The Chemical Basis of LifeThe Chemical Basis of Life

Chapter 4Chapter 4

MatterMatter

Anything that occupies space.Anything that occupies space.Composed of one or more chemical Composed of one or more chemical

elements.elements.

Examples?Examples?

Element vs. CompoundElement vs. Compound

Element: A pure substance that can not be Element: A pure substance that can not be broken down into other substances by broken down into other substances by chemical means. chemical means.

Compound: Composed of two or more Compound: Composed of two or more elements that are chemically combined in elements that are chemically combined in a fixed ratio.a fixed ratio.

4 elements make up 96% of living matter in 4 elements make up 96% of living matter in your body.your body.

They are:They are:

O – OxygenO – Oxygen

H – HydrogenH – Hydrogen

C – CarbonC – Carbon

N – NitrogenN – Nitrogen

ExamplesExamples

H2O

Iron is an Element: Fe

Salt is a compound: NaCl

+ =

Water is a compound:Water is a compound:

Different elements have different Different elements have different propertiesproperties

These properties are based on the These properties are based on the structure of their atoms.structure of their atoms.

AtomsAtomsAre made up of subatomic particlesAre made up of subatomic particles

ProtonsProtonsNeutronsNeutronsElectronsElectrons

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Atomic NumberAtomic Number

The number of protons in an atomThe number of protons in an atomAll atoms of the same element have the All atoms of the same element have the

same atomic number. same atomic number.

Electrons and ReactivityElectrons and Reactivity

An atom’s electrons determine its An atom’s electrons determine its reactivity.reactivity.

There are different energy levels There are different energy levels surrounding the nucleus into which surrounding the nucleus into which electrons are placed.electrons are placed.

11stst Energy Level Energy Level

Closest to the nucleusClosest to the nucleusHolds 2 electronsHolds 2 electrons

Holds 8 electronsHolds 8 electrons

22ndnd Energy Level Energy Level

The energy levels closest to the nucleusThe energy levels closest to the nucleusHaving partially filled energy levels is what Having partially filled energy levels is what

makes atoms reactive. makes atoms reactive. Carbon:Carbon:

Draw models for:Draw models for:

Neon (10 electrons)Neon (10 electrons)

Nitrogen (7 electrons)Nitrogen (7 electrons)

Lithium (3 electrons)Lithium (3 electrons)

Which atom(s) is/are reactive? Which is/are Which atom(s) is/are reactive? Which is/are not as reactive?not as reactive?

Ionic BondsIonic Bonds

When an When an atom atom

transfers an transfers an electron to electron to

another atom.another atom.

Example:Example:

Lithium Fluoride (LiF)Lithium Fluoride (LiF)

Lithium (3 electrons) + Lithium (3 electrons) + Flourine (9 electrons)Flourine (9 electrons)

Ionic Bonds (continued)Ionic Bonds (continued)

When the electron moves from one atom When the electron moves from one atom to another, the atoms now become to another, the atoms now become charged (ions).charged (ions).

What are the charges on each atom?What are the charges on each atom?Li (+)Li (+)F (-)F (-)

What happens now with these two ions?What happens now with these two ions?

Covalent BondsCovalent Bonds

When two atoms share electronsWhen two atoms share electronsStronger than an ionic bondStronger than an ionic bond

Structure of WaterStructure of Water

H & O covalently bonded together.H & O covalently bonded together.

Water is polarWater is polar It has a slightly positive charge on one end It has a slightly positive charge on one end

and a slightly negative charge on the other. and a slightly negative charge on the other.