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Ionic Bonding Section 4.1. Introduction to Bonding Chemical bond: an interaction between atoms or ions that results in a reduction of the potential energy.

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Presentation on theme: "Ionic Bonding Section 4.1. Introduction to Bonding Chemical bond: an interaction between atoms or ions that results in a reduction of the potential energy."— Presentation transcript:

1 Ionic Bonding Section 4.1

2 Introduction to Bonding Chemical bond: an interaction between atoms or ions that results in a reduction of the potential energy of the system, thereby becoming more stable Chemical bond: an interaction between atoms or ions that results in a reduction of the potential energy of the system, thereby becoming more stable Three types of bonds: ionic, metallic, and covalent Three types of bonds: ionic, metallic, and covalent The bond type depends on the atom's electronegativitites The bond type depends on the atom's electronegativitites

3 More If the atoms have very different electronegativities, then ionic bonding occurs If the atoms have very different electronegativities, then ionic bonding occurs If they both have high electronegativities, then covalent bonding occurs If they both have high electronegativities, then covalent bonding occurs If they both have low electronegativities, then metallic bonding occurs If they both have low electronegativities, then metallic bonding occurs

4 Practice: What Kind of Bond? Na and Cl Na and Cl Sr and O Sr and O C and O C and O Ni and Fe Ni and Fe N and O N and O Li and N Li and N Ti and Cr Ti and CrIonicIonicCovalentMetallicCovalentIonicmetallic

5 Valence Electrons Valence electrons are the electrons in the outermost energy level, which is the highest occupied energy level Valence electrons are the electrons in the outermost energy level, which is the highest occupied energy level They are the electrons responsible for the chemical properties of atoms They are the electrons responsible for the chemical properties of atoms Core electrons – are those in the energy levels below. Core electrons – are those in the energy levels below.

6 Keeping Track of Electrons Atoms in the same group have the same outer electronic structure and therefore the same number of valence electrons. Atoms in the same group have the same outer electronic structure and therefore the same number of valence electrons. The number of valence electrons is easily determined. It is the group number for a short group element The number of valence electrons is easily determined. It is the group number for a short group element Group 2: Be, Mg, Ca, etc. Group 2: Be, Mg, Ca, etc. Each has 2 valence electrons Each has 2 valence electrons

7 Electron Dot (Lewis Dot)diagrams A way of showing & keeping track of valence electrons. A way of showing & keeping track of valence electrons. Write the symbol - it represents the nucleus and inner (core) electrons Write the symbol - it represents the nucleus and inner (core) electrons Put one dot for each valence electron (8 maximum) Put one dot for each valence electron (8 maximum) They don’t pair up until they have to (Hund’s rule) They don’t pair up until they have to (Hund’s rule) X

8 The Electron Dot Diagram (Lewis Structure) for Nitrogen Nitrogen has 5 valence electrons to show. First we write the symbol. N Then add 1 electron at a time to each side. Now they are forced to pair up as one side has two electrons

9 The Octet Rule The noble gases are unreactive in chemical reactions In 1916, Gilbert Lewis used this fact to explain why atoms form certain kinds of ions and molecules The Octet Rule: in forming compounds, atoms tend to achieve a noble gas structure; 8 in the outer level is stable Each noble gas (except He, which has 2) has 8 electrons in the outer level

10 Formation of Cations Metals lose electrons (are oxidized) to attain a noble gas structure. Metals lose electrons (are oxidized) to attain a noble gas structure. They make positive ions (cations) They make positive ions (cations) If we look at the electronic structure, it makes sense to lose electrons: If we look at the electronic structure, it makes sense to lose electrons: Na: 1s 2 2s 2 2p 6 3s 1 shows 1 valence electron Na: 1s 2 2s 2 2p 6 3s 1 shows 1 valence electron Na 1+ : 1s 2 2s 2 2p 6 This is a noble gas structure with 8 electrons in the outer level. Na 1+ : 1s 2 2s 2 2p 6 This is a noble gas structure with 8 electrons in the outer level.

11 Electron Dots For Cations Metals have few valence electrons (usually 3 or less); calcium has only 2 valence electrons Metals have few valence electrons (usually 3 or less); calcium has only 2 valence electrons Ca

12 Electron Dots For Cations Metals will lose the valence electrons Ca

13 Electron Dots For Cations Form positive ions Form positive ions Ca 2+ No dots are now shown for the cation. This is named the “calcium ion”.

