Transcript Modern Atomic Theory

Grade 9 Science
Chemistry
Modern Atomic Theory
•Atoms are made of 3 particles; protons, neutrons and
electrons
•Atoms have a nucleus that is made of protons and
neutrons with electrons orbiting around it.
•Protons and electrons have opposite charges, therefore,
they attract.
•This attraction holds the electrons around the nucleus.
Elements vs. Compounds
• An element is a pure substance made up of one
type of particle, or atom. Each element has its
own distinct properties and cannot be broken
down into simpler substances by means of a
chemical change.
• Compounds are pure substances that are made up
of two or more elements chemically combined
together. They can be broken down into elements
again by chemical means.
Difference Between Theories
and Laws
• Laws do not explain anything . They just
describe and summarize what happens.
• Theories are imaginative ways to explain
why something happens.
Democritus
Around 400 BC, a Greek philosopher
named Democritus suggested the first
atomic theory
He explained that all things are "composed
of minute, invisible, indestructible particles
of pure matter which move about eternally
in infinite empty
Even though there was no technology to
help research Democritus‘s theory, he was
very precise
John Dalton, J.J. Thompson, Ernest
Rutherford, Niels Bohr, and Ernest
Schrodinger all contributed significantly to
the modern atomic theory by finding the
actual evidence.
John Dalton
Lived from 1766-1844
Was one of the earliest scientists to
contribute to the modern atomic theory.
Dalton’s Theory
•All elements are composed of atoms.
•All atoms of the same element are identical
– in particular they have the same mass.
•The atoms of one kind of element are
different from the atoms of all other
elements - in particular the atoms of one
element have a different mass than those of
other elements.
•Atoms are indestructible and retain their
identity in chemical reactions.
•Compounds are formed by joining atoms in
specific whole number ratios.
J.J Thompson
Lived from 1856-1940
Won a noble prize for his great work on
the electron.
Realized that if there ware negative parts
to atoms, then there must be positive
parts as well to balance it, because most
matter is neutral.
His theory of electron distribution inside
an atom was later proved to be incorrect
by Ernest Rutherford.
In 1897,discovered first subatomic
particle, a component of all atoms, the
electron
Ernest Rutherford
Lived from 1871 – 1937
Made blueprints of an atom.
Said to be the father of
nuclear physics.
Said that radiation was caused
by the destruction of atoms
and that the alpha particle is
the helium nucleus.
Niels Bohr
Lived from 1871 - 1937
Discovered the proton in
1910
Won the 1922 Nobel Prize
for physics, mainly for his
work on the structure of
atoms
Erwin Schrodinger
Lived from 1887 to 1961
Viewed electrons as
continuous clouds
Introduced "wave
mechanics" as a
mathematical model of
the atom.