2.  Matter is anything that occupies space.  All matter is made of atoms.  Atoms are the building blocks of matter.

4.  This model of the atom may look familiar to you. This is the Bohr model. In this model, the nucleus is orbited by electrons, which are in different energy levels.

5.  A model uses familiar ideas to explain unfamiliar facts observed in nature.  A model can be changed as new information is collected.

6.  In 1908, the English physicist Ernest Rutherford began to unravel the mysteries of the atomic structure.  Through his experiments he discovered that atoms were mostly open space.

7.  Rutherford concluded that an atom had a small, dense, positively charged center.  He called the center of the atom the “nucleus”  The nucleus is tiny compared to the atom as a whole.

8.  In 1913, the Danish scientist Niels Bohr proposed an improvement. In his model, he placed each electron in a specific energy level.

9.  According to Bohr’s atomic model, electrons move in definite orbits around the nucleus, much like planets circle the sun. These orbits, or energy levels, are located at certain distances from the nucleus.

10.  According to the modern atomic model, an atom has a small positively charged nucleus surrounded by a large region in which there are enough electrons to make an atom neutral.

11.  A space in which electrons are likely to be found.  Electrons whirl about the nucleus billions of times in one second  They are not moving around in random patterns.  Location of electrons depends upon how much energy the electron has.

12.  Depending on their energy they are locked into a certain area in the cloud.  Electrons with the lowest energy are found in the energy level closest to the nucleus  Electrons with the highest energy are found in the outermost energy levels, farther from the nucleus.

14.  The Atomic - Molecular Theory of Matter states that all matter is composed of small, fast moving particles called atoms. These atoms can join together to form molecules.

15.  Nucleus - the central portion of the atom. Contains the protons and neutrons.

16.  Electron Cloud - area around the nucleus where electrons are found. Electrons are arranged within the electron cloud in energy levels. (Energy levels are sometimes called shells or orbits).

17. è Proton - positive charged particle found in the nucleus. è Neutron - particle with no charge. Found in the nucleus. è Electron - negative charged particle found within the electron cloud

18.  In an atom, valance electrons can be found in the outermost electron shell. They are the main point of interaction between one atom and another, and are very important for the formation of molecules.

19.  A molecule is the smallest particle of a pure chemical substance that still retains its composition and properties.  Molecules are made of two or more atoms.