Unit 2 - Chapter 3
Elements, Atoms,
Ions
The elements
• Can we name some?
• How many are there?
• Where would you find that
information?
Element
Symbols
• Each element has a unique symbol.
• The first letter is always capitalized
• if a second letter, it is always lower case
• Usually the 1st letter of its name, then the 2nd
letter or unique letter.
• Carbon, Calcium, Cadmium, Californium
• Some unusual symbols - mostly based on latin
roots
• sodium, potassium, gold, lead, mercury, iron,
etc.
Atomic size
• We can take a chunk of matter and break in
apart into smaller and smaller pieces, eventually
we would get down to individual atoms. Each
piece would behave like the original chunk with
all of its properties.
• The atom is the smallest particle of an element
that retains the properties of the element.
•
8
10
copper atoms lined up would be 1 cm. What
would be the diameter of a single copper atom?
• Democritus (ancient greek philosopher)
Atomic theory
stated that if you broke down matter
- Chpt 3.2
eventually you would get to the smallest
particle of matter that could not be divided
(atomos)
• John Dalton - 1800s - Did Chemical
Experiments!
• Things (matter, compounds) always
combined in the same proportions SIMPLE
WHOLE NUMBER RATIOS
• Law of Constant Composition - a compound
always has the same composition
regardless of where it comes from or how it
is made
Dalton’s Atomic
Theory
• Elements are made of tiny particles - atoms
pg. 56 Textbook
• All atoms of an element are identical.
• Atoms of an element are different from all
other elements.
• Atoms can combined to form compounds. A
compound always has the same number and
types of atoms. SIMPLE WHOLE NUMBER
RATIOS
• Atoms are not created nor destroyed by
chemical reactions, simply rearranged or
Compounds
• Compound is a distinct substance, that is
composed of 2 or more elements, always in
the same proportions (whole number ratios)
• Can we name some?
• A compound has a unique chemical formula,
which indicates which elements and how
many are in that particular substance.
Atomic Structure - Chpt
• What is a Model of 3.3
the atom?
• How did we get there?
• Dalton - Chemical Experiments determined
atom was indivisible (a solid sphere)
• Cathode Ray tube experiments by J.J.
Thomson (plum pudding model or TODAY
maybe chocolate chip ice cream)
• Gold foil experiment by E. Rutherford (nuclear
atom - the marble in the Metrodome)
• The cathode
ray tube discovered was a beam
J.J. Thomson’s
of particles
Experiment
• The beam was deflected by magnets
• changed the gas -> didn’t change beam,
• changed metal anode -> didn’t change
beam
• Particle was a fundamental particle of all
substances!
• Particle was a part of all atoms!!!! 1st
Subatomic particle, so the atom was made of
smaller particles
Rutherford’s
Gold foil Experiment
• Bombarded a thin gold foil with positively
charged alpha particles. Looked at flashes of
light when film was hit.
• Most of the particles went straight through
• 1 out of 20,000 bounced almost directly back
• Conclusions:
• Atom is mostly empty space
• positively charged nucleus with most of the
mass
• Not all atoms of an element are the same!
Isotopes
• The identity of an atom is determined by the
number of protons.
• Atomic number is the # of protons in an atom,
Z.
• atomic number is found on periodic table!
• # of protons
= # of electrons in neutral
atom.
• Mass number is the sum of the protons +
neutrons in the nucleus of the atom, A
• #of neutrons = Mass number - Atomic number
=A-Z
• For the masses of atoms we use amu
Isotope examples
(atomic mass unit) - 1 amu is defined
as one-twelfth the mass of the carbon12 atom.
•
•
hydrogen-1, hydrogen-2, hydrogen-3
also written
1H
2H
3H
AH
• the number is the mass number, the
atom name tells us how many protons!
• how many protons does hydrogen
have?
• how many neutrons does each isotope
have?
•
oxygen-16, oxygen-17,
oxygen-18
Atomic Mass
• Atomic mass from periodic table is a
weighted average of the stable isotopes
found on earth.
• If we are given the percentage of each
isotope and its mass can calculate the
atomic mass.
• Simply multiply the percentage times
the mass for each isotope and add up
each isotopes contribution to get the
atomic mass.
• Write the key terms (pg. 68) in your
Periodic Table - Chpt 3.4
notebook.
• The elements were organized into the
Periodic Table by Mendeleev in 1869.
• Columns (groups or families) of elements
have similar chemical properties
• He left blank spaces • prediction of previously unknown
elements
• These were found and confirmed his
predictions!!
• 7 periods (rows) , 18 groups (columns)
Mendeleev’s 1869
Periodic Table
Properties of metals
• Solid, shiny
• Conduct electricity
• Conduct heat
• Malleable (hammer into shapes) and
Ductile (drawn into wires)
Types
of
elements
• Metals
• Non-metals
• Metalloids (semimetals) -
along the
staircase - separates the metals from the
nonmetals
• Most elements are considered single atoms,
a few are only found as diatomics - two
atoms together, H2, N2, O2, F2, Cl2, Br2,
I2
• hockey stick and puck
or
Extra Credit - Unit 2
• Chapter 3 - pg. 86-88 ,
# 5, 6, 7, 10,
12, 14, 17, 18, 19, 21, 23, 29, 30, 33,
35, 39, 40, 41, 42, 46, 53, 55