Hewitt Suchocki Hewitt Conceptual Physical Science Fourth Edition Chapter 15 HOW ATOMS BOND AND MOLECULES ATTRACT Copyright 2008 Pearson Education Inc publishing as Pearson Addison Wesley This lecture will help you understand Electron Dot Structures The Formation of Ions Ionic Bonds Metallic Bonds Covalent Bonds Polar Covalent Bonds Molecular Polarity Molecular Attractions Copyright 2008 Pearson Education Inc publishing as Pearson Addison Wesley Electron Dot Structures Atoms bond together through their electrons To learn about bonding therefore we need to know something about how the electrons within an atom are organized Electrons behave as though they are contained within a series of seven concentric shells Copyright 2008 Pearson Education Inc publishing as Pearson Addison Wesley Electron Dot Structures The numbers indicate the maximum number of electrons each shell may contain Note This is a conceptual model and not a representation of what an atom looks like Rather it helps us to understand how the electrons within atoms behave Copyright 2008 Pearson Education Inc publishing as Pearson Addison Wesley The shells are more easily drawn in two dimensions Each atom has its own configuration of electrons Elements in the same group have similar configurations which is why they have similar properties Copyright 2008 Pearson Education Inc publishing as Pearson Addison Wesley Electron Dot Structures Valence electrons Electrons in the outermost shell of an atom These are the ones that can participate in chemical bonding Electron dot structure A notation showing the valence electrons surrounding the atomic symbol Copyright 2008 Pearson Education Inc publishing as Pearson Addison Wesley In class activity 1 Draw the dot diagram for sodium and chlorine ATOMS Copyright 2008 Pearson Education Inc publishing as Pearson Addison Wesley Special Note For heavier atoms some valence electrons are more available than others Krypton for example has 18 valence electrons but only eight of these are typically shown within an electron dot structure These are the eight that extend farthest away from the nucleus Kr Copyright 2008 Pearson Education Inc publishing as Pearson Addison Wesley Electron Dot Structures Note that elements within the same group have the same electron dot structure Copyright 2008 Pearson Education Inc publishing as Pearson Addison Wesley Electron Dot Structures CHECK YOUR ANSWER Sodium Na atomic number 11 has only one valence electron Upon losing this electron what other atom in the periodic table does the sodium thus resemble A B C D Neon Ne atomic number 10 Magnesium Mg atomic number 12 Lithium Li atomic number 3 Sodium can only resemble sodium Explanation With 10 electrons the sodium has enough electrons to fill the first and second shells just like neon Ne Copyright 2008 Pearson Education Inc publishing as Pearson Addison Wesley The Formation of Ions Ion An atom that has lost or gained one or more electrons Copyright 2008 Pearson Education Inc publishing as Pearson Addison Wesley The Formation of Ions Ion An atom that has lost or gained one or more electrons Copyright 2008 Pearson Education Inc publishing as Pearson Addison Wesley The Formation of Ions H H O Water H Hydrogen ion Molecular ion Typically formed by the loss or gain of a hydrogen ion H Copyright 2008 Pearson Education Inc publishing as Pearson Addison Wesley The Formation of Ions H H O H Hydronium ion H3O Molecular ion Typically formed by the loss or gain of a hydrogen ion H Copyright 2008 Pearson Education Inc publishing as Pearson Addison Wesley Ionic Bonds Ion An atom that has lost or gained one or more electrons Ionic Bond The electrical force of attraction between oppositely charged ions Copyright 2008 Pearson Education Inc publishing as Pearson Addison Wesley In class activity 2 What is the charge of an ion that is formed from a magnesium atom Why does it have this sign and amount of charge Copyright 2008 Pearson Education Inc publishing as Pearson Addison Wesley Ionic Bonds Ion An atom that has lost or gained one or more electrons Ionic Bond The electrical force of attraction between oppositely charged ions Na Copyright 2008 Pearson Education Inc publishing as Pearson Addison Wesley F Ionic Bonds Ion An atom that has lost or gained one or more electrons Ionic Bond The electrical force of attraction between oppositely charged ions Na F Copyright 2008 Pearson Education Inc publishing as Pearson Addison Wesley In class activity 3 Draw the dot diagrams of sodium and chlorine IONS Copyright 2008 Pearson Education Inc publishing as Pearson Addison Wesley Ionic Bonds CHECK YOUR ANSWER What is the chemical formula for a compound made of aluminum ions Al3 and oxygen ions O2 A B C D AlO Al3O2 Al2O3 Al6O6 Copyright 2008 Pearson Education Inc publishing as Pearson Addison Wesley Ionic Bonds CHECK YOUR ANSWER What is the chemical formula for a compound made of magnesium ions Mg2 and oxygen ions O2 A B C D MgO Mg2O2 Mg4O4 Any of the above Explanation The chemical formula is used to show the ratio by which atoms combine By convention the lowest numbers are preferred so 1 1 is used rather than 2 2 The numeral 1 however is implied when no subscript is written Copyright 2008 Pearson Education Inc publishing as Pearson Addison Wesley In class activity 4 Is the change from sodium and chlorine a physical or a chemical change Copyright 2008 Pearson Education Inc publishing as Pearson Addison Wesley In class activity 5 Write the chemical formula of the ionic compound calcium fluoride Copyright 2008 Pearson Education Inc publishing as Pearson Addison Wesley Metallic Bonds Outer electrons in metal atoms are held only weakly by the nucleus This weak attraction allows the electrons to move about quite freely This mobility of electrons accounts for many metallic properties Copyright 2008 Pearson Education Inc publishing as Pearson Addison Wesley Metallic Bonds An alloy is a mixture of metallic elements Copyright 2008 Pearson Education Inc publishing as Pearson Addison Wesley Covalent Bonds The type of electrical attraction in which atoms are held together by their mutual attraction for shared electrons Copyright 2008 Pearson Education Inc publishing as Pearson Addison Wesley Covalent Bonds The type of electrical attraction in which atoms are held together by their mutual attraction for shared electrons There are two electrons within a single covalent bond The covalent bond is represented using a straight line F F Copyright 2008 Pearson
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