UNIT 1
The Atom and Its Variations
Hierarchy of Chemistry
•
ELEMENT -
pure substance made of only one
type of atom.
Hierarchy of Chemistry
•
ATOM
– The smallest unit of an element that
maintains the properties of that element.
Hierarchy of Chemistry
•
MOLECULE
– Two or more atoms bonded
together. The atoms can be of the same
element or different elements.
Hierarchy of Chemistry
•
REACTION –
The process by which one or
more substances are changed into one or
more different substances.
– The are described (written) through the use of
chemical equations.
REACTANTS
PRODUCTS
Structure of the Atom
•
REGIONS OF THE ATOM
– NUCLEUS – Contains protons (p+) and neutrons
(no).
– Discovered by Rutherford et al in 1909.
• Alpha particles (naturally occurring radiation derived as positively charged Helium atoms) were fired at a very thin Gold film.
• The trajectories of the particles were then detected. • The results were astonishing…the particles collided
Structure of the Atom
– The Rutherford et al Experiment
Macro View
NU
Atomic ViewCL
EU
Structure of the Atom
– ELECTRON CLOUD – Region where electrons are
most likely to be found.
• ENERGY LEVELS – More specific regions of the electron clouds.
– Each energy level holds a specific number of electrons.
Energy Level #3 Energy Level #2
Energy Level #1
2 ELECTRONS 8 ELECTRONS 18 ELECTRONS
Structure of the Atom
•
VALENCE ELECTRONS
– Electrons in the
highest (furthest from the nucleus) energy
level.
– These electrons are important in creating
chemical bonds between atoms. REMEMBER – When atoms bond, molecules are created!!!
– When electrons fill the energy levels, the lowest
Structure of the Atom
STABLE
Structure of the Atom
•
SUB-ATOMIC PARTICLES
– ELECTRONS – (e-)
• Charge = -1
• Relative Mass = 0 AMU
– PROTONS – (p+)
• Charge = +1
• Relative Mass = 1 AMU
– NEUTRONS – (n0)
• Charge = 0
• Relative Mass = 1 AMU
AMU = ATOMIC MASS UNIT Where do protons and neutrons exist?
Structure of the Atom
IMPORTANT!!!!!!!
-Most of the mass of the atom is in the nucleus!
-Most of the volume (space occupied) of the
The Periodic Table
•
The numbers on the periodic table tell us ALL
about the structure of an atom of a specific
element!
O
8
Oxygen 16.00
Atomic Number Element Symbol
Element Name
The Periodic Table
•
ATOMIC NUMBER – Tells us the number of
PROTONS (p
+) and ELECTRONS (e
-)
– On the periodic table the POSITIVES must equal the
NEGATIVES!!!!
•
ATOMIC MASS – Tells us the MASS of the
PROTONS, NEUTRONS (n
o), and ELECTRONS.
– This number is always written to TWO DECIMAL PLACES!!
•
MASS NUMBER – The ATOMIC MASS rounded to
the nearest whole number.
Determination of the NUMBER of
SUBATOMIC PARTICLES
•
# PROTONS = ATOMIC NUMBER (Little
Number)
•
# ELECTRONS = ATOMIC NUMBER (Little
Number)
– In a NEUTRAL ATOM the POSITIVE particles MUST
be EQUAL to the NEGATIVE particles.
•
# NEUTRONS = MASS NUMBER – ATOMIC
NUMBER
Determination of the NUMBER of
SUBATOMIC PARTICLES
•
WHY??
– PROTONS and NEUTRONS are of EQUAL RELATIVE
MASS.
– SUBTRACT the MASS of the PROTON from the
MASS of the ENTIRE ATOM and YOU GET THE NUMBER OF NEUTRONS!!!!
DON’T WORRY!! WE’RE GONNA DO A LOT OF THESE PROBLEMS!!
EXAMPLE!!!!!
•
HOW MANY PROTONS, NEUTRONS, AND
Valence Electrons
•
WHOA! WAIT!! WHAT IS A
VALENCE
ELECTRON
AGAIN???!!!!
– The electrons found in the outermost energy
level!!