14 Electron Configurations: Anions Nonmetals gain electrons to attain noble gas electronic structures. Nonmetals gain electrons to attain noble gas electronic structures. They make negative ions (anions) They make negative ions (anions) S = 1s 2 2s 2 2p 6 3s 2 3p 4 = 6 valence electrons S = 1s 2 2s 2 2p 6 3s 2 3p 4 = 6 valence electrons S 2- = 1s 2 2s 2 2p 6 3s 2 3p 6 = noble gas structure. S 2- = 1s 2 2s 2 2p 6 3s 2 3p 6 = noble gas structure. Halide ions are ions from chlorine or other halogens that gain electrons Halide ions are ions from chlorine or other halogens that gain electrons

15 Electron Dots For Anions Nonmetals will have many valence electrons (usually 5 or more) Nonmetals will have many valence electrons (usually 5 or more) They will gain electrons to fill outer shell. They will gain electrons to fill outer shell. P 3- (This is called the “phosphide ion”, and should show dots)

16 Stable Electron Configurations All atoms react to try and achieve a noble gas structure. All atoms react to try and achieve a noble gas structure. Noble gases have 8 valence electrons and so are already stable Noble gases have 8 valence electrons and so are already stable This is the octet rule (8 in the outer level is particularly stable). This is the octet rule (8 in the outer level is particularly stable). Ar

17 Ionic Bonding Anions and cations are held together by opposite charges (+ and -) Anions and cations are held together by opposite charges (+ and -) Simplest ratio of elements in an ionic compound is called the formula unit (also called the empirical formula). Simplest ratio of elements in an ionic compound is called the formula unit (also called the empirical formula). The bond is formed through the transfer of electrons (lose and gain) The bond is formed through the transfer of electrons (lose and gain) Electrons are transferred to achieve noble gas structure. Electrons are transferred to achieve noble gas structure.

18 Ionic Bonding NaCl The metal (sodium) tends to lose its one electron from the outer level. The nonmetal (chlorine) needs to gain one more to fill its outer level, and will accept the one electron that sodium is going to lose.

19 Ionic Bonding Na + Cl - Note: Remember that no dots are now shown for the cation

20 Ionic Bond Negative charges are attracted to positive charges. Negative charges are attracted to positive charges. Negative anions are attracted to positive cations. Negative anions are attracted to positive cations. The result is an ionic bond. The result is an ionic bond. A three-dimensional crystal lattice of anions and cations is formed. A three-dimensional crystal lattice of anions and cations is formed.

21 Ionic Compounds The ionic substance is held together by strong electrostatic attractions between all ions in all three dimensions The ionic substance is held together by strong electrostatic attractions between all ions in all three dimensions No molecules present No molecules present An ionic lattice is formed An ionic lattice is formed This gives them distinct physical properties This gives them distinct physical properties

22 Preserve Electroneutrality When ions combine, electroneutrality must be preserved. When ions combine, electroneutrality must be preserved. In the formation of magnesium chloride, In the formation of magnesium chloride, 2 Cl - ions must balance a Mg 2+ ion: 2 Cl - ions must balance a Mg 2+ ion: Mg Cl - → MgCl 2 Mg Cl - → MgCl 2

23 NaCl CsCl TiO 2

24 Please go to the “Naming ions, compounds and molecules presentation.

25 Properites of Ionic Compounds Hard, brittle crystalline solids Hard, brittle crystalline solids Relatively high melting and boiling points Relatively high melting and boiling points Do not conduct electricity when solid, but do when molten or in aqueous solution Do not conduct electricity when solid, but do when molten or in aqueous solution Are more soluble in water than other solvents Are more soluble in water than other solvents

26 - Page 198 The ions are free to move when they are molten (or in aqueous solution), and thus they are able to conduct the electric current.

27 Predicting Ionic Charges Group 1A: Lose 1 electron to form 1+ ions H+H+H+H+ Li + Na + K+K+K+K+ Rb +

28 Predicting Ionic Charges Group 2: Loses 2 electrons to form 2+ ions Be 2+ Mg 2+ Ca 2+ Sr 2+ Ba 2+

29 Predicting Ionic Charges Group 3: Loses 3 Loses 3 electrons to form 3+ ions B 3+ Al 3+ Ga 3+

30 Predicting Ionic Charges Group 5: Gains 3 Gains 3 electrons to form 3- ions N 3- P 3- As 3- Nitride Phosphide Arsenide

31 Predicting Ionic Charges Group 6: Gains 2 Gains 2 electrons to form 2- ions O 2- S 2- Se 2- Oxide Sulfide Selenide

32 Predicting Ionic Charges Group 7: Gains 1 electron to form Gains 1 electron to form 1- ions F-F-F-F- Cl - Br - Fluoride Chloride Bromide I-I-I-I- Iodide

33 Predicting Ionic Charges Group 0: Stable noble gases do not form ions! Stable noble gases do not form ions!

34 Predicting Ionic Charges Many transition elements Many transition elements have more than one possible oxidation state. have more than one possible oxidation state. Iron (II) = Fe 2+ Iron (III) = Fe 3+ Note the use of Roman numerals to show charges


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