Unit 8 - Why Do Electrons Matter? PDF

Unit 8 – Why do electrons matter? Mr. Alan Braschinsky Unit 7 Recap What does an atom consist of? How do you calculate AR? Equation for alpha decay Unit Outline Factual: How does the main energy level affect an atom’s chemical reactivity? How can we represent the organization of el...

Unit 8 – Why do electrons matter? Mr. Alan Braschinsky Unit 7 Recap What does an atom consist of? How do you calculate AR? Equation for alpha decay Unit Outline Factual: How does the main energy level affect an atom’s chemical reactivity? How can we represent the organization of electrons in an atom? Conceptual: How does the organization of electrons in shells contribute to an atom’s oxidation state? Debatable: To what extent could human progress be defined by its ability to control the reduction and oxidation of metals? Atomic Structure Physicists made a lot of progress for chemists Thomson – plum pudding model Rutherford – atoms contain a dense nucleus Bohr – electrons occupy orbits around the nucleus Can absorb specific, fixed amounts of energies (quantum) Schrodinger’s wave equation is the most accurate model to date Atomic Structure Electrons can be excited with a specific amount of energy When they decay, they release this energy Would you expect electrons of different elements to absorb different amounts of energy? Why? Energy level and atom’s reactivity Make two tables in your notebooks Table 1: Name of compound Chemical formula Observations Flame Test – Discussing Observations Metal vs non-metal – what is responsible for the effect? Physical change or a chemical reaction? Use the table to identify the wavelengths of colour changes Could this be used in fireworks? Emission Spectra Wavelength and frequency are inversely proportional c=fxλ c = speed of light = 3.00 x 108 m/s λ = wavelength (m) f = frequency s–1 Frequency also related to energy E=hxf h = Planck’s constant = 6.63 x 10–34 J s Unit 7 Review – Practice Problems Go to p. 164 Work through problems 1, 3 4,6 7, 9 11, 14 Atomic radius Atoms increase in size through the addition of electrons Octet rule Electrons fill the orbits nearest to the nucleus first Circular disks represent energy levels First level fills 2 electrons, second 8 etc. Electron arrangement (EA) EA is a simple way to show electron configuration Group electrons together, separated by a comma https://www.youtube.com/watch?v=hSkJzE2Vz_w Na: 2,8,1. What about Na+? Patterns Outermost shell is called the valence shell Contains valence electrons 1) Atoms of noble gas elements (except He) have 8 electrons in their valence shells 2) 2n2 describes the maximum number of electrons in any shell If n = 1, then 2 electrons 3) Shells are not always immediately filled to the maximum number of electrons Inner shell electrons are referred to as core electrons Atomic radius Radius decreases across periods, why? Nuclear charge Increases down the groups Increased shells Core electrons participate in shielding Ionization Energy Minimum energy required to eject an electron out of a neutral atom or molecule in its ground state First ionization energy (IE1) decreases down the groups and increases across the periods Going across the periods, the number of outermost electrons increases and outermost electrons are held closer to the nucleus by the increased nuclear charge Remember, the nucleus is positively charged! Electronegativity (χ) Helps to predict whether a bond is ionic or not Electronegativity – the ability of an atom to attract a pair of covalently bonded electrons Pauling scale Values are dimensioness and range between 0.8 and 4.0 What is the electronegativity of fluorine? Caesium is 0.8 Noble gases not assigned values The larger the EN difference between atoms, the more ionic character their bond has Ionic bonding occurs when the electronegativity difference is greater than 1.8 Valency Elements in each group share the same number of electrons Valency Some elements lose electrons and others gain electrons to form ions Oxidation number – number of electrons lost or gained to achieve noble gas configuration Valency Valency vs oxidation number 3 vs +3 Transition metals show variable valency Copper ions form copper(I) (Cu+) and copper(II) (Cu2+) ions Electron arrangement notation only works for 20 elements Iron = 2, 8, 14, 2 How many electrons can the third shell contain? 2n2 Third shell not filled Dot and cross diagrams Expansion of an electron shell diagram Shows how atoms of different valencies form compounds In NaCl, sodium (Na) becomes oxidized and chlorine becomes reduced OILRIG – Oxidation Is Loss, Reduction Is Gain Dot-and-cross diagrams for ionic compounds Dot-and-cross diagrams for ionic compounds Brackets are used to denote ionic bonds Electrons not shared in ionic compounds Diagrams for multiple covalent bonds Representing multiple covalent bonds = Double bond represented as four closely grouped electrons Also referred to as two electron pairs Lewis Structures Alternative method for depicting the octet rule Always focuses on valence electrons What is the octet rule? All elements in the same group have the same number of valence electrons i.e. F, Cl, Br, I etc. all have 7 valence electrons Lewis Structure Paired electrons shown as two dots side by side “Non-bonding electrons”, or simply “lone pair” Unpaired electrons shown as single dots Bracketing notation used for ionic bonds Covalent bond ionic notation Single, double and triple bonds between atoms indicated by Side-by-side dots OR Number of lines Steps to draw Lewis structures Practicing Lewis structures Water – Worked Example Redox reactions with Lewis structures Redox = reduction + oxidation What are reduction and oxidation? OILRIG Oxidation Is Loss, Reduction Is Gain Homework: Practice Lewis structures Draw the Lewis structures for Water (H2O) Nitrogen trichloride (NCl3) Carbon dioxide (CO2)