Notes Powerpoint - Bremen High School District 228

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Transcript Notes Powerpoint - Bremen High School District 228

Elements & Atoms
What is chemistry?
• Chemistry is the study of matter and its
Matter is anything that has volume (takes up
space) and has mass (weight).
• All matter is made of atoms
• Atoms are the building blocks of matter, sort of
how bricks are the building blocks of houses
• Atoms are the smallest individual particles of
matter which still have their own properties.
An atom refresher
• An atom has three
fundamental particles:
• Proton = positive charge
• Neutron = no charge
• Electron = negative charge
• The proton & neutron are
found in the center of the
atom, a place called the
• The electrons orbit the
nucleus in the electron
Mass of the Subatomic Particles
• Protons = 1 AMU
• Neutrons = 1 AMU
• Electrons = 0 mass
AMU = Atomic Mass Unit; an incredibly small unit
of mass created only to describe the mass of
atoms and their particles
Structure of the atom
• Structure of the atom
• Nucleus: positively-charged center core which
contains the protons (+) and the neutrons (no
charge). The nucleus contains all the mass of
the atom.
Protons (+) and electrons (-) have equal
but opposite charges
• Electrons move in the space outside the
nucleus called the electron cloud
• The nucleus is incredibly small and contains all
the mass of the atom. Atoms are mostly empty
Diagram of an Atom
What are elements?
• The elements are
different types of atoms.
• The periodic table lists
all the elements that are
known to man.
• The periodic table
organizes all the
elements in rows and
columns based on their
Information & picture from Chem4kids at
Atoms of Elements
• Atoms are arranged on the periodic table by
increasing atomic number. (1 to 117)
• Atomic Number- the number of protons an
atom has in its nucleus
• Mass number: the total number of protons and
nuetrons an atom has in its nucleus
• Mass number – atomic number = # of neutrons
• *The number of electrons equals the number of
protons in a neutral atom.
• Chlorine
Atomic Number 17
Mass Number 35
Number of protons:
Number of nuetrons:
Number of electrons
Flip Card – 2 cuts, 3 flaps
Number of Protons
Atomic Number
Number of Neutrons
Mass Number –
Atomic Number
Number of
Same as the
number of protons
Atomic #
Mass #
Iron- Fe
Silicon- Si
Sulfur- S
# of +
# of -
# of
Periodic Table
Atomic Number:
The symbol of the
Elements Name
Atomic Mass/Weight:
Number of protons +
Graphic from
More about Elements..
• Elements are the building
blocks of all matter.
• The periodic table is a list of
all of the elements that can
build matter. It’s a little like
the alphabet of chemistry.
• The periodic table tells us
several things…
Properties of Metals
Located in the
center and the
left side of the
periodic table.
Properties of Metals
• Metals are usually solids at room temperature
• Good conductors of heat and electricity
• High melting points and boiling points (except Hg)
• High densities (except some group 1 metals)
• Metals are shiny and reflect light
Properties of Nonmetals
• Nonmetals
are located to
the right of
the stair step
Properties of Nonmetals
• The nonmetals exist in all three of the states of matter at
room temperature: gases (such as oxygen), liquids (such
as bromine), and solids (such as carbon).
• Nonmetals do not conduct electricity or heat very well.
• Nonmetals have much lower melting and boiling points
than metals. (Consider all of the ‘red’ ones.)
• Nonmetals are not nearly as dense as metals.
The nonmetals have no metallic luster, and do not reflect
• Nonmetallic elements are very brittle, and cannot be rolled
into wires or pounded into sheets.
Properties of Semimetals
Metalloids are
located on the
staircase line,
dividing metals
from non metals.
Have a mixture of
metallic and
Can conduct heat
and electricity to
some extent.
• Columns of elements are
called groups or families.
• Elements in each group
have similar but not
identical properties.
Valence Electrons
• Valence electrons are
critically important since
they determine the
reactivity of an atom.
• How can you determine
how many valence
electrons an atom has?
• For example, lithium (Li),
sodium (Na), potassium
• For groups 1,2, and 13-18(K), and other members of
the group number is the
group 1 are all soft, white,
number of valence
shiny metals. (not H)
electrons (drop the 1 in 1318)
• All elements in a group
have the same number of
outermost electrons.
How many valence electrons
do the following atoms have?
