The Outer Electrons, Ions & Chemical Bonding 1

Ch. 5 - Atoms, Ions & Chemical Bonds I. Why Atoms Combine (p.150-156) Chemical Formula Chemical Bond Stability

B. Chemical Bond Strong attractive force between atoms or ions in a molecule or compound. Formed by: transferring e- (losing or gaining) sharing e-

Outer Shells Electrons (valance electrons) Most atoms form bonds using only their outside electrons, these are known as valance electrons; the electrons in an atom’s outermost energy level. 4

Outer Shells Electrons (valance electrons) continued……… Valence Electrons and the Periodic Table Remember…… You can use the periodic table to determine the number of valence electrons in some elements 5

When using a table with groups 3A to 8A Listed, the group # equals the number of Valence electrons (These are Groups 3A-8A) 1A 2A 3A 4A 5A 6A 7A (Groups 3B-12B) 6

Ions…….. An atom is neutral because the number of (-) electrons in an atom equals the number of (+) protons. The (+) and (-) charges cancel each other out. But when an atom gains or loses electrons, it becomes a charged particle called an ion. 7

Forming Positive Ions Atoms of most metals have few valence (outside) electrons They tend to lose these valence electrons and form positive ions This leaves 8 electrons in the remaining outside shell 8

Forming Negative Ions The outer energy level of nonmetal atoms is almost full. Nonmetal atoms tend to gain electrons and become negative ions This brings their outside shell to 8 electrons 9

Why would atoms want to swap or share electrons? It’s all about atoms wanting a full outside or valence shell (they want 8 e-) Remember, the number of electrons in an atoms outside shell or valence level can be determined from the periodic table group number It is the number of electrons in the outermost level that determine how an atom will bond 10

Ne C. Stability Octet Rule (The Rule of Eight) most atoms form bonds in order to have 8 valence e- full outer energy level like the Noble Gases! Ne Stability is the driving force behind bond formation!

C. Stability Transferring e- Sharing e-

To Bond or Not to Bond Filling the Outermost Level An atom that has fewer than 8 valence electrons wants to form bonds by gaining or losing electrons Atoms bond by gaining or losing electrons (ionic) or sharing electrons (covalent) to fill the outermost energy level 13

To Bond or not to Bond The number of electrons in the outermost energy level of an atom determine whether an atom will form bonds. Atoms that have 8 electrons in their outermost energy level do not usually form bonds. The outermost energy level is considered to be full if it contains 8 electrons These are the noble gases (Group 8A or 18) 14

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Today’s Lesson…… Ions & Ionic Compounds 16

Ions make molecules & compounds….. Remember……. When an atom gains or loses electrons, it becomes a charged particle called an ion Whether electrons are lost or gained depends on the number of valence electrons When ions are formed by transferring electrons from one atom to another atom an ionic bond is formed When this happens a molecule is formed 17

Ions Atoms where the number of ELECTRONS are different than the number of protons 1e- Sodium Cl -1 8e- Na +1 2e- Anion 8e- 7e- 11 p+ 8e- 12 N 2e- This is a shorter version of the same lesson. Use this if you intend to do a basic introduction or would like to spend the other half of class doing an isotope/ions worksheet. This slide is on “Hide” mode. To allow it to show, right-click it to and select “Hide Slide”. 17 p+ 18 N Cation Chlorine 18 18

A positively charged ion Cation…… pronounced “cat” - “i on ”: A positively charged ion Anion…… pronounced “Ann” – “i on ”: A negatively charged ion 19

Name: ________________ Period : ______ Ions Atoms where the number of ELECTRONS are different than the number of protons S -2 Mg +2 This is a shorter version of the same lesson. Use this if you intend to do a basic introduction or would like to spend the other half of class doing an isotope/ions worksheet. This slide is on “Hide” mode. To allow it to show, right-click it to and select “Hide Slide”. 20 20

Name: ________________ Period : ______ Ions Atoms where the number of ELECTRONS are different than the number of protons O -2 Be +2 This is a shorter version of the same lesson. Use this if you intend to do a basic introduction or would like to spend the other half of class doing an isotope/ions worksheet. This slide is on “Hide” mode. To allow it to show, right-click it to and select “Hide Slide”. 21 21

Ionic Compounds When ionic bonds form, the number of electrons lost by the metal atoms equals the number gained by the nonmetal atoms. The ions that bond are charged, but the compound formed is neutral because the charges of the ions cancel each other. 22

Ionic Compounds, continued When ions bond, they form a repeating three-dimensional pattern called a crystal lattice, such as the one shown below. Properties of ionic compounds include brittleness, high melting points, and high boiling points. Cl-1 Na+1 23

Ionic Compounds, continued   Ionic Compounds, continued NaCl  Sodium chloride AlBr3  Aluminum bromide Ca3P2  Calcium phosphide SrI2  Strontium iodide FeCl2  Iron(II) chloride or ferrous chloride      The cation charge must be specified       since iron can form more than one charge. CuSO4 Cu2+ S042- 24

H2O A. Chemical Formula Shows: 1) elements in the compound 2) ratio of their atoms H2O 1 oxygen atom 2 hydrogen atoms

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The number of valance electrons determines the typical charge on the ions that atoms form 27

What you should have learned so far……. Why ionic bonds form What a cation and anion are What charge will be on the ions in an ionic bond How to determine the molecular formula from the type of ions that form You can do it! 28

Periodic Table: electron behavior The periodic table can be classified by the behavior of their electrons

3. Trend in Ionization Potential The energy required to remove the valence electron from an atomic specie. Largest toward NE corner of PT since these atoms hold on to their valence e- the tightest.