Chemical Bonds

Chapter 20

• What do these have in common?

Combined Elements

• The statue of liberty is green but it is made of copper.

• Because the surface copper has combined with oxygen and sulfur to become a new element Copper Sulfate

Compounds

• Compound – a substance formed from two or more elements in which the exact combination and proportion of elements is always the same

• H20 – 1 water molecule is a compound that always has 2 hydrogen atoms and one oxygen atom

Compounds

• When compounds are formed they take on new properties and characteristics different from the elements they were made from

– Ex. Chlorine is a greenish-yellow gas that is poisonous, Sodium is a shiny, soft silvery metal that reacts violently with water. But together these two elements form Sodium Chloride, NaCl (table salt).

Chemical Formula

• A chemical formula tells what elements a compound contains and the exact number of the atoms of each element in the unit of that compound

• Subscript in a chemical formula tells how many atoms of that element are found in that compound– C6H12O6 – has 6 carbons, 12 hydrogens, and 6 Oxygens– If no subscript is found after an element symbol then

the number of atoms is one (SiO2 – sand)

How many atoms of each are found in the following?

• C12H22O11

• HCl • H2SO4

• N2O • CH3COOH

How many atoms of each are found in the following?

• C12H22O11 – Cane Sugar (Sucrose)• HCl – Stomach Acid (Hydrochloric Acid)• H2SO4 – Battery Acid (Sulfuric Acid)• N2O – Laughing Gas (Dinitrogen Oxide)• CH3COOH – Vinegar (Acetic Acid)

Chemical Stability

• An atom is chemically stable when its outer energy level is complete.

• Noble gases – outer energy level is full – thus are stable

• Outer energy levels– The outer energy levels of hydrogen and helium

will be stable with two electrons. The outer energy levels of all the other elements are stable when they contain eight electrons

Chemical Stability

• With the exception of Noble Gases most elements are in a state of instability.

• To obtain stability atoms will lose, gain, or share electrons in its outer energy level.

• They do this by combining with other atoms that also have partially complete outer energy.

• Ex. Sodium Chloride

Electron Dot Diagrams

• Show the electrons in the outer energy level of an atom

• Most atoms need eight electrons to complete their outer energy level.

Chemical Bond

• When atoms gain, lose, or share electrons, an attraction forms between the atoms, pulling them together to form a compound.

• A chemical bond is the force that holds atoms together in a compound.

Types of Bonds

• Ionic Bond• Covalent Bond

Gain or loss of electrons

• When an atom gains or loses an electron it forms an ion.

• Ion – is a charged particle because it now has either more or few electrons than protons

Ionic Bond

• If an atom loses an electron it becomes a positive ion (cation) because it now has more protons than electrons

• If an atom gains an electron it becomes a negative ion (anion) because it now has more electrons than protons

Ionic Bond

• When these atoms become charged they now have attractive forces and will form an ionic bond.

• This will maintain that the compound that has now been formed will be a neutral compound.

• Examples: NaCl and MgCl2

Ionic Bonds

• Usually formed by bonding between metals and nonmetals.

Covalent Bonds

• The attraction that forms between atoms when they share electrons.

• Some elements do not want to lose or gain their electrons because they have too many to lose or gain.

Covalent Bonds

• A Molecule is a neutral particle formed as a result of electrons being shared.

• Single covalent bond – made up of two shared electrons – one from two different atoms

• Multiple bonds – more than one electron are shared between two atoms

Electron Dot Diagrams

• How to write electron dot diagrams for ionic and covalent bonds