Atomic Structure

Matter is anything that takes up space

and has mass

All matter is made of atoms

the building blocks of matter, sort of how bricks are the building blocks of houses.

Smallest particles of matter

• An atom has three parts:

• Proton = positive

• Neutron = no charge

• Electron = negative

• The proton & neutron are found in the center of the atom, a place called the nucleus.

• The electrons orbit the nucleus.

HISTORY OF THE ATOM

460 BC Democritus develops the idea of atoms

he pounded up materials in his

pestle and mortar until he had

reduced them to smaller and

smaller particles which he

called ATOMA (greek for

indivisible)

Democritus’ Atom

Indivisible particle

HISTORY OF THE ATOM

1808 John Dalton

suggested that all matter was

made up of tiny spheres that

were able to bounce around

with perfect elasticity and

called themATOMS

Postulated the Atomic Theory

Dalton’s Atom

HISTORY OF THE ATOM

Thompson develops the idea that an atom was made up of

electrons scattered unevenly within an elastic sphere

surrounded by a soup of positive charge to balance the

electron's charge

1904

like plums surrounded by pudding.

PLUM PUDDING

MODEL

Electrons embedded in positive mass

HISTORY OF THE ATOM

1910 Ernest Rutherford

He suggested that the

positive charge was all in a

central nucleus. With this

holding the electrons in place

by electrical attraction

Positive nucleus

HISTORY OF THE ATOM

1913 Niels Bohr

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.

Bohr’s Atom

electrons in orbits

nucleus

Bohr’s Atom

Electron

Nucleus

Fixed electron orbit

Electron Cloud model

Electron Cloud model

Electron Cloud model

DE BROGLIE’S ATOM

DE BROGLIE’S ATOM

Isotopes Atoms that have the same number of

protons but different numbers of neutrons

Example:

the number of protons in an atom

the number of protons and neutrons in an atom

He2

4Atomic mass

Atomic number

number of electrons = number of protons

Mass defect is the difference between the mass of nucleons

(protons and neutrons) and the mass of the nucleus

HELIUM ATOM

+N

N

+-

-

proton

electron

neutron

Shell

What do these particles consist of?

Particle Electrical Charge

Mass (amu)

Proton +1 1.0072766 or 1

Neutron 0 1.0086654 or 1

Electron -1 0.000549

Particle

proton

neutron

electron

Charge

+ ve charge

-ve charge

No charge

1

1

0.000549

Mass

Total Mass of Nucleus = 1.00794

Total Mass of Nucleus= 4.00260

Total Mass of Nucleus= 12.011

Ground State – lowest energy level of an electronExcited State – the electron goes into a higher energy level

An electron emits energy as it returns to its ground state

When an electron absorbs

energy in the form of light or

heat, it goes into a higher

energy level. The electron is

said to be in the excited state.

When an excited electron

returns to its ground state, it

emits the energy it previously

absorbed .

SPECTRUM

If light is passed

through a

prism, an array

of colors called

SPECTRUM is

formed.