The Structure of Matter Section 1 – Compounds and Molecules Section 2 – Ionic and Covalent Bonding Section 3 – Compound Names and Formulas State Standards • CLE.3203.1.6 – Distinguish between common ionic and covalent compounds • CLE.3202.1.7 – Construct chemical formulas for common compounds • CLE.3202.TE.4 – Describe the dynamic interplay among science, technology, and engineering within living, earth-space, and physical systems 1 – Compounds and Molecules KEY QUESTIONS • What holds a compound together? • How can the structure of chemical compounds be shown? • What determines the properties of a compound? Chemical Bonds • Forces that hold atoms or ions together in a compound are chemical bonds – H and O form bonds when water is formed Chemical Structure • The way that atoms are bonded together to make a compound results in chemical structure • This structure can be shown by various models – Example : Ball and Stick Model Chemical Structure • Some models show bond length and bond angles – Ball and stick • Other models show space occupied by compounds – Space-filling model ( Figure 2 in Chapter 6 – page 178 ) – ETHANOL Bonds are like SPRINGS • Bonds are flexible and act like springs • Bonds can bend, stretch, compress, and twist – Do this without breaking • Temperature affects this motion ( Kinetic Theory ) How Structure Affects Properties • Chemical structure determines properties • Network structures form strong solids – Quartz ( network of rigid Si-O-Si bonds ) • Some networks consist of bonded ions – Salt ( NaCl formed from Na+ and Cl- ions ) – Group 1 elements form cations / Group 17 anions • Some compounds are made of molecules – Sugar is a group of single ( the same ) molecules Attractive Forces Vary • Example : H2O • Water is liquid at room temp • Sugar is solid at room temp • Indicates that water has weaker attractive forces Attractive Forces Vary • Forces between molecules • Example : H2O • Water has higher melting point than H2S • Indicates that water has stronger attractive forces 1 – Compounds and Molecules KEY QUESTIONS • What holds a compound together? • How can the structure of chemical compounds be shown? • What determines the properties of a compound? 2 – Ionic and Covalent Bonding KEY QUESTIONS • Why do atoms form bonds? • Why do ionic bonds form? • What do atoms joined by covalent bonds share? • What gives metals their distinctive properties? • How are polyatomic ions similar to other ions? Why do Chemical Bonds Form? • In general, atoms join to form bonds so that each atom may have a stable electron configuration • They want a full level of valence electrons!! Ionic Bonding • Formed from the attraction between ions • Ions are formed by transfer of electrons – Na and Cl form salt • Ionic compounds form as networks – Solids are the result • Ionic compounds dissolved in water conduct electricity Covalent Bonds • These are formed when electrons are SHARED • EXAMPLES : O2, Cl2, N2 • Atoms may share more than one pair of electrons • Atoms do not always EQUALLY SHARE electrons Metallic Bonds • A type of covalent bond • Occurs between metals • Electrons move freely between metal atoms • Metals are flexible and conduct electricity well because their atoms and electrons can move freely throughout the packed structure Polyatomic Ions • Acts as a single unit in a compound, like ions that consist of a single atom do ( like Cl, Na ) • Hydroxide ( OH - ) – NaOH • Carbonate ( CO3 2- ) – CaCO3 • Ammonium Sulfate : (NH4)2SO4 +1 -2 Polyatomic Ions • Some of these are named based on the number of oxygen atoms in compound • Nitrate vs Nitrite – NO3- vs NO2- • Chlorate vs. Chlorite – ClO3- vs ClO2- 2 – Ionic and Covalent Bonding KEY QUESTIONS • Why do atoms form bonds? • Why do ionic bonds form? • What do atoms joined by covalent bonds share? • What gives metals their distinctive properties? • How are polyatomic ions similar to other ions? 3 – Compound Names & Formulas KEY QUESTIONS •How are ionic compounds named? •What do the numerical prefixes used in naming covalent compounds tell you? •What does a compound’s empirical formula indicate? Naming Ionic Compounds • Ionic compounds are named based on the constituent ions • Cations ( + ) are named based on the element – “calcium” – “magnesium” Naming Ionic Compounds • Anions ( - ) are altered names of elements – “oxide” – “chloride” Put ‘Em Together • sodium chloride ( NaCl ) • magnesium chloride ( MgCl2 ) • aluminum oxide ( Al2O3 ) Formula Unit • • • • sodium chloride ( NaCl ) magnesium chloride ( MgCl2 ) aluminum oxide ( Al2O3 ) calcium fluoride ( CaF2 ) Wikepedia.org Naming Ionic Compounds • Charge ( + ) of many transition metals varies – Fe may have 2+ or 3+ • Thus, some names show cation charge – iron(III) oxide [common form ] – iron(II) oxide • Can also see charge in chemical formulas – Fe2O3 [ Fe3+ since Oxygen is often O2- ] – FeO [ both ions have a ‘2’ charge ] Naming Covalent Compounds • Numerical prefixes indicate chemical formula when more than atom is involved • Examples: – carbon dioxide ( CO2 ) – silicon dioxide ( SiO2 ) – boron tetrafluoride ( BF3 ) – Dinitrogen tetroxide ( N2O4 ) N2O4 via Wikepedia.org Empirical Formulas • Indicates the smallest whole-number ratio of atoms in a compound – Some are same as chemical formula • Hydrogen Peroxide is exception: • Chemical Formula – H2O2 • Empirical Formula – HO • Formaldehyde, acetic acid, and glucose have same empirical formula Empirical Formula • Molecular Formulas ( had Formula Unit for Ionics ) • Emprirical formula can be determined by analyzing mass of each element in a compound 3 – Compound Names & Formulas KEY QUESTIONS •How are ionic compounds named? •What do the numerical prefixes used in naming covalent compounds tell you? •What does a compound’s empirical formula indicate?