1. Chemical Bonds and Compounds

2.  Compounds have different properties from the elements that make them Most substances are compounds  Compound: substance made of atoms of two or more different elements Held together by chemical bonds Bonds help to determine the properties of a compound  Properties of compounds are often very different from the properties of the elements

3.  Chemical formulas: *combinations of chemical symbols which represent the atoms of the elements and their ratios in a chemical compound Subscript: a number written to the right of a chemical symbol and slightly below it.  Carbon dioxide: CO 2 One carbon bonded to two oxygen  Using the same elements in different ratios will change the compound H 2 O = Water H 2 O 2 = Hydrogen peroxide

4. Compound Name AtomsAtomic ratio Chemical Formula Hydrogen Chloride H Cl 1:1HCl WaterH H O 2:1H20H20 AmmoniaN H H H 1:3 NH 3 MethaneC H H H H 1:4CH 4 Propane H H H H C C C H H H H 3:8C3H8C3H8

5.  Chemical bonds between atoms involve electrons: Chemical bonds form when the electrons in the electron clouds around two atoms interact. The type of bond is determined by the way the electrons interact.

6.  Ions: Formed by gaining or losing electrons:  Gain electrons = negative ion  Lose electrons = positive ion  Periodic table location: All metals lose electrons to form positive ions Nonmetals gain electrons to form negative ions Transition metals lose electrons to form positive ions Noble gases (group 18) do not normally gain or lose electrons and do not normally form ions

7.  The force of attraction between positive and negative ions  When a sodium atom bonds to a chlorine atom, they are attracted to each other by electrical attraction  The outer shell of sodium contains one electron  The outer shell of chloride contains 7 electrons (both want to have a full outer shell of 8)  They join together giving both atoms a “full shell”

9.  Based on the ions it is made of  Positive ions: Same as the name of the atom it is formed from  Negative ions: Formed by dropping the last part of the name of the atom and adding the suffix –ide  Compounds: Positive ion first, followed by name of negative ion Sodium chloride (sodium + and chlorine is - )

10.  A bond formed by the sharing of electrons Neither atom gains or loses an electron No ions are formed  Depends on the number of electrons available Halogens (group 17) and hydrogen = 1 Group 16 = 2 Group 15 = 3 Carbon and Silicon (group 14) = 4

11.  Double and Triple bonds: Double bonds consist of four (two pairs of) shared electrons Triple bonds consist of six (three pairs of) shared electrons  Molecule: Group of atoms held together by covalent bonds Some molecules contain atoms of only one element:  H 2, N 2, O 2, F 2, Cl 2, Br 2, I 2

12.  A covalent bond in which the electrons are shared unequally  Polar means anything that has two extremes  In water (H 2 0) Oxygen has 8 protons in the nucleus Hydrogen has 1 proton in the nucleus Oxygen has a stronger + pull which pulls the electron from hydrogen toward it

13.  Ionic Compounds: Most have a regular crystal structure When put under pressure they will shatter  Covalent compounds: Each molecule has a specific 3-D shape called its molecular structure Common shapes are: linear, bent, pyramid  Molecular structure influences everything from how it feels when touched to how it will interact with other substances.

14.  Metals have unique bonds: Metallic bond: the equal sharing of electrons by metals allowing the electrons to move easily among the atoms of the metal. Properties of metals are determined by metallic bonds:  Good conductors of electric current and heat  Have high melting points  Solids at room temperature except Hg  Easily shaped

15.  Ionic compounds: Mostly solids at room temperature Usually have extremely high melting and boiling points Hard and brittle Poor conductors of electricity Dissolve easily in water where they separate + and – ions and become good conductors  Covalent compounds: Lower melting and boiling points Stay together when dissolved in water Poor conductors of electricity

16.  Carbon has three specific forms: Diamond:  Hardest natural substance  Carbon atoms covalently bonded with 4 other carbon atoms (3-D crystal shape) Graphite:  Dark and slippery  Carbon atoms covalently bonded with 3 other carbon atoms (2-D layers stacked on top of each other) Fullerene:  Large molecules shaped like a soccer ball  Buckyballs and carbon nanotubes