Transcript Atomic Structure PowerPoint

HIROSHIMA 1945
August 6th, 1945
ATOMIC THEORY
Part 1: Atomic Structure
The Origin of the Atom
Changes in the Model of the Atom
1. DALTON
- everything is made of atoms
- different elements combine to form compounds in
simple whole ratios
- each element has its own unique type of atom
with a characteristic weight
- small indivisible solid particle model
2. THOMSON
- discovery of subatomic particle (electron)
Cathode ray experiment
- rays are particles, not waves
- new particles are negative, lighter than smallest
atom (hydrogen)
- plum pudding model
3. RUTHERFORD
Thin gold foil experiment
-alpha particles mostly pass through foil
-but sometimes deflected back when they hit
something massive
-thus, atom made mostly of empty space
-core of positively charged material, where most of
the mass of the atom is (nucleus)
-why don’t negative electrons give in to the pull of
the positive nucleus and collapse inwards?
4. BOHR
- negatively charged electrons found in concentric circular orbits around
the positive charged nucleus
- electrons found at fixed energy levels orbiting at fixed distances from
the nucleus
- path closest to nucleus = lowest energy level
- energy higher the farther the orbits are from the nucleus
- the farther the electron is from the nucleus, the less attraction it feels
- electrons can jump from one energy level to another, but are not found
between levels
- they lose or gain a discrete package of energy (quantum of energy)
every time it jumps levels  quantum leap
- explains why each element has a certain number of electrons available
for reactions
- the electrons found on the outer most orbit
 valence electrons
- planetary model
EXAMPLES
1. Any atom containing 3 protons must be…?
2. A neutral sodium atom has _____ electrons
IONS
If electrons are added to or subtracted from a
neutral atom, the resulting particle is called an
ION
Electrons have a NEGATIVE charge so:
-SUBTRACTING a NEGATIVE charge produces a
POSITIVE ion
-ADDING a NEGATIVE charge produces a
NEGATIVE ion
EXAMPLES
1. If an electron is added to a neutral F atom,
then the ion is written as:
2. If two electrons are removed from a neutral
Ba atom, then the ion is written as:
Atomic Mass
Since both neutrons and protons have a molar mass of
approximately 1 g, then:
- Total mass of an atom = total number of protons and neutrons
*the electrons are too light to make an appreciable contribution
to the mass of an atom
ATOMIC MASS = the total # of protons and neutrons
Thus,
NUMBER OF NEUTRONS = ATOMIC MASS – ATOMIC NUMBER
EXAMPLES
Find the number of protons, neutron and
electrons in the following atoms:
a) Al
b) C
…But, then why is it that the atomic mass of
some elements is not a whole number?...

or..
- atomic species having the same atomic
number, but different mass numbers
Now try it with ions!
Find the number of protons, neutron and electrons
in the following ions:
1)
56Fe3+
2)
76As3-
3)
201Au+
4)
82Br -
Extra Practice…
Extra Practice…
Natural Mixtures
The molar mass of chlorine is 35.5 g. Since there
can’t be 0.5 of a proton or neutron, then this
atomic mass MUST represent an AVERAGE value of
a MIXTURE of isotopes…
Example: Find the average atomic mass of
1) Cl, given that is composed of 75.77% Cl-35 and
24.23% Cl-37
Natural Mixtures
Now you try…
Find the average atomic mass of:
2) B, given that is is composed of 18.8% B-10 and
81.2% B-11