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Electron Configuration EQ: How are electrons arranged around an atom? HEISENBURG UNCERTAINTY PRINCIPLE: • Impossible to know precisely both velocity & position of a particle at the same time. • In order to find position of an electron, need photon of light. • Photon “bumps” into electron, changing its position. Quantum – Mechanical Model of the Atom • Our current model. • Atomic Orbital: – Describes the electron’s probable location – 3-D region around the nucleus; a blurry cloud of negative charge (discuss with your neighbor) Compare and contrast the plum pudding model and the quantum mechanical model. Electron Configuration • This is the arrangement of electrons in an atom. • Electrons are arranged so that the atom has the lowest possible energy • The most stable electron arrangement is called the element’s ground-state electron configuration Arrangement of Electrons in Atoms Electrons in atoms are arranged as: LEVELS (n) SUBLEVELS (l) •Each energy level has a number called the Principal Quantum Number, n •Currently n can be 1 thru 7, because there are 7 periods on the periodic table Learning Check 1. Who wrote the uncertainty principle? 2. What was uncertain about it? 3. Create a simile, metaphor, or other figure of speech to help you remember this principle. 4. How many energy levels are there and what do the correspond to? Sublevels • The most probable area to find electrons takes on a particular shape. • So far, we have 4 shapes. They are named s, p, d, and f. • No more than 2 e- assigned to an orbital – one spins clockwise, one spins counterclockwise. 4 Orbitals (s, p, d and f) f-orbitals The Four Orbitals • All s orbitals are spherical shaped (1 per level) • All p orbitals are dumbbell shaped and along three axis’s (x, y, z) (3 per level) • All d (5 per level) and f (7 per level) orbitals are complex shapes Orbitals and Electron Capacity of the First Four Principle Energy Levels Number of Maximum Principle Number of Type of orbitals number of energy orbitals sublevel per electrons level (n) per type level(n2) (2n2) 1 s 1 1 s 2 4 8 p 3 1 3 p 9 d 5 s 1 3 4 32 d f 7 Orbitals and Electron Capacity of the First Four Principle Energy Levels Number of Maximum Principle Number of Type of orbitals number of energy orbitals sublevel per electrons level (n) per type level(n2) (2n2) 1 s 1 1 2 s 1 2 4 8 p 3 s 1 3 p 3 9 18 d 5 s 1 p 3 4 16 32 d 5 f 7 Aufbau principle • Each electron occupies the lowest energy orbital available • They are filled in order s, p, d, and f (there is some overlap between d and f) Learning Check 1. Which orbital is the simplest? Why? 2. (think and pair share) Which orbital do you like the best? Why? Pauli exclusion principle • a maximum of two electrons may occupy a single atomic orbital, but only if the electrons have opposite spins Hund’s rule • Single electrons with the same spin must occupy each equal-energy orbital before additional electrons with opposite spins can occupy the same orbitals. • Ex. p then p _ Quiz • According to Aufbau, electrons fill the orbital having the _________ energy. • Pauli’s Exclusion Principle states that if 2 electrons are in the same orbital they must have __________ spins. • Hund’s Rule states that when filling p, ____, and f orbitals, you must first fill in a single electron, same _________ in each orbital before pairing up. See Other Powerpoint Writing Configurations • Start by finding the number of electrons in the atom • Identify the sublevel that the last electron added is in by looking at the location in periodic table • Draw out lines for each orbital beginning with 1s and ending with the sublevel identified • Add arrows individually to the orbitals until all electrons have been drawn Electron Configurations 4 Number of electrons in the sublevel Energy Level Sublevel 1s2 2s2 2p6 3s2 3p6 4s2 3d10 4p6 5s2 4d10 5p6 6s2 4f14… What is the ending configuration for the following elements? • • • • • • • • • • H He Li Na Mg Al Ar K Sc (“d” is 1 step behind) U (“f” is 2 steps behind) ELECTRON NOTATION • Summarize electron configuration. • 1s2 2s2 2p4 NOBLE GAS NOTATION: • 1) Write previous noble gas in brackets. • 2) Then write each block that is left over. • Ex. for P, # 15. What is the previous noble gas? • 1) Write previous noble gas: Ne • This represents Neon’s 10 electrons. • 2) Write what is left over: • Ne 3s23p3. VALENCE ELECTRONS • Electrons in the atom’s outermost energy level • Include: s & p orbitals only or • Look at the Group Number • Which group has a full set of valence electrons? The Noble gases. This is what makes the noble gases stable. Electron Dot/Lewis Dot Diagrams • A visual representation used by scientists to help show chemical bonds • Only involves valence electrons • Consists of the elements symbol, which represents the innermost electrons too, and the valence electrons surrounding it. • Example: Lithium has 3 electrons but only 1 valence----Li • The number of valence electrons determines how many and what this atom (or ion) can bond to in order to make a molecule Valence Electrons • In order to be stable, atoms must empty or fill their outermost level. • Since the outer level contains two s electrons and six p electrons (d & f are always in lower levels), the optimum number of electrons is eight. • This is called