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Chemical Names and Formulas for ionic compounds

Chemical Names and Formulas for ionic compounds. Significance of a Chemical Formula. Review. Chemical formulas form the basis of the language of chemistry and reveal much information about the substances they represent.

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Chemical Names and Formulas for ionic compounds

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  1. Chemical Names and Formulas for ionic compounds

  2. Significance of a Chemical Formula Review • Chemical formulas form the basis of the language of chemistry and reveal much information about the substances they represent. • To describe the atomic makeup of compounds chemists use systematic methods for naming compounds and for writing chemical formulas.

  3. Review • A chemical formula indicates the relative number of atoms of each kind in a chemical compound. • For a molecular compound, the chemical formula gives the number of atoms of each element contained in a single molecule of the compound. • Example: octane C8H18 The subscript after the H indicates that there are 18 hydrogen atoms in the molecule. The subscript after the C indicates that there are 8 carbon atoms in the molecule.

  4. The chemical formula for an ionic compound represents one formula unit – the simplest ratio of the compound’s (+) ions and (-) ions. • Example: aluminum sulfate Al2(SO4)3 • Parentheses surround the polyatomic ion (SO4) to identify it as a unit. The subscript 3 refers to the unit. Al2(SO4)3 3 sulfur atoms and 12 oxygen atoms 2 aluminum atoms • Ionic compounds exist as crystalline solids. • Aluminum sulfate crystal

  5. Ions • A positive ion, called a cation, is produced when one or more electrons are lost from a neutral atom. • Metals tend to lose electrons, thus forming positive ions or cations. • When a neutral atom gains electrons, an ion with a negative charge is formed, called an anion. • Nonmetals tend to gain electrons, thus forming negative ions, or anions.

  6. Monatomic Ions • Monatomic ions are ions formed from a single atom. mono (one) Na+ • Monatomic cations are identified by the element’s name (Na+ is sodium). • When naming monatomic anions, you drop the ending of the element’s name and add –ide. • F-, Fluorine → Fluoride

  7. The periodic table is very useful when we want to know what type of ion is formed by a given atom. • Note that the Group 1 atoms all form 1+ ions and the Group 2 metals all form 2+ ions.

  8. Many of the transition metals lose different numbers of electrons and follow the Stock System of naming ions and elements. • Example: copper(I) → Cu+ • or copper(II) → Cu2+ copper(I) ion – lost one electron copper(II) ion – lost two electrons

  9. Binary Ionic Compounds • Binary ionic compounds are compounds composed of twodifferent elements. • The total number of positive and negative charges must be equal. • For any ionic compound, • Total charge of cations + Total charge of anions • = Zero net charge • Use your ion handout to help you with the charges on ions.

  10. O N O O Polyatomic Ions • In a polyatomic ion, two or more atoms are covalently bonded together.

  11. 1– O N O O • Together, they carry a charge.

  12. O O N N O O Mg O O • When balancing charges in an ionic compound, the polyatomic ions acts as a single unit of charge. 1- 1- 2+ Mg(NO3)2

  13. O O N N O O Mg O O 1- 1- 2+ Mg(NO3)2 2+

  14. O O N N O O Mg O O the charges are balanced 1- 1- 2+ Mg(NO3)2 2+ 2- Remember a parentheses is placed around the polyatomic ion to identify it as a unit.

  15. Naming Binary Ionic Compounds • The nomenclature, or naming system, or binary ionic compounds involves combining the names of the compound’s positive and negative ions. • The name of the cation is given first, followed by the name of the anion (-ide). • Example: Al2O3 • aluminum oxide

  16. Some elements such as iron, form two or more cations with different charges. • The Stock System of nomenclature uses a Roman numeral to indicate an ion’s charge. • The numeral is enclosed in parentheses and placed immediately after the metal’s name. • Example: Fe2+ - iron(II), Fe3+ - iron(III).

  17. Example: write the name for the following compound. SnI4 • First determine the charge on the Sn ion. • The iodine ion has a charge of 1- and the formula contains 4 I- ions therefore, the overall negative charge is 4-. • In order for the charges to equal the Sn ion must have a charge of 4+. • The name would be tin(IV) iodide.

  18. Compounds containing Polyatomic Ions • Most polyatomic ions are negatively charged and are oxyanions – contain oxygen. • Compounds containing polyatomic ions are named in the same way as binary ionic compounds. • Name the cation first, then the anion. • Example: Ca(OH)2 Name cation first, then the anion. calcium hydroxide

  19. If more than one oxyanion is formed by the same two elements (Ex. N and O) the most common ion is given the ending – ate. • The one with one less oxygen ends in –ite. • Example: NO2- - nitrite, NO3-, nitrate. • Some elements can form more than two types of oxyanions. • Example: chlorine can form • ClO- (hypochlorite) • ClO2- (chlorite) • ClO3- (chlorate) • ClO4- (perchlorate)

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