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Topic 7

Topic 7. Types of Compounds: Basic Concepts. Topic 7. Hydrates. Hydrates. Diatomic: Molecular Elements. Naming Molecules. Types of Compounds: Basic Concepts. Topic 7. Hydrates.

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Topic 7

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  1. Topic 7

  2. Types of Compounds: Basic Concepts Topic 7 Hydrates • Hydrates • Diatomic: Molecular Elements • Naming Molecules

  3. Types of Compounds: Basic Concepts Topic 7 Hydrates • Many ionic compounds are prepared by crystallization from a water solution, and water molecules become a part of the crystal. • A compound in which there is a specific ratio of water to ionic compound is called a hydrate. • In a hydrate, the water molecules are chemically bonded to the ionic compound.

  4. Types of Compounds: Basic Concepts Topic 7 Hydrates • Some ionic compounds can easily become hydrates by absorbing water molecules from water vapor in the air. • These compounds are called hygroscopicsubstances, and one example is sodium carbonate (Na2CO3). • In a hydrate, the water molecules are chemically bonded to the ionic compound.

  5. Types of Compounds: Basic Concepts Topic 7 Hydrates • Substances that are so hygroscopic that they take up enough water from the air to dissolve completely and form a liquid solution are called deliquescent.

  6. Types of Compounds: Basic Concepts Topic 7 Hydrates • To write the formula for a hydrate, write the formula for the compound and then place a dot followed by the number of water molecules per formula unit of compound. • The dot in the formula represents a ratio of compound formula units to water molecules. • For example, CaSO4 • 2H20 is the formula for a hydrate of calcium sulfate that contains two molecules of water for each formula unit of calcium sulfate.

  7. Types of Compounds: Basic Concepts Topic 7 Hydrates • To name hydrates, follow the regular name for the compound with the word hydrate, to which a prefix has been added to indicate the number of water molecules present.

  8. Types of Compounds: Basic Concepts Topic 7 Hydrates • The name of the compound with the formula CaSO4 • 2H2O is calcium sulfate dihydrate.

  9. Types of Compounds: Basic Concepts Topic 7 Hydrates • Heating hydrates can drive off the water. • This results in the formation of an anhydrous compound—one in which all of the water has been removed. • In some cases, an anhydrous compound may have different color from that of its hydrate.

  10. Types of Compounds: Basic Concepts Topic 7 Properties of Molecular Substances • You know that ionic compounds share many properties. • The properties of a molecularsubstance—a substance that has atoms held together by covalent rather than ionic bonds—are more variable than the properties of ionic compounds.

  11. Types of Compounds: Basic Concepts Topic 7 Properties of Molecular Substances • Molecular substances usually have lower melting points, and most are not as hard as ionic compounds. • In addition, most molecular substances are less soluble in water than ionic compounds and are not electrolytes.

  12. Types of Compounds: Basic Concepts Topic 7 Properties of Molecular Substances • A molecule that forms when atoms of the same element bond together is called a molecular element. • Note that molecular elements are not compounds—they contain atoms of only one element.

  13. Types of Compounds: Basic Concepts Topic 7 Properties of Molecular Substances • When they bond together, each atom achieves the stability of a noble-gas electron configuration. • Seven nonmetal elements are found naturally as molecular elements of two identical atoms.

  14. Types of Compounds: Basic Concepts Topic 7 Properties of Molecular Substances • The elements whose natural state is diatomic are: • hydrogen, • chlorine, • bromine, • nitrogen, • and iodine • oxygen, • fluorine, Memory Aide: HONCl BrIF

  15. Types of Compounds: Basic Concepts Topic 7 Properties of Molecular Substances • Their formulas can be written as: • H2, • Cl2, • Br2, • N2, • and I2, respectively • O2, • F2,

  16. Types of Compounds: Basic Concepts Topic 7 Properties of Molecular Substances • If two chlorine atoms combine, they share a single pair of electrons, and each atom attains a stable octet configuration.

  17. Types of Compounds: Basic Concepts Topic 7 Properties of Molecular Substances • Two oxygen atoms share two pairs of electrons to form O2, and two nitrogen atoms share three pairs of electrons to form N2.

  18. Types of Compounds: Basic Concepts Topic 7 Allotropes • Although the diatomic form of oxygen, O2, is most common in our atmosphere, oxygen also exists as O3—ozone. • The structure of ozone is different from that of diatomic oxygen. • It consists of three atoms of oxygen rather than the two atoms in diatomic oxygen.

  19. Types of Compounds: Basic Concepts Topic 7 Allotropes • Molecules of a single element that differ in crystalline or molecular structure are called allotropes.

  20. Types of Compounds: Basic Concepts Topic 7 Allotropes • The properties of allotropes are usually different even though they contain the same element. • This is because structure can be more important than composition in determining properties of molecules.

  21. Types of Compounds: Basic Concepts Topic 7 Allotropes • Phosphorus has three common allotropes: white, red, and black. • All are formed from P4 molecules that are joined in different ways, giving each allotrope a unique structure and properties.

  22. Types of Compounds: Basic Concepts Topic 7 Formulas and Names of Molecular Compounds • Chemists have devised a naming system for molecular compounds that is based on a much smaller number of rules than there are compounds. • Substances are either organic or inorganic. Compounds that contain carbon, with a few exceptions, are classified as organic compounds.

  23. Types of Compounds: Basic Concepts Topic 7 Formulas and Names of Molecular Compounds • Compounds that do not contain carbon are called inorganic compounds. • To name these compounds, write out the name of the first nonmetal and follow it by the name of the second nonmetal with its ending changed to -ide.

  24. Types of Compounds: Basic Concepts Topic 7 Naming Organic Compounds • You have learned that most compounds that contain carbon are organic compounds. • Organic compounds make up the largest class of molecular compounds known. • This is because carbon is able to bond to other carbon atoms in rings and chains of many sizes.

  25. Types of Compounds: Basic Concepts Topic 7 Naming Organic Compounds • The name of even the most complex organic compound is based on the name of a hydrocarbon, an organic compound that contains only the elements hydrogen and carbon.

  26. Basic Assessment Questions Topic 7 Question 1 Determine the ratio of the atoms in the ionic compound formed in each case. A. aluminum (Al) and fluorine (F) B. lithium (Li) and oxygen (O)

  27. Basic Assessment Questions Topic 7 Answers A. aluminum (Al) and fluorine (F) one AL for every three F B. lithium (Li) and oxygen (O) two Li for every O

  28. Basic Assessment Questions Topic 7 Question 2 Write the correct formula for the ionic compound formed between atoms of each of the following pairs of elements. A. sodium (Na) and sulfur (S) B. magnesium (Mg) and nitrogen (N)

  29. Basic Assessment Questions Topic 7 Answers A. sodium (Na) and sulfur (S) Na2S B. magnesium (Mg) and nitrogen (N) Mg3N2

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