Download CHAPTER 2 MATTER IS MADE UP OF ATOMS

CHAPTER 2
MATTER IS MADE UP OF ATOMS
What is Matter?
What two components must all matter have?
Is this matter?
HYPOTHESIS THEORIES AND LAWS
GOAL OF SCIENCE:
to understand the world around us thru ovbservation
and it is a process of problem solving techniques
SCIENTIFIC METHOD
systematic approach to solving a problem involving a
series of steps
Scientific Method Steps
Steps
1. Make an observation
2. Form a hypothesis
3. Experiment to test
hypothesis
4. Record and analyze data
- charts
- tables
- observable changes
5. Draw a conclusion
6. Retest and share results
THEORY
Logical time tested explanation for hypothesis and observations
- heavily supported by experimental evidence
- can predict an observation in the future
- can be changed with new data
- CAN BE BROKEN
LAW
Summarizing statemtne of observed experimental facts that has
been tested many times and is accepted as true
- CAN NOT BE BROKEN
DIFFERENCE
Theory explains, law only summarizes.
ATOMIC STRUCTURE TIMELINE
GREEK ERA
I. Democritus (460-370 BC)
- First proposed the existence of an ultimate
particle
- He said that the world is made up of empty space
and tiny particles “atoms”. Comes from the word
“atomos”
Atomos- uncutable or indivisible
- Different types of atoms exist for every type of
matter.
II. Aristotle (384- 322 BC)
- believed in the four elements of air,
earth, water and fire.
(HOT, COLD, WET, DRY: ASSOCIATED WITH EACH)
- felt that if you keep dividing matter, there was
an ultimate smallest particle of matter that
could not be divided any further.
- view held for 2000 years
MODERN ATOMIC THEORY
1782: Antoine Lavosier (1743-1794) French
A. represents the beginning of modern chemistry
B. made measurements of chemical change in a sealed
container
C. observed that the mass of reactants in a container
before a chem. rxn. = mass of the products after
the reaction
D. responsible for
LAW OF CONSERVATION OF MATTER(MASS)
Matter is neither created or destroyed, it just
changes form in a chemical reaction.
How does the Law of Conservation of Matter relate to
how we handle our garbage?
Late 1700’s: Joseph Priestly- English
- repeated his experiments and determined the
following:
- heated mercury oxide, metallic mercury remained
and oxygen was given off
(proved by burning candle in it, and put mouse in
sealed jar of it and mouse lived)
- theory: air is made up of more than one gas
1799: Joseph Proust- French
Law of Definite Proportions
pure compounds always contain definite or constant
proportions of the elements by mass
ex: observed that water is always 11% H and 89% O
- no matter where water came from it was always in
the same proportion
Iron pyrite (FeS )
46.5% iron
53.5% sulfer (by mass)
2
1803: John Dalton- English
- studied experiments of Lavosier, Proust
and other scientists
- backed up Proust’s theory of law of definite
proportions
- responsible for modern atomic theory
DALTON’S ATOMIC THEORY (1803)
1. All matter is made up of atoms
2. Atoms are indestructible and cannot be divided
into smaller particles (atoms are indivisible)
(only part of theory that has changed)
3. All atoms of one element are exactly alike, but
they are different from atoms of other elements
- Solid ball model of atom
DISCOVERY OF ATOMIC STRUCTURE
- Daltons theory almost true
- He felt that atoms were ultimate smallest particles of
matter that couldn’t be broken up – this was thought
to be true thru most of the 1800’s
- Theories can be broken with new experimentation…….
- Experiments in late 19th and early 20th centuries
showed that this was close, but not true
- We now know that the atom is made up of subatomic
particles
DISCOVERY OF SUBATOMIC PARTICLES
1897: JJ Thomson- English
- Discovered that Daltons solid ball theory
was not true
- Said atoms not made of solid ball and had
sub-atomic particles called electrons
- Plum pudding model: negative electrons
embedded in solid positively charged ball
Thompson’s Experiment
Cathode Ray Tube Experiment
PROCESS:
Sent a charge thru the electrode which caused rays to travel from
the negative side(cathode) to the positive side (anode)
RESULT:
Rays bent away from negative plate and toward positive plate(like
charges repel each other, unlike attract each other)
CONCLUSION:
Cathode rays are made up of electrons (negative)
Electrons had to come from the matter (atoms) of the negative
electrode.
