Transcript Chemistry 1 – Tollett Chapter 5 – Atomic Structure & The Periodic

Chemistry 1
Chapter 5 – Atomic Structure
& The Periodic Table
5.1
Early Models of the Atom
Dalton’s Atomic Theory
1. All elements are composed of tiny
indivisible particles called atoms.
2. Atoms of the same element are identical.
The atoms of any one element are different
form those of any other element.
3. Atoms of different elements can
physically combine with one another in
simple whole-number ratios to form
compounds.
4. Chemical reactions occur when atoms are
separated, joined, or rearranged. Atoms
of one element, however, are never
changed into atoms of another element
as a result of a chemical reaction.
Atom – the smallest particle of an element
that retains the properties of that element .
Example: How many atoms are in each
compound?
CO2
H 2O
H2SO4
3
3
7
5.2
Structure of the Nuclear Atom
Electron
- negatively charged subatomic particle.
They have a –1 charge and are 1/1840
the mass of a hydrogen atom
Cathode Ray Tube (CRT)
- device used to originate a flow of
charged particles
CRT
J.J. Thomson - credited with
discovering the electron
• He used CRT's to measure deflection of charged
rays using different gasses, magnets, and
different metal electrodes.
• Found that the ray moved from the anode (-) to
the cathode (+)
• He proposed that the ray was composed of
negatively charged particles which he called
electrons.
• He also calculated the charge-to-mass ratio of
the electron.
Robert Millikan –
His studies led to the determination of
the properties of the electron in 1916.
E. Goldstein – discovered positively
charged particles in cathode ray tubes.
– These particles were later called protons.
Proton – positively charged subatomic
particle.
Neutron - discovered by James Chadwick
1932.
•Has approximately the same mass as a
proton.
•They are located in the nucleus.
•It has no charge.
Once subatomic particles had
been discovered, Dalton’s model
of the atom had to be modified.
Thomson proposed the “Plumb
Pudding” Model of the atom.
Rutherford – credited with
discovering the nucleus.
• Gold Foil Experiment
Nucleus – the central core of an atom and is
composed of protons and neutrons.
• It accounts for more than 99% of an atoms
mass.
• The nucleus is also positively charged.
Niels Bohr
• Niels Bohr applies quantum theory to
Rutherford's atomic structure by assuming that
electrons travel in stationary orbits defined by
their angular momentum.
• This led to the calculation of possible energy
levels for these orbits and the hypothesis that the
emission of light occurs when an electron moves
into a lower energy orbit.
5.3
Distinguishing Between Atoms
Atomic Number
– the number of protons in the nucleus of
an atom.
Example:
• What is the atomic number for the following
elements?
Al
C
Br
I
Na
Ag
13
6
35
53
11
47
• How many protons are there in each?
The SAME
# of protons = Atomic #
• Mass Number
– the number of protons and neutrons in
the nucleus of an atom.
• Isotopes
– atoms that have the same number of
protons but different numbers of neutrons.
Example:
• What is the number of neutrons in each of
the following isotopes?
27Al
12C
80Br
127I
23Na
108Ag
Find the missing values for the
NEUTRAL
atoms in the table below.
Element
Atomic Number Mass Number # protons
12
# electrons
25
6
K
# neutrons
6
40
23
28
Atomic Mass – a weighted average mass
of the atoms in a naturally occurring sample of
the element.
Atomic Mass Unit (amu) – is defined as
one-twelfth the mass of a carbon-12 atom.
Example:
A sample of cesium is 75% 133Cs, 20%
132Cs, and 5% 134Cs.
Calculate its average atomic mass?
.75
.20
.05
x 133
x 132
x 134
=
99.75
=
=
26.4
6.7
132.85
amu
Compare this value to that of the
periodic table. Is it accurate?
Calculated Value
132.85 amu
Periodic Table
132.905 amu
I would say…YES!
The Periodic Table
The Periodic
Table was
first put
together by
Demitri
Mendeleev.
Mendeleev’s Table (~1872)
• Arranged according to increasing atomic
mass
• Elements with similar properties placed in
the same vertical column
• Missing elements were yet to be
discovered and were left blank
Henry Moseley – (1887-1915)
• British Physicist determined the atomic
numbers of the elements
• He arranged the periodic table in order of
atomic number
• His periodic table is the one used today
Periodic Law –
• When the elements are arranged in order
of increasing atomic number, there is a
periodic repetition of their physical and
chemical properties.
Periods –
• horizontal rows of the Periodic Table
Groups –
• vertical
columns of
elements
on the
Periodic
Table
Representative Elements
• Group A elements
•
•
•
•
Alkali Metals – Group 1-A elements
Alkaline Earth Metals – Group 2-A elements
Halogens – Group 7-A elements
Noble Gases – Group 0 elements
Group B Elements
• Transition Metals – In the middle of the Periodic
Table
• Inner Transition Metals (rare earth metals) –
bottom of the Periodic Table
Classification of Elements
•Metalloids
semi-metals)
– along
••Nonmetals
Metals – found
–(or
found
on the
on the
left-side
right-hand
of thethe
sidestairof
step
line Table
the
Periodic
Periodic
Table
Properties are intermediate between metals
and nonmetals