MATTER UNIT

STRUCTURE OF AN ATOM

WHAT IS AN ATOM? Atom: the smallest unit of matter that retains the identity of the substance

THE EVOLUTION OF ATOMIC STRUCTURE

•THE NUCLEUS IS THE SMALLEST PART

OF THE ATOM, BUT CONTAINS ALMOST ALL OF THE MASS OF AN ATOM.

•THE MAJORITY OF THE ATOM IS EMPTY SPACE.

ATOM

ATOMIC STRUCTURE Atoms are composed of 2 regions:

Nucleus: the center of the atom that contains the mass of the atom

Electron cloud: region that surrounds the nucleus that contains most of the space in the atom Nucleus

Electron

Cloud

ATOMIC STRUCTUREThe nucleus contains 2 of the 3 subatomic particles:

Protons: positively charged subatomic particlesNeutrons: neutrally charged subatomic particles

The 3rd subatomic particle resides outside of the nucleus in the electron cloud

Electron: the subatomic particle with a negative charge and relatively no mass

Atomic ParticlesParticle Charg

eMass

#Location symbol

Electron

-1 0 Electron cloud

e-

Proton +1 1 Nucleus p+

Neutron

0 1 Nucleus n0

HOW DO THESE PARTICLES INTERACT?

Protons and neutrons are in the tiny positively charged nucleus accounting for most of the mass of the atom

The negatively charged electrons are small and have a relatively small mass but occupy the larger volume of space outside the nucleus

HOW DO THE SUBATOMIC PARTICLES BALANCE EACH OTHER?

In an atom: The # of protons = The # of electrons

If 20 protons are present in an atom then 20 electrons are there to balance the overall charge of the atom—atoms are neutral

The neutrons have no charge they do not have to equal the number of protons or electrons

THE NUMBER OF PROTONS

IDENTIFIES THE ATOM.

• AN ATOM WITH 6 PROTONS = CARBON

• AN ATOM WITH 8 PROTONS = OXYGEN

• AN ATOM WITH 20 PROTONS = CALCIUM

ATOMIC STRUCTURE

the number of protons in an atom

the number of protons and neutrons in an atom

He2

4 Atomic mass

Atomic number

# of electrons = # of protons

# of neutrons = Atomic mass – # of protons

HOW EXACTLY ARE THE PARTICLES ARRANGED?

Bohr Model of the atom:All of the protons and the neutrons

The 1st ring can hold up to 2 e-

The 2nd ring can hold up to 8 e-

The 3rd ring can hold up to 8 e-

The 4th ring and any after can hold up to 18 e-

ATOMIC STRUCTURE

Electrons are arranged in Energy Levels

or Shells around the nucleus of an

atom.• First Shell a maximum of 2 electrons

• Second Shell a maximum of 8

electrons

• Third Shell a maximum of 8

electrons

• Fourth Shell a maximum of 18

electrons

DETERMINING THE NUMBER OF PROTONS AND NEUTRONS

Li has a mass number of 7 and an atomic number of 3 Protons = 3 (same as atomic #) Neutrons= 7-3 = 4 (mass # - atomic

#) Ne has a mass number of 20 and

an atomic number of 10 Protons = 10 Neutrons = 20 - 10= 10

WHAT ABOUT THE ELECTRONS?

The electrons are equal to the number of protons So e- = p = atomic #

Ex: He has a mass # of 4 and an atomic # of 2 p+ = 2 no = 2 e- = 2

DETERMINE THE NUMBER OF SUBATOMIC PARTICLES IN THE FOLLOWING: Cl has a mass # of 35 and an

atomic # of 17 p+ = 17, no = 18, e- = 17

K has a mass # of 39 and an atomic # of 19 P+ = 19, no = 20 e- = 19

WHAT DOES CARBON LOOK LIKE?

Mass # = 12 atomic # = 6

p+ = 6 no = 6 e- = 6

6 p and 6 n live in the nucleus

PRACTICE BOHR DIAGRAMS