1904: Hantaro Nagaoka- Japanese
- Planetary Model (Saturnian model)
- a very massive nucleus (like a very massive planet)
- electrons revolving around the nucleus in fixed
positions (like Saturn’s rings)
- some details of the model were incorrect and
Nagaoka abandoned it in 1908
1910: JJ Thompson
- concluded that atoms must be made of
electrons and protons
1911: Rutherford- English
- Responsible for determining that
most of the atom is composed of
empty space with a very
small dense central core
Rutherford’s Gold Foil Experiment
Goal: to test plum pudding model of atom
Method: used positively charged particles
emitted by radioactive atoms like
atomic bullets to hit a thin sheet
of gold foil
Results: - most of particles passed
straight through gold foil
- few of the particles were
deflected slightly
- few of the particles bounced
almost straight back
Conclusion: the atom is nearly all empty
space
1913: Neils Bohr- Danish
- proposed that electrons orbit the nucleus
in different energy levels called shells
- correct atomic model
Structure of the Atom
Atom: basic unit of matter, pure
substance
Subatomic particles
Protons – positive, inside nucleus
Neutrons- neutral, inside nucleus
Electrons- negative, outside nucleus
revolve around nucleus
(size of nucleus compared to whole
atom is like pea in giants stadium )
Atomic number = protons
Protons = Electrons
Atomic mass = protons + neutrons
Structure of the Atom
Nucleus
- very small and dense
- 100,000 times smaller than whole atom
- positively charged
- neutrons act as nuclear glue and holds nucleus
together
- contains most of the mass of the atom
Electron Orbitals (shells/clouds)
- Electrons keep the atom stable (neutral)
- Electrons equal protons
- Electrons located in orbitals
a) orbitals fill from closest to nucleus outward
b) each successive orbital has higher energy
than the last
c) electrons can jump to outer shells
- Valence electrons: located in outermost shell
Orbitals
s – 2 elec.
p – 8 elec.
d – 8 elec.
f – 8 elec.
lowest energy
higher energy
higher energy
highest energy
Electron Distributions Into Shells for
the First Three Periods
Lewis Dot Diagrams
One electron
•Shorthand method
representing valence electrons
–Each dot represents one
electron
Two electrons
Three electrons
Four electrons
Five electrons
Six electrons
Seven electrons
Eight electrons
Steps for Drawing Lewis Diagrams
1.
Find number of electrons
number protons = number electrons
2. Determine number of valence electrons
S 2
P
8
D 8
F
8
3. Draw structure
one electron per side before doubling up
no more than 2 electrons per side of atom
ex: draw the lewis dot diagrams for the following:
sodium
Na
carbon
C
argon
Ar
Lewis Dot Diagrams of Selected Elements
Atoms have no electronic charge (neutral)
WHY?
PROTONS (+)
equal
ELECTRONS (-)
NEUTRONS act like nuclear glue and hold nucleus together.
NUCLEUS has a POSITIVE charge.
Atom Identification
ATOMIC NUMBER
- Number of protons
- Determines identity of element
- Never changes
MASS NUMBER/ ATOMIC MASS/ ATOMIC WEIGHT
- Number of protons + neutrons
- Can change if atom has different numbers of neutrons in
nucleus
Key Rules
atomic # = # protons = # electrons
atomic mass = protons + neutrons
# neutrons = atomic mass - # protons
Isotopes: different form of the same element due to
different number of neutrons
- most are radioactive
(unstable nuclei which break down and emit particles)
Ex: C 12,
6 protons
6 neutrons
H1
protium
1 proton
0 neutron
C13,
6 protons
7 neutrons
C14
6 protons
8 neutrons
H2
deuterium
1 proton
1 neutron
H3
tritium
1 proton
2 neutrons
ELECTROMAGNETIC SPECTRUM
Electromagnetic radiation: Light released by electrons in reactions
- travels in waves through empty space
ex: radiant energy from sun travels to earth at speed of light
waves transfer energy from one place to another
Electromagnetic spectrum: whole range of elecrotmagnetic radiation
Includes:
Radio waves – radio and tv
Microwaves – ovens
Radiant heat – toasters
Visible light – white light
Xrays
ELECTROMAGNETIC SPECTRUM
Energy travels in waves
Wavelength
Distance between the crest of
one wave and crest of another
wave
Frequency
Number of complete waves that
go through a measured space
per second
The higher the frequency, the
higher the energy of the wave
Aurora Borealis (northern lights)
-electrically charged particles from
the sun trapped by earths
magnetic field
-collide with Oxygen and Nitrogen
and transfer energy to them (O
gives off whitish green light, Nred light)
-causes electrons to jump shells
and when return to lower energy
levels, release light
- seen at poles because that is
where earth magnetic field line
are located
Neon lights
-Electric current is run through
a closed tube with a specific
gas
-Electrons are energized and
jump to outer shells
-As electrons return to original
shell, they lose energy in the
form of light
-Different gases emit different
colors
Study for the test!