For more information see:http://www.chem4kids.com/files/atom_structure.html
Atoms are the basic unit of matter. They are the building
blocks of all materials including elements and compounds.
There are 3 basic parts of an atom.
Protons - found in the nucleus of an atom and have a positive (+) charge
Neutrons = found in the nucleus of an atom and have zero or no charge
Electrons = found in the electron cloud that surrounds the nucleus of the atom.
The electron is composed mainly of empty space. They are in constant motion
and they have a negative charge. Electricity is the flow of electrons.
Most atoms are stable and have equal numbers of protons and electrons.
Elements are pure substances made of only one type of atom. Below you will
find an example of an element block from the Periodic Table. Elements are
arranged on the Periodic Table in order of their number of protons.
The atomic number will be a whole
number on the block. This tells you the number of protons and electrons in an
atom. The Atomic mass shows the average weight of the atoms in that element.
The number of protons and electrons for the element can be found by looking at
the atomic number.
To determine the number of neutrons you must take the atomic mass number
and subtract the atomic number.
# Neutrons = atomic mass – atomic number
History of the Atomic Theory
Democritus- was the first person to use the term atom. He was a Greek
philosopher that studied under Aristotle. The Greek term, “atomos” means
indivisible. He believed that matter was made up of tiny indivisible particles
called atoms.
John Dalton
J.J Thomson Plum Pudding Model
The first person who discovered electrons, Sir J.J Thompson, put forth his
'Plum Pudding' Model of an atom. He believed that the atom was a uniform
sphere with a positive charge and had electrons embedded in it. He could
explain the electrical neutrality of an atom but could not explain the
arrangement of the fundamental particles in an atom.
James Chadwick discovered the neutron.
Niel’s Bohr
Bohr Model of an Atom
Ernest Rutherford
Henry Moseley
Frederick Soddy
Louis deBroglie
Dmitri Mendeleev
Johann Dobereiner
John Newlands
Atoms group together to form molecules. Molecules are held together by atomic
bonds. Molecules can be elements or compounds.
The two basic types of bonds are Ionic and Covalent
An ionic bond is formed when 2 ions of opposite charge combine. These usually
form between atoms of metals and non-metals.
Such as: Na-Cl H-F
K-Cl
A covalent bond is formed when two atoms share electrons. These usually occur
between 2 atoms of non-metals.
Such as H-H
C-O
Cl-Cl
Br-Br
P-O P-Cl
Compounds are the sub-units for compounds. Compounds are made of 2 or
more different elements.
Compounds have different properties than the elements that they are made of.
For example: Table salt, NaCl
Sodium is a silvery white metal that reacts violently with water and Chlorine is a
green poisonous gas.
Table salt dissolves in water calmly and is not poisonous to living things.
Compounds are chemically combined. Water is composed of hydrogen and
water.
Mixtures are made of substances that are not chemically combined. For example
salt and pepper, sugar and tea, salt and water, alloys
Alloys are mixtures of two or more metals such as found in sterling silver, bronze,
10 kt gold, steel, pennies
Mixtures can be easily separated by filtering, magnetic properties or evaporation.
All substances have both chemical and physical properties.
Physical properties are properties that describe a substance and can be examined
without altering the substance. They include color, texture, malleability, ductility,
density, and viscosity, state of matter at room temp, melting point, and boiling
point
Chemical properties are properties that cannot be examined without changing
the substance. They deal with how the substance reacts chemically with other
matter. They include toxicity, flammability, oxidation, will it explode