Atomic Structure

The Atoms Family• Atom: the smallest

part of an element. Name means “indivisible”

Who’s atom is it?

Dalton (bb)

Thompson (Plum Pudding)

Electron cloud model

Rutherford

Bohr

(planetary)

Standard Model

Parts of an Atom

• Nucleus:The main center of an atom. Made up of protons and neutrons

• Proton:In the nucleus. Has a + charge. Atomic number tells the number of protons

• Neutron:In the nucleus. Has NO charge. Is there to keep protons apart

Parts of an ATOM

Electrons: In the electron cloud, has a negative charge.

• Isotopes:An element with different numbers of neutrons.

•

The Same, But Different

•

• Example: Hydrogen 3 3(mass) - 1 (atomic #) =

2 neutrons

• Having an unequal number of neutrons and protons can make an atom unstable!

• Atomic mass - atomic number = number of neutrons.

B. Subatomic Particles

POSIT IVECHARG E

PROT ONS

NEUT RALCHARG E

NEUT RONS

NUCLEUS

NEG AT IVE CHARG E

ELECT RONS

AT OM

Most of the atom’s mass. Atomic Numberequals the # of...

NUCLEUS ELECTRONS

PROTONS NEUTRONS NEGATIVE CHARGE

POSITIVE CHARGE

NEUTRAL CHARGE

ATOM

Let’s review• Name the two sub-atomic particles found in

the nucleus of an atom:Proton and Neutron

• What is the charge of a proton?

• What is the charge of a neutron?

• Where are the electrons at?

Positive

No charge (neutral)

Orbiting the nucleus

Atomic Structure

II. Electron Cloud Model Orbital

Energy Levels

Bohr Model Diagrams

Niels Bohr (1913)

Bright-Line Spectrum

• tried to explain presence of specific colors in hydrogen’s spectrum

Energy Levels

• electrons can only exist in specific energy states

Planetary Model

Demonstration Time

Niels Bohr (1913)

Planetary Model:

• electrons move in circular orbits within specific energy levels

Bright-line spectrum

electron shells

a) Electrons different amounts of energy and at different energy levels or electron shells.

b) Electron shells (levels) determine… how an atom behaves when it encounters other atoms

Levels• 1st Level: closest to nucleus. Has 1 orbital. Can

hold 2 electrons

• 2nd level: next one out. Has 2 orbitals. Can hold 8 electrons.

• 3rd level: Holds 8 electrons.

• 4th level: Holds 18 electrons

Why are electrons important?

1) Elements have different electron configurations so different levels of bonding

2) Valence electrons are the electrons in the outer most shell.

3) Valence electrons are important because they affect how the element reacts with other elements.

How many valence electrons are in these different atoms?

Octet Rule = atoms tend to gain, lose or share electrons so as to have 8 electrons

C would like to N would like toO would like to

Gain 4 electrons

Gain 3 electronsGain 2 electrons

C. Stability Octet Rule

• most atoms form bonds in order to have 8 valence e-

• full outer energy level• like the Noble Gases! Ne

Stability is the driving force behind bond formation!

Electron Dot StructuresSymbols of atoms with dots to represent the valence-shell electrons

1 2 13 14 15 16 17 18

H He:

Li Be B C N O : F :Ne :

Na Mg Al Si P S :Cl :Ar :

Learning Check A. X would be the electron dot formula for

1) Na 2) K 3) Al

B. X would be the electron dot formula

1) B 2) N 3) P

Stability

Why is it important for an atom to be “stable”?• So it is less reactive.

Why are noble gases stable?• They have a full energy level.