Honors Chemistry. Chapter 7 Chemical Formulas

Transcription

1 Honors Chemistry Chapter 7 Chemical Formulas

2 7.1 Names and Symbols Elems are named for many things: Some property of the elem Place of discovery To honor a place or person Chemical symbols form of shorthand that takes the place of the complete names of the elems Contain only 1 capitalized leeer & may contain a sm case 2 nd leeer

3 7.1 Names and Symbols W/ some elems, the LaLn name is used for symbol: Lead plumbum Pb Iron Ferrium Fe J. J. Berzelius credited for crealng modern symbols for elems

4 7.2 Chemical Formulas Chemists use combinalons of symbols to represent compounds Chemical Formula a combinalon of symbols which represents the composilon of a compound. Shows 2 things: 1. Elems present in the comp 2. RelaLve # of atoms of ea elem in comp Ex) H 2 O contains 2 atoms of H and 1 atom of O (no subscript 0 assume 1) C 12 H 22 O C atoms, 22 H atoms, 11 O atoms

5 7.2 Chemical Formulas Compounds containing C are called Organic Comps Formulas wrieen w/ diff set of rules

6 7.3 OxidaLon Number Atoms can acquire an electric charge by gaining or losing e- s Ions charged atoms Polyatomic Ion group of atoms which acquire a charge The charge on a single atom is called its oxidalon number.

7 7.3 OxidaLon Number Charges & oxidalon # s are used to write correct chemical formulas Atoms & ions combine in definite ralos Oxid. # s of elems & charges of polyatomic ions tell us these ralos To write a chemical formula for an ionic comp., the charges (or oxid. # s) must balance Their algebraic sum must = 0

8 Examples for WriLng Chemical Sodium chloride Na+ Cl- NaCl Calcium bromide Ca +2 Br - CaBr 2 Aluminum sulfide Al +3 S - 2 Al 2 S 3 Formulas

9 Examples for WriLng Chemical Formula Aluminum sulfate Al +3 SO4-2 Al 2 (SO 4 ) 3 - must use ( ) Calcium carbonate Ca +2 CO CaCO 3 - don t need ( )

10 7.3 OxidaLon Number When ions combine to form a new subst, this subst is an ionic compound When neutral atoms combine, they make molecules. Some elems cannot exist as single atoms They must exist as diatomic molecules (2- atomed) There are 7 of these elems Br 2, I 2, N 2, Cl 2, H 2, O 2, F 2

11 4.4 Naming Compounds Binary Compounds compounds containing only 2 elements To name: 1. Write name of elem w/ (+) charge 2. Add name of (- ) elem (ion) Must end in i- d- e Example: AlN - aluminum nitride

12 4.4 Naming Compounds If elem has more than 1 oxidalon #, must write the oxid # of the (+) ion acer the name of the element Use Roman numerals in ( )

13 4.4 Naming Compounds Some comps are named by an older syst which used prefixes instead of oxid # s Usually used if both elems are nonmetals Binary Molecular Compounds Rules 1. If only 1 atom of 1 st elem is needed, no prefix used 2. If more than 1 atom is needed, use a prefix 3. Always use a prefix for 2 nd elem 4. End in I- d- e

14 Examples of binary molecular compounds CO carbon monoxide CO 2 carbon dioxide CS 2 carbon disulfide N 2 O 3 - dinitrogen pentoxide

15 4.4 Naming Compounds Not all comps ending in i- d- e are binary NaOH - sodium hydroxide When naming comps w/ an elem & a polyatomic ion or 2 polyatomic ions, name (+) ion first then (- ) ion. Do not change the ending of the polyatomic ion.

16 Naming Simple Organic Compounds Simplest group of organic comps hydrocarbons Composed only H & C Carbon atoms can ink to ea other in chains or rings To name hydrocarbons: 1. Count # of C atoms in chain or ring 2. Use hydrocarbon prefix which corresp. To # C atoms 3. (for now) Add suffix a- n- e 4. If C atoms are linked in a ring, begin name w/ cyclo (Leave room for examples from class discussion)

17 4.5 Molecular and Empirical Formulas Molecular Formulas formulas for comps that exist as molecules Ex) H 2 O 2 hydrogen peroxide Simplest formula is HO - lowest ralo Empirical Formula formula which indicates the simplest whole- number ralo of atoms or ions in a comp C 6 H 6 (benzene) & C 2 H 2 (ethyne) have the same empirical formula CH

18 4.5 Molecular and Empirical Formulas For many substs, the empirical formula is the only formula possible. Molecular formula is always some whole number mullple of the empirical formula.

19 4.6 Coefficients The formula of a comp represents a definite amt of that comp This amt is called a formula unit Ex) H2O 1 molecule (formula unit) of water If you need more that 1 formula unit (molecule, ionic comp, etc) you must use coefficients Ex) 2H2O means 2 formula units of H2O 3NaCl means 3 formula units of NaCl 6HCl means 6 formula units of HCl If there is no coeff, we assume it is 1.