11 Remember…Ionic compounds are made up of a metal & a nonmetal chemically bonded together.The METALLIC element is always named 1st in the compound name.Sodium chloride – sodium is the metal &chlorine is the nonmetal
12 Steps for writing ionic compound formulas Write the chemical symbol for the metallic ion first.Write the chemical symbol for the nonmetallic ion.Make sure the ions’ charges equal zero.Metallic ions always have a positive charge.Nonmetallic ions always have a negative charge.An ion’s charge is the same as the number of electrons its group will gain or lose to become stable.Add subscripts to the chemical symbols to make the compound’s charge equal zero.
13 Sodium chloride Sodium’s chemical symbol is Na. Na Chlorine’s chemical symbol is Cl.Sodium is in group 1. It’s charge is 1+.Chlorine is in group It’s charge is 1-.(+1) + (-1) = 0. No subscripts are needed.NaClChemical formula: NaCl
14 If the ions’ charges do not equal zero… Aluminum oxideFind the LCM of the ions’ charges.Add subscripts where needed to equal the LCM.Al – group 13 – charge 3+O – group 16 – charge 2-LCM of 3 & 2 is 6Subscript for Al is 2 (2 x 3=6)Subscript for O is 3 (3 x 2=6)4. Formula: Al2O3
15 Now You try…..Potassium chlorideMagnesium chlorideSodium fluorideAluminum sulfideKClMgCl2NaFAl2S3
24 Law of conservation of mass Mass is neither created nor destroyed in an ordinary chemical or physical change.Chemical equations must show the same numbers & kinds of atoms on each side of the arrow.
25 Subscripts vs. coefficients Written to the lower right of a chemical symbolWritten smaller than chemical symbolOnly apply to single atomsWritten to the left of the chemical symbolWritten the same size as the chemical symbolApply to every atom in molecule, including subscripts
26 Subscript or coefficient? H2O22 CO2SubscriptCoefficientBoth!
27 Calculating the number of atoms A coefficient applies to every atom & every subscript in a molecule.If there is a subscript, multiply the coefficient by the subscript to find the number of atoms.Coefficients in an equation are “stopped” by the plus sign or the arrow.
28 2 H2 + O H2OReactant side has 4 hydrogen atoms & 2 oxygen atoms. The coefficient 2 applies only to the hydrogen.Product side also has 4 hydrogen atoms & 2 oxygen atoms. The coefficient 2 applies to everything here. There is no plus sign or arrow to stop the coefficient.
29 Calculate the total number of atoms 2 HCO33 C6H12O6NaF4 CaO
30 Steps for balancing chemical equations Set up a T-chart for the reactants & products.reactant product
31 Ca + O2 CaO Write the chemical symbol & number of atoms for each side. reactant productCa – 1 Ca – 1O – O – 1Compare to see if the equation is balanced.This equation is not balanced.
32 Ca + O2 CaO Find the LCM for each element that is unbalanced. reactant productCa – 1 Ca – 1O – O – LCM = 2
33 Ca + O2 2 CaO Add coefficients to balance the elements. NEVER CHANGE A SUBSCRIPT!!Recount the number of atoms for eachelement. Repeat steps as needed.reactant productLCM = 2 Ca – 1 Ca – O – O – 1 2
34 2 Ca + O CaOreactant product LCM = 2 Ca – 1 2 Ca – 1 2 O – 2 O – 1 2 LCM = 2 The equation is now balanced.