1. Chemical Bonds and Compounds www.physicalgeography.net

2. Elements combine to form compounds Compounds have different properties from the elements that make them Compounds have different properties from the elements that make them Atoms of different elements are held together by chemical bonds Atoms of different elements are held together by chemical bonds Bonds help to determine the properties of a compound Bonds help to determine the properties of a compound

3. Properties of Compounds Depend on atoms in the compound Depend on atoms in the compound Depend on how the atoms are arranged in the compound Depend on how the atoms are arranged in the compound Example: Example: C and H combine to form natural gas, auto gas, waxes in candle, plastics…etc.C and H combine to form natural gas, auto gas, waxes in candle, plastics…etc. www.alibaba.com

4. Properties of Compounds are different than the elements that make them H 2 O (water) H 2 O (water) H and O are colorless gases at room temperatureH and O are colorless gases at room temperature Water is a liquid at room temperatureWater is a liquid at room temperature NaCl (salt) NaCl (salt) Na is a metallic solidNa is a metallic solid Cl is a greenish-yellow gas that is poisonousCl is a greenish-yellow gas that is poisonous Table salt (NaCl) is used to flavor and preserve foodsTable salt (NaCl) is used to flavor and preserve foods www.sciencelearn.org.nz waterworks4u.com

5. Atoms combine in predictable numbers A given compound always contains atoms of elements in a specific ratio A given compound always contains atoms of elements in a specific ratio Ammonia NH 3 always has a 1:3 ratio of Nitrogen to Hydrogen Ammonia NH 3 always has a 1:3 ratio of Nitrogen to Hydrogen www.uh.edu

6. Chemical Formula Chemical Formula: uses the chemical symbols to represent the atoms of the elements and their ratios in the chemical compound. H 2 O 2:1 ratio of H to O Chemical Formula: uses the chemical symbols to represent the atoms of the elements and their ratios in the chemical compound. H 2 O 2:1 ratio of H to O www.brooklyn.cuny.edu

7. www.bennett29j.k12.co.us

8. Chemical Bonds hold Compounds Together Chemical bonds are the “glue” that holds the atoms of elements together Chemical bonds are the “glue” that holds the atoms of elements together Chemical bonds form when the electrons in the electron clouds interact Chemical bonds form when the electrons in the electron clouds interact bioactive.mrkirkscience.com

9. Atoms can transfer electrons Ions are formed when atoms gain or lose electrons Ions are formed when atoms gain or lose electrons Gaining electrons = negative charge Gaining electrons = negative charge Losing electrons= positive charge Losing electrons= positive charge

10. An elements location on the periodic table gives a clue as to the type of ions the atoms of that element will form An elements location on the periodic table gives a clue as to the type of ions the atoms of that element will form Group 1 metals (Li, Na, K…) usually lose one electron to form positive ions. Group 1 metals (Li, Na, K…) usually lose one electron to form positive ions. Group 2 metals (Be, Mg, Ca…) usually lose two electrons to form positive ions. Group 2 metals (Be, Mg, Ca…) usually lose two electrons to form positive ions. Group 17 nonmetals (F, Cl, Br…) gain one electron to form ions with a 1- charge. Group 17 nonmetals (F, Cl, Br…) gain one electron to form ions with a 1- charge. Group 16 nonmetals (O, S, Se…) gain two electrons to form ions with a 2- charge. Group 16 nonmetals (O, S, Se…) gain two electrons to form ions with a 2- charge.

11. Group 1 Group 1 lose e-Group 17 gains 1 e- Group 1 lose e-Group 17 gains 1 e- Group 2 lose 2e-Group 16 gains 2 e- Group 2 lose 2e-Group 16 gains 2 e-

12. Ionic Bonds The force of attraction between positive and negative ions. The force of attraction between positive and negative ions. Particles with opposite electrical charges attract each other Particles with opposite electrical charges attract each other Atom from element group 1 (1+) combines with an atom from element group 17 (1-) to form an ion. Atom from element group 1 (1+) combines with an atom from element group 17 (1-) to form an ion. Example Na combines with Cl Example Na combines with Cl Na loses 1 electron and Cl gains the electronNa loses 1 electron and Cl gains the electron Creating an ionic bondCreating an ionic bond

13. Ionic compounds Ionic bonds form between all nearby ions of opposite charge. Ionic bonds form between all nearby ions of opposite charge. Ionic compounds are very stable and their crystals are very strong. Ionic compounds are very stable and their crystals are very strong. The shape of the crystals formed depends on the ratio of positive to negative ions and the sizes of the ions The shape of the crystals formed depends on the ratio of positive to negative ions and the sizes of the ions

