ATOMIC THEORY.

ATOMIC THEORY

The basic building blocks of matter that make-up everyday objects.
Defining the Atom An atom is the smallest particle of an element that retains its identity in a reaction. The basic building blocks of matter that make-up everyday objects.

How small is an atom?

About a million atoms stacked on top of each other = the thickness of a sheet of paper.
Copyright © 2010 Ryan P. Murphy

About 5 million atoms make up a period at the end of a sentence.

Video Link! The size of atoms

DemoCritus Early Greek Scholar-was the first to suggest the existence of atoms He believed that atoms were indivisible and indestructible. Never developed a theory  lacked experimental support

John Dalton’s Atomic Theories
-All matter is composed of tiny indestructible particles called atoms. -Atoms cannot be made or destroyed. -All atoms of the same element are identical. -Different elements have different types of atoms. -Chemical reactions occur when atoms are rearranged. -Atoms of different elements can mix together to form compounds.

Dalton’s Theory Revised
Most of Dalton’s theory is still accepted today EXCEPT that atoms are known to be divisible. Atoms can be broken down into 3 subatomic particles: electrons, protons and neutrons.

J.J. Thomson Used a cathode ray tube to prove the smallest particles present must have a negative charge.

+ - Like charges (-) (-) repel. The Electron is negative. - +

+ - Opposite charges attract (+) (-). The electrons are negative. + -

+ - What did this study find? + -
J.J. Thompson discovered the ELECTRON!!! + - + - Copyright © 2010 Ryan P. Murphy

J.J. Thomson Atoms were electrically neutral, so there must be a + particle to cancel out the – charge from the electron. Developed the Plum Pudding Model (positive ball containing scattered electrons)

Ernest Rutherford Former student of Thomson, DISPROVED the Plum Pudding Model of the atom. The Gold Foil Experiment: Sent a beam of + charges (alpha particles) through a piece of very thin gold foil. Angles of deflection were measured.

Rutherford Results: Most of the alpha particles passed straight through, most of the foil must be regions of “empty” space – not a + sphere like Thomson believed. + charges and the atoms mass must be found in the center  discovered the nucleus

The Nuclear Atom In Rutherford’s atomic model, the protons and neutrons are located in the nucleus. The electrons are distributed around the nucleus and occupy almost all the volume of the atoms.

Video! Rutherford’s Gold Foil Experiment

The atom consists of three fundamental particles
- Copyright © 2010 Ryan P. Murphy

Proton + (positive charge)

Neutron 0 (neutral charge / no charge)

Neutron 0 (neutral charge / no charge).

A neutron walks into a video store.

He asks the clerk “How much are the movies?”

“For you…” “No Charge.” He asks the clerk “How much are the movies?”

He asks the clerk “How much are the movies?”

Electron – (negative charge)

ATOMIC STRUCTURE Particle Charge Mass proton + ve charge 1 neutron No charge 1 electron -ve charge nil

number of electrons = number of protons
ATOMIC STRUCTURE He 2 Atomic number the number of protons in an atom 4 Atomic mass the number of protons and neutrons in an atom number of electrons = number of protons

Why are atoms electrically neutral?
HELIUM ATOM shell proton N + - + N - neutron electron Why are atoms electrically neutral?

What atom is this? How can you tell?

Answer! (2 Protons) Atomic #2

Answer! (2 Protons) Atomic #2 (Helium)

Review! To find # of protons and electrons

Answer! Count the 11 Protons or 11 Electrons

Answer! Atomic Number 11. What element is #11

Answer! Atomic Number 11. What element is #11 Sodium

Review! To find # of neutrons

Atomic Mass Review! To find # of neutrons
Subtract the atomic number from the atomic mass to determine the difference. How many neutrons does Lithium have? Atomic Mass Copyright © 2010 Ryan P. Murphy

Atomic Mass Atomic Number Review! To find # of neutrons
Subtract the atomic number from the atomic mass to determine the difference. How many neutrons does Lithium have? Atomic Mass Atomic Number Copyright © 2010 Ryan P. Murphy

6.94 amu – 3 = Atomic Mass Atomic Number Review! To find # of neutrons
Subtract the atomic number from the atomic mass to determine the difference. How many neutrons does Lithium have? Atomic Mass Atomic Number 6.94 amu – 3 = Copyright © 2010 Ryan P. Murphy

6.94 amu – 3 = Atomic Mass Atomic Number Answer! 6.94 – 3 = 3.94

Complete the following table in your notes
Atomic # Mass # # of Protons # of Neutrons # of Electrons 9 10 14 15 47 22 55 25

ATOMIC THEORY.

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ATOMIC THEORY.

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