Atomic Structure

• The smallest part of an element is an ATOM

• All atoms consist of subatomic particles:– Protons– Neutrons– Electrons

Nucleus

• The “core” of the atom

• Contains 99.9% of the mass of the atom

• Protons and neutrons are found in the nucleus of an atom

Mass Number = mass of the nucleus or mass of protons + neutrons

Protons

• Positively charged particles

• The number of protons identifies the element

• 1 proton = 1 atomic mass unit (amu)

# protons = Atomic Number (whole number)

Neutron

• Neutral Particles

• Found in the nucleus

• 1 neutron = 1 amu

# neutrons = Mass number – Atomic Number

Electrons

• Negatively charged particles

• Found in the electron cloud

• Electrons have a very small mass, so we don’t even count it!

• Electrons give atoms their chemical properties

• Atoms are neutral so;

# electrons = # protons

Mass Number

• mass # = protons + neutrons

• always a whole number

• NOT on the Periodic Table!

+

+

+

+

+

+

NucleusElectrons

Nucleus

Neutron

Proton

Carbon-12Neutrons 6Protons 6Electrons 6

e-

e-

e-

e-

e-

e-

Shorthand Notation

Mass number

SYMBOL OF ELEMENT

Atomic number

Isotopes• Atoms of the same element with different

mass numbers.

• Different number of neutrons & different mass

Mass #

Atomic #

• Nuclear symbol:

• Hyphen notation: carbon-12; carbon-12; carbon-13carbon-13Courtesy Christy Johannesson www.nisd.net/communicationsarts/pages/chem

12

6 C

Isotopes

+

+

+

+

+

+

NucleusElectrons

Nucleus

Neutron

Proton

Carbon-12Neutrons 6Protons 6Electrons 6

Nucleus

Electrons

Carbon-14Neutrons 8Protons 6Electrons 6

+

+

+

+

+

+

Nucleus

NeutronProton

3 p+

3 n02e– 1e– 3 p+

4 n02e– 1e–

6Li 7Li

+

+

+NucleusElectrons

Nucleus

Neutron

Proton

Lithium-6Neutrons 3Protons 3Electrons 3

NucleusElectrons

Nucleus

Neutron

Proton

Lithium-7Neutrons 4Protons 3Electrons 3

+

+

+

Isotopes

• Chlorine-37

– atomic #:

– mass #:

– # of protons:

– # of electrons:

– # of neutrons:

17

37

17

17

20

Courtesy Christy Johannesson www.nisd.net/communicationsarts/pages/chem

Cl37

17

37

17 Cl

Average Atomic Mass

• weighted average of all isotopes

on the Periodic Table• round to 2 decimal places

Courtesy Christy Johannesson www.nisd.net/communicationsarts/pages/chem

Avg.AtomicMass

= (mass)(%) + (mass)(%)

100

Calculating Average Atomic Mass

You will be given the mass number and the Percent Abundance (how common the isotope is in nature) of the isotope

Atomic mass = (% abundance in decimal form isotope1)(mass isotope1) +

(%abundance in decimal form isotope2)(mass isotope2)

Average Atomic Mass

• EX: Calculate the avg. atomic mass of oxygen if its abundance in nature is 99.76% 16O, 0.04% 17O, and 0.20% 18O.

Courtesy Christy Johannesson www.nisd.net/communicationsarts/pages/chem

Avg.AtomicMass

= (16)(99.76) + (17)(0.04) + (18)(0.20)

100= 16.00

amu

Example

• Carbon has 6 protons and 6 neutrons, what is Carbon’s mass number?

C-12

• An isotope of Carbon has 6 protons and 8 neutrons, what is carbon’s mass number?

C-14

Remember the number of protons NEVER changes for an element!

Isotope Review

• Same element different number of

NEUTRONS

• Different Mass number

• Same Atomic number, therefore the same number of protons and electrons

Isotope Applications

• Complete the read around the room station activity

Atomic Structure

• ATOMSATOMS– Differ by number of protons

• IONSIONS– Differ by number of electrons

• ISOTOPESISOTOPES– Differ by number of neutrons

Electrons

• Electrons give elements their chemical properties

• The arrangement of the electrons will determine how it reacts with other substances

• Gain electron the atom becomes negative (anion)

• Lose an electron the atom becomes positive (cation)

Humor

Two atoms are walking down the street.One atom says to the other, “Hey! I think I lost an electron!”The other says, “Are you sure??”“Yes, I’m positive!”

A neutron walks into a restaurant and orders a couple of sodas. As she is about to leave, she asks the waiter how much she owes. The waiter replies, “For you, No Charge!!!”

Electrons are found in the electron cloud

The cloud has regions of space called energy levels

• The first energy level holds 2 electrons

• The second energy level holds 8 electrons.

• The third energy level holds 18 electrons

Valence Electrons

• Are found furthest from the nucleus

• Dictate the physical and chemical properties of an element

• Use the periodic table to determine the number of valence electrons.

• All atoms want 8 valence electrons

Lewis Dot Diagram

• A way to illustrate the number of valence electrons– Use one dot for each valence electron– Place the dot around each side of the symbol

before pairing the electrons– The symbol represents the nucleus plus all

the inner electrons for the element.

Examples

H

O

N

F

Ne

Electrons and Light

• Electrons are normally in the ground state

• When the atom is given energy the electrons move to the excited state.

• When the electrons lose this energy they fall back to the ground state and emit light.

• Each element has a unique emission spectrum

Electromagnetic Spectrum

• Electromagnetic Radiation – – A broad range of energetic emissions– made up of photons

• Photons – bundles of energy– Travel like waves– Move at the speed of light = 3.0 x 108 m/s– Electromagnetic waves do not require a

medium to move

Parts of the wave

• Amplitude – the height of the wave

• Wavelength – the distance between the two successive waves

• Frequency – the number of waves that pass a given reference point per second

• Wavelength = lamda unit is nanometer

• Frequency = nu in units of 1/s or s-1

What is the difference between these waves?