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Honors Chemistry

Honors Chemistry. Chapter 7 Chemical Formulas. 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

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Honors Chemistry

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  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 letter & may contain a sm case 2nd letter

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

  4. 7.2 Chemical Formulas • Chemists use combinations of symbols to represent compounds • Chemical Formula – a combination of symbols which represents the composition of a compound. • Shows 2 things: • Elems present in the comp • Relative # of atoms of eaelem in comp Ex) H2O contains 2 atoms of H and 1 atom of O (no subscript 0 assume 1) C12H22O11 – 12 C atoms, 22 H atoms, 11 O atoms

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

  6. 7.3 Oxidation 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 oxidation number.

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

  8. Examples for Writing Chemical Formulas • Sodium chloride • Na+ Cl- • NaCl • Calcium bromide • Ca+2 Br- • CaBr2 • Aluminum sulfide • Al+3 S-2 Al2S3

  9. Examples for Writing Chemical Formula • Aluminum sulfate • Al+3 SO4-2 • Al2(SO4)3 - must use ( ) • Calcium carbonate • Ca+2 CO3-2 • CaCO3 - don’t need ( )

  10. 7.3 Oxidation 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 • Br2, I2, N2, Cl2, H2, O2, F2

  11. 4.4 Naming Compounds • Binary Compounds – compounds containing only 2 elements • To name: • Write name of elem w/ (+) charge • 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 oxidation #, must write the oxid # of the (+) ion after 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 • If only 1 atom of 1stelem is needed , no prefix used • If more than 1 atom is needed, use a prefix • Always use a prefix for 2ndelem • End in I-d-e

  14. Examples of binary molecular compounds • CO – carbon monoxide • CO2 – carbon dioxide • CS2 – carbon disulfide • N2O3 - dinitrogenpentoxide

  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: • Count # of C atoms in chain or ring • Use hydrocarbon prefix which corresp. To # C atoms • (for now) Add suffix a-n-e • 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) H2O2 – hydrogen peroxide • Simplest formula is HO - lowest ratio • Empirical Formula – formula which indicates the simplest whole-number ratio of atoms or ions in a comp • C6H6 (benzene) & C2H2 (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 multiple 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.

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