All kinds of atoms contain varying quantities of subatomic particles, arranged around a __________, as if in a solar system.

In an atom, electrons occupy __________, or areas where they are most likely to be found.

The mass of particles within an atom are measured in Atomic __________ Units (a.m.u.).

Because electrons move at speeds near to that of light, we need to think of them as matter (having __________ is a property of matter), and energy ( or quanta of energy), like photons. This is also known in physics as wave-particle duality.

The __________ number of an element is the number of protons contained in its nucleus.**

The atomic __________ is the number of protons plus neutrons in an atom.++

++The number of protons--the atomic number--is unique for each element, e.g. Carbon is 6. However, the number of neutrons can differ, resulting in substances known as __________.

A majority of isotopes show nuclear __________, e.g. the tendency of C-14 to convert into C-12. They disintegrate spontaneously with a release of energy, resulting in a process known as radioactive decay.**

Around the nucleus, electrons are arranged in orbitals, and each orbital can hold only __________ electrons.++

The orbitals (types s,p,d and f) are arranged in __________, or increasing energy levels from the nucleus outward.++

What you see below is the Modern Periodic Table of elements. Phosphorous in column 15, row 3 has five electrons in its outer shell, and has __________ shells in total.

The rightmost column of the periodic table contains inert elements known as the noble gases, because they tend to occur in elemental form and are least likely to __________.++

Most atoms found in biological systems tend to gain or lose their outer electrons to achieve a Noble Gas, outer electron shell configuration of two or __________ electrons. The number of electrons that are gained or lost is characteristic for each element, and is the cause of atomic bonding.++

Take the case of Chlorine, which belongs to a group of elements with seven electrons in the outer shell, instead of the desired eight. Thus, it will tend to gain one electron in any reaction, gaining a charge of (-1), which makes it a charged atom known as an __________.++

In an __________ bond, two or more atoms bond together to form a molecule by transferring electrons to each other.++

++Ionic bonds generally form between elements in Group I (having __________ electron in their outer shell) and Group VII-A (having seven electrons in their outer shell).

Covalent bonds are formed when atoms __________ electrons. Like child custody between two parents, the electrons tend to spend more time with one atom than the other. The number of electrons shared differs based on the atoms involved.++

++In covalent bonds, when electrons spend more time with one atom than the other, a type of covalent bond, known as a __________ bond develops. Water (H₂O) is an example. Since the electrons spend so much time with the oxygen (oxygen having a greater electronegativity, or electron affinity), that end of the molecule acquires a slightly negative charge.

In ice, we find another type of bond called __________ bonds. These result from the weak electrical attraction between the positive end of one H₂O molecule and the negative end of another.++

__________ are compounds with elements in definite, fixed ratios, like water. Those atoms are held together usually by one of the three bonds - ionic, covalent or hydrogen. On the other hand, soil is a mixture with uncertain components.++

If molecular weight is the addition of the atomic masses in a molecule, the weight of __________ (C₆H₁₂O₆) is 180.**

In chemical reactions, when two reactants bond together we call it a __________, as in A+B -> C. In dissociation, we represent the reaction by C -> A+B. (note: -> represents a right arrow)+

The element carbon is the basis of known life. Biological systems, while unique to each species, are based on its __________ bonding properties.

It is vital to life, and yet a strange molecule. __________ participates in virtually every process that occurs in plants and animals. Although the molecules are simple in structure (H₂O), the physical and chemical properties of the compound are extraordinarily complicated.*

By combining oxygen with __________, an isotope of hydrogen, one gets heavy water ( D2O).

In its solid form -- ice -- water is __________ dense than when it is liquid, another unusual property! The root of these anomalies in the water molecule is its electronic structure, due to a polar covalently bonded molecule.

Due to hydrogen bonding, water molecules associate strongly. In an ice crystal, the association is a highly ordered, but loose structure. When the ice melts, this orderly arrangement breaks down partially and the molecules pack __________ closely together. This makes the liquid denser than the solid, which is why ice forms on top of liquid water.

The __________ bonds make water molecules sticky, a property known as cohesion.

The polarity of the water molecule plays a major part in the formation of __________ solutions. If an ionic compound, such as sodium chloride, is placed in water, the polar water molecules reduce the electrostatic attraction between the positively charged sodium and negatively charged chloride ions.++

"Mixing like oil and water," is an old adage, but it has a fair bit of science behind it. Fatty (oily) substances are a part of organic macromolecules known as lipids , which have areas lacking polar __________ bonds. Water molecules dislike such molecules, causing fats to clump together.**

Water tends to dissociate into H+ and OH- ions, where the oxygen retains the electrons and only one hydrogen. Thus, becoming a negatively charged ion known as __________ (OH-).

The pH scale is a logarithmic scale representing the concentration of H+ ions in a solution. It is represented as the __________ logarithm of the H+ ion concentration. If the pH of water is seven, then the concentration of H+ ions is 10^-7.

The triple point of water represents the unique conditions at which it can exist in all three phases in __________.

In the early days of science, inorganic substances could be extracted from the rocks, sediments, or waters of the Earth, whereas __________ substances were found only in the tissues or remains of living organisms.

A __________ is a compound that is made up only of C (carbon) and H (hydrogen) atoms. The carbon atoms join together to form the framework of the compound; the hydrogen atoms attach to them in many different configurations. Benzene and methane are good examples.

Hydrocarbons are insoluble in __________ and are less dense than water, so they float on its surface. They are usually soluble in one another, however, as well as in certain organic solvents.

