Presentation on theme: "Unit 2 – Electrons and Periodic Behavior"— Presentation transcript:
1 Unit 2 – Electrons and Periodic Behavior Cartoon courtesy of NearingZero.net
2 Wave-Particle Duality JJ Thomson won the Nobel prize for describing the electron as a particle.His son, George Thomson won the Nobel prize for describing the wave-like nature of the electron.The electron is a particle!The electron is an energy wave!
3 The Wave-like Electron The electron propagates through space as an energy wave. To understand the atom, one must understand the behavior of electromagnetic waves.Louis deBroglie
4 Spectroscopic analysis of the visible spectrum… …produces all of the colors in a continuous spectrum
5 Electron transitions involve jumps of definite amounts of energy. This produces bandsof light with definitewavelengths.
6 Quantum NumbersEach electron in an atom has a unique set of 4 quantum numbers which describe it.Principal quantum numberAngular momentum quantum numberMagnetic quantum numberSpin quantum number
7 Pauli Exclusion Principle No two electrons in an atom can have the same four quantum numbers.WolfgangPauli
8 Principal Quantum Number Generally symbolized by n, it denotes the shell (energy level) in which the electron is located.Number of electrons that can fit in a shell:2n2
9 Angular Momentum Quantum Number The angular momentum quantum number, generally symbolized by l, denotes the orbital (subshell) in which the electron is located.
10 Magnetic Quantum Number The magnetic quantum number, generally symbolized by m, denotes the orientation of the electron’s orbital with respect to the three axes in space.
11 Assigning the NumbersThe three quantum numbers (n, l, and m) are integers.The principal quantum number (n) cannot be zero.n must be 1, 2, 3, etc.The angular momentum quantum number (l) can be any integer between 0 and n - 1.For n = 3, l can be either 0, 1, or 2.The magnetic quantum number (m) can be any integer between -l and +l.For l = 2, m can be either -2, -1, 0, +1, or +2.
12 Principle, angular momentum, and magnetic quantum numbers: n, l, and ml
13 Spin Quantum NumberSpin quantum number denotes the behavior (direction of spin) of an electron within a magnetic field.Possibilities for electron spin:
14 An orbital is a region within an atom where there is a probability of finding an electron. This is a probability diagram for the s orbital in the first energy level…Orbital shapes are defined as the surface thatcontains 90% of the total electron probability.
15 Sizes of s orbitals Orbitals of the same shape (s, for instance) grow larger as n increases…Nodes are regions of low probability within anorbital.
16 The s orbital has a spherical shape centered around the origin of the three axes in space.s orbital shape
17 P orbital shape There are three dumbbell-shaped p orbitals in each energy level above n = 1, each assigned toits own axis (x, y and z) in space.
18 Things get a bit more complicated with the five d orbitals that are found in the d sublevels beginning with n = 3. To remember the shapes, think of “double dumbells”d orbital shapes…and a “dumbellwith a donut”!
28 PeriodThe Periodic TableGroup or FamilyGroup or familyPeriod
29 The Properties of a Group: the Alkali Metals Easily lose valence electron(Reducing agents)React violently with waterLarge hydration energyReact with halogens to formsalts
30 Properties of MetalsMetals are good conductors of heat and electricityMetals are malleableMetals are ductileMetals have high tensile strengthMetals have luster
31 Examples of MetalsPotassium, K reacts with water and must be stored in keroseneCopper, Cu, is a relatively soft metal, and a very good electrical conductor.Zinc, Zn, is more stable than potassiumMercury, Hg, is the only metal that exists as a liquid at room temperature
32 Properties of Nonmetals Carbon, the graphite in “pencil lead” is a great example of a nonmetallic element.Nonmetals are poor conductors of heat andelectricityNonmetals tend to be brittleMany nonmetals are gases at room temperature
33 Examples of NonmetalsMicrospheres of phosphorus, P, a reactive nonmetalSulfur, S, was once known as “brimstone”Graphite is not the only pure form of carbon, C. Diamond is also carbon; the color comes from impurities caught within the crystal structure
34 Properties of Metalloids Metalloids straddle the border between metals and nonmetals on the periodic table.They have properties of both metals and nonmetals.Metalloids are more brittle than metals, less brittle than most nonmetallic solidsMetalloids are semiconductors of electricitySome metalloids possess metallic luster
35 Silicon, Si – A Metalloid Silicon has metallic lusterSilicon is brittle like a nonmetalSilicon is a semiconductor of electricityOther metalloids include:Boron, BGermanium, GeArsenic, AsAntimony, SbTellurium, Te
36 Determination of Atomic Radius: Half of the distance between nucli incovalently bonded diatomic molecule"covalent atomic radii"Periodic Trends in Atomic RadiusRadius decreases across a periodIncreased effective nuclear charge dueto decreased shieldingRadius increases down a groupAddition of principal quantum levels
38 Increases for successive electrons taken from the same atom Ionization Energy - the energy required to remove an electron from an atomIncreases for successive electrons taken fromthe same atomTends to increase across a periodElectrons in the same quantum level donot shield as effectively as electrons ininner levels Irregularities at half filled and filledsublevels due to extra repulsion ofelectrons paired in orbitals, making themeasier to removeTends to decrease down a groupOuter electrons are farther from thenucleus
42 Electronegativity A measure of the ability of an atom in a chemical compound to attract electronsElectronegativities tend to increase acrossa periodElectronegativities tend to decrease down agroup or remain the same
45 Ionic Radii Cations Anions Positively charged ions formed when an atom of a metal loses one ormore electronsCationsSmaller than the correspondingatomNegatively charged ions formedwhen nonmetallic atoms gain oneor more electronsAnionsLarger than the correspondingatom