Transcript atomic theory part 1

Introduction to Atomic Structure
Chemistry
Chemistry is the study of matter and the
changes it undergoes.
The type of matter that is changing and
what types of changes it undergoes
determines the field of chemistry that is
being studied.
Branches of Chemistry
Physical Chemistry: the study of matter and the physics behind its changes
Branches of Chemistry
Physical Chemistry: the study of matter and the physics behind its changes
Biochemistry: the study of the makeup and changes undergone by living species
Branches of Chemistry
Physical Chemistry: the study of matter and the physics behind its changes
Biochemistry: the study of the makeup and changes undergone by living species
Analytical Chemistry: The study of the composition (or analysis) of substances
Branches of Chemistry
Physical Chemistry: the study of matter and the physics behind its changes
Biochemistry: the study of the makeup and changes undergone by living species
Analytical Chemistry: The study of the composition (or analysis) of substances
Organic Chemistry: The study of compounds which primarily contain Carbon
Branches of Chemistry
Physical Chemistry: the study of matter and the physics behind its changes
Biochemistry: the study of the makeup and changes undergone by living species
Analytical Chemistry: The study of the composition (or analysis) of substances
Organic Chemistry: The study of compounds which primarily contain Carbon
Inorganic Chemistry: The study of compounds which do NOT contain Carbon
Matter
You will recall that we define matter as anything that has mass and takes
up space.
Atoms of an element
Molecules of a
compound
Molecules of a
diatomic
element
Mixture of
elements
and a
compound
Dalton's Postulates
Building on Democritus' idea, in the
early 1800s, English chemist John
Dalton was the first scientist to observe
the physical world and matter and via
these observations, this draw some
conclusions about atoms.
Dalton's Four Postulates
(1) Matter is made of atoms; atoms
are indivisible and indestructible.
(2) All atoms of one element are
exactly identical to one another;
atoms of different elements are
different from one another.
Various atoms and molecules as depicted in John Dalton's 1808 book:
A New System of Chemical Philosophy
Dalton’s Four Postulates
(3) Atoms of an element are not changed into atoms of a different element by chemical reactions;
atoms are neither created nor destroyed in chemical reactions.
(4) Compounds are formed when atoms of more than one element combine; a given compound
always has the same relative number and kind of atoms.
Hydrogen
Oxygen
Water
Law of Conservation of Mass
The total mass of substances present at the end of a chemical
process is the same as the mass of substances present before the
process took place.
click here for an explanation of conservation of mass
26
Which one of the following is not one of the postulates of Dalton's atomic
theory?
A
Atoms are made of protons, neutrons, and electrons.
B
All atoms of a given element are identical
C
Atoms are neither created nor destroyed in chemical reactions.
D
Compounds are formed when atoms of more than one element combine
E
Each element is composed of extremely small particles called atoms.
Scientists
J. J. Thomson (1903)
 Discovered
electron
 Electrons have a
negative charge!!
 Theorized about
protons
J. J. Thomson (1903)
 Made
a piece of equipment
called a cathode ray tube.
 It
is a vacuum tube - all the air
has been pumped out.
Thomson’s Experiment
Voltage source
-
+
Vacuum tube
Metal Disks
Thomson’s Experiment
Voltage source
-
+
Thomson’s Experiment
Voltage source
-
+
Thomson’s Experiment
Voltage source
-
+
Thomson’s Experiment
Voltage source
 Passing
+
an electric current makes a
beam appear to move from the
negative to the positive end
Thomson’s Experiment
Voltage source
 Passing
+
an electric current makes a
beam appear to move from the
negative to the positive end
Thomson’s Experiment
Voltage source
 Passing
+
an electric current makes a
beam appear to move from the
negative to the positive end
Thomson’s Experiment
Voltage source
 Passing
+
an electric current makes a
beam appear to move from the
negative to the positive end
Thomson’s Experiment
Voltage source
 By
adding an MAGNETIC field
Thomson’s Experiment
Voltage source
+
 By
adding an electric field
Thomson’s Experiment
Voltage source
+
 By
adding an electric field
Thomson’s Experiment
Voltage source
+
 By
adding an electric field
Thomson’s Experiment
Voltage source
+
 By
adding an electric field
Thomson’s Experiment
Voltage source
+
 By
adding an MAGNETIC field
Thomson’s Experiment
Voltage source
+
 By
adding an electric field he found
that the moving pieces were negative
J. J. Thomson (1903)
Plum-pudding Model

positive sphere
(pudding) with
negative electrons
(plums) dispersed
throughout
JJ Thomson’s Idea

He knew that the
atom contained +
and – charges.

The atom was like
“Plum Pudding” a
mix of + and - .
Ernest Rutherford (1911)

Gold Foil Experiment

Discovered the nucleus

The protons in the nucleus
Rutherford’s experiment

Used radioactive alpha particles to prove
the existence of protons.(He+2)

Alpha particles (He+2) - positively charged
pieces- helium atoms minus electrons

Shot them at gold foil which can be made a
few atoms thick.
Lead
block
Uranium
Fluorescent
Screen
Gold Foil
What he expected
Because
He thought the mass was evenly
distributed in the atom
What he got
+
Why did JJ believe electrons
have charges?
Ernest Rutherford (1911)

Developed the Planetary Model

dense, positive nucleus surrounded
by negative electrons
James Chadwick (1932)
James Chadwick (1932)

Discovered neutrons

neutral particles in the
nucleus of an atom
Atom is mostly empty.
 Small dense,
positive piece
at center.
 Alpha particles
are deflected by
it if they get close
enough.

Mass Number
Mass number is simply the sum total of protons and neutrons in the nucleus
of an atom. Recall that electrons have insignificant mass compared to
protons and neutrons.
12
6
C
Mass numbers are always whole numbers
Mass numbers are NOT on the Periodic Table
Atoms of the same element can have different mass numbers
Figuring out number of neutrons
in an element
The number of neutrons for any element can be found by subtracting the
element's Atomic Number ("Z") from the element's Mass Number ("A")
A - Z = Number of Neutrons
Some elements can have many different numbers of neutrons. Atoms with
the same Z but different A are called Isotopes.
Symbols
Symbols on the periodic table contain the symbol (letter) of the element, the mass number and the atomic
number
The letter symbol refers to an atom with a specific number of protons.
# protons
+ # neutrons
mass number
# protons
Mass
Number
Atomic
Number
X
Remember, when the atom is neutral,
the number of protons equals electrons
Atomic Number and Mass Number
Atomic Number
Number of protons
Atomic Number also equals number of
electrons in a neutral atom
12
6
14
C
6
Mass Number
12
Mass Number
Number of protons + neutrons
Atomic Number
6
C
C
1
Find the atomic number.
23
11
Na
Sodium Atom
2
Find the mass number.
23
11
Na
Sodium Atom
3
How many protons does this element have?
23
11
Na
Sodium Atom
4
How many electrons does this element have?
23
11
Na
Sodium Atom
5
How many neutrons does this element have?
23
11
Na
Sodium Atom
6
Find the atomic number.
80
35
Br
Bromine Atom
7
Find the mass number.
80
35
Br
Bromine Atom
8
How many protons does this element have?
80
35
Br
Bromine Atom
9
How many electrons does this element have?
80
35
Br
Bromine Atom
10
How many neutrons does this element have?
80
35
Br
Bromine Atom
1
The atomic number indicates __________.
A
the number of neutrons in a nucleus
B
the total number of neutrons and protons in a nucleus
C
the number of protons or electrons in a neutral atom
D
the number of atoms in 1 g of an element
E
I don't know how to answer this question.