2. Atomic Models (History) for grade 7.pptx

Anything that has mass and
occupies space is called
matter. A matter is made up
of tiny particles called atoms

A particle of matter that
uniquely defines a chemical
element.Consists of a central
nucleus that is surrounded by
one or more negatively
charged electrons.

•INTRODUCTION
460-370 B.C
He asked if matter could be divided into smaller and
smaller pieces forever
Ernest Rutherford (1871–1937)
He described the structure of atom
Neils Bohr (1885–1962)
He explained how atomic spectra worked
DEMOCRITUS
John Dalton (1766-1844)
He proposed the Atomic theory of matter based on his
experimental observations
DALTON
BOHR
THOMSON
RUTHERFORD
John Thomson (1856-1940)
He proposed the plum pudding model of atom

•Timeline of Atomic Models
Timeline of Atomic Structure
460 – 370 BC
Democritus
proposes
the 1st
atomic
theory

460 – 370 BC
Matter could
not be divided
into smaller and
smaller pieces
forever

460 – 370 BC
Named the
smallest atom
“atomos” meaning
not to be cut

460 – 370 BC
Atoms move
around in space,
and can collide to
stick together, causing
changes to the matter
of a material.

460 – 370 BC
His atomic
model essentially
consisted of solid
spheres of different
sizes for different types
of atoms.

• DEMOCRITUS'S ATOMIC THEORY

John Dalton
proposes his
atomic theory in
1803
1766 – 1844

All matter
consists of
extremely small
particles called
atoms
1766 – 1844

Atoms are
indivisible and
indestructible
1766 – 1844

Compounds are
formed by a
combination of
two or more
different kinds of
atoms
1766 – 1844

A chemical
reaction is a
rearrangement
of atoms.
1766 – 1844

Atoms can be
neither created
nor destroyed.
1766 – 1844

J.J. Thomson
discovers the
electron and
proposes the
Plum Pudding
Model in 1897
1856 – 1940

Multiple
experiments were
performed that
proved that
charged particles
exist.
1856 – 1940

He discovered a
negatively
charged particle,
which he called
the electron.
1856 – 1940

The existence
of the electron showed
that the old concept of
atom as homogeneous
particle was wrong and
that atom has a complex
structure
1856 – 1940

He noted that the
Dalton model of the atom
did not include the idea
of charge, and he
theorized that electrons
must be within the atoms
of elements.
1856 – 1940

The Plum Pudding model
indicated that there were
pockets of negative
charges within the sphere
of the atom.
1856 – 1940

1871 – 1937
Ernest Rutherford
performs the Gold
Foil Experiment in
1909

1871 – 1937
Performed alpha
particle experiments
that led to the
overturning of
Thomson’s model.

1871 – 1937
They aimed
alpha particles at a
thin sheet of gold
foil and recorded
the location of the
alpha particle with a
fluorescent screen.

1871 – 1937
Majority of the
alpha particles
passed through the
gold foil as if the
foil was not there

1871 – 1937
They also found
that small number of
these alpha particles
deflected with some
of the alpha particles
even bouncing back
along the initial path

1871 – 1937
He theorized that
this atomic nucleus was
positively charged and
surmised that the
electrons orbited
around it.

1871 – 1937
Many physicists
doubted the
Rutherford atomic
model because it was
difficult to reconcile
with the chemical
behaviour of atoms.

1871 – 1937
The model
suggested that the
charge on the nucleus
was the most important
characteristic of the
atom, determining its
structure.

1885 – 1962
Neil’s Bohr
explained
how atomic
spectra
worked

1885 – 1962
He proposed his
quantized shell model
of atom to explain
how electrons can
have stable orbits
around the nucleus

1885 – 1962
He suggested that
each orbit has
different energy level
associated with it.

1885 – 1962 He found that
energy can be
absorbed by electrons
to move from a lower
energy orbit to a
higher energy orbit
and release energy.

• The Greek philosopher Democritus began the search for a
description of matter more than 2400 years ago. He asked:
• Could matter be divided into smaller and smaller pieces
forever, or was there a limit to the number of times a piece of
matter could be divided?
• His theory: Matter could not be divided into smaller and
smaller pieces forever, eventually the smallest possible piece
would be obtained. This piece would be indivisible. He
named the smallest piece of matter “atomos,” meaning
“not to be cut.”To Democritus, atoms were small, hard
particles that were all made of the same material but were
different shapes and sizes. Atoms were infinite in number,
always moving and capable of joining together.
• DEMOCRITUS'S ATOMIC THEORY

He proposed the Atomic theory of matter based on his
experimental observations. The main postulates of Dalton’s
atomic theory are as follows.
To Dalton :
All matter is made of atoms. Atoms are indivisible and =>
indestructible.
All atoms of a given element are identical in mass and
properties.
Compounds are formed by a combination of two or more
different kinds of atoms
A chemical reaction is a rearrangement of atoms.
Atoms can be neither created nor destroyed.
He also calculated the atomic weight of various elements
• DALTON'S ATOMIC THEORY

Thomson's atomic theory proposed a model of atom which is
known as plum pudding model
• In the year 1897 He totally changed the view of an atom by
discovering electron. Thomson’s atomic theory suggested that the
atom is not indivisible as it was of smaller pieces – electrons and
protons.
• An atom consists of a sphere of positive charge with negatively
charged electron embedded in it.
• The positive and the negative charges in an atom are equal in
magnitude, due to which an atom is electrically neutral. It has no
over all negative or positive charge.
• THOMSOM'S ATOMIC THEORY

• Ernest Rutherford presented a paper , accurately describing the
structure of the atom. Based on an experiment he had performed -
with totally unexpected results - he realized that the atom must
have almost all of its mass concentrated at its center, in a nucleus,
with the vast majority of the atom consisting chiefly of empty space.
Two years earlier, in 1909, he had conducted an experiment with
two other scientists, in which they studied the deflection angles of
"alpha particles" that they shot through a microscopically thin layer
of gold. Alpha particles are just helium atoms stripped of their 2
electrons.
• He showed that while the nucleus contains virtually all of the mass of
the atom, it only takes up one-billionth of the volume of the atom,
an inconceivably tiny amount. Much smaller particles - electrons -
orbit the nucleus at a great distance, relatively speaking.
• RATHERFORD'S ATOMIC THEORY

• RATHERFORD'S ATOMIC THEORY

• BOHR'S ATOMIC THEORY
Neils Bohr refined Rutherford's model in 1913 by
proposing that electrons:
• Orbit the nucleus without losing energy;
• Could move only in fixed orbits of specific energies.
• Electrons with low energy would orbit closer to the
nucleus while electrons with high energy orbit further
from the nucleus.

• QUIZ # 1: SCIENTIFIC MODEL
A. Fill in the Blanks.
1. The atomic model has changed over
time as scientists discovered new
___________.
2. The nucleus is made up of ___________
and ___________.
3. Electrons are found in regions around the
nucleus called ___________.
4. An atom is mostly empty ___________.
5. The atomic number of an element is the
number of ___________ in its nucleus.
B. Make a diagram of a simple atom and
label the nucleus, protons, neutrons and
electrons.

2. Atomic Models (History) for grade 7.pptx

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2. Atomic Models (History) for grade 7.pptx