Transcript Introductory Chemistry PowerPoint 2013

Introductory Chemistry
Mrs. Taktak
and
Mrs. Storey
Atoms
• Most of the Universe
consists of matter and
energy.
• All matter is
composed of basic
elements.
• All elements are
composed of Atoms.
What is an atom???
– The smallest unit of
matter that has all the
properties of a given
element.
• Ex.: Gold is made up
of only gold atoms!
What does an Atom look like?
• In the center is a Nucleus
• In the nucleus are 2 smaller particles
called: Protons and Neutrons
– Protons have a (+) charge and Neutrons have
(0) charge.
• Each element has a different number of
protons in the nucleus.
• It is this proton # that gives the atom
(element) its characteristics.
What does an Atom look like?
• Outside the nucleus are rings called
shells.
• Floating around in the shells are Electrons.
• Each shell holds a specific # of electrons.
(We will talk more about this later.)
• What charge do you think an electron
has?
Time Out!! Label this atom
Here are some pictures of Atoms
Drawing Atoms
• To draw an atom
correctly, you need to
use the Periodic
Table of Elements.
How to Use the Table for Drawing
Atoms
• Atomic # = # Protons = # Electrons
• Why does the proton # = the electron #?
Let’s practice!!
• The 1st Element on the Periodic Table is
Hydrogen.
• It has an Atomic # of 1, so it has ___
Proton and ___ Electron.
1
Electron
Nucleus with 1
proton
1st shell
You Practice!
• Using your periodic table, can you guess
which element this is?
Drawing larger atoms
• After Hydrogen and Helium, we have to
add another shell to put electrons on.
• Why? Because: The 1st shell only holds 2
electrons.
All other shells want to hold 8 electrons.
Practice drawing Lithium, Beryllium, Boron,
and Carbon.
How do we find # of Neutrons?
• We know that the Atomic # = # Protons
and # Electrons, but how do we find # of
Neutrons?
• It’s easy!
• Take the Atomic Mass # and subtract the
Atomic #. (A.M.- A. # = # of Neutrons)
• What is the # of Neutrons for Carbon?
Isotopes
• Most atoms have different forms
due to differing #’s of neutrons.
• These different forms of a
particular atom are known as
isotopes of that atom.
• Why can the neutron # be
different without affecting the
atom?
Isotope Practice
• There are two forms of carbon:
Carbon-12 (C-12) and Carbon-14 (C-14)
Show the proton, electron, and neutron #’s for
each isotope of carbon:
Carbon-12:
p+ =
e- =
n0 =
Carbon-14:
p+ =
e- =
n0 =
Do Atoms Ever Combine?
• Yes! They form compounds. Define a
compound:
• Why do elements combine to form
compounds?
• It has to do with the # of electrons in the
outer shell of the atoms.
• All electrons in the outermost shell are
called Valence Electrons
Bonding
• There are 2 “rules” that you need to know
about atoms.
• 1. The first shell wants to hold 2
electrons
• 2. The 2nd, 3rd,..shells want to hold 8
electrons
Is this a happy atom?
Is this a happy atom?
Covalent Bonding
• This occurs when atoms share electrons
to become stable, or “happy”!
• The shared pair of electrons provides
each hydrogen atom with two electrons
in its valence shell
More Examples
• A molecule of water is formed by a
covalent bond.
• Oxygen has 6 electrons on its outer shell,
so it wants _____ more?
• Hydrogen has 1 on its outer shell, it would
like to have ____ more?
• Can you guess how this bond is drawn?
http://www.kentchemistry.com/links/bondin
g/bondingflashes/bond_types.swf
How do we write the formulas
for these molecules?
• There are chemical formulas, which are
the written chemical symbols and their
subscripts.
• Example: Water is written as H2O. This is
the chemical formula for water!
• There are structural formulas which are
the atomic drawings for molecules, such
as what you drew for water.
Practice (Covalent)!
• Try drawing a molecule of Oxygen
gas which is O2.
OR
• Try drawing a molecule of methane,
which is CH4.
More On Covalent Bonds
• Covalent bonds are very strong bonds. It
is hard to break a covalent bond.
• Example, your hair is held together by
covalent bonds. It takes energy to break
these bonds, and a strand of your hair!
Are there other kinds of bonds?
• Yes! There are also Ionic Bonds.
• Ionic Bonds are formed by an attraction of
positive and negative charges.
• Where do the charges come from if the
atoms are neutral????
Example of an Ionic Bond
• Draw the atoms Na and Cl.
• Notice that Na has 11protons and 11
electrons. This gives Na 1 electron in
its outer shell. Is Na happy this way?
Is it likely to share to make 8?
• Notice that Cl has17 protons and 17
electrons. This gives Cl 7 electrons in
the outer shell. Is Cl happy?
A solution!
• If Na could lose an electron, and Cl could
gain an electron, they would both be
“happy.”
• This is how Ionic Bonds are formed. An
Ionic Bond is formed when electrons are
transferred from one atom to another,
which results in opposite charges that
attract each other.
http://www.kentch
emistry.com/links/
bonding/bondingfl
ashes/bond_types
.swf
How are the charges formed?
• When Na loses its electron, how many
electrons does it have now? How many
protons does it have? This gives Na a (+)
charge, making it a + ion (cation).
• Understanding this, explain how Cl
becomes (-) charged when it takes on
Na’s electron, making it a – ion (anion).
• +/- attract, and a molecule of NaCl is
formed, which is the molecular formula for
table salt!
More on Ionic Bonding
• When these atoms lose or gain electrons,
they get “new names”.
• Na is now called Na+ or a (Sodium Ion)
• Cl is now called Cl- or a (chloride ion)
• Any positive ion is called a Cation
• Any negative ion is called an Anion
Practice Problems (select 2, get
checked when finished with 1)
•
•
•
•
•
MgO
LiF
PbBr4
Li I
K2O
CaBr2
Be3P2
Be3N2