Transcript Atomic structure

Bellwork
• Which of the following is most likely a
pure substance?
A- a smooth cake batter
B- a glass of water that tastes salty
C- a dark gray solid that attracts iron
filings
D- a sample of air captured from the
atmosphere
Outline
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Bellwork
Quiz- It’s TUESDAY!!! YOU KNOW THE RULES!!!
New Vocabulary
ATOMS!!!!
Review
Closure (Homework)
New Vocabulary
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Electron
Nucleus
Proton
Neutron
Atomic number
Atomic mass
Isotope
Valence electron
S.MORRIS 2006
HISTORY OF THE ATOM
460 BC
Democritus develops the idea of atoms
he pounded up materials in his pestle and
mortar until he had reduced them to smaller
and smaller particles which he called
ATOMA
(greek for indivisible)
HISTORY OF THE ATOM
1808
John Dalton
suggested that all matter was made up of
tiny spheres that were able to bounce around
with perfect elasticity and called them
ATOMS
HISTORY OF THE ATOM
1898
Joseph John Thompson
found that atoms could sometimes eject a far
smaller negative particle which he called an
ELECTRON
HISTORY OF THE ATOM
1904
Thompson develops the idea that an atom was made up of
electrons scattered unevenly within an elastic sphere surrounded
by a soup of positive charge to balance the electron's charge
like plums surrounded by pudding.
PLUM PUDDING
MODEL
HISTORY OF THE ATOM
1910
Ernest Rutherford
oversaw Geiger and Marsden carrying out his
famous experiment.
they fired Helium nuclei at a piece of gold foil
which was only a few atoms thick.
they found that although most of them
passed through. About 1 in 10,000 hit
HISTORY OF THE ATOM
helium nuclei
gold foil
helium nuclei
They found that while most of the helium nuclei passed
through the foil, a small number were deflected and, to their
surprise, some helium nuclei bounced straight back.
HISTORY OF THE ATOM
Rutherford’s new evidence allowed him to propose a more
detailed model with a central nucleus.
He suggested that the positive charge was all in a central
nucleus. With this holding the electrons in place by electrical
attraction
However, this was not the end of the story.
HISTORY OF THE ATOM
1913
Niels Bohr
studied under Rutherford at the Victoria
University in Manchester.
Bohr refined Rutherford's idea by adding
that the electrons were in orbits. Rather
like planets orbiting the sun. With each
orbit only able to contain a set number of
electrons.
Bohr’s Atom
electrons in orbits
nucleus
HELIUM ATOM
Shell
proton
+
-
N
N
+
electron
What do these particles consist of?
-
neutron
Bell work
What was Niels Bohr’s prediction about
the location of the electrons in an
atom?
A. Electrons pair with protons and stay in the
nucleus of the atoms.
B. Electrons can be found at various levels within
an energy cloud surrounding the nucleus.
C. Electrons orbit the nucleus in well-defined
energy levels or orbitals.
D. Electrons are scattered randomly in a positive
background matrix.
ATOMIC STRUCTURE
Particle
Charge
Mass
proton
+ ve charge
1
neutron
No charge
1
electron
-ve charge
nil
Atomic Structure
• Atoms are composed of 2 regions:
– Nucleus: the center of the atom that
contains the mass of the atom
– Electron cloud: region that surrounds the
nucleus that contains most of the space in
the atom
Electron
Cloud
Nucleus
Describe Electron
Electrons are negatively charged particles
that surround the atom's nucleus.
Electrons were discovered by J. J.
Thomson in 1897.
Electrons determine properties of the atom.
Chemical reactions involve sharing or
exchanging electrons.
Describe Nucleus
The nucleus is the central part of an atom. It
is composed of protons and neutrons.
The nucleus contains most of an atom's
mass.
It was discovered by Ernest Rutherford in
1911.
Describe Neutron
• Neutrons are uncharged particles found in
the atomic nucleus.
Describe Proton
• Protons are positively charged particles
found in the atomic nucleus. Protons were
discovered by Ernest Rutherford..
B. Subatomic Particles
ATOM
ATOM
NUCLEUS
NUCLEUS
ELECTRONS
ELECTRONS
PROTONS
PROTONS
NEUTRONS
NEUTRONS
POSITIVE
CHARGE
NEUTRAL
CHARGE
Most of the atom’s mass.
