Molecules, Bonding, Acids and Bases. Chemical Bonds molecule A group of atoms bonded to one another form a molecule. compound If the molecule has more.

Molecules, Bonding, Acids and Bases

Chemical Bonds• A group of atoms bonded to one another form a

moleculemolecule.• If the molecule has more than one type of

element present it is a compoundcompound.

• Examples: • O2 (two atoms of oxygen) is a molecule• H2O (two atoms of Hydrogen and one oxygen) is a

molecule and a compound

• Different types of bondsbonds hold molecules and compounds together.

Chemical FormulasFormulas are short hand way to tell you what is in

a moleculeThey include:• The symbol of each element in the molecule• The number of atoms of each element in the

molecule written as a subscript after the symbol

• Example: H2SO4 (sulfuric acid) is made up of 2 Hydrogen, one Sulfur and 4 Oxygen atoms

Chemical FormulasTypes of Formulas

Molecular formulas Only show the symbols of elements and their

proportions

Examples: Water Methane Carbon dioxide

H2O CH4 CO2

Chemical FormulasStructural formulas

show the relative positions and number of bonds between the elements in a compound

Examples: Water Methane Carbon dioxide

H H O H C HH O H C O

Composition of Matter - Compounds

Chemical BondsA chemical bond is the “glue” that holds the

elements together in compounds.The types studied this semester are:

Ionic, Covalent, HydrogenThe valence electrons of atoms determine how

an element will react and bond

Types of Chemical Bonds – Ionic Bonds Electrons can be lost or gained by atoms to fulfill the Octet

Rule.

When atoms lose or gain electrons, they become charged atoms, or ionsions– Atoms that lose an electron become Positive– Atoms that gain electrons become Negative

• Ionic bondsIonic bonds are formed when positive and negative ions are attracted to one another and bond together forming a molecule

• Usually between a metal and non metal that are far apart horizontally on the periodic table.

• A saltsalt is a dry solid composed of atoms connected by ionic bonds.

Example:

Sodium (one valence electron)

Loses the electron

Becomes positive (+)

Chlorine (seven valence electrons)

Gains the electron

Becomes negative (-)

Opposites Attract!

Each outer shell has eight electrons

Types of Chemical Bonds – Ionic Bonds

Types of Bonds – Covalent Bonds

• Formed when electrons are sharedshared among elements in a compound.

• Atoms can share one, two or three electrons based on their needs. (Octet rule)

• Usually formed between two non metals or a non metal and hydrogen

• Models or diagrams can be drawn to show the shared electrons

Types of Chemical Bonds

Chemical Equations• Short hand way to show how atoms bond and react with Short hand way to show how atoms bond and react with

each othereach otherEquationsEquations show the:• Reactants - chemicals that are reacting (at the beginning of

the equation)• Products - chemicals that are made (at the end of the

equation)• amount of each chemical involved – using coefficients before

the molecular formula• The reactants and products are separated with an arrow

Example:Two Water molecules produce two hydrogen and one oxygen molecule

2H2O 2H2 + O2

Reactants Reactants Products Products

Chemical Reactions

• Identify the reactantsreactants.

• Identify the productsproducts.

6 CO2 + 6 H2O C6H12O6 + 6 O2

carbondioxide water oxygenglucose

The chemical reaction for photosynthesis

Water, Acids, Bases and pHDissociationDissociation occurs when an ionic compound separates into its ions.

Example:Salt (NaCl) breaks apart into Na+ and Cl-

Na+ Cl-

Acids and Bases

• When water dissociates, it releases an equal number of ions.– Hydrogen ions (H+)– Hydroxide ions (OH-)

H – O – H H+ + OH-

Water, Acids, Bases and pHAcids

Acids will dissociate in water to release a hydrogen ion (H+)

Examples:HCl H2SO4

HC3H5O3

(Notice the H at the front of the formula)

Water, Acids, Bases and pHBases will dissociate in

water and release OH- (hydroxyl) ions

They have a low concentration of H+

Examples: NaOH KOH

(notice they end in –OH)

pH and the pH scale

• The pHpH is a mathematical way of indicating the number of H+ ions in a solution.

• The lower the number, the higher the concentration.

- pH of 1 is more acidic than a pH of 5• The pH scalepH scale is used to express acidity or

basicity (alkalinity).

Water, Acids, Bases and pHAcids have a low pH (less than 7) and bases have

a high pH (more than 7) 1 7 14

Strong Neutral Strong Acid Base

The farther away from neutral, the stronger the acid or base.

Water, Acids, Bases and pH• Extremely acidic: lemon=2.5; vinegar=3.0; stomach acid=2.0• Very strongly acid: tomatoes=4.5 • Strongly acid: carrots=5.0; asparagus=5.5; cabbage=5.3 • Moderately acid: potatoes=5.6 • Slightly acid: salmon=6.2; cow's milk=6.5 • Neutral: saliva=6.6–7.3; blood=7.3; shrimp=7.0 • Slightly alkaline: eggs=7.6–7.8 • Moderately alkaline: sea water=8.2; sodium bicarbonate=8.4 • Strongly alkaline: borax=9.0 • Very strongly alkaline: milk of magnesia=10.5, ammonia=11.1;

Water, Acids, Bases and pH• Mixing an acid with a base a chemical reaction

will change the pH of the mixture• Hydrogen ions will react with the hydroxyl

ions and form waterH + + OH- HOH

• If the ions are in equal amounts, the mixture becomes neutral (pH 7)

• This is called a neutralizationneutralization reaction.• The remaining ions form a salt.

Buffers and pH• It is very important for the body to maintain the

proper pH in different parts of the body. • The pH is kept in a narrow range to maintain

health. • One way the body does this is by producing

Buffers.

• A bufferbuffer is a chemical or combination of chemicals that keeps a pH within a given range.

• Buffers resist changes in pH by bonding to extra H+ or OH- in the solution.

Buffers and pH