Chemistry of Life Notes

Composition of Matter

All living things are made of the same basic materials: carbon, hydrogen, oxygen, and nitrogen.
Living things are made of cells that are composed primarily of water.
Chemical reactions of life occur in the aqueous environment of the cell.
Understanding basic principles of chemistry gives a better understanding of living things and how they function.

Matter

Matter is anything that occupies space and has mass.
Mass is the quantity of matter an object has.
Weight is the force produced by gravity acting on mass. Weight is not the same as mass.
Chemical changes in matter are essential to all life processes.
Biologists study chemistry because living things are made of the same kinds of matter that make up nonliving things.

Elements and Atoms

Elements are substances that cannot be broken down chemically into simpler kinds of matter.
More than 100 elements have been identified; fewer than 30 are important to living things.
More than 90 percent of the mass of living things is composed of combinations of oxygen, carbon, hydrogen, and nitrogen.
Information about elements is summarized on the periodic table.
Each element has a different chemical symbol with one, two, or three letters (e.g., Cl for chlorine, Na for sodium).
The simplest particle of an element that retains its properties is an atom.
Atoms are too small to be directly observed, so scientists use models.

The Nucleus

The nucleus is the central region of an atom.
It contains protons (positively charged) and neutrons (no charge).
The atomic number is the number of protons in an atom.
The mass number is the total number of protons and neutrons in an atom.

Electrons

Electrons are negatively charged particles that balance the positive charge of protons, making the net electrical charge of an atom zero.
Electrons have very little mass and move around the nucleus at high speeds in orbitals.
An orbital is a three-dimensional region around the nucleus indicating the probable location of an electron.
Electrons farther from the nucleus have greater energy.
Each energy level corresponds to a group of orbitals that can hold a limited number of electrons.
The first energy level holds up to two electrons, and the second can hold up to eight.

Isotopes

Atoms of the same element with different numbers of neutrons are called isotopes.
Isotopes affect the mass of the element.
The average atomic mass of an element considers the relative amounts of each isotope.

Compounds

Under natural conditions, most elements do not exist alone.
Compounds are made up of atoms of two or more elements in fixed proportions.
A chemical formula shows the kinds and proportions of atoms (e.g., $H_2O$ ).
Physical and chemical properties differ between compounds and their constituent elements.
The way elements combine depends on the number and arrangement of electrons in their orbitals.
Atoms are chemically stable when their highest energy level orbitals are filled with the maximum number of electrons.
Noble gases (e.g., helium and neon) do not react with other elements under normal conditions because they have filled orbitals.
Most atoms are not stable in their natural state and tend to react with other atoms to form chemical bonds.
Chemical bonds are the attractive forces that hold atoms together.

Covalent Bonds

A covalent bond forms when two atoms share one or more pairs of electrons.
For example, water is made up of one oxygen atom and two hydrogen atoms held together by covalent bonds.
A molecule is the simplest part of a substance that retains all of its properties and can exist in a free state.

Ionic Bonds

Ionic Bonds: Sodium (Na) and chlorine (Cl) atoms achieve stability by transferring an electron from Na to Cl.
An ion is an atom or molecule with an electrical charge.
Na becomes a positive ion ( $Na^+$ , Sodium ion) after losing an electron, while Cl becomes a negative ion ( $Cl^-$ , Chloride ion) after gaining an electron.
The attraction between positive and negative ions is called an ionic bond.
Sodium chloride (NaCl), or table salt, is an example of an ionic compound.

Energy

All living things use energy.
The amount of energy in the universe remains the same, but energy can change from one form to another.
Biologists study the transfer of energy from the sun through organisms on Earth.

Energy and Matter

Energy is defined as the ability to do work.
Energy can occur in various forms, and one form can be converted to another (e.g., electrical energy to radiant energy).
Forms of energy important to biological systems include chemical, thermal, electrical, and mechanical energy.

States of Matter

Atoms and molecules in any substance are in constant motion.
The motion and spacing determine the substance’s state: solid, liquid, or gas.
In general, atoms/molecules of a solid are more closely linked than in a liquid or gas.
A solid maintains a fixed volume and shape.
A liquid maintains a fixed volume but can flow and conform to the shape of its container.
Particles of a gas move the most rapidly and fill the volume of the container they occupy.
Thermal energy must be added to cause a substance to change states.

