Chapter 4

1. Chapter 4 The Structure of Matter

2. 4.1Compounds & Molecules • A compound is different from the elements it contains. • NaCl, Sodium chloride, is totally different than the metal, sodium, or the gas, chlorine.

3. Chemical bonds distinguish compounds from mixtures • The forces that hold compounds together are called chemical bonds. • During a chemical reaction chemical bonds are broken & atoms are re-arranged to form a new substance.

4. A compound has a specific formula • The formula for water is H2O • The formula for table sugar is C12H22O11. • Compounds are always made of specific elements in specific numbers. • A molecule of water is always H2O. [two hydrogen atoms bonded to one oxygen atom.]

5. Chemical structure illustrates the bonding within a compound • The way the atoms are arranged in a compound determine many of its properties. [water is polar; oil is non-polar] • Two terms are used to specify the positions of atoms relative to one another. • 1. Bond length: the average distance between the nuclei of the 2 bonded atoms • 2. Bond angle: the angle formed by two bonds to the same atom

6. Models of Compounds • A model helps you to “visualize” something. • 1. Ball & stick model: ball is the atom & the stick is the bond. • 2. Structural formulas: use symbols & lines to depict the structure. • 3. Space filling model: can’t “see” the bonds. [Fig. 4.4 P.111]

7. Structure • Different structures give compounds different properties. • Network structure: SiO2is an ionic compoundwhichhas a strong, rigid structure. All the angles are the same (109.5o). • This is why rocks containing SiO2 are hard & inflexible. It takes a lot of energy to break these bonds. (high melting point)

8. Some network bonds are ionic • Some networks are made of bonded ions (charged particles). NaCl is made of a network of tightly packed positive Na+ and negative Cl- ions. • The result is strong, rigid bonds that have high melting & boiling points. • Ionic bonds occur between a positive metal ion & a negative nonmetal ion.

9. Some compounds are molecules • Molecules are made when nonmetals combine with nonmetals. • The bonds can be weak or strong. • Molecules of gases have little attraction to each other, so they spread out & fill any size container.

10. Strength of attraction between molecules • Attraction forces are greatest in solids. • Attraction forces are less in liquids, and even less in gasses. (see data table 4.2 on p. 113) • The higher melting & boiling points of water are due to the strong bonds within the water molecule. • Each water molecule is attracted to the molecule next to it, due to the polar nature of the molecule. • Teacher demo p.113

11. 4.2Ionic & Covalent Bonding • Atoms bond when their valence electrons interact. • When atoms gain or lose electrons they form ionic compounds. • When atoms share electrons they form molecules.

12. 4.2Ionic & Covalent Bonding • Bonds between atoms act like flexible springs, because they can bend & stretch without breaking

13. Ionic Bonds • Ionic bonds occur between ions of opposite charge. • Metals lose electrons to become positive ions, called cations. • Nonmetals gain electrons to become negative ions, called anions.

14. Ratio’s • NaCl means 1 atom of Na is bonded to 1 atom of Cl. The Na+ is attracted to the Cl-(opposites attract). • Within a network there are millions of positive ions being attracted to the millions of negative ions. NaCl is the formula unit. • The formula unit varies according to the compound. Ex.: CaF2

15. Ionic compounds conduct electricity when melted • Electric current is the result of moving charges. • When in solid form, ionic compounds do not conduct electricity because the ions are locked in position (crystal). • However, in liquid form, the ions are free to move about and they do conduct electricity

16. Metallic Bonds • Metals conduct electricity, are malleable & ductile. • Electrons move freely between metal atoms. “sea of electrons” • The atoms are packed so closely that the valence electrons overlap each other (sea of electrons). This frees up the electrons to move from atom to atom. • Remember, electricity is the result of moving charges.

17. Covalent Bonds • Covalent bonds form molecules (nonmetals bonding to nonmetals) • Covalent compounds can be solid, liquid or gas. • Most covalent substances have low melting points. • Covalent bonds do not conduct electricity.

18. Covalent bonds share electrons • Electrons are shared so that both atoms achieve the “magic number” of chemistry – 8, valence electrons. • If the shared electrons are equally attracted to each nucleus, they produce a nonpolar covalent bond. • The sharing is represented by a single line between the atoms. See p.119

19. Atoms may share more than 1 pair of electrons • In a double covalent bond, 2 pairs of electrons are shared. • In a triple covalent bond, 3 pairs electrons are shared. • Triple bonds are stronger than double bonds. • Triple & double bonds are shorter than single bonds.

20. Electrons are not always equally shared • In some instances electrons are attracted more to one nucleus than another. • This results in a polarmolecule. • Usually electrons are more attracted to elements on the upper right side of the Periodic Table. • Water is a good example of a polar molecule.

