Molecules and Compounds

Molecule  A molecule is formed when two or more atoms join together chemically.atoms  Ex: O ₂, NaCl, H ₂ O

Compounds  A compound is a molecule that contains at least two different elements.elements  Ex: NaCl, H ₂ O, O ₂  NOTE: All compounds are molecules but not all molecules are compounds.

Compound or Molecule?  CO ₂ H₂H₂  H ₂ SO ₄ N₂N₂

 Water (H 2 O), carbon dioxide (CO 2 ) and methane (CH 4 ) are compounds because each is made from more than one element.  For example, a single molecule of molecular hydrogen is made from two atoms of hydrogen (H ₂ )  A single molecule of water is made from two atoms of hydrogen and one atom of oxygen (H 2 O)

Chemical Equations  Chemical equations are used to show what happens in a chemical reaction.  This reaction shows the reaction of zinc with hydrochloric acid: Zn (s) + 2HCl (aq) → ZnCl 2(aq ) + H 2(g)

Parts of a Chemical Equation:  (s) = solid  (l) = liquid  (g) = gas  (aq) = aqueous solution (the substance is dissolved in water) Zn (s) + 2HCl (aq) → ZnCl 2(aq ) + H 2(g) Physical States

Parts of a Chemical Equation:  Reactants are the chemicals used in the reaction.  Products are the chemicals produced as a result of the reaction.  The arrow separates the reactants from the products and is pronounced as “yields” or “produces”. Zn (s) + 2HCl (aq) → ZnCl 2(aq ) + H 2(g) ReactantsProducts Arrow(Yields)

Parts of a Chemical Equation:  Coefficients are use to show how many molecules of that chemical is required for the reaction.  e.g. There are 2 molecules of HCl in this reaction.  Subscripts are used to show how many atoms of that element is in each molecule.  e.g. Each hydrogen gas molecule is made of two hydrogen atoms. Zn (s) + 2HCl (aq) → ZnCl 2(aq ) + H 2(g) CoefficientsSubscripts

Parts of a Chemical Equation:  Additional symbols may be used depending on the nature of the reaction: The reaction is reversible. Heat is used in this reaction. A catalyst is used in this reaction. In this case it is platinum.

Chemical Bonds  For compounds or molecules to form, bonds must be created between them  A chemical bond is an attraction between atoms that allows the formation of chemical substances that contain two or more atoms.  The bond is caused by the electrostatic force of attraction between opposite charges known as electrons

Chemical Bonds  There are two different types of chemical bonds, ionic bonds and covalent bonds  Covalent bonds are formed when atoms share electrons and are generally weaker  Ionic bonds are formed when atoms give their electrons to other atoms and are generally stronger

Structural Formulas  When atoms bond together to form molecules or compounds, they take on a structure  We can represent this as a structural formula which shows us how many atoms make up the compound and the bonds between them

Structural Formulas  Example: Hydrogen Gas H

Structural Formulas  Example: Hydrogen Chloride H Cl

Structural Formulas  Example: Sodium Chloride Na Cl

Structural Formulas  Example: Water O H H

Structural Formulas  Example: Ammonia H N H H

Structural Formula Example: Rust

Structural Formula Example: Sulfuric Acid

Condensed Formulas  We can write our structural formulas as molecular formulas that will still show the structure  We call these condensed formulas

Skeletal Formulas  Skeletal formulas are used in organic chemistry when learning about Carbon and Hydrogen bonding  When one Carbon atom bonds with Hydrogen, there must be four Hydrogen Atoms

Methane This is the structural formula for Methane gas We can represent this as a condensed formula CH ₄

Butane This is the structural formula for butane. We can represent this as a condensed formula CH ₃(CH₂)₂CH₃

Hexane This is the structural formula for hexane gas We can represent this as a condensed formula CH 3 (CH 2 ) 4 CH 3

Propane The is the structural formula for Propane We can represent this as a condensed formula

Skeletal Formulas  Skeletal formulas are used in organic chemistry when learning about Carbon and Hydrogen bonding  When one Carbon atom bonds with Hydrogen, there must be four Hydrogen Atoms This is the structural formula for butane

Butane This is the skeletal formula for butane CH ₃(CH₂)₂CH₃

Hexane  This is the skeletal formula for hexane CH 3 (CH 2 ) 4 CH 3

Propane