13 chemical bonding

Chemical BondingChapter 13

To Bond or Not to Bond

But instead there is an attraction.

Atoms bond by gaining, losing or sharing electrons.

Common Chemical Formulas

• C6H12O6 Glucose

• C6H8O6 Vitamin C

• C6H8O7 Citric Acid

• C2H5OH Ethyl Alcohol

Definitions

• Compound: A substance made up of atoms of 2 or more different elements joined by Chemical Bonds.

• Molecule: The smallest unit of a substance that keeps all of the physical and chemical properties of that substance.

• Rule of 8 (Octet):Elements gain or lose electrons to become like the closest Noble gas.

More Definitions

• Ion: A charged particle that forms when an atom or group of atoms gains or loses one or more electrons.

• Anion: A negatively charged particle

• Cations: A positively charged particle

Remember!!

8 valence electrons in the outer shell is considered complete except for Helium which has a complete outer shell of 2.

The Goal of Bonding

Create Neutrally Charged Particles!

Valence Electrons are the Key

Element Types

• Metals usually give up electrons.– 1 to 2, rarely 3.– Atoms become

ElectroPositive (Cations)

• Non Metals gain electrons easily.– Atoms become

Electronegative (Anions)

Element types

• Metalloids and Noble gases are least likely to bond.

Types of Bonding

• Ionic• Covalent• Metallic

Ionic Compounds

• Salts• Created when metal

ions and non Metal ions bond.

• They have a strong attraction!

Energy is needed to gain or lose electrons

Only small amounts of energy is needed to take an electron from

a metal!

When an atom gains electrons they give off energy as well.

The easier an atom gains electrons the more energy they

give off.

Magnesium

• 2 Valence Electrons• Neutral

Magnesium Ion (Mg2+)

• Loses 2 electrons• Becomes a Positive

Ion (Cation)

Oxygen

• 6 Valence electrons• Neutral

Oxygen Ion (O2-)

• Gains 2 electrons• Becomes a negative

ion (anion)• ‘ide’ is added to the

end of an ion that gains electrons.

• Oxide

Magnesium Oxide

• MgO

Sometimes it takes more than one of each atom to make an

Ionic Compound

Magnesium Chloride MgCl2

+

Remember that the total electrons lost must equal the total

electrons gained.

Al3O2

Aluminum Oxide

• Aluminum has 3 valence electrons

• Oxygen needs 2 to complete the Octet.

Aluminum Oxide

OR

Aluminum Oxide

Al3+

Al3+

O2-

O2-

O2-

Properties of Ionic Compounds

Most have similar characteristics

Remember

Ionic Compounds are created because of a strong attraction

between Metals and Non Metals

Form Crystals

• The salt you eat is a crystal!

Brittle

• Can be ‘Cleaved’– Split

• When hit (pressure) the layers shift and line up making a crack.

High Boiling and Melting Point

• Sodium Chloride melts at 801oC

• Boils at 1465oC or 2669oF

• Salt water Boils at a higher temperature than regular water.

When placed in water it will dissolve.

Called electrolytes

Covalent Bonding

Non Metal Bonding

Covalent Bonds form when atoms share one or more electrons

The bond is more like a marriage rather than one atom taking over

the others electrons.Called Covalent because each

atom contributes equally!

RememberAtoms like complete outer shells.

Simplest Example is Hydrogen

• When one hydrogen encounters another hydrogen, their electrons pair up.

Hydrogen Molecule H2

• Each hydrogen atom thinks it has a full outer shell.

• Stable• Normal temperature,

hydrogen is found this way.

This type of molecule is called a Diatomic molecule

• Hydrogen

• Oxygen

• Nitrogen

• Fluorine

• Chlorine

• Bromine

More Complex

And these where mild!

Plastics

Proteins

DNA

Properties of Covalent Compounds

• Molecules are bonded weakly together(but not the single molecule)

• Low melting and boiling points

• Poor Conductors– Water needs a salt dissolved in it to conduct

electricity

• Sometimes Flammable– Organic compounds like wood

Metallic Bonds

Bonds that are formed by the attraction between positively charged metal ions and the

electrons around them

Metallic Atoms Come Close Together

Their Electrons Create a “Sea” of Electrons blending their outer shells

Basically the Valence electrons “Swim” around the Metal Ions

Keeping them together.

Properties

• Conduct electrical Current

• Malleable• Ductility• Flexible (non-brittle)

Naming Covalent Compounds

Rules

• 1. The first word is the first element.

• 2. Second word is the Second atom.– Add “ide” to the end like in Ionic compounds.

Rules

• 3. Add prefixes if more than one atom or molecule is present.– 1 mono– 2 di-– 3 tri-– 4 tetra-– 5 penta-– 6 hexa-– 7 hepta-– 8 octa-

Rules

• 4. Special cases:– Water H20

– Ammonia NH3

– Methane CH4

– There are others

You Try

• PCl3

• CO2

• SF6

• NCl3

• Phosphorus Trichloride

• Carbon Dioxide

• Sulfur Hexafloride

• Nitrogen Trichloride

Formulas from Names

Reverse the Process

Try

• Hydrogen Bromide

• Silicon Dioxide

• Oxygen Dichloride

• HBr

• SiO2

• OCl2

Homework

Photos taken from

• The Cartoon Guide To Chemistry

• Google Search “Crystals”