Chemical Bonds and Compounds

1. Chemical Bonds and Compounds www.physicalgeography.net

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

3. Properties of Compounds • Depend on atoms in the compound • Depend on how the atoms are arranged in the compound • Example: • 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 • H2O (water) • H and O are colorless gases at room temperature • Water is a liquid at room temperature • NaCl (salt) • Na is a metallic solid • Cl is a greenish-yellow gas that is poisonous • Table 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 • Ammonia NH3 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. H2O 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 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 • Gaining electrons = negative 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 • 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 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.

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

12. Ionic Bonds • The force of attraction between positive and negative ions. • 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. • Example Na combines with Cl • Na loses 1 electron and Cl gains the electron • Creating an ionic bond

13. Ionic compounds • Ionic bonds form between all nearby ions of opposite charge. • 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

14. Names of Ionic Compounds • First, take the name of the positive metal element • Second, take the name of the negative, nonmetal element and give it an –ide ending • Third, combine the two names • Example: BaI2 • 1: barium • 2: Iodine…add ide…Iodide • 3: barium iodide

15. Covalent Bonds • A pair of shared electrons between atoms.(prefix co- means partner) • 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) • A covalent bond is represented by a line between the two atoms • I2 • 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. • Atoms of Group 16 (O,S…)can form two covalent bonds. • Atoms of group 15 (N,P…) can form three bonds • Atoms of group 14 (C, Si…)can form four bonds

17. Valence Electrons • Valence electrons: are the electrons in the outer electron cloud. • 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.  • Elements in group 1 have 1 valence electron.  • Elements in group 2 have 2 valence

18. Finding Valence Electrons • For example: • Sodium has an Atomic Number of 11 • This means an atom of Sodium has 11 Protons and therefore 11 electrons. • The electrons are arranged as: • First Shell = 2, • Second Shell = 8, • Third Shell = 1 • (Giving a total of 11.) (2+8+1=11) • 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-) • Most have a crystal structure • Solid at room temperature • High melting and boiling points (takes a lot of energy to break the bond) • Hard, brittle, good conductors of electricity once the ions are separated • Dissolve easily in water

20. Chemical Bonds Give all Materials their Structure • Covalent Compounds (sharing valence e-) • Exist as individual molecules • Chemical bonds give each molecule a specific three-dimensional shape • Molecular 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)

21. www.ndt-ed.org Metals have unique bonds • 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 • Properties of metals depend on bonds • Good conductors of electric current • High melting point • Solid at room temperature (except Hg) • Easily shaped and pounded