Download Chapter 3: Atom Powerpoint

The building blocks of matter!
The Atom: From
Philosophical Idea to
Scientific Theory
A MODEL in science is often an
explanation of how phenomena occur
and how data or events are related.
Models may be visual, verbal, or
mathematical.
Democritus called nature’s basic particle an
atom, based on the Greek word meaning
“indivisible.”
The view of Democritus was not supported
by experimental evidence.
An atom is the smallest particle of an element
that retains the chemical properties of that
element.
The smallest particle of an element that retains the chemical
properties of the element is a (n) _____.
molecule
salt
atom
compound
John Dalton (1766-1844) is the scientist
credited for proposing the atomic theory.
This theory explains several concepts that
are relevant in the observable world: the
composition of a pure gold necklace, what
makes the pure gold necklace different
than a pure silver necklace, and what
occurs when pure gold is mixed with pure
copper. The theories that Dalton used as a
basis for his theory: the law of conservation
of mass and the law of constant
composition.
Dalton’s Atomic Theory
1.
2.
3.
4.
5.
All matter is composed of extremely small
particles called atoms.
Atoms of a given element are identical in
size, mass, and other properties; atoms of
different elements differ in size, mass, and
other properties.
Atoms cannot be subdivided, created, or
destroyed.
Atoms of different elements combine in
simple whole-number ratios to form chemical
compounds
In chemical reactions, atoms are combined,
separated, or rearranged.
J. J. Thomson
In Thomson’s "Plum
Pudding Model" each
atom was a sphere filled
with a positively charged
fluid. The fluid was
called the "pudding."
Scattered in this fluid
were electrons known as
the "plums.”
Fixed electrons
surrounded by
positive material
Thomson’s experiment
revealed that the
electron has a very
large charge for its tiny
mass.
Central positive
center (nucleus)
Surrounded by
Electrons
Ernest
Rutherford
Rutherford’s Gold Foil Experiment
The Discovery of the Nucleus
1. Most of the alpha particles passed through the gold foil
indicating most of the atom is empty space.
2. A few of the alpha particles rebounded back indicating there is
a small dense central positive part of the atom called the
nucleus.
RUTHERFORD’S
GOLD
FOIL EXPERIMENT
Positive center surrounded
by electrons that travel in
fixed orbits
Neils Bohr
Bohr Model
1st energy level
K-shell max. 2
electrons
2nd energy level
L-shell max. 8
electrons
3rd energy level
M-shell max. 18
electrons
Emission spectra
•A diffraction grating and a spectrometer can be used to look at the emission
spectrum from a light source.
•If all possible wavelengths of light are present it would look like a continuous
spectrum of colors.
•However hot gases emit only particular characteristic colors of light.
•Each line in the emission spectrum corresponds to an electron moving from
a higher energy level to a lower energy level.
•To do this it emits photon of light.
•The energy of the photon of light is equal to the difference in the energy of
the two energy levels.
Positive nucleus surrounded by an
electron cloud where electrons are
likely found
Which model best describes
the structure of an atom?
1) Atoms are like tiny
solid spheres like marbles.
2) Atoms have tiny
particles orbiting the
nucleus like planets in the
solar system.
3) Atoms have tiny
particles randomly
traveling outside the
nucleus.
4) Atoms are charged
particles that make up all
matter.
http://www.colorado.edu/physics/2000/applets/a2.html (shows electrons , orbitals and nucleus
Dalton turned Democritus' idea into a
scientific theory that could be tested
by experiment.
Modern Atomic Theory Revised
1. Today we know that atoms are
divisible into even smaller particles.
(protons, neutrons, electrons)
2. We know that a given element can
have atoms with different masses.
(isotopes)
GROUND STATE VS EXCITED STATE
When
an atom is in its lowest energy state,
it is said to be in its ground state.
When an atom absorbs a specific amount
of energy, one of its electrons can “jump”
into the next energy level. When this
happens, the atom is said to be in the
excited state.
Atoms emit light as this excited electron
returns to the ground state.
A proton, neutron, and electron went out to dinner one
night. After a luxurious meal, the waiter brought the check
to the proton and the electron. The neutron was perplexed
as to why the waiter didn't bring him his check. So, he
summoned the waiter to the table and asked him about it.
The waiter explained to the neutron, "For you, there's no
charge!"
