Lecture Presentation Chapter 4 Subatomic Particles Bradley Sieve

4. 1 Physical and Conceptual Models • Atoms are so small we cannot “see”

4. 1 Physical and Conceptual Models • Atoms are imaged indirectly – Scanning probe

4. 1 Physical and Conceptual Models • Physical model – A model of something very large or very small – Replicates an object in a convenient scale • Conceptual model – Helps predict how a system behaves – The more accurate the model, the more accurately it makes predictions © 2014 Pearson Education, Inc.

Concept Check A basketball coach describes a playing strategy to her team by way of sketches on a game card. Do the illustrations represent a physical model or a conceptual model? © 2014 Pearson Education, Inc.

Concept Check The sketches are a conceptual model the coach uses to describe a system (the players on the court), with the hope of achieving an outcome (winning the game). © 2014 Pearson Education, Inc.

4. 1 Physical and Conceptual Models • Conceptual model of an atom – Contains three main parts • Electron, proton, and neutron • Planetary model of the atom – Limited in ability to make predictions – Has been updated to include shells • While limited, such models are excellent guides © 2014 Pearson Education, Inc.

4. 2 The Electron Was the First Subatomic Particle Discovered • Scientists realized that electricity could pass through glass tubes as glowing rays – Both with and without a gas in the tube © 2014 Pearson Education, Inc.

4. 2 The Electron Was the First Subatomic Particle Discovered • The rays exhibited a negative charge – Became known as cathode rays – Appeared to behave as a beam of particles © 2014 Pearson Education, Inc.

4. 2 The Electron Was the First Subatomic Particle Discovered J. J. Thomson – Reasoned that the amount of deflection related to mass and charge • The greater the mass the less the deflection • The larger the charge the more the deflection • © 2014 Pearson Education, Inc.

4. 2 The Electron Was the First Subatomic Particle Discovered Robert Millikan – Conducted the oil drop experiment – Was able to calculate the electric charge of a cathode particle • Found value to be 1. 60 x 10 -19 coulomb – Derived the cathode ray particle’s mass • Found to be 9. 1 x 10 -31 • Much less than the hydrogen atom’s mass © 2014 Pearson Education, Inc.

4. 2 The Electron Was the First Subatomic Particle Discovered © 2014 Pearson Education,

4. 2 The Electron Was the First Subatomic Particle Discovered • Electron – The particle found in cathode rays – A fundamental unit of all atoms – Exhibits a negative charge – Possesses a very small mass (9. 1 x 10 -31 kg) – Determine many physical and chemical properties of atoms © 2014 Pearson Education, Inc.

4. 3 The Mass of an Atom Is Concentrated in Its Nucleus • Plum-pudding

4. 3 The Mass of an Atom Is Concentrated in Its Nucleus Ernest Rutherford

4. 3 The Mass of an Atom Is Concentrated in Its Nucleus • Most particles passed right through the foil • Some alpha particles were deflected – Deflected particles must have interacted with a dense positively charged center • Named these centers the atomic nucleus © 2014 Pearson Education, Inc.

4. 3 The Mass of an Atom Is Concentrated in Its Nucleus • Atomic

4. 4 The Atomic Nucleus Is Made of Protons and Neutrons • Protons – Positively charged particles in the nucleus – Nearly 2000 times as massive as the electron – Number of protons is equal to number of electrons if charges are balanced • Atomic number – The number of protons an element contains © 2014 Pearson Education, Inc.

Concept Check How many protons are in an iron atom, Fe (atomic number 26)?

Concept Check The atomic number of an atom and its number of protons are the same. Thus, there are 26 protons in an iron atom. Another way to put this is that all atoms that contain 26 protons are, by definition, iron atoms. © 2014 Pearson Education, Inc.

4. 4 The Atomic Nucleus Is Made of Protons and Neutrons • Neutron – Discovered by James Chadwick in 1932 – Roughly the same mass as a proton – Exhibits no electric charge – Contributes mass to the atom along with the proton © 2014 Pearson Education, Inc.

4. 4 The Atomic Nucleus Is Made of Protons and Neutrons • Nucleons –

4. 4 The Atomic Nucleus Is Made of Protons and Neutrons Subatomic Particles ©

4. 4 The Atomic Nucleus Is Made of Protons and Neutrons • Isotopes – Atoms with the same number of protons but different numbers of neutrons – Exhibit different mass numbers © 2014 Pearson Education, Inc.

4. 4 The Atomic Nucleus Is Made of Protons and Neutrons • Isotope Symbol – Shows element, atomic number, and mass – Number of neutrons can be found by subtracting atomic number from mass © 2014 Pearson Education, Inc.

4. 4 The Atomic Nucleus Is Made of Protons and Neutrons • Atomic Mass – Total mass of an atom – Electron mass is negligible – Uses a special unit called the atomic mass unit (amu) • 1 amu is equal to 1. 661 x 10 -24 grams © 2014 Pearson Education, Inc.

