Download Atoms - Jensen Chemistry

Unit 3.1
 An
atom is
the smallest
physical
particle of an
element that
still retains the
properties of
that element.
At sea level, one cubic
centimeter of air (size of
a sugar cube, or marble)
will have 45 billion atoms
within it.

◦ 45,000,000,000
One century after Dalton,
Viennese scientist Ernst Mach
wrote that “atoms cannot be
perceived by the senses… they
are things of thought.”

Many scientists that made
contributions to atomic
structure – J.J. Thomson,
Robert Millikan, Chadwick,
Ernest Rutherford, and Neils
Bohr, Erwin Schrödinger.

1.
2.
3.
All elements are composed
of tiny particles called
atoms.
Atoms of the same element
are identical. Atoms of
different elements are
always different.
Atoms of different elements
can chemically combine in
fixed ratios to form
compounds.

Law of Conservation of Mass
Mass is not created or destroyed in a chemical reaction
or physical change

Law of Constant Composition

Law of Multiple Proportions
Cr2O3
CrO3

Atoms are solid and indivisible.

Electrons
◦ J.J. Thomson in
1897
◦ Particles deflected
in Cathode Ray
tube
◦ Negative one
charge
◦ Very small mass
1/2000 that of
the lightest atom
Thompson passed electric current through
gases in a glass tube. The result was a glowing
beam flowing from the negative side to the
positive side.

Glowing ray (cathode ray) was attracted to a
positive magnet on the side of the tube.


Beam must be negatively charged.
Thompson
hypothesized that all
atoms had such negative
charges within. (plum
pudding model)

Later, scientists proved
that atoms contained
both positive and
negative charges (which
balance each other out).

Born in New
Zealand.
 Terrible at
mathematics.
 Diligent problem
solver.
 First to discover
the power of the
atom, power to
make bombs that
could “make this old
world vanish in
smoke.”

◦ Ernest Rutherford 1911
◦ Gold Foil Experiment using
alpha particles
◦ nucleus
Shot radioactive particles
through a sheet of gold
foil.

Most went straight
through, but others were
knocked off course or
bounced back.

“Like shooting a fifteeninch shell at a sheet of
paper and having it bounce
off.”

Nucleus – compact
center of the atom
where protons and
neutrons are located

Nucleus has very
little of the atom’s
volume, but contains
most of the atom’s
mass.

Chadwick found that the
mass of an atom is
greater than the mass of
protons plus electrons.

Neutrons – portion of an
atom with no charge

Protons, neutrons, and
electrons are called
subatomic particles.


Proton



Mass equal to H
Positive one charge
Found in the nucleus

Neutron

Mass equal to H
 No charge
 Found in the nucleus
Electron
 Mass 1/2000 of H
 Negative one charge
 Found in the e- cloud

Electrons orbit the nucleus in orbits, like a solar
system.

Planetary Model




Born in Vienna, Austria
University of Berlin professor
Nobel Prize 1933
Based on waves of light and probability.
 Quantum
Mechanical Model –
like a shot gun blast.
Atomic structure
Atoms of different
elements have different
structures.

Elements differ
because their atoms
contain different
numbers of protons!

Atomic Number –
number of protons in
the atom




The number of protons determine the
properties (identity) of the element.
Atoms are neutral so the number of protons
= number of electrons
How many protons does Hydrogen have?
◦
◦
◦
◦
ANSWER: 1
How many electrons does hydrogen have?
Answer: 1
How many protons and electrons does silver have?
 Answer: 47
Electrons have negligible
mass compared to protons
and neutrons.

Mass of a neutron is
approximately equal to
mass of a proton.

Mass Number - number
of protons plus number of
neutrons in an atom.


Hyphen notation

◦ Name of elementmass number
Atomic #
◦ Examples
◦ Silver-108
◦ Carbon-12
Why is it not necessary
to show the atomic
number?
Nuclear symbol
Mass # element symbol
It is not necessary to put the
atomic number
Examples:
108
Ag
12C
6
Mass number
(p+ + no)
Atomic number
(number of p+)
Element symbol
 Beryllium
– 5 neutrons
◦ Mass Number – ?
 Sodium
– 12 neutrons
◦ Mass Number – ?
 Gold
– 118 neutrons
◦ Mass Number = ?

How many protons, neutrons, and electrons
in each?
◦ Magnesium-23
Answer: protons= 12 neutrons=
electrons = 12
◦
mass – atomic
119Sn
Answer: protons = 50, neutrons = 69, e-= 50
=11
Atoms of the same
element with different
number of neutrons

Chemically
equivalent

Most elements occur
as a mixture of
isotopes

Same atomic #,
different mass#

One amu (atomic
mass unit) is
defined as 1/12
the mass of a
Carbon-12 atom

1 amu is approx.
equal to the mass
of a proton or
neutron

Atomic masses found on
periodic table are averages of all
isotopes of that element

Based on abundance (weighted
mass)

To calculate the atomic
mass of an element, multiply
the mass of each isotope by
its natural abundance
(expressed as a decimal),
and then add the products.



Chlorine is a mixture of Cl-35 and Cl-37.
75.77% Cl-35 (35)
24.23% Cl-37 (37)
0.7577 x 35 amu = 26.50 amu
 0.2423 x 37 amu = 8.957 amu

Added together… 35.45 amu
+
 Carbon-12
 Carbon-13
 Atomic
Mass?
98.89%
1.11%
18
Arsenic
75
Phosphorus
8
16
8
18
33
15
75
31
Unit 3.3





The mole is the SI unit for amount of
substance (counting number)
1 dozen = 12
1 gross = 144
1 ream = 500
1 mole = 6.02 x 1023
6.02 x 1023 is called “Avogadro’s Number” in honor of the Italian chemist
Amadeo Avogadro (1776-1855).
I didn’t discover it. Its just named
after me!
Amadeo Avogadro



1 mole of books = 6.02 x 1023 books
1 mole of atoms = 6.02 x 1023 atoms
1 mole of molecules = 6.02 x 1023 molecules
Conversion factor: 6.02 x 1023 atoms
(use to convert atoms>mol)

1 mole
or
1 mol
6.02 x 1023 atoms
If you have 1 mole of books and 1 mole of feathers
you have the same amount of each, but does 1
mole of books have the same mass as 1 mole of
feather?


Mass in grams of 1 mole of a substance
1 carbon-12 atom has a mass of 12 amu
but 1 mole of carbon atoms (6.02 x 1023
atoms) has a mass of 12 g
The molar mass of carbon is 12 g/mol
The molar mass of any atom is its average atomic
mass (you can find it on the periodic table)
What is the molar mass of
 Ca
40.1 g/mol

S
32.1 g/mol

Conversion factor: 40.1 g Ca or 1 mole Ca
(use to convert mass <->mol)
1 mol Ca
40.1 g Ca
How many grams of lithium are in 3.50 moles of
lithium?
3.50 mol Li
6.94 g Li
=
1 mol Li
24.3 g Li
How many moles of lithium are in 18.2 grams of
lithium?
18.2 g Li
1 mol Li
= 2.62 mol Li
6.94 g Li
How many atoms of lithium are in 3.50 moles of
lithium?
3.50 mol Li
6.022 x 1023 atoms Li
= 2.11 x 1024 atoms Li
1 mol Li
How many atoms of lithium are in 18.2 g of
lithium?
18.2 g Li
1 mol Li
6.94 g Li
(18.2)(6.022 x 1023)/6.94
6.022 x 1023 atoms Li
1 mol Li
= 1.58 x 1024 atoms Li