Structure of the atom:
Two main parts:
1. Nucleus
A) made of two kinds of particles
1. Protons- positive charge (mass 1.673 x 10-27kg)
2. Neutrons-electrically neutral
(mass1.675x10-27kg)
3. Mass of protons is a some less than the mass of
neutrons
B) Very small, dense central part of the atom
C) Most of the mass of the atom
2. Electron cloud
A) Probable location of the electron
B) Most of the volume of the atom
C) Electron-negative charge( mass 9.109 x 10-31kg)
D) The electron has the least mass
Identify in order from largest to smallest the relative size of each particle.
p+, n0, ee-, p+, n0
p+, e-, n0
n0, p+, eMost of the volume of an atom is made up of the _____.
nucleus
nuclides
protons
electron cloud
How would two protons in close proximity interact with each other?
repel
attract
have no interaction
How would one proton and one neutron in close proximity interact with each other?
repel
attract
have no interaction
How would one proton and one electron in close proximity interact with each other?
repel
attract
have no interaction
A positively charged particle found in the nucleus if called
a (n) _____.
proton
neutron
electron
quark
A nuclear particle that has no electrical charge is called a
(n) _____.
proton
neutron
electron
quark
Atoms are electrically neutral
because they contain equal
numbers of protons (charged
positive) and electrons (charged
negative).
PROPERTIES OF ATOMS
 Atomic Number-
Atomic number of an element is the number of protons in the
nucleus of each atom of that element.
•
•
•
Mass Number-
Mass number is the total number of protons and neutrons in the
nucleus of an isotope.
Mass number is the average atomic mass rounded to the nearest
whole number.
 To
figure out the number of neutrons in an atom,
subtract the atomic number from the mass
number.
ATOMIC SYMBOLS
51
23
V
23 protons
28 neutrons
23 electrons
The symbol tells you the number of each
subatomic particle in one atom of the
element.
The number in the top left is the mass #.
- The number of protons plus
neutrons.
The number in the bottom left is the
atomic #.
- The number of protons.
Complete chemical symbols
are written like this:
atomic mass
Symbol
charge
atomic #
Don’t worry about this yet!
Here is the periodic table entry for barium…
56
How many neutrons in a barium atom?______________
81
How many electrons in a barium atom?______________
56
How many protons in a barium atom?______________
What do you do with dead people?
Barium!
This information can be found on the periodic table…
Atomic Number
Atomic Mass
Round it!
The total number of protons and neutrons in the nucleus of an isotope is called its
_____.
mass number
atomic mass unit
atomic number
molar mass
The number of protons in the nucleus of an element is called its _____.
atomic mass unit
atomic number
mass number
molar mass
The atomic number of nickel-60 is 28. The number of neutrons of the isotope is
_____.
60
28
32
3
Carbon-14 has 8 neutrons. The atomic number of carbon-14 is _____.
32
8
14
6
An atom of silicon-30 contains 14 protons. The number of electrons it has is _____.
30
14
44
16
Isotopes are atoms of the same element that
have different masses.
Hydrogen-1 protium
Hydrogen-2deuterium
Hydrogen-3tritium
Atoms of one element that have different masses are called
_____.
isotopes
moles
molecules
Mixtures
What is true when comparing isotopes carbon-12 and carbon-14
a) they have the same number of neutrons
b) they are different elements
c) they have the same number of protons
d) they have the same mass
Atoms of the same element can differ in _____.
chemical properties
mass number
atomic number
number of protons and electrons
Law of conservation of mass states that
mass is neither destroyed nor created
during ordinary chemical or physical
reaction.
Example: A glass of ice cubes will have the
same mass when the ice has completely
melted into water even though its volume
will change.
The law of definite proportions states that a
chemical compound contains the same element
in exactly the same proportions by mass
regardless of the size of the sample or source of
the compound.
84.01 g of baking soda, NaHCO3, always
contains 22.99 g of sodium, 1.01 g of hydrogen,
12.01 g of carbon, and 48.0 g of oxygen. What
percentage of each of these elements is present
in baking soda?
_____________Na
_____________C
_____________H
_____________O
The law of multiple proportions: If two or
more different compounds are composed
of the same two elements, then the ratio of
the masses of the second element
combined with a certain masses of the
first element is always a ratio of small
whole numbers.
An example of the law of multiple
proportions is the existence of
A) FeCl3 and Fe(S04)3 C) CO and CO2
B) O2 and O3
D) FeCl2 and Fe(NO3)2
For each compound, different elements combine in a simple numerical ratio. The
illustration below describes this rule.
The second equation for the reaction is incorrect because half of an atom does not
exist.
Atomic Radius: one-half the distance
between the nuclei of identical atoms that
are bonded together
Relative Scale:
One atomic mass unit , or 1
amu, is exactly 1/12 the mass of
a carbon-12 atom.
Average atomic mass is the
weighted average of the atomic
masses of the naturally
occurring isotopes of an
element.
Calculating Average Atomic Mass
Isotope
Percentage
Natural Abundance
Uranium-234 0.005%
Uranium-235 0.720%
Uranium-238 99.275%
Atomic mass
(amu)
234.040947
235.043924
238.050784
•Oxygen has three naturally occurring isotopes in the
following proportions:
oxygen-16, 99.762% (15.99492 amu)
oxygen-17, 0.038000% (16.99913 amu)
oxygen-18, 0.20000% (17.99916 amu).
•What is the average atomic mass of oxygen?