the octet rule. EQ #3 What is the orbital configuration of a neutral atom? EQ #11 How can an element be identified by light emission and the movement of electrons? WAVE NATURE OF LIGHT: Important in understanding electrons. • Electromagnetic radiation – This is the form of energy which includes visible light, microwaves, X-rays, radio waves, etc. Long wavelength --> small frequency Short wavelength --> high frequency ELECTROMAGNETIC RADIATION TRAVELS IN WAVES • Wavelength () – distance between 2 waves • Units: m, cm, nm (1nm = 1 x 10-9 m) • Frequency () - # waves that pass a given point per second • Units: waves/sec, hertz (1 wav/s = 1 hz) • Amplitude - wave’s height from origin (middle) to crest. PARTICLE NATURE OF LIGHT: Explains why heated objects emit specific frequencies of light. • Iron – dark gray at room temperature, red when hotter, bluish when very hot. • It is emitting a photon of light that carries the electromagnetic radiation. VELOCITY: All electromagnetic radiation travels at the speed of light, “c”. • c = 3.00 x 108 m/s • c = • Wavelength & frequency: inversely proportional • If wavelength increases, frequency decreases. WHITE LIGHT: Prism separates into a continuous spectrum -- ROYGBIV Red Light – Lower Frequency (longer wavelength) than violet light. Quiz • 1) Name 3 types electromagnetic radiation. • 2) What is the velocity of all electromagnetic radiation? • 3) The distance between waves is ____(). • 4) The number waves per second is ___(). • 5) The higher the frequency, the ___the wavelength. • 6) A prism separates white light into the ___ spectrum. MAX PLANCK (1900) Quantum concept of energy: • Matter gains or loses energy in small specific amounts called quanta. • Quantum – minimum amount of energy that can be gained/lost by an atom. ATOMIC EMISSION SPECTRA: Set of frequencies of electromagnetic waves emitted by atoms of an element • Spectrum is unique for each element. • Ex. Strontium atoms – Emit a characteristic red color. • Can use spectrum to identify an element. • Atomic spectrum consists of several individual lines of color • (Not continuous). Flame Tests •Elements emit a characteristic color. •When the element is heated and gains energy, the electron moves to higher energy level. •When electron returns to the ground state, a photon of light is emitted corresponding to the difference in energy An excited lithium atom emitting a photon of red light to drop electrons to a lower energy state. An excited H atom returns to a lower energy level. Quiz • The set of frequencies emitted by atoms of an element is called the atomic ____ _____. • In the flame tests, what causes the characteristic color of the element? EQ #11 How can an element be identified by light emission and the movement of electrons? EQ #4 How does an atom’s electron configuration affect its chemical properties? Valence Electron Review • Electrons in the atom’s outermost energy level • Include: s & p orbitals only or • Look at the Group Number • Which group has a full set of valence electrons? • The Noble gases. This is what makes the noble gases stable. Valence Electrons Review • In order to be stable, atoms must empty or fill their outermost level. • Since the outer level contains two s electrons and six p electrons (d & f are always in lower levels), the optimum number of electrons is eight. • This is called the octet rule. Write Orbital Notation for each of the following and determine the number of valence electrons. Will each of these gain or lose electrons for a stable octet? • • • • Lithium Magnesium Chlorine Sulfur Bohr’s Model Increasing energy Fifth Fourth Third Second First Nucleus Further away from the nucleus means more energy. There is no “in between” energy Energy Levels Bohr’s Model Nucleus Electron Orbit Energy Levels Bohr Model • We use the Bohr Model because of the simplicity of drawing the valence electrons and the sharing or loss/gain of these valence electrons. • Nucleus is far too large relative to the distance of the electrons. • Remember that electrons do not orbit the nucleus, but drawing and using a model of the quantum mechanical atom is complex. Valence Electrons and Chemical Properties • The number of valence electrons determines the atom’s ability to gain, lose, or share electrons to combine and form compounds. • Atoms gain or share valence electrons in order to achieve a stable noble gas configuration with a full energy level. EQ #4 How does an atom’s electron configuration affect its chemical properties? EQ #12 Compare and contrast the types of chemical bonds. Periodic Table • Metals – Cations (+) • Nonmetals – Anions (-) • Metalloids Cations • Metals • Positive Ion • Metal atoms loses 1 or more valence electrons to have a stable octet. Anions • Nonmetals • Negative Ion • Nonmetal atoms gain electrons to have a stable octet (8) in valence shell. Periodic Table • Main Group Elements • Transition Metals • Inner Transition Metals Chemical Bond • The force of attraction between two elements. • Three Types of Bonds: 1. Ionic 2. Covalent Polar and Nonpolar 3. Metallic 1. Ionic Bonds Transfer of electrons (from metal to nonmetal). 1. Ionic Bonds continued • The bone represents an electron. • The dog that takes the bone is negative. • The dog that loses the bone is positive. 