2 8.1 Forming Chemical Bonds The force that holds two atoms together is called a Chemical Bond. Chemical Bonds (ionic, covalent, metallic) :May form due to the attraction between “+” charged nucleus and “–” charged electrons, orMay form due to the attraction between a Positive ion and a negative ion.
3 Cation - A positively charged ion Cation - A positively charged ion. Formed when an atom loses an electron, thereby gaining a net positive charge. (K+)Anion – A negatively charge ion. Formed when an atom gains and electron, thereby gaining a net negative charge. (F-)Look for the oxidation number on the periodic table to indicate the type of ion formed.(+2,-2, etc.)
4 Ions that are formed from a single atom are called monatomic ions Ions that are formed from a single atom are called monatomic ions. They will be shown by only one chemical symbol of the element and either a (+) or (-) sign above it. (Mg+2 or F- )If ions are formed from groups of atoms they are called polyatomic ions. These will have several element symbols listed.(OH- or SO42-)
5 Valence Electrons are responsible for the chemical properties of atoms. Located in the outer energy levelInvolved in the formation of chemical bonds between two atoms.Total number of valence electrons = group number. (Na has 1, (Group 1 element)
6 Valence Electrons are shown using a diagram called, the Electron Dot structure. “Dots” are valence electrons (total number 1-8 and equal to the group number).Element’s Symbol is in the middle.
7 X Write the symbol of the element “X”. Put one dot for each valence electronDon’t pair up until they have toX
8 Example: The Electron Dot diagram for Nitrogen Nitrogen has 5 valence electrons. (group 5)First we write the symbol.NThen add 1 electron at a time to each side.Until they are forced topair up.
9 Learning Check A. X would be the electron dot formula for A. X would be the electron dot formula for1) Na 2) K 3) Al B X would be the electron dot formula1) B 2) N 3) P
10 Elements in the same group have similar chemical properties. Electron Affinity – Attraction an atom has for electrons. High=ReactiveIonization Energy- How easily an atom loses an electron. Low=ReactiveHigh IE and low EA = lack of chemical reactivity.Low IE and high EA = Chemically reactive.
11 Stable Electron Configurations All atoms react so as to achieve a noble gas configuration of 8 valence electrons.ls called the octet rule.Ar
12 8.2 IONIC BONDSIonic Bond-The electrostatic force that holds oppositely charged particles (anions and cations) together in an ionic compound.Ionic compounds result when metals react with nonmetals. Ionic compounds are called salts.Simplest ratio is called the formula unit (Ca3P2).The ionic bond is formed through the transfer of electrons.Electrons are transferred to achieve noble gas configuration (8).
15 Properties of Ionic Compounds Crystalline lattice structure.A 3-dimensional geometric arrangement of particles. Regular repeating arrangement of ions in the solid.Ions are strongly bonded.Structure is hard and rigid.High melting points and boiling points- because of strong forces between ions.
16 An ionic compound is an electrolyte if it conducts electricity when it is liquid or in aqueous solution.Lattice energy- The strength of the force holding the ions together in an ionic compound. The more negative the number, the stronger the force.Lattice energy must beexceeded in order tobreak the ionic bond.
17 8.3 Names and Formulas for Ionic Compounds Writing the chemical formula of an ionic compound:****Need the oxidation number from periodic table.Write the symbol of the positive ion first with its charge.( Mg+2), from the PT or common ions table.Write the symbol for the negative ion and its charge next to the positive one. (Mg+2 O-2 ).Rewrite the formula and move the numbers to the opposite corner and drop the signs. (Mg2O2) then reduce to simplest ratio (MgO). (swap and drop then reduce).
18 4. If there is a polyatomic ion involved use a parenthesis. Al+3 SO4-2 becomesAl2(SO4)3Remember: The charge number comes from the oxidation number on the periodic table (single ion), or common ions table for polyatomic ions (2or>).
19 When naming binary ionic compounds the name of the (+) cation goes first, followed by the name of the (-) anion.Anions are named by replacing the suffix of the elements name with the suffix “ide” (CsBr is Cesium Bromide).If there is more than one oxidation number (charge), which ever one is used goes in parenthesis as a roman numeral. (Fe+3O-2 becomes Fe2O3 and is called Iron(III) Oxide.(Iron can be a +3 or +2)
20 When naming an ionic compound with a polyatomic ion(s) in it, use the table of common ions. (Example: Cu(NO3)2 would be called Copper(II) Nitrate.
21 Naming Ionic Compounds (continued) * Polyatomic ions each have specific names which should be memorized so they can be recognized on sight.(At this point, if you are asked to name any compound that contains more than two elements, it will contain at least one polyatomic ion.)A few of the more common polyatomic ionsFormulaNameC2H3O21-acetateCO32-carbonateHCO31-bicarbonateNH41+ammoniumFormulaNameNO31-nitrateOH1-hydroxidePO43-phosphateSO42-sulfate
22 Naming Ionic Compounds: Examples Na2SO4sodium sulfateC2H3O21-acetateCO32-carbonateHCO31-bicarbonateNH41+ammoniumNO31-nitrateOH1-hydroxidePO43-phosphateSO42-sulfate* Groups I & II, Al, Zn, Cd, and Ag need no Roman numeral.Fe(NO3)2iron (II) nitrateAlCl3aluminum chloridePbI4lead (IV) iodide(NH4)3PO4ammonium phosphateMg3N2magnesium nitrideAgC2H3O2silver acetate
23 8.4 Metallic BondsMetallic bonds are formed when metal (+) cations attract free valence (-)electronsA sea of electrons moves throughout the entire metallic crystal, producing this attraction.Metals hold onto their valence electrons very weakly.The electrons are called decentralized electrons because they are free to move and not attached to any one atom.
24 Electron Sea Model + Explains the properties of metals. Conduct electricityDuctileMalleable+
25 AlloysSolutions made by dissolving metal into other elements- usually metals.Melt them together and cool them.If the atoms of the metals are about the same size, they substitute for each otherCalled a substitutional alloy
26 AlloysIf they are different sizes the small one will fit into the spaces of the larger oneCalled and interstitial alloy