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Chapter Three
Atoms and the Periodic Table
Lesson 3-1
Inside the Atom
• An atom consists of a nucleus surrounded
by one or more electrons.
• The central core is the nucleus.
• The smallest particles inside the nucleus are
protons and neutrons.
• The energetic particles moving in all
directions around the nucleus are electrons.
• Protons carry (+) a positive charge.
• Neutrons are neutral – they carry no
electrical charge.
• An electron carry (-) a negative charge.
Protons and Neutrons have the
approximately the same mass.
The Atom
• The atomic number is the number of
protons in its nucleus.
• The number of protons equals the number
of electrons. This creates a balanced
charge, making a neutral atom.
• Because atoms are so small, scientists have
created the atomic mass (amu) to measure
the particles of the atoms.
• The mass of a proton is about one atomic
mass unit. It takes almost 2,000 electrons to
equal one atomic mass unit.
3-1 Electrons
• Electrons move so rapidly in the space
around the nucleus that is impossible to
know exactly where any electron is at a
particular time.
• The electrons in an atom aren’t all the same
distance away from the nucleus. ONLY the
electrons that are the FURTHEST from the
nucleus are involved in bonding.
3-1 Valance Electrons
• The electrons involved in bonding are called
valance electrons.
• A chemical bond forms between two atoms when
valence electrons move between them. Electrons
may be transferred from one atom to another, or
they may be shared between the atoms.
• One way to show the number of valence electrons
is with an electron dot diagram. It includes the
symbol for an element surrounded by dots. Each
dot stands for one valence electron.
8 (atomic number)
Oxygen (element name)
3-1- # of Protons
8 (atomic number)
Oxygen (element name)
The number of
protons equals
the atomic
Oxygen has 8
3-1 # of Electrons
8 (atomic number)
Oxygen (element name)
The number of electrons
= the number of
Oxygen has 8 protons,
therefore, oxygen has
8 electrons.
3-1 # of Neutrons
8 (atomic number)
Oxygen (element name)
The number of neutrons
= mass number –
atomic number.
Mass of oxygen = 15.999
Atomic # of O = - 8.000
# of neutrons = 7.999
round off :
Oxygen = 8 neutrons
3-1 You Try:
36 (atomic number)
Krypton (element name)
• Number of protons?
• Number of electrons?
• Number of neutrons?
3-1 You Try Answer
• Krypton has 36 Protons.
• Krypton has 36 Electrons.
• Krypton has 48 neutrons.
(round off: 84 - 36 = 48)
3-1 Paying Attention?
• If Nickel has 28
protons and 28
electrons, what is the
atomic #?
3-1 Finding the Atomic Mass
• If the protons = 28 and
the neutrons = 31,
what is the atomic
• Add the two together:
28 + 31 = 59.
• The arrangement of the periodic table is by
increasing atomic mass.
• Mendeleev was the first person to arrange
the elements in a pattern.
• Each row going across the periodic table is
called a period.
Quiz Review
Know how to label an element box: (atomic number, symbol, name,
and atomic mass).
Know the diagram of an atom.
Know how the periodic table is arranged.
Know what a period is.
Know the first person to arrange the elements in a pattern.
Know how to find the number of neutrons.
How to determine the atomic number with given information.
Know how to figure out the atomic mass with given information.
*Extra credit: Who is afraid of Krypton?*
Lesson Two 3-2
Organizing Elements
3-2 Organizing Elements
• Mendeleev noticed that patterns appeared
when the elements were arranged in order
of increasing atomic mass.
– The atomic mass of an element is the average
mass of one atom of the element.
– In the periodic table, the properties of the
elements repeat in each row,or period, of the
3-2 Organizing the Elements
• The modern periodic table contains over 100 squares, one
for each element, arranged in order of atomic number.
• An element’s properties can be predicted from its location
in the periodic table.
– The elements in a column are called a group,or family. The groups
are numbered 1-18. Elements in each group have similar
– Each horizontal row of the table is called a period. The elements
in a period are not alike in properties. There are seven periods.
– The periodic table works because it’s based on the structure of
atoms, especially the valence electrons. The number of valence
electrons that an element has increases from left to right across a
Lesson 3-3
3-3 Metals
• Most of the elements are metals, which are found to the
left of the zig-zag line in the periodic table.
• Chemists classify an element as a metal based on physical
properties such as: hardness, shininess, malleability, and
– Malleable means to pound into shape.
– Ductile means that the material can be pulled or drawn
into a long wire (copper).
– Many metals are good conductors of electricity – Gold
is the best conductor of electricity, however, it is not
used because of its value.
3-3 Metals
• Metals show a wide range of chemical
– Some metals are reactive. They combine with
other elements and compounds quickly, and
give off energy.
– A metal can wear away – this is called
corrosion (rust is a chemical reaction).
3-3 Metals
• The metals in a group, or family, have similar properties, and these
properties change gradually as you move across the table.
– Group One – Alkali metals: Highly reactive - so reactive they are never
found uncombined in nature.
– Group Two – Alkaline Earth Metals: reactive, but not as reactive as alkali
metals, also not found uncombined in nature.
– Group 3 – Group 12 – Transition Metals: They form a bridge between the
very reactive metals on the left and the less reactive metals on the right.
– Group 13-16 – includes metals, non-metals, and metalloids. The metals in
this group are not nearly reactive as those on the left side of the periodic
– The elements on the bottom of the periodic table are called lanthanides
and actinides. They are known as rare earth elements.
Nonmetals and Metalloids
Lesson 3-4
• Nonmetals are elements that lack most of the
properties of metals. The nonmetals are located to
the right of the zig-zag line in the periodic table.
• Physical Properties – nonmetals:
Low density
Poor conductors of electricity.
• Many metals and nonmetals react with each
• Many nonmetals also form molecules of
two identical atoms, O2.
• Molecules containing two atoms are called
diatomic molecules.
3-4 Element Families
The elements in group 14, the Carbon Family, have atoms with 4 valence
electrons. Carbon is the only nonmetal in the group.
The elements in group 15 is the Nitrogen Family. Each element in the nitrogen
family has 5 valence electrons. The two non-metals are phosphorus and
The elements in group 16, the Oxygen Family, have 6 valence electrons.
These atoms typically gain or share two atoms in a reaction. The Oxygen we
breath is O2 and Ozone = O3.
Group 17 is known as the Halogen Family. All but one of these elements in
the Halogen Family are nonmetals. A halogen atom has 7 valence electrons
and typically gains or shares one electron when it reacts.
Group 18 is known as the Nobel Gases. These elements do not ordinarily form
compounds, because the Nobel gases do not share or gain electrons.
• Hydrogen is the simplest element. Its atoms
generally contain only one proton and one
electron. Hydrogen is not grouped in a
family – it is on its own because hydrogen’s
chemical properties are so different from the
other elements.
• On the border between the metals and the nonmetals are
seven elements called metalloids.
• The metalloids have some of the characteristics of metals
and some of the characteristics of nonmetals.
• The most useful property of the metalloids is their varying
ability to conduct electricity.
– Some metalloids are used to make semiconductors.
Semiconductors are substances that under some
conditions can carry electricity, and under other
conditions cannot. Semiconductors are used to make
computer chips, transistors, and lasers.