Introduction to Atoms
Chapter 4 sec 1/ 2
Mr. Sapalicio
Physical Science
Key Terms
•Atom- smallest particle of an element
An atom is made up of;
•Protons- positively charged particles (+)
•Electrons- negatively charged particles (-)
•Neutrons- no electric charge, it is neutral and used to keep the nucleus together. ()
Box from the Periodic Table
26
Fe
Iron
55.845
atomic number
chemical symbol
element name
Key to the Periodic Table
• Elements are organized
on the table according to their atomic number, usually found near the top of the square.
▫ The atomic number refers to how many protons & electrons an atom of that
element has. ▫ For instance,
hydrogen has 1
proton, so it’s atomic number is 1.
▫ The atomic number is unique to that
What’s in a square?
•Different periodic tables can include various bits of
information, but usually:
▫atomic number ▫symbol
▫atomic mass
▫number of valence electrons
Atomic Number
•This refers to how many
protons & electrons an atom of that element has.
•No two elements, have the same
number of protons.
Bohr Model of Hydrogen Atom
Atomic Mass
•Atomic Mass refers to the “weight” of the atom.
•It is derived at by
adding the number of protons with the number of
neutrons.
•Look for the decimal!
This is a helium atom. Its atomic mass is 4 (protons plus neutrons).
Atomic Mass and Isotopes
• While most atoms have
the same number of
protons and neutrons,
some don’t.
• Some atoms have more
or less neutrons than protons. These are
called isotopes.
• An atomic mass number
with a decimal is the total of the number of protons
plus the average number
Protons have a positive charge + Neutrons have no charge + + + + + +
-Particl
e
Symbo
l
Charge amu model
proton p+ 1+ 1
neutron n 0 1
electron e- 1- 1
Key terms (cont.)
•Energy Levels- the electrons cannot choose any orbit they wish. They are restricted to
orbits with only certain energy levels. http://cas.sdss.org/ dr6/en/proj/advanced/spectraltypes/energylevels.asp
•AMU- atomic mass unit.
•Valence electron- chapter 5 =)
•Atomic number- the number of protons in the nucleus of an atom’s element.
Atomic theory’s growth
•Dalton- atoms were small, hard, round spheres that could not be broken down
into smaller pieces. Everything took place in the ball.
•Thomson- atoms were made of smaller parts
with negative and positive charges. He theorized that the atoms looked like a
Atomic Theory’s Growth
• Rutherford- Thomson’s student found that
atoms had to have a tiny positively charged nucleus and electrons moving around the nucleus because of his light beam
experiment. (like charges repel) p. 126.
• Bohr’s model- similar but
found that the electrons move in
Atomic Theories growth
•Cloud Model-1920’s scientists determined that electrons do not orbit like planets
around the sun but can be found
anywhere in a cloudlike region around the nucleus due to their energy levels.
▫Electrons can be found in different spots based on their energy level or how much energy it has.
+
Modern Atomic Model
•1932 James Chadwick discovered another particle in the nucleus, the Neutron. It has been very similar and accepted by scientists since.
•An atom is mostly empty space.
•At the center of an atom is a tiny,
massive nucleus containing protons and neutrons. Surrounding the
Rules of the shells (elements 1-18) shell k holds only 2 electrons
Mendeleev
• In 1869, Dmitri Ivanovitch
Mendeléev created the first
accepted version of the periodic table.
• He grouped elements according
to their atomic mass, and as he did, he found that the families had similar chemical
properties.
• Blank spaces were left open to
The Periodic Table
•The periodic table arranges the elements in a repeating pattern of their properties. •“Periodic” means in a regular, repeated
pattern.
•A great deal of information about an
element can be gathered from its position in the period table.
•For example, you can predict with
reasonably good accuracy the physical and chemical properties of the element. Based on where the element is on the periodic table.
•You can also predict what other elements a particular element will react with
The Periodic Table
•Scientists have identified 90 naturally
occurring elements, and created about 28 others.
Families Periods
• Columns of elements are called groups or families.
• Elements in each family have similar but not
identical properties.
• For example, lithium (Li), sodium (Na), potassium (K), and other members of family IA are all soft, white, shiny metals.
• All elements in a family have the same number of valence electrons.
• Each horizontal row of
elements is called a period.
• The elements in a
period are not alike in properties.
• In fact, the properties
change greatly across even given row.
• The first element in a
period is always an