Energy and Chemical Reactions

In a chemical reaction, one or more substances change to produce different substances.
Energy is absorbed or released when chemical bonds are broken and new ones are formed.
A reversible reaction can proceed in either direction and is indicated by a two-direction arrow ( $\rightleftharpoons$ ).
Metabolism describes all chemical reactions in an organism.

Activation Energy

Activation energy is the energy needed to start a chemical reaction.
Catalysts reduce the amount of activation energy required for a reaction.
Enzymes are proteins or RNA molecules that act as catalysts in living things, speeding up metabolic reactions without being permanently changed.

Oxidation Reduction Reactions

Oxidation-reduction reactions (redox reactions) involve the transfer of electrons between atoms.
In an oxidation reaction, a reactant loses one or more electrons and becomes more positive in charge.
In a reduction reaction, a reactant gains one or more electrons and becomes more negative in charge.
Oxidation and reduction reactions always occur together.

Water and Solutions

Living things are made of cells that consist mostly of water.
The chemical reactions of all living things take place in the aqueous environment of the cell.
Water has several unique properties that make it important in living things.

Polarity

In a water molecule ( $H_2O$ ), hydrogen and oxygen atoms share electrons unequally.
The oxygen atom has a greater ability to attract electrons, resulting in a partial negative charge ( $\delta$ −) near the oxygen and partial positive charges ( $\delta$ +) near the hydrogen atoms.
Water is called a polar compound because of this uneven distribution of charge.

Hydrogen Bonding

The positively charged region of one water molecule is attracted to the negatively charged region of another water molecule.
This attraction is called a hydrogen bond.
Hydrogen bonds in water exert an attractive force strong enough so that water “clings” to itself and some other substances.
Hydrogen bonds form, break, and reform with great frequency.
The number of hydrogen bonds depend on the state that water is in. The solid state all it's water molecules are hydrogen bonded and do not break. As water liquifies, more hydrogen bonds are broken than are formed, until an equal number of bonds are formed and broken.
Hydrogen bonding accounts for water's unique properties, including cohesion and adhesion, and the ability of water to absorb large amounts of energy as heat, ability to cool surfaces through evaporation, density of ice, and ability to dissolve many substances.

Cohesion and Adhesion

Cohesion is an attractive force that holds molecules of a single substance together.
Adhesion is the attractive force between two particles of different substances.
Capillarity is the attraction between molecules that results in the rise of the surface of a liquid when in contact with a solid.
Cohesion, adhesion, and capillarity help water rise through narrow tubes against gravity.

Temperature Moderation

Water has a high heat capacity, meaning it can absorb or release relatively large amounts of energy as heat with only a slight change in temperature.
Energy must be absorbed to break hydrogen bonds, and energy is released as heat when hydrogen bonds form.
Evaporative cooling prevents organisms that live on land from overheating.

Density of Ice

Solid water (ice) is less dense than liquid water.
The angles in the molecules cause ice crystals to have large amounts of open space.
Ice floats on water, insulating the water below from the cold air and allowing aquatic creatures to survive.

Solutions

A solution is a mixture in which one or more substances are uniformly distributed in another substance.
A solute is a substance dissolved in the solvent.
A solvent is the substance in which the solute is dissolved.
The concentration of a solution is the amount of solute dissolved in a fixed amount of the solution.
A saturated solution is one in which no more solute can dissolve.
Aqueous solutions are solutions in which water is the solvent and are universally important to living things.

Acids and Bases

Acidity or alkalinity is a measure of the relative amounts of hydronium ions and hydroxide ions dissolved in a solution.
If the number of hydronium ions ( $H_3O^+$ ) equals the number of hydroxide ions ( $OH^-$ ), the solution is neutral.
Pure water contains equal numbers of hydronium ions and hydroxide ions and is therefore a neutral solution.

Acids

If the number of hydronium ions in a solution is greater than the number of hydroxide ions, the solution is an acid.

Bases

A base has excess hydroxide ions in water, and commercial soap is a reaction between a base and fat.

The pH scale compares the relative concentrations of hydronium ions and hydroxide ions in a solution, ranging from 0 to 14.
A solution with a pH of 0 is very acidic, a solution with a pH of 7 is neutral, and a solution with a pH of 14 is very basic.
The pH of a solution can be measured with litmus paper or some other chemical indicator that changes color at various pH levels.

Buffers

Buffers are chemical substances that neutralize small amounts of either an acid or a base added to a solution and maintain pH values in a normal healthy body.