* Ca
• H
• Cl
• He
• P
• Se
• Li
• Ba
• C
• I
• Ar
• Al
• N
Another Way to Represent
Atoms- Lewis Diagrams
• Lewis Diagrams- a model of the atom in which
the element’s symbol represents the nucleus
and the inner electrons and dots around the
symbol represent valance electrons.
• Example:
• What are INCORRECT ways that dots are
placed around the symbol?
Write out the Lewis Dot Diagrams for
the following elements.
Period- Rows of Elements
• Each horizontal
row of elements is
called a period.
• The first element
in a period is
always an
extremely reactive
• The elements in a
solid. The last
period are not
element in a
alike in properties.
period, is always
an inactive gas.
• In fact, the
properties change • Elements in a
greatly across
period have the
every given row.
same number of
energy levels.
Identify the following elements:
• Group 2, period 4
• Ca
• Group 16 , period 3
• S
• Group 8, period 4
• Fe
• Period 3, noble gas
• Ar
Atom Models
• There are two models of the atoms we will be
using in class.
• Bohr Model
• Lewis Dot Structure
Bohr Model
• The Bohr Model shows
all of the particles in the
• In the center is circles
representing the
nucleus. Each circle
represents a single
neutron or proton.
Protons should have a
plus (+). Neutrons
should have an N.
• In a circle around the
nucleus are the
electrons. Electrons
should have a minus
+ N
N +
1st Energy Level
2nd Energy Level
3rd Energy Level
So let’s try it….
• How to draw a Lithium atom
• First, look at the Periodic Table
• Second, determine the number of
protons (Look @ the atomic number)
• Then determine the number of
neutrons (mass # – atomic #)
• Then determine the number of
electrons (Look @ the # of protons)
Mass # = 7
Electrons have special rules….
• Electrons live in something called shells or
energy levels.
• You can’t just shove all of the electrons into the
first energy level of an electron.
• Only so many electrons can be in any certain
energy level.
• 1st energy level = 2 electrons
• 2nd energy level = 8 electrons
• 3rd energy level = 18 electrons
• The electrons in the outer most energy of any
element are called valance electrons.
Lewis Dot Structure
• The Lewis Dot
Structure is a bit
different from the Bohr
• It only shows the
element symbol and
it’s outer most electron
• The symbol
represents the nucleus
and the inner
• Dots around the
nucleus represent the
valence electrons.
+ + +
+ + +
• O ••
Determining the number of
Valence Electrons
• It is very easy to determine the number of
valance electrons (outermost electrons) for
many element from the periodic table.
• For groups 1 and 2 and 13-18, the number of
valence electrons is equal to the element’s
group number.
• Group 1 and 2 elements have 1 or 2 valence
• Groups 13-18 have 3-8 valance electrons.
(Simply drop the 1 from the group number.)
Which group and how many valence electrons
(outermost electrons) do the following elements
have? Draw the Lewis Structure.
• Ca
• N
• Cl
• H
• P
• He
• Li
• Se
• C
• Ba
• Ar
• I
• Al
Importance of Valence Electrons
• Valence electrons are critical to an element’s
• Valence electrons are the only particles that
interact when atoms come into contact with one
• Elements in a group have the same number of
valence electron causing them to have similar
properties. In other words, elements in a group
behave generally the same since they have the
same number of valence electrons.
Elements in Periods
• Elements in a period have the same number of
energy levels but they have differing number of
valence electrons.
• Because elements in a period have differing
numbers of valence electrons, they have very
different properties. For example:
• Sodium is in period 3 and is a very reactive,
solid metal.
• Argon is in period 3 and it is a very stable,
nonreactive gas which is a nonmetal.
• All atoms of a given element have the same
number of protons but could have different
numbers of neutrons.
• Atoms with the same number of protons but
different numbers of neutrons are called
• The major difference between isotopes of an
atom is the amount of neutrons not its
• The mass number states the number of
protons and neutrons within the nucleus of an
• Isotopes have different mass numbers. The
atomic number for the element is the same.
• For example: (note the different way they are
How isotopes are written:
• C12 and C13
or Chlorine-37 or Chlorine-35
• Only the mass number is given. The atomic
number is not given since it never changes for
an element.
Another way to represent the isotope is by
• zX : the
X = symbol
A= mass number
Z = atomic number
• For example
Identify the following
Atomic Number
Mass Number
Number of Protons
Atomic Number
Mass Number
Number of Protons
Number of Neutrons
Number of Electrons
Number of Neutrons
Number of Electrons