Molecules and Compounds. Molecule A molecule is formed when two or more atoms join together...
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Transcript of Molecules and Compounds. Molecule A molecule is formed when two or more atoms join together...
Molecules and Compounds
Molecule
A molecule is formed when two or more atoms join together chemically.
Ex: O₂, NaCl, H₂O
Compounds
A compound is a molecule that contains at least two different elements.
Ex: NaCl, H₂O, O₂
NOTE: All compounds are molecules but not all molecules are compounds.
Compound or Molecule?
CO₂
H₂
H₂SO₄
N₂
Water (H2O), carbon dioxide (CO2) and methane (CH4) 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 (H₂)
A single molecule of water is made from two atoms of hydrogen and one atom of oxygen (H2O)
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) → ZnCl2(aq) + H2(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) → ZnCl2(aq) + H2(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) → ZnCl2(aq) + H2(g)
Reactants ProductsArrow(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) → ZnCl2(aq) + H2(g)
Coefficients Subscripts
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 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 gasWe can represent this as a condensed formula CH₄
Butane
This is the structural formula for butane. We can represent this as a condensed formula CH₃(CH₂)₂CH₃
Hexane
This is the structural formula for hexane gas
We can represent this as a condensed formula CH3(CH2)4CH3
Propane
The is the structural formula for PropaneWe 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
CH₃(CH₂)₂CH₃
Hexane
This is the skeletal formula for hexane
CH3(CH2)4CH3
Propane