Chapter 4 The Chemical Basis of Life 4.1 Elements Matter: anything that occupies space and has mass Element: pure substance that cannot be broken down.

Chapter 4

The Chemical Basis of Life

4.1 ElementsMatter: anything that occupies space and has massElement: pure substance that

cannot be broken down into other substances by chemical means

– Ex. gold(Al), carbon(C), oxygen(O)– 25 essential to life

• 96% of our body= oxygen, nitrogen, carbon, hydrogen• 4% = calcium, phosphorous, potassium, sulfur, & others• < 0.01% are Trace Elements like iodine and iron

Compound: 2 or more elements– Ex. Carbon dioxide(CO2), water(H2O)

4.2 Atoms atom: smallest possible

particle of an elementSubatomic particles– proton: single unit of positive electrical charge (+)– electron: negative electrical charge (-)– neutron: electrically neutral = no charge

An element’s physical and chemical properties depend on the number and arrangement of its subatomic particles– Ex. Shiny luster of copper metal

Atom Structure

Nucleus: central core composed of neutrons and protonsElectron “cloud”:

area in which the electrons travel

– No exact path– Much larger than nucleus

Atomic number: number of protons in an atom– Differentiates elements

Isotopes

Isotope: an element that has the same number of protons but different number of neutrons– Can make an element

radioactive– ex: 12C = normal, 14C

=radioactive

Radioactive Isotope: nucleus decays over time giving off radiation in the form of matter and energy– ex. Carbon dating

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Energy LevelsThe structure of the atom determines how it reacts with other atoms– Based on electrons

Electrons differ in the amount of energy they have and how tightly they are held by the protonsEnergy Levels– First level = lowest, nearest to

nucleus– Most reactive when they have

partially full energy levels

4.3 Chemical Bonds

ionic bond: an atom transfers an electron to another atom– ex. NaCl

ion: atoms that have become electrically charged as a result of gaining or losing electrons

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Covalent Bonds

covalent bonds: two atoms share electrons – Number of bonds

formed= additional in highest level

Molecular Formulas

molecule: 2 or more atoms held together by covalent bonds

Chemical formula = number and types of atoms in a molecule– ex. H2O

Structural formula= how atoms are linked by bonds

Space-filling model= colored spheres

Chemical Reactions chemical reactions: bonds break or form new bonds which result in the formation of one or more new substances– Some absorb energy and

some release more than they absorb

reactants: starting material products: ending materials

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4.4 Properties of Water

~70-95% in cells

polar molecule: a molecule in which ends have opposite electric charge

hydrogen bond: weak attraction between hydrogen and another slightly negative atom– Covalent bond

DiCaprio Water Movie

Cohesion and AdhesionHydrogen bonds between molecules of liquid water lasts only a few trillionths of a second

– New form as old break

cohesion: tendency of molecules of the same kind to stick to one another

– Much stronger for water than other liquids

– Water through plants

– Surface tension: water molecules pulled tightly together at surface

adhesion: attraction between unlike molecules

– Capillary action

Temperature Moderation

Better ability to resist temperature change than most other substancesThermal energy: total amount of energy associated with the random movement of atoms and molecules in a sample of matter– Warm to cold

Temperature: measure of the average energy of random motion of the particles in a substance– Heating=breaks bonds– Cooling= forms H bonds

Low Density of Ice

density: amount of matter in a given volume

Ice is less dense than liquid water

Hydrogen bonds keep molecules spaced evenly

Dissolve Substances solution: uniform mixture of two or more substances– Salt water

solvent: the substance that dissolves the other substance and is present in great amounts– Water

solute: the substance being dissolved – Salt

aqueous solution (aq): water is the solventMain solvent in cells, blood, & plant sap– Dissolves ionic compounds by attracting opposite charge and

pulling apart (NaCl)– Dissolves nonionic compounds similarly eventhough there is

only a slight charge (sugar)

Acids, Bases, and pH

In some aqueous solutions, some water molecules break into ions– H+ and OH-

acid: a compound that donates H+ to a solution– HCl = H+ and Cl-

base: a compound that removes H+

ions pH scale: describes how acidic or basic a solution is– 0 = most acidic– 7 = neutral (pure water)– 14 = most basic

buffers: substances that cause a solution to resist changes in pH– Blood pH