Unit 2 Atomic Structure

What is a Theory? A set of statements or principles devised to Explain a group of facts or phenomena.

Describe the Discontinuous Theory of Matter.Matter is made of tiny particles that cannot be cut any smaller. 2,500 years ago, Greek for not-cut is “a-tom” atoms (Democritus).

What Theory of Matter was commonly accepted for most of the last 2,000 years? Four Elements: Earth, Air, Fire, and Water and Four Qualities. Matter can be Continuously Divided into smaller parts.How did the current Atomic Theory evolve?The modern model of the atom evolved over a long period of time through the work of many Scientists and many, many Experiments.

What does this data indicate? 1. Atoms of different elements may have ___________ ___________.

2. Mass is ____________________ in a chemical change.

3. Different Atoms combine in ___________ _________ to form Compounds.

= = =

different masses

Conserved

Definite Ratios

Atomic Theory

Mass is Conserved in a Chemical ChangeThe mass of tin usually increase as it reacts in air to form tin oxide. What might this experiment show?

The glass dome seemed to be “stuck” like a suction cup after the reaction. WHY?

Matter (Mass) is Neither Created nor Destroyed in a Chemical Change.

The air inside produces a lower pressure without the Oxygen molecules. Outside air pressure has not changed and is higher by comparison.

A Chemical Change is a Rearrangement of the original Atoms.

Link to Dalton’s Playhouse Interactive.

Atoms Have an Electrical NatureWhat did Thomson discover using a cathode ray tube?Atoms contain “Electrons”: Negatively Charged Sub-Atomic Particles.

What Model of the Atom Resulted from such discoveries?

The “Plum Pudding” model resulted.

The Nuclear AtomDescribe Rutherford’s Gold Foil Experiment.

What did Rutherford infer about the structure of Atoms?

Most radioactive Alpha particles go straight through thin Gold Foil.

A few (+) Alpha particles are deflected and very few bounce back.

1. Atoms are Mostly Empty Space.

2. Atoms have a very dense, very tiny, and positively charged Nucleus.

The Nature of LightDoes Light behave as a Particle or as Electric and Magnetic Waves?Light shows Both types of Behaviors!

Describe the relationship between the Wavelength, Frequency, and Energy of Electromagnetic Radiation?Shorter Waves have a Higher Frequency and a Higher Energy.

What is the difference between blue light and red light? Blue light has a shorter wavelength, higher frequency and higher energy.

What is Electromagnetic Radiation? Waves of Electric and Magnetic Forces that Radiate at the speed of light.

“Particle” is called a Photon.

Link to Waves Go to: 1. Radio Waves 2. Microwaves 3. Photoelectric Effect Link to Electricity Go to: 1. Balloons 2. Generator

Higher Energy

The Bohr ModelHow does the Emission Spectra produced by atoms relate to atomic structure?

Each Electron in an Atom has a Distinct Amount of Energy.

Spectroscopes show that Atoms produce light with Distinct Amounts of Energy.

How do atoms produce light?1. Electrons can Absorb Energy and change to a Higher Energy State (Excited State).

2. When an excited electron Returns to a Lower Energy State it emits a “Quanta” of light with specific energy and specific color.

Link to Spectra (Click Emission)

Link to Model

The Wave-Mechanical ModelHow does the Wave-Mechanical Model describe the behavior and the location of Electrons in an atom?Electrons have a wave character and are located in Orbitals.Orbitals (electron clouds) are regions of probable location of electrons.

How can one orbital hold up to two electrons?

Electrons with Opposite Spins create Opposite Magnetic Forces = Attraction.

Sub-Atomic ParticlesCompare the three types of sub-atomic particles...In terms of charge,

In terms of location,

In terms of mass,

Protons are positive (+1), Electrons are equally negative (-1), and Neutrons are neutral.

Protons and Neutrons are in the nucleus while Electrons are in Orbitals outside the nucleus.

