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Transcript
Activity 4: Are Atoms Divisible?
Ancient Greece
1. Greek philosopher
Democritus
2. He thought atoms were uncuttable
3. Therefore: Atoms are indivisible
particles
Atomos—Greek meaning ‘indivisible
470-380 B.C.
John Dalton—late 18th century
1. What are atoms?
Dalton’s Atomic Model:
Hard, indivisible sphere
1766-1834
2. Do Carbon atoms differ from
Oxygen atoms?
Yes
HAS THIS EVER
HAPPENED TO YOU?
Are there things inside the atom?
YES!
Subatomic particles
e- p+ n0
Discovery of electron (e-)
Credited with the discovery of the
electron in 1897.
J.J. Thomson
1856-1940
•Thomson identified a glowing
beam of particles that traveled
through a chamber of gas when
exposed to an electrical current.
Cathode ray tube
-This beam (cathode ray) was attracted to
positive charges and repelled by negative
charges.
-Thomson concluded the beam must be
composed of negatively charged
particles. These came to be known as
electrons.
Thomson’s Atomic Model
“Plum Pudding” Model
POSITIVE
CHARGE
Negative electron plums are
floating around in a sphere of
positive pudding.
ELECTRONS
EMBEDDED
WITHIN
Discovery of the Nucleus
1871-1937
Ernest Rutherford
Rutherford’s Au foil Experiment
“+” charge
Rutherford’s experiment
Rutherford’s Nuclear Atom
Negative electrons
surround nucleus
amidst lots of empty
space.
Positive
Nucleus
Discovery of the proton
Eugen Goldstein
In 1886, Goldstein
observed rays in a
cathode ray tube
that traveled
oppositely than the
electrons previously
discovered.
Protons
Located in nucleus
Determine which element
# of protons = atomic number

equal to # of electrons in a neutral atom
Chadwick
1. 1932 discovered the neutron
2. This subatomic particle is heavy enough to
split a nucleus
3. Led the way to the creation of the atomic
bomb
LETS HAVE SOME PRACTICE
Element
Symbol
Element
Name
Mass Number
(Protons+Neutrons)
Atomic
Number
(Protons)
Atomic
Number
(Protons)
6
C
Carbon
12
12
6
Mass Number
(Proton+Neutrons)
C
Mass Number
Almost all the mass of an atom comes
from protons & neutrons
# Protons + # Neutrons = mass
number
LETS HAVE SOME PRACTICE
Atomic # = # of protons
# protons = # electrons in an atom
Mass # = number of protons and neutrons
So,to get the # of neutrons we must Subtract
Atomic # from the Mass # = # Neutrons
12
6
C
6 neutrons
Practice
Determine the # of protons,neutrons, & electrons
Protons
Neutrons
Electrons
He
2
2
2
B
5
6
5
Mg
12
12
12
Zn
30
35
30
Subatomic Particles
Electron: enegative charge
-31 kg
 9.11 x 10

Proton: p+
positive charge
-27 kg
 1.67 x 10

Neutron: n or n0
no charge
-27 kg
 1.67 x 10

What did Battleship teach us?
Battleship simulated Rutherford’s Gold Foil Experiment.
Rutherford
Alpha Particles
Battleship
Your missiles
Nucleus
Pattern Drawn
Atom is mostly empty
space
All of the empty boxes
Atoms vs Ions
ATOMS
IONS
Protons = Electrons
Protons ≠ Electrons
Cations= More Protons
Positive Charge
Anions= More Electrons
Negative Charge
IONS
cation (+)
anion (-)
Li+1
Cl-1
3 Protons
2 Electrons
17 Protons
18 Electrons
Ions
An ion is a particle
with a positive (+) or
negative (-) charge
Atoms that gain
electrons have charges
Atoms that lose
electrons have +
charges
Isotopes
Atoms of an element
can have different
numbers of neutrons –
these are isotopes
The number of protons
and electrons is always
the same, but since
more neutrons add
more mass, the mass
number can be
different
Isotopes
Isotope
Protons = Protons
BUT……Neutrons are Different
So
Mass # is Different
Atom
Protons
Neutrons
Electrons
Mass #
Carbon12
Carbon13
Carbon14
6
6
6
12
6
7
6
13
6
8
6
14
How Big Is An Atom?
Practice
•
The atomic number of an atom is always
equal to the total number of:
a. Neutrons in the nucleus
b. Protons in the nucleus
c. Neutrons plus protons in the nucleus
d. Protons plus electrons in the atom
Practice
•
An atom of 42Ca contains:
a. 20 protons and 22 neutrons
b. 20 protons and 42 neutrons
c. 20 electrons and 42 neutrons
d. 20 electrons and 22 protons
Practice
•
The nucleus of an Fe-56 atom contains:
a. 26 protons, 30 neutrons and 26
electrons
b. 26 protons, 26 neutrons and 30
electrons
c. 26 protons and 56 neutrons
d. 26 protons and 30 neutrons
Practice
•
A 52Cr3+ ion contains:
a. 24 protons, 52 neutrons, 21 electrons
b. 24 protons, 28 neutrons, 24 electrons
c. 24 protons, 28 neutrons, 27 electrons
d. 24 protons, 28 neutrons, 21 electrons
Practice
•
What is the total number of electrons in
an atom with an atomic number of 30
and a mass number of 65?
a. 30
b. 65
c. 35
d. 95