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Physical Science 1 Chapter 20 – Chemical Bonds Meet the Elements – They Might be Giants Elemental Funkiness Combining Elements • The chemical & physical properties of the elements are different than the properties of the compound they make up • Na + Cl2 → NaCl → • Reaction of Sodium with Chlorine Chemical Formulas • Chemical shorthand of compounds and molecules • Uses the chemical symbols and trailing subscripts to illustrate the type and number of each atom involved in the chemical bond. • Water = H2O No subscript is understood to Hydrogen mean 1 atom of the previous element Oxygen 2 atoms of the previous element = 2 hydrogen atoms Practice with Chemical Formulas Common Name Chemical Formula • Sand SiO2 • Milk of Magnesia Mg(OH)2 • Sucrose C12H22O11 • Vinegar HC2H3O2 • Ethanol C2H5OH → Types & Number of Elements involved Type of Bond (ionic - covalent) Atomic Stability • Why do atoms form compounds? – To become stable • What does stable mean to an atom? – Full Set of Valence electrons • Atoms want to have the electron configuration of a noble gas • Atoms will gain, lose or share electrons in order to obtain a full set of valence electrons – Chemical Bonds Types of Bonds • IONIC BONDS – between metals & nonmetals – Electrons form a give take relationship • metals give e- (cation) • nonmetal take e- (anion) – Held together by attraction of opposite charges IONIC ANIMATION • Chemical Bonds Table Polyatomic Ions Ion – a charged particle due to gaining or losing eCations = positive ions, lost e- METALS Anions = negative ions, gained e- NONMETALS Polyatomic Ions – – – – – – The prefix poly- means many in Greek. ion consisting of a molecule with many covalently bonded atoms act as a single unit polyatomic ion is also referred as a radical Usually end in –ate & –ite -ide usually indicates binary compounds +1 CHARGE ion -1 CHARGE name ion -2 CHARGE name ion name -3 CHARGE ion name NH4+ ammonium NO2- nitrite CO32- carbonate PO33- phosphite H 3O + hydronium NO3- nitrate SO32- sulfite PO43- phosphate Hg22+ mercury(I) OH- hydroxide SO42- sulfate CH3COOC2H3O2- acetate S2O32- thiosulfate CN- cyanide CrO42- chromate CNS- thiocyanate Cr2O72- dichromate MnO4- permanganate ClO3- chlorate ClO4- perchlorate IO2- iodite IO3- iodate Name & Formula 2-D Structure 3-D Representation Ammonium NH4+ + 1 cation Hydroxide OH– – 1 anions Nitrate NO3– Nitrite NO2– Acetate C2H3O2 – CH3COO Carbonate CO32- – 2 anions Sulfate SO42- Sulfite SO32Phosphate PO43- – 3 anion • COVALENT BONDS – Between 2 nonmetals – Electrons are shared between both elements – Polar Bonds • an unequal sharing of the e• Due to a difference of electro-negativity of the atoms – F is the most electronegative element on PT – A simulation of polar covalent bonding in the H2O molecule Only valence electrons are shown – Non-polar Bonds • an equal sharing of e• nonpolar bond animation – Multiple Bonds – More than one pair of electrons can be shared between atoms • Double Bonds = 2 shared pairs of e• Triple Bonds= 3 shared pairs of e- Chemical Bonding • COVALENT QUIZ Comparing ionic and molecular compounds Molecular compounds Ionic compounds Smallest particles molecules cations and anions Origin of bonding electron sharing electron transfer Forces between particles strong bonds between atoms weak attractions between molecules Strong attractions between anions and cations. strong repulsions between ions of like charge Elements present close on the periodic table widely separated on the periodic table Metallic elements present rarely usually electrical conductivity poor good, when melted or dissolved state at room temperature solid, liquid, or gas solid melting and boiling points lower higher other names covalent compounds salts • Name this compound Ba(Na)2 • BANANA • http://www.accessexcellence.org/RC/VL/GG/ecb/covalen t_ionic_bonds.html • http://misterguch.brinkster.net/ioniccovalentwork sheets.html • http://www.visionlearning.com/library/module_viewer.php ?mid=55 Group the compounds by ratios 1:1, 1:2, 2:1 1:3 & 2:3 Using a PT record the group for each element in all compounds Record each group Based on your patterns, Write rules for the ratio of elements in a compound LiBr Al2O3 BeS Na2O CaBr2 K2Se AlF3 MgCl2 B2S3 MgTe NaF KCl CaI2 NaAt BI3 1. Using your rules, predict a formula between Li & F and between Li & O 2. Using your rules, choose elements to make four compounds that are not already on the sheet. 3. Explain why MgCl2 is correct and Cl2Mg is incorrect. 4. How is MgCl2 possible and MgLi2 is not?