4. 5 Light Is a Form of Energy • Electromagnetic waves – Oscillations of electric and magnetic fields – Wavelength • The distance between two crests of a wave – Wave frequency • Measure of how rapidly waves oscillate © 2014 Pearson Education, Inc.

4. 5 Light Is a Form of Energy • Electromagnetic spectrum – Full range

Concept Check Can you see radio waves? Can you hear them? © 2014 Pearson

Concept Check Radio waves are one type of electromagnetic radiation, but their frequency is much lower than what your eyes can detect. Nor can you hear them. A radio translates radio waves into signals that drive a speaker to produce sound waves your ears can hear. © 2014 Pearson Education, Inc.

4. 5 Light Is a Form of Energy • Spectroscope – An instrument used

4. 6 Atomic Spectra and the Quantum Hypothesis • Atoms only emit certain frequencies based on the type – Each atom type emits a discrete and distinct pattern – This pattern is called the atomic spectrum © 2014 Pearson Education, Inc.

Concept Check How might you deduce the elemental composition of a star? © 2014

Concept Check Aim a well-built spectroscope at the star, and study its spectral patterns.

4. 6 Atomic Spectra and the Quantum Hypothesis Max Planck – Hypothesized that light energy is quantized – The total amount of energy must be equal to a multiple of a fundamental unit of energy – Identified each discrete parcel as a quantum © 2014 Pearson Education, Inc.

4. 6 Atomic Spectra and the Quantum Hypothesis Niels Bohr – Explained the atomic spectra using Planck’s quantum hypothesis 1. An electron has more potential energy when farther from the nucleus 2. When an atom absorbs a photon of light, it is absorbing energy © 2014 Pearson Education, Inc.

4. 6 Atomic Spectra and the Quantum Hypothesis © 2014 Pearson Education, Inc.

4. 6 Atomic Spectra and the Quantum Hypothesis • Energy of an electron is

4. 6 Atomic Spectra and the Quantum Hypothesis • Bohr’s planetary model – Electrons

4. 6 Atomic Spectra and the Quantum Hypothesis • Bohr’s explanation of why only

4. 7 Electrons Exhibit Wave Properties • Wave-Particle Duality – Idea that matter can behave as a wave or as a particle • Electron wave behavior explains why electrons are restricted to particular energy levels © 2014 Pearson Education, Inc.

Concept Check What must an electron be doing to have wave properties? © 2014

Concept Check According to de Broglie, particles of matter behave like waves by virtue of their motion, which is a form of energy. An electron must therefore be moving to have wave properties. © 2014 Pearson Education, Inc.

4. 8 The Noble Gas Shell Model Simplifies the Energy-Level Diagram • Energy level diagrams – Shows orbitals of similar energy together – Contains seven rows of grouped orbitals • Corresponding to the seven periods of the periodic table – The higher the energy, the further the grouping from the nucleus © 2014 Pearson Education, Inc.

• Pairing of electrons occurs only after the shell is half full ©

Concept Check Why are there only two elements in the first period of the

Concept Check The number of elements in each period corresponds to the number of electrons each shell can hold. The first shell has a capacity of only two electrons, which is why the first period has only two elements. © 2014 Pearson Education, Inc.

4. 9 The Periodic Table Helps Us Predict Properties of Elements • Periodic Trend – Gradual change of a property across the periodic table – Largely due to two concepts • Inner-shell shielding • Effective nuclear charge © 2014 Pearson Education, Inc.

4. 9 The Periodic Table Helps Us Predict Properties of Elements • Inner-shell shielding – Inner shell electrons reduce the attraction of the nucleus on outer shell electrons © 2014 Pearson Education, Inc.

4. 9 The Periodic Table Helps Us Predict Properties of Elements • Effective nuclear charge – The reduced attraction the outer shell electrons experience – Abbreviated as Z* © 2014 Pearson Education, Inc.

4. 9 The Periodic Table Helps Us Predict Properties of Elements • Calculating Z*

4. 9 The Periodic Table Helps Us Predict Properties of Elements • Atomic diameter trends – Atoms in the upper right of the periodic table are smaller – This is due to two behaviors • The further left an element is, the higher the effective nuclear charge the outer electrons feel • Atoms higher on the periodic table have fewer occupied shells © 2014 Pearson Education, Inc.

4. 9 The Periodic Table Helps Us Predict Properties of Elements © 2014 Pearson

4. 9 The Periodic Table Helps Us Predict Properties of Elements • Smallest atoms have the most strongly held electrons – Exhibit higher Z* values on the outermost electrons – Have fewer inner shells, so the outer electrons are closer to the nucleus – Described by the ionization energy needed to free an electron © 2014 Pearson Education, Inc.

Concept Check Which loses one of its outermost electrons more easily: a francium, Fr,

Concept Check A francium, Fr, atom loses electrons more easily than does a helium, He, atom. Why? Because a francium atom’s outer electrons are not held as tightly by its nucleus, which is buried deep beneath many layers of shielding electrons. © 2014 Pearson Education, Inc.