NEGATIVE
CHARGE
NEGATIVE CHARGE
in a neutral atom
Atomic Number
equals the # of...
A. Chemical Symbols
• Capitals matter!
• Element symbols contain ONE capital
letter followed by lowercase letter(s) if
necessary.
Metal that
forms bright
blue solid
compounds.
Co vs. CO
Poisonous
gas.
ATOMIC STRUCTURE
He
2
4
Atomic number
the number of protons in an atom
Atomic mass
the number of protons and
neutrons in an atom
number of electrons = number of protons
How do the subatomic particles
balance each other?
• In an atom:
– The protons = the electrons
• If 20 protons are present in an atom then 20
electrons are there to balance the overall
charge of the atom—atoms are neutral
– The neutrons have no charge; therefore
they do not have to equal the number of
protons or electrons
How do we know the number of
subatomic particles in an atom?
• Atomic number: this number indicates the
number of protons in an atom
– Ex: Hydrogen’s atomic number is 1
• So hydrogen has 1 proton
– Ex: Carbon’s atomic number is 6
• So carbon has 6 protons
**The number of protons identifies the
atom.
Ex. 2 protons = He, 29 protons = Cu
How do we know the number of
subatomic particles in an atom?
• Mass number: the number of protons
and neutrons in the nucleus
– Ex: hydrogen can have a mass of 3.
Since it has 1 proton it must have 2
neutrons
– # of neutrons = mass # - atomic #
Determining the number of
protons and neutrons
• Li has a mass number of 7 and an atomic
number of 3
– Protons = 3 (same as atomic #)
– Neutrons= 7-3 = 4 (mass # - atomic #)
• Ne has a mass number of 20 and an
atomic number of 10
– Protons = 10
– Neutrons = 20 - 10= 10
What about the electrons?
• The electrons are equal to the number
of protons
– So e- = p = atomic #
• Ex: He has a mass # of 4 and an atomic
# of 2
– p+ = 2
– no = 2
– e- = 2
Determine the number of
subatomic particles in the
following:
• Cl has a mass # of 35 and an atomic #
of 17
– p+ = 17,
no = 18,
e- = 17
• K has a mass # of 39 and an atomic #
of 19
– P+ = 19,
no = 20
e- = 19
ATOMIC STRUCTURE
Electrons are arranged in Energy Levels or
Shells around the nucleus of an atom.
•
first shell
a maximum of 2 electrons
•
second shell
a maximum of 8 electrons
•
third shell
a maximum of 8 electrons
ATOMIC STRUCTURE
There are two ways to represent the atomic
structure of an element or compound;
1.
2.
Electronic Configuration
Dot & Cross Diagrams
ELECTRONIC CONFIGURATION
With electronic configuration elements are represented
numerically by the number of electrons in their shells
and number of shells. For example;
Nitrogen
2 in 1st shell
5 in
2nd
shell
configuration = 2 , 5
2
+
5 = 7
N
7
14
ELECTRONIC CONFIGURATION
Write the electronic configuration for the following
elements;
a)
Ca
20
b)
Na
40
2,8,8,2
d)
Cl
17
35
2,8,7
11
23
c)
2,8,1
e)
Si
14
28
2,8,4
O
8
16
2,6
f)
B
5
11
2,3
DOT & CROSS DIAGRAMS
With Dot & Cross diagrams elements and compounds
are represented by Dots or Crosses to show electrons,
and circles to show the shells. For example;
X
Nitrogen
X X
N
XX
X X
N
7
14
DOT & CROSS DIAGRAMS
Draw the Dot & Cross diagrams for the following
elements;
X
8
17
X
a) O
b)
Cl 35 X
16
X
X
X
X
X
X
X X X Cl X X
X
X
X
O
X
X
X
X
X
X
X
X
X
SUMMARY
1. The Atomic Number of an atom = number of
protons in the nucleus.
2. The Atomic Mass of an atom = number of
Protons + Neutrons in the nucleus.
3.
The number of Protons = Number of Electrons.
4.
Electrons orbit the nucleus in shells.
5.
Each shell can only carry a set number of electrons.