The general formula C_x(H₂O)_x is commonly used to represent many __________, which means "watered carbon." They are formed by green plants from carbon dioxide and water during the process of photosynthesis.

There are two main types of __________: sugars and starches.

__________ are molecules with identical molecular formulas but a different arrangement of their atoms.

Functional groups are clusters of atoms with characteristic structure and functions. For instance, polar molecules (with +/- charges) are attracted to water molecules and are termed "__________".

A hydrocarbon is hydrophobic except when it has an attached ionized functional group such as carboxyl acid (COOH). If so, the molecule is __________.

One of the most common functional groups is the -OH (hydroxyl) group. Its presence will enable a molecule to be water __________.

Since carbon can make covalent bonds with another carbon atom, carbon chains and rings that serve as the backbones of __________ molecules are possible. This property is known as catenation.

Chemical bonds store __________. The C-C covalent bond has 83.1 Kcal (kilocalories) per mole, while the C=C double covalent bond has 147 Kcal/mole.

Each organic molecule group has small molecules (__________) that are linked repeatedly to form a larger organic molecule (macromolecule).

During a condensation reaction of monomers, a hydroxyl (OH) group is removed from one monomer and a hydrogen (H) is removed from the other. This results in a covalent bond between them, thereby forming a __________.

Sugars are structurally the simplest __________. They are the structural unit which makes up the other types of carbohydrates.

The products of __________ are assembled to make glucose. Thus, energy from sunlight is converted into the C-C covalent bond energy.

Disaccharides are formed when two __________ are chemically bonded together.

The formation of the __________ bond by condensation (the removal of water from a molecule) allows the linking of monosaccharides into disaccharides and polysaccharides.

__________ is a polysaccharide that forms the fibrous part found in plant cell walls.

__________ are involved mainly with long-term energy storage. They are generally insoluble in polar substances such as water.

The presence of a double C=C covalent bond __________ the number of hydrogens that can bond to the carbon chain, hence termed unsaturated.

Fats and oils function for energy storage. Animals convert excess sugars (beyond their glycogen storage capacities) into fats. Fats yield 9.3 Kcal/gm, while carbohydrates yield 3.79 Kcal/gm. Fats store __________ times as much energy as glycogen.

__________ are attempts to reduce the amount of fats present in specialized cells known as adipose cells that accumulate in certain areas of the human body.

Proteins constitute about 80 percent of the dry weight of muscle, __________ percent of that of skin, and 90 percent of that of blood.

__________ are the building blocks of proteins.

A peptide bond is a link between the amino group [-NH₂] of one amino acid and the carboxyl group [-COOH] of the next amino acid in the protein chain. All living things (and even viruses) use various combinations of the same __________ amino acids.

Nucleic Acids are substances that comprise the __________ material of living cells. They direct the course of protein synthesis, thereby regulating all cell activities. Furthermore, by their transmission from one generation to the next, they are the vehicle for inherited characteristics.

Of the two major types of nucleic acids, deoxyribonucleic acid (better known as DNA) is the physical carrier of inheritance for 99% of living organisms. DNA functions in information storage. The English alphabet has 26 letters and over 50,000 words. DNA has 4 letters (C, __________, A, and T) and 20 words (the 20 amino acids) that can make an infinite variety of sentences (polypeptides).

The four "letters" in the DNA code are cytosine, guanine, adenine, and __________ (list them separated by commas).

Another nucleic acid known as Ribonucleic Acid (RNA) is commonly present in the __________ and cytoplasm of cells. Most cytoplasmic RNA is associated with the ribosomes in a cell, where protein synthesis occurs.

According to the most widely accepted theory, the universe began 10 to 20 billion years ago with the Big Bang , when a very small "egg" of high __________ and temperature exploded and formed the expanding universe.

When stars/galaxies are moving away from us, the energy they emit is shifted to the red side of the visible-light spectrum. Those moving towards us are shifted to the violet side. A phenomenon called __________ is a strong evidence in the favor of the Big Bang theory.

After the formation of the earth, there are several theories for how life began, leaving aside the supernatural. The idea of __________ hypothesized that life originated out in space and came to earth inside a meteorite.

In 1950, __________ designed an experimental test for Oparin's hypothesis that cellular life was preceded by a period of chemical evolution. According to the theory, pre-cellular life would have begun with the formation of Nucleic Acids.

Biochemically, living systems are separated from other chemical systems by three things - the capacity of replication from one generation to another, the presence of __________ and other necessary complex molecules for living, and a membrane that separates the internal cells from the outer environment.

The oldest known rocks on Earth are 3.96 billion years old and are from Arctic __________. Thus, life appears to have begun soon after the cooling of the Earth and formation of the atmosphere and oceans.

A(n) __________ (other-feeder) is an organism that obtains its energy from another organism.

A(n) __________ (self-feeder) is an organism that makes its own food--it converts energy from an inorganic source by photosynthesis or chemosynthesis.

A __________ is any self-contained cell or organism that lacks internal unit membranes. Bacteria are among the best-known organisms of this kind.

The cell membrane is found in all cells. It __________ the inner parts of the cell from the outer environment.

__________ are substances located on the outside of cells, viruses, and in some cases other chemicals.

About two thirds of the body is made up of __________.

A lack of Vitamin C results in __________.

Prokaryotic cell DNA forms __________chromosome(s).

The breakdown of a disaccharide releases energy which is stored as ATP. This is an example of a __________.