1. Lecture 3 Atoms and electron configurations Chemical bonds Polar covalent bonds and the water molecule

2. Atom: the fundamental unit of an element. Mostly empty space: if an atom were expanded to a diameter of 3 km, the nucleus would be the size of a basketball.

4. Element: a substance that cannot be broken down into simpler substances by chemical or physical means. –Composed entirely of one type of atom.

5. Periodic Table: arranges elements into rows so that those with the same properties are found in the same column.

8. Subatomic Particles Protons: Atomic number: number of protons in the nucleus of an atom. Elements are defined by their atomic number. Number of protons = Number of electrons in an electrically neutral atom.

9. Subatomic Particles Neutrons: Accompany protons in the nucleus. Atomic Mass Number: total number of protons and neutrons in the nucleus of an atom.

10. 1 atomic mass unit = 1.661 X 10 -24 grams

11. Chemical Reactions Chemical reactions = interactions of the electrons between atoms. Chemical Bond: the sharing or transfer of electrons to attain a stable electron configuration. Molecules: made from two or more chemically bonded atoms.

12. Electrons move within regions called principle shells. Each shell can hold a specific number of electrons. Outermost electrons are called valence electrons -involved in chemical bonding.

13. When an atom’s outermost shell does not contain the maximum number of electrons, an atom is likely to bond with other atoms.

15. 2 8 8 18 32 Each period on the periodic table corresponds with an electron shell being filled: 7 periods = 7 principle shells.

16. The noble gases have completely filled valence shells - are already stable. Other elements will gain or lose electrons in order to have a similar stable configuration – results in chemical bonds with other atoms.

18. Chemical Bonding Unpaired valence electrons are less stable have a strong tendency to participate in chemical bonding.

19. Compound: a substance consisting of chemically bonded atoms of different elements. Elements to Compounds

20. Compounds have properties uniquely different from the elements from which they are made. Elements to Compounds

21. Chemical formula: used to show the proportion by which elements combine to form a compound. CompoundFormula Sodium chloride NaCl Ammonia NH 3 Water H2OH2O Chemical Compounds Silica SiO 2

22. Ion: any atom with a net electrical charge Proton # does not equal electron #

24. Ionic Bond: a chemical bond in which valence electrons are transferred.

25. Ionic compounds: compounds containing ions. Bonds between elements on opposite sides of table are often ionic bonds.

27. Chemical Bonds Metallic Bond: a chemical bond in which positively charged metal ions are held together by a “fluid” of electrons.

28. Mobility of electrons in metals allows for: –significant conduction of heat and electricity. –malleability (can be deformed without breaking). –an opaque and shiny appearance.

29. Chemical Bonds Covalent Bond: a chemical bond in which valence electrons are shared – an overlap of outer electron shells. –Forms molecules in which atoms are bonded together without a complete transfer of electrons.

32. Polar Covalent Bonds

33. Dipole: a separation of charge due to an unequal attraction of bonding electrons. Electronegativity: attraction that an atom has for bonding electrons. –Greater towards the right-hand side of the periodic table. –Lowest on the left-hand side of the periodic table.

34. Electronegativities of Elements

35. Between elements on opposite sides of the periodic table. (metal + nonmetal) Between nonmetal atoms that are different. (transition between covalent and ionic) Between nonmetal atoms of the same element.

36. Polar Covalent Bonds The farther apart on the periodic table, the more polar the bond between elements (Hydrogen is the exception).

39. Polar Chemical Bonds Substances composed of polar molecules have higher boiling points. –Water molecules are electrically attracted to one another and are more difficult to separate.

40. Nonpolar substances have very low boiling points.

42. Dipole Attractions Dipole-Dipole attraction: electrical attraction between two polar molecules. Hydrogen Bonds = dipole-dipole attractions.

43. Water has high surface tension Molecules on the surface are attracted to the sides and inwards.

44. Ions and Dipoles Ion-dipole attraction between the dipole of a polar molecule and an ion.

45. Ion-Dipole attractions cause ionic substances to dissolve.

46. Properties of Water Water dissolves so many substances that it is considered a universal solvent.