Science at a Distance

Physical Structure

Lecture notes - Part 2 Lecture notes - Part 3

Lecture Notes

a check up

Use this section to check up on the accuracy of your lecture notes. Make sure that you have written down the following definitions, explanations and important concepts in your notes.

Physical Structure - Part One


An atom is the smallest unit of a pure substance or element that can exist and still retain the properties of the original substance or element.

Atoms of Life

The three most abundant elements on earth are oxygen, silicon and aluminum; in living organisms the six most abundant elements are carbon, hydrogen, nitrogen, oxygen, phosphorus and sulfur.

Subatomic particles

There are three types of subatomic particles that are found in the atoms of all but one element.

Atomic substructure

Every atom has the same substructure with a dense positively charged center (sometimes called the atomic nucleus) surrounded by diffused, rapidly moving number of negatively charged particles.

Physical Properties of Atoms

Two important physical properties of all atoms depend on their atomic mass and the relative number of protons and neutrons in the atomic center.


Isotopes are families of atoms that have the same atomic number but different atomic masses.

Electron Arrangements

Electrons are negatively charged and so are attracted to the positively charged protons in the center of the atom. They are also repelled by the negative charges on other electrons. Electrons hold fixed amounts of energy and this level of energy determines how near of far from the atomic center they are located.


As they diffuse and move about the nucleus, electrons are restricted to certain volumes or shapes of space called orbitals.

Atomic Stability

Atoms are at their most stable and least reactive when their outermost energy level is either completely filled with electrons or completely empty of electrons.

Stability I: ions

One way for an atom to move to a more stable state is to gain or lose electrons from its outermost energy level until the energy level is either full, or empty of electrons.

Stability II: sharing

Atoms can combine together and share electrons between them. Atoms that share electrons are linked to each other in a form, called a molecule that is in a lower energy state than either of the separate atoms alone.

Methane: an organic molecule

Atoms of different elements can share electrons, form covalent bonds between them and create complex molecules.

The Water Molecule

A molecule of water consists of one atom of oxygen held to two atoms of hydrogen by two covalent bonds. The electrons in these bonds are not shared equally by the atoms. This type of covalent bond is called polar.

Special Properties of Water I: a liquid

The polarity of the water molecule gives it some special properties, the first of which is that water is a liquid at room temperature.

Special Properties of Water II: a solvent

A solvent is a liquid in which other solids and liquids will dissolve. Water is almost a universal solvent in which most other substances will dissolve to some extent.

Test Yourself with Quick Check Number PS-1030
Lecture Notes - Part 2 Lecture Notes - Part 3
Physical Structure

Science at a Distance
© 1997, 1998, 1999, 2000, Professor John Blamire