21. Polyatomic ions • Some compounds have both ionic and covalent bonds; such compounds contain polyatomic ions. • Polyatomic ions are groups of covalently bonded atoms that have either lost or gained electrons. • Polyatomic ions act just like normal ions. • Parentheses are used to denote when more than one ion is bonded to another. • The corresponding subscript indicates that everything inside the parentheses is effected by that subscript.

22. Naming the polyatomic ions • -ite & -ate are suffixes that indicate the presence of oxygen. • These endings do NOT tell you how many oxygen atoms are present. • If there is –ate at the end of the name, there is 1 more oxygen atom than if there is an –ite at the end. • The charge is the same for each ion • Some have neither –ite or –ate, these don’t follow the rules.

23. 4.3Compound Names & Formulas • Naming ionic compounds – cations & anions form compounds with strong bonds. • Both elements’ names are represented in the name. Ex.: BaF2 is Barium Fluoride. • In many cases, the name of the cation is simply the name of the element. • When the anion is made of 1 element, the anion has a name similar to the name of the element but the ending is different. See fig. 4.5 on p. 124

24. Some cation names reflect the charge • According to what we have learned, FeO and Fe2O3 should both be called iron oxide. • Iron (Fe) is a transition metal. • Transition metals can lose 1 or 2 or 3 valence electrons. To distinguish between the two a Roman numeral is added in parentheses. • The Roman numeral tells the charge • Iron (III) oxide tells us iron is Fe3+ (a cation that lost 3 electrons).

25. Determining the charge of transition metals • Total charge of every compound must be zero. • In Fe2O3 there are 3 oxygen atoms. • Oxygen & all elements in column 6 have oxidation #’s of 2- • 3 oxygen atoms times – 2 charge = -6 • To total zero for the whole compound, iron must have a charge of +6. • There are 2 iron atoms, so each must have a +3 charge • Therefore we are working with iron (III)

26. Naming Covalent Bonds • With two element covalent bonds, numerical prefixes tell us the number of atoms present in the compound. • If there is only 1 atom of the 1st element listed, there is no prefix. For 2 atoms use the prefix di-, for 3 atoms tri- etc. • The element furthest to the right on the Periodic Table is named 2nd & ends in -ide

27. Naming Covalent Compounds

28. Naming Covalent Compounds • BF3Boron trifluoride • N2O4Dinitrogen tetroxide

29. A compound’s simplest formula is its empirical formula • Empirical formula: the smallest whole number ratio of the atoms in a compound. • We use the molecular formula to denote exactly how many atoms are in one molecule of a compound. • Some compounds have the same empirical formula, but different molecular formulas. For example, formaldehyde, CH2O; acetic acid, C2H4O2; & glucose, C6H12O6 – all have the empirical formula of CH2O

30. 4.4Organic & Biochemical Compounds • An organic compound is a covalently bonded compound made of molecules. • Organic compounds contain carbon & usually hydrogen. • When a compound has only carbon & hydrogen it is called a hydrocarbon. • Methane, CH4, has 4 single bonds. Methane is formed when living matter decays. • Carbon can also form double bonds when it shares 2 of its electrons. Triple bonds are also possible but carbon can never forms more than 4 bonds.

31. Alkanes • An alkane is a hydrocarbon that has only single bonds – like we mentioned for CH4. • Alkanes can have C-H bonds or C-C bonds. • Alkanes names end in –ane.

32. Alkenes • Hydrocarbons that have at least 1 double bond, C=C • Alkenes names end in –ene. • Alcohols • Alcohols are organic compounds that contain hydrogen, carbon & oxygen. • Alcohols have hydroxyl or –OH groups

33. Polymers • A polymer is a large organic molecule made of many smaller bonds. • Small organic molecules bond to form long chains called polymers. • Polymers are found in your body, wood, rubber & plastic. • Rubber, wood, cotton are examples of natural polymers. • Man-made polymers are usually either plastic or fibers. • The structure determines its properties, just as for other compounds. • Polymers are likened to a bowl of spaghetti, tangled but can slide over one another.

34. Biochemical Compounds • A biochemical compound is any organic compound that is important to living things. • Some examples include carbohydrates for energy & proteins that form all the organs in our body. • Carbohydrate: any organic compound that is made of carbon, hydrogen & oxygen & that provides nutrients to the cells of living things.

35. Proteins • A protein is a biological polymer made of bonded amino acids. • An amino acid is any of 20 different naturally occurring organic molecules that combine to form proteins. • Amino acids (there are 20) are made C, H, O, & N. • How they combine determines the protein. • Proteins are long chains of amino acids.

36. DNA is a polymer w/complex structure • DNA determines entire genetic make up & is made of C, H, O, N & P. • DNA has the shape of a twisted ladder known as a double helix. • Every cell in your body has a copy of your genetic make up.