

The first two electrons designated 1s 2 would have the quantum numbers. 1, 0, 0, +1/2 1, 0, 0, -1/2

Full energy level Full sublevel (s, d, f). The “p” is not listed here because it is part of the full energy level Half-full sublevel (only for p, d, f) D. Stability

Electron Configuration Exceptions –Copper EXPECT :[Ar] 4s 2 3d 9 ACTUALLY :[Ar] 4s 1 3d 10 –Copper gains stability with a full d-sublevel which is of lower energy and is therefore the ground state of copper. D. Stability

Electron Configuration Exceptions Chromium EXPECT :[Ar] 4s 2 3d 4 ACTUALLY :[Ar] 4s 1 3d 5 Chromium gains stability with a half-full d-sublevel which is of lower energy and is therefore the ground state of chromium. D. Stability