Describe the shape of an atom using your background knowledge. Bell Ringer Describe the shape of an atom using your background knowledge.

Topic 9 Charge Behavior and Interactions © 2014 Pearson Education, Inc.

Review Atomic Structure

Atomic Structure All matter is composed of atoms. Understanding the structure of atoms is critical to understanding the properties of matter

HISTORY OF THE ATOM ATOMS John Dalton 1808 suggested that all matter was made up of tiny spheres that were able to bounce around with perfect elasticity and called them ATOMS

Subatomic Particles mass p = mass n = 1840 x mass e-

HISTORY OF THE ATOM ELECTRON Joseph John Thompson 1898 found that atoms could sometimes eject a far smaller negative particle which he called an ELECTRON

A = alpha B = gamma C = beta J.J. Thomson, measured mass/charge of e- (1906 Nobel Prize in Physics)

HISTORY OF THE ATOM Ernest Rutherford 1910 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

Rutherford’s experiment.

Density and the Atom Since most of the particles went through, the atom was mostly empty space. Because the alpha rays were deflected so much, the positive pieces it was striking were heavy. Small volume and big mass = big density This small dense positive area is the nucleus

Plum Pudding model of an atom.

Results of foil experiment if Plum Pudding model had been correct.

Actual Results.

A nuclear atom viewed in cross section.

Rutherford’s Model of the Atom atomic radius ~ 100 pm = 1 x 10-10 m nuclear radius ~ 5 x 10-3 pm = 5 x 10-15 m

HISTORY OF THE ATOM Niels Bohr 1913 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.

n (principal quantum number) = 1,2,3,… Bohr’s Model of the Atom (1913) e- can have only specific (quantized) energy values light is emitted as e- moves from one energy level to a lower energy level En = -RH ( ) 1 n2 n (principal quantum number) = 1,2,3,… RH (Rydberg constant) = 2.18 x 10-18J

Atomic Structure Atoms are composed of -protons – positively charged particles -neutrons – neutral particles -electrons – negatively charged particles Protons and neutrons are located in the nucleus. Electrons are found in orbitals surrounding the nucleus.

HELIUM ATOM Shell proton N + - + N - neutron electron

Atomic Structure Every different atom has a characteristic number of protons in the nucleus. atomic number = number of protons Atoms with the same atomic number have the same chemical properties and belong to the same element.

number of electrons = number of protons ATOMIC STRUCTURE He Atomic number 2 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