•
FINDING THE NUMBER OF VALENCE
Valence Electron
•
Elements in the same GROUP have the same
NUMBER of VALENCE ELECTRONS!
– GROUP 1 and 2 – SAME NUMBER OF VALENCE
ELECTRONS AS THE GROUP NUMBER!
– GROUPS 13 – 18 – GROUP NUMBER MINUS 10
– GROUPS 3 – 12 – TRANSITION METALS YOU HAVE
Valence Electrons
•
CARBON
•
SILICON
•
TIN
•
LEAD
•
ALL OF THESE ARE IN GROUP 14!!
A Little More About the Periodic Table
•
PERIOD – The Horizontal Row of ELEMENTS!
– The period number is equal to the number of
energy levels for a given atom.
– EXCEPTION – To find the energy level of a
TRANSITION METAL (Groups 3 – 12) just take the PERIOD NUMBER SUBTRACT 1…
•
FAMILY, GROUP, ROW – Vertical columns of
Variations of the Atom
•
ALL ATOMS represented on the PERIODIC
TABLE are NEUTRAL!
– THEY HAVEN’T REACTED YET!
•
ION –
An atom with a charge! Could be +
could be -.
– The charge of an ion is written in superscript. – For EXAMPLE – Li+ (Lithium Ion)
– This occurs when an atom LOSES or GAINS
Variations of the Atom
•
Why does an atom LOSE or GAIN valence
electrons??
– It is all because of this RULE!
– THE STABLE OCTET RULE!
• The STABLE OCTET RULE states that an atom is MOST
ENERGETICALLY STABLE when it has 8 VALENCE ELECTRONS!
•
EXCEPTION!!! If you look at HELIUM it only
Variations of the Atom
•
CATION
– Positive Ion
– If an atom has 1 or 2 electrons in its valence
energy level, it is EASIER to give them away in order to satisfy the STABLE OCTET RULE.
– THE NUMBER OF PROTONS NEVER CHANGES! SO
WHEN ELECTRONS ARE LOST, THERE ARE MORE PROTONS THAN ELECTRONS!
• PROTONS ARE POSITIVE • ELECTRONS ARE NEGATIVE
Variations of the Atom
•
EXAMPLE!!
Variations of the Atom
•
ANION
– A negative ion
– MORE ELECTRONS than PROTONS
– ELECTRONS ARE NEGATIVE!
– The atom GAINS ELECTRONS in order to satisfy the
STABLE OCTET RULE
– GAINED ELECTRON makes for a NEGATIVELY
CHARGED ATOM!
– If the atom has 6 or 7 electrons in the highest
Variations of the Atom
•
EXAMPLE!!!
Variations of the Atom
• ISOTOPES – Are atoms of the SAME element that
have DIFFERENT MASSES, because they have a DIFFERENT NUMBER OF NEUTRONS.
– Isotopes are important because the react the same but are heavier or lighter and can be detected by instrumentation.
• CHANGES IN THE NUMBER OF NEUTRONS DOES NOT
CHANGE THE IDENTITY OF THE ATOM!!
•
PROTON NUMBERS ARE ALWAYS THE
Variations of the Atom
•
There are 2 ways to represent isotopes
– Hyphen Notation
• Carbon – 13
• Can you tell me how many PROTONS, NEUTRONS, and
ELECTRONS?
– Nuclear Notation
C
13 6
13 = MASS NUMBER 6 = ATOMIC NUMBER
Go Ahead! GIVE ME PROTONS, NEUTRONS, AND ELECTRONS IN Oxygen – 18
Representing Molecules
•
MOLECULAR FORMULA
– Tells the types and
numbers of each atom in a molecule
•
SUBSCRIPT
– Gives the number of atoms of that
element in one molecule of the compound.
•
EXAMPLES!!!
– Nitrogen Gas (N2) – Water (H2O)
Representing Molecules
•
COEFFICIENT
– Tells the number of molecules
•
Example!!!
– 3CO2
– There are three molecules of CO2
– If there are 3 molecules of CO2, how many CARBON and OXYGEN atoms are there in all?
TRY THESE ON YOUR OWN!
-2H
2O