14. Names of Ionic Compounds First, take the name of the positive metal element First, take the name of the positive metal element Second, take the name of the negative, nonmetal element and give it an –ide ending Second, take the name of the negative, nonmetal element and give it an –ide ending Third, combine the two names Third, combine the two names Example: BaI 2 Example: BaI 2 1: barium 1: barium 2: Iodine…add ide…Iodide 2: Iodine…add ide…Iodide 3: barium iodide 3: barium iodide

15. Covalent Bonds A pair of shared electrons between atoms.(prefix co- means partner) A pair of shared electrons between atoms.(prefix co- means partner) Neither atom gains or loses an electron Neither atom gains or loses an electron The shared electrons are attracted to both positively charged nuclei. (nucleus has a positive charge because of protons) The shared electrons are attracted to both positively charged nuclei. (nucleus has a positive charge because of protons) A covalent bond is represented by a line between the two atoms A covalent bond is represented by a line between the two atoms I 2 I 2 I-I I-I

16. Covalent Bond The number of covalent bonds that an atom can form depends on the number of electrons that it has available for sharing. The number of covalent bonds that an atom can form depends on the number of electrons that it has available for sharing. Atoms of Group 16 (O,S…)can form two covalent bonds.Atoms of Group 16 (O,S…)can form two covalent bonds. Atoms of group 15 (N,P…) can form three bondsAtoms of group 15 (N,P…) can form three bonds Atoms of group 14 (C, Si…)can form four bondsAtoms of group 14 (C, Si…)can form four bonds

17. Valence Electrons Valence electrons: are the electrons in the outer electron cloud. Valence electrons: are the electrons in the outer electron cloud. Electrons orbit in shells: 2, 8, 18, 32, 50 Electrons orbit in shells: 2, 8, 18, 32, 50 (Inner shell is 2, next shell has 8 electrons…) A quick way to determine the number of valence electrons for a representative element is to look at which group it is in. A quick way to determine the number of valence electrons for a representative element is to look at which group it is in. Elements in group 1 have 1 valence electron. Elements in group 1 have 1 valence electron. Elements in group 2 have 2 valence Elements in group 2 have 2 valence

18. Finding Valence Electrons For example: For example: Sodium has an Atomic Number of 11 Sodium has an Atomic Number of 11 This means an atom of Sodium has 11 Protons This means an atom of Sodium has 11 Protons and therefore 11 electrons. The electrons are arranged as: The electrons are arranged as: First Shell = 2,First Shell = 2, Second Shell = 8,Second Shell = 8, Third Shell = 1Third Shell = 1 (Giving a total of 11.) (2+8+1=11)(Giving a total of 11.) (2+8+1=11) Na has 1 valence electron and is in group 1 Na has 1 valence electron and is in group 1 http://www.ecawa.asn.au/home/jfuller/chemistry/chem2.htm

19. Chemical Bonds Give all Materials their Structure Ionic Compounds (losing/gaining e-) Ionic Compounds (losing/gaining e-) Most have a crystal structureMost have a crystal structure Solid at room temperatureSolid at room temperature High melting and boiling points (takes a lot of energy to break the bond)High melting and boiling points (takes a lot of energy to break the bond) Hard, brittle, good conductors of electricity once the ions are separatedHard, brittle, good conductors of electricity once the ions are separated Dissolve easily in waterDissolve easily in water

20. Chemical Bonds Give all Materials their Structure Covalent Compounds (sharing valence e-) Covalent Compounds (sharing valence e-) Exist as individual moleculesExist as individual molecules Chemical bonds give each molecule a specific three-dimensional shapeChemical bonds give each molecule a specific three-dimensional shape Molecular shape can affect properties of the compoundsMolecular shape can affect properties of the compounds Melt and boil at lower temperatures (takes less energy to break up because atoms are organized as individual molecules)Melt and boil at lower temperatures (takes less energy to break up because atoms are organized as individual molecules)

21. Metals have unique bonds Metallic bond: the equal sharing of electrons in all directions so electrons move easily among the atoms of the metal Metallic bond: the equal sharing of electrons in all directions so electrons move easily among the atoms of the metal Atoms can slide past one another in metallic bonds which allows for easy shaping Atoms can slide past one another in metallic bonds which allows for easy shaping Properties of metals depend on bonds Properties of metals depend on bonds Good conductors of electric currentGood conductors of electric current High melting pointHigh melting point Solid at room temperature (except Hg)Solid at room temperature (except Hg) Easily shaped and poundedEasily shaped and pounded www.ndt-ed.org