1. Ionic Bonds continued • Electrons are transferred from a metal to a nonmetal. – Cations give up electrons; anions take electrons – Both atoms achieve an octet in their outermost orbital – The attractive forces bring the cation and anion together Ionic Bonds Quiz • 1) In an ionic bond, electrons are _____. • 2) The type of electrons involved are ___ or outer shell electrons. • 3) Metals ___ electrons, nonmetals ___ electrons in order to get a ___ gas configuration (stable octet). • 4) Cations have a __ charge and are formed by __. • 5) Anions have a __ charge and are formed by __. • 6) ____ charges hold the compound together. 2. Covalent Bonds • Valence Electrons are shared by both atoms – Between nonmetals and nonmetals – Electron pairs form a bond – Both atoms achieve an octet in their outermost orbital 2. Covalent Bonds Continued 2 Types of Covalent bonds • 1. Polar Covalent: Electrons are shared unequally. 2. Nonpolar Covalent Electrons are shared equally. Polar Covalent Molecules • Unevenly matched but willing to share • Stronger dog gets a larger portion of the bone • Element that’s more electronegative pulls the pair of electrons towards it Nonpolar Covalent Molecules • Dogs of equal strength • Both dogs have equal attraction for the bone 3. Metallic Bonds • Occur when the large d and f sublevels of transition metals overlap and allow the electrons to travel freely between them. 3. Metallic Bonds continue • “Mellow dogs with plenty of bones to go around.” • Electrons move through the substance with little restriction EQ #12 Compare and contrast the types of chemical bonds. EQ #6 Compare and contrast alpha, beta, and gamma radiation. Keep in Mind: Nuclear Reactions vs. Chemical Changes • Nuclear reactions involve the nucleus (protons and neutrons and electrons) (change of element). • Chemical Reactions involve electrons (bonding) (no change of element). • The opening of the nucleus releases a tremendous amount of energy. • Chemical reactions involve releases of smaller amounts of energy. What is Radiation? • When an unstable isotope nucleus decays (to become more stable), radiation is released. • This releases a tremendous amount of energy. • The element decays into a new element. • There are three types of radiation 1. alpha 2. beta 3. gamma TYPES OF RADIATION Type Relative Size and Composition Penetration Alpha Large Helium Nucleus (positive +) Very Small Electrons (negative -) Sheet of Paper Beta Gamma Not a particle, only energy (no size, no charge) Aluminum Foil Lead Shielding EQ #6 Compare and contrast alpha, beta, and gamma radiation. EQ #7 Compare and contrast fission and fusion. Fission Fusion Fission • This is the process of breaking larger, unstable atoms apart into smaller ones. • Fission releases tremendous amounts of energy. • Nuclear power plants Chain Reaction Fission – Chain Reaction Fission in Nuclear Power Plants Fission in Nuclear Power Plants Fusion • Fusion is the process of fusing together smaller elements to make larger ones. • Fission releases tremendous amounts of energy. • Occurs in the sun and other stars. EQ #7 Compare and contrast fission and fusion. EQ #8 How does nuclear fusion create all elements heavier than helium? Fusion • In stars, nuclear fusion of hydrogen atoms with other elements creates elements with even larger atomic numbers. EQ #8 How does nuclear fusion create all elements heavier than helium? EQ #10 What are the pros and cons to nuclear energy as an alternative energy source? Nuclear Energy Pros • Nuclear energy does not cause air pollution. Cons • There is a limited amount of nuclear fuel. • The spent fuel is radioactive, causing a transportation and storage issue. • The water used in the cooling process can cause problems when released into the environment. Nuclear Power Plant Locations Nuclear Fission and Power • Currently about 103 nuclear power plants in the U.S. and about 435 worldwide. • 17% of the world’s energy comes from nuclear energy. EQ #10 What are the pros and cons to nuclear energy as an alternative energy source? EQ #9 How is the process of half-life related to radioactive decay? Decay of 20.0 mg of 15O. What remains after 3 half-lives? _____ After 5 half-lives? _____ Half-Life • Half-life is the average time for one-half of a radioisotope to decay into more stable isotopes. • The amount of the radioisotope follows the sequence ½, ¼, 1/8, 1/16 …0 after each half-life. Don’t Forget: Radiation is released during radioactive decay. Half-Life Problem: • The half-life of tritium, H-3 is 12 years. • If you start with 200 g of tritium, then how many half-lives have passed if you only have 25 g remaining? • 200 g 100 g (1 half-life) • 100 g 50 g (2 half-lives) • 50 g 25 g (3 half-lives) • Ans. 3 half-lives. Half-Life Quiz • Half-life of Ra-222 is 3.8 seconds. How much of a 200 g sample remains after 11.4 seconds? • # half-lives = 11.4 sec/3.8 sec = 3 • After 0 half-life = 200 g (0 s) • 1 = 100 g (3.8s) • 2 = 50 g (7.6s) • 3 = 25 g (11.4s) Half-Life Quiz • What is the half-life of an isotope of Tritium (H-3) if a 400 g sample decays to 50 g in 36 years? • Find # half lives: • • • 400 g = 0 half life 200 g = 1 half life 100 g = 2 half lives 50 g = 3 half lives • It took 36 years for 3 half-lives. • 36 years/3 half-lives • = 12 yrs./half-life EQ #9 How is the process of half-life related to radioactive decay? Atomic Theory The End