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Living organisms are composed of MATTER, which is anything that occupies space and has

mass.

An ELEMENT is a substance that cannot be broken down to other substances by ordinary

chemical means.

TRACE ELEMENTS- essential but only in minute quantities.

The four most abundant elements in the human body are Carbon, Oxygen, Hydrogen, and

Nitrogen.

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Goiter in a Malaysian woman, a symptom of Iodine deficiency.

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A COMPOUND is a substance consisting of two or more different elements combined in a

fixed ratio.

Pure sodium is a metal and pure chlorine is a poisonous gas, but when chemically

combined they make the compound sodium chloride an edible compound used daily.

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An ATOM is the smallest unit of matter that still retains the properties of an element.

Atom’s have 3 important subatomic particles: 1.) PROTON is a subatomic particle with a

single positive charge(+)

2.) ELECTRON is a subatomic particle with a single negative electrical charge (-)

3.) NEUTRON is electrically neutral (has no electrical charge)

The NUCLEUS of an atoms houses NUETRONS and PROTONS

Elements differ in the number of subatomic particles in their atoms. All atoms of a

particular element have the same unique number of protons. The number of protons that

an atoms has is called the ATOMIC NUMBER.

The atom’s MASS NUMBER is the sum of the protons and neutrons in its nucleus.

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ISOTOPES- An element have the same numbers of protons and electrons and behave

identically in chemical reactions, but they have different numbers of neutrons.

RADIOACTIVE ISOTOPES- is one in which the nucleus decays spontaneously, giving off

particles and energy.

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Basic research- Biologist often use radioactive tracers to follow molecules as they undergo

chemical changes in a organism.

Medical Diagnosis- By injecting a radioactive chemical into a patient’s blood and then

measuring the amount of radioactive material passed in the urine. Radioactive tracers are

often used for diagnosis in combination with sophisticated imaging instruments like the

image above.

Dangers- Though radioactive isotopes have many beneficial uses, uncontrolled exposure to

them can harm living organisms by damaging molecules, especially DNA. The particles and

energy thrown off by radioactive atoms can break chemical bonds and also cause abnormal

bonds to form.

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Only electrons are directly involved in the chemical activity of an atom. Electrons vary in

the amount of energy they possess. The farther an electron is from the nucleus , the

greater its energy. Electrons occur only at certain energy levels, called ELECTRON SHELLS. It

is the number of electrons in the outer most shell that determines the chemical properties.

When two atoms with incomplete outer shells react, each atom either shares, donates, or

receives outer electrons, so that both partners end up with completed outer shells. These

interactions usually result in atoms staying close together, held by attractions known as

CHEMICAL BONDS.

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ION- is an atom or molecule with an electrical charge resulting from a gain or loss of one or

more electrons. Two ions with opposite charges attract each other: when the attraction

holds them together, it is called an IONIC BOND, also known as a salt.

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The second type of strong chemical bond is the COVALENT BOND, in which two atoms

share one or more pairs of outer-shell electrons. Two or more atoms held together by

covalent bonds form a MOLECULE. H2, called the molecular formula, tells you that the

molecule consists of two atoms of hydrogen. The line between the hydrogen atoms

represents the single covalent bond formed by the sharing of a pair of electrons. DOUBLE

BONDS form when atoms share two pairs of electrons.

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Atoms in a covalent bonded molecule are in a constant tug-of-war for the shared electrons

of their covalent bonds. An atom’s attraction for shared electrons is called its

ELECTRONEGATIVITY. The more electronegative an atom, the more strongly its pulls shared

electrons towards its nucleus. In NONPOLAR COVALENT BONDS- electrons are shared

equally between the atoms. The unequal sharing of electrons produces a POLAR COVALENT

BOND, which is the pulling of shared, negatively charged electrons closer to the more

electronegative atoms makes that atom partially negative and the other atom partially

positive. POLAR MOLECULES- has an unequal distribution of charges.

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Large molecules are held in their three-dimensional shape by weak bonds. In addition,

molecules in a cell may adhere briefly by weak bonds, respond to one another in some way,

and then separate. When a hydrogen atom is part of a polar covalent bond, its partially

positive charge allows it to share attractions with other electronegative atoms. Because the

positively charged region in this special type of bond is always a hydrogen atoms, the bond

is called a HYDROGEN BOND. You will learn how hydrogen bonds help to create a proteins

shape (and thus its function) and hold the two strands of a DNA molecule together.

Indeed, these weak bonds are involved in many of the activities of a cell.

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Cohesion in water is much stronger for water than for most other liquids. The veins of trees

use the strong cohesion of water molecules to pull it against gravity. Adhesion helps the

water molecules to ride on the cell walls of the veins.

Cohesion: The tendency of molecules to stick together

Adhesion: The clinging of one substance to another

Surface tension: A measure of how difficult it is to stretch or break the surface of a liquid

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Because of hydrogen bonding, water has a better ability to resist temperature change than

most other substances.

HEAT- is the amount of energy associated with the movement of atoms and molecules in a

body of matter.

TEMPERATURE- Measures the intensity of heat- that is, the average speed of molecules

rather than the total amount of energy in a body of matter.

Heat must be absorbed in order to break hydrogen bonds, and heat is released when

hydrogen bonds form.

Water moderates internal temperatures by evaporative cooling. When a substance

evaporates, the surface of the liquid remaining behind cools down as the molecules with

the greatest energy leave.

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Water exists in nature as a gas, liquid, and solid. As water freezes, each molecule forms

stable hydrogen bonds with four neighbors, holding them at arms length and creating a 3D

crystal. Compare the specially arranged molecules in the ice crystal with the more tightly

packed molecules in the liquid water.

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A SOLUTION is a liquid consisting of a uniform mixture of two or more substances. The

dissolving agent is the SOLVENT and a substance that is dissolved is a SOLUTE. An

AQUEOUS SOLUTION is one in which the water is the solvent. Waters versatility as a solvent

results from the polarity of its molecules. Only polar or Ionic compounds may be dissolved

by water.

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In aqueous solution only some water molecules break apart into ions (H+,OH-). But some

chemical compounds contribute additional H+ to an aqueous solution, which is an ACID- A

compound that donates hydrogen ions to a solution. An acidic solution has a higher

concentration of H+ ions rather than OH- ions. A BASE- is a compound that accepts

hydrogen ions and removes them from solution. Bases actually donate OH- ions which than

combine with H+ ions to form H2O. We use the pH scale to describe how acidic or basic a

solution is (pH stands for potential of hydrogen). The scale ranges from 0 (most acidic) to

14 (most basic). Each pH unit represents a tenfold change in concentration of H+ in a

solution. Pure water and aqueous solutions that are neither basic nor acidic are said to be

neutral; they have a pH of 7. BUFFERS- substances that minimize changes in pH, buffers do

this by accepting H+ when it is in excess and donating H+ when it is depleted.

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Water is the substance that makes life as we know it possible. The chemical reactions that

occur in cells use water as a reactant or is a product. Most organisms consist of more than

65% water by weight. The emergent properties of water molecules contribute to Earth’s

fitness for life. These properties include the cohesion of water molecules, water’s ability to

moderate temperature, the insulation of bodies of water by floating ice, and waters

versatility as a solvent.

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A CHEMICAL REACTION is the making and breaking of chemical bonds, leading to changes

in the composition of matter. The REACTANTS are the starting materials and are found at

the start of the arrow. The PRODUCTS are found were the arrow points and are the ending

products after a chemical reaction has occurred. Remember that chemical reactions do not

create nor destroy matter; they only rearrange it in various ways.

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