Protons and Neutrons have similar masses of approximately one atomic mass unit (amu) while Electrons have much, much less mass (1/1,849 amu) often considered nearly zero or zero.

What does the Atomic Number of an Element indicate?1. Atomic Number indicates the Number of Protons in an Atom.

3. The Atomic Number is Different for each Element.

2. Atomic Number indicates the Nuclear Charge (+).

What does the Mass Number of an atom indicate?Mass Number is the Sum of Protons and Neutrons in the Nucleus.

How are Atoms Different from Ions?Atoms are Always Neutral: # Protons = # Electrons.

Ions are Charged. # Protons and # Electrons are NOT Equal.

Isotopes and Atomic MassWhat are Isotopes? Isotopes are Atoms of the Same Element, but with Different Masses due to Different… numbers of neutrons.

Ex. How is Carbon-12 different from Carbon-14? Different Mass Numbers. Both Isotopes have 6 Protons. A C-12 nucleus also has 6 neutrons while a C-14 nucleus has 8 neutrons (6p + 8n = 14 amu) *

*Both Chemically similar, however, C-14 is Radioactive while C-12 is not.

What is the Atomic Mass of an Element?

Mg12

Magnesium

24.3050

Atomic Number = Number of Protons in the nucleus of every atom of magnesium.

Atomic Mass = Average Mass (amu) of naturally occurring Isotopes of Mg.

What Isotope of Mg is probably most common?

24.3050 24 Mg-24 is probably most common. (Round to nearest whole number)

What are the most common isotopes of Carbon, Nitrogen, Oxygen, Fluorine?

Carbon-12 Nitrogen-14 Oxygen-16 Fluorine-19

Determination of Atomic MassGiven Relative Abundance of Isotopes and Actual Mass* (amu), determine the Atomic Mass of an Element. * Note: Actual mass of protons and neutrons can vary with different nuclei!! The atomic mass unit (amu) is based on Carbon-12. (1 amu = 1/12 the mass of a C-12 atom) Ex. Determine the average atomic mass of chlorine.

ChlorineIsotopes Natural %

AbundanceMass (amu)

Cl-35 75.77% 34.969

Cl-37 24.23% 36.966

75.77% 0.7577

24.23% 0.2423

0.7577 X 34.969 amu = 26.50 amu

0.2423 X 36.966 amu = 8.957 amu

Atomic mass = 35.46 amu

+______

CopperIsotopes Natural %

AbundanceMass (amu)

Cu-63 69.2% 62.93

Cu-65 30.8% 64.93

Determine the atomic mass of Copper.

Atomic mass = 63.5 amu

Atoms, Ions and IsotopesDifferentiate between Atomic Mass and Mass Number.Atomic Mass is a Measured* Average Mass of all naturally occurring Isotopes of an element. * Includes significant figures.Mass Number is the Sum* of protons and neutrons in specific atom of an element. *A Counted value: No significant figures. Always

a Whole Number. Never given in the Periodic Table.

How can one give the proper notation to represent a specific isotope? Ex. Carbon-14….. C-14 14C 14

6C

How can one properly represent a specific atom of an element?A Chemical Symbol is either a single capital letter or a capital and a lower case letter.

How can one represent the charge of an ion? Ex. Magnesium with 12 protons and 10 electrons. Mg

2+

Give the proper notation for a particle containing 8 protons, 9 neutrons, and 10 electrons.

178O2-

8 protons = Oxygen

Sum of protons + neutrons(+8) + (-10) = -2

Protons = At. No.?

Link to Build an Atom

Isotopic Notation

Number of Protons

Number of Neutrons

Number of Electrons

42He

14__C

13 14 10

3216S 18

23Na 10

Practice With Particles Complete each item with what can be known.

Use “?” for what cannot be known.

Isotopic Notation

Number of Protons

Number of Neutrons

Number of Electrons

42He 2 2 2

14_6_C 6 8 6

2713Al3+ 13 14 10

3216S2- 16 16 18

2311Na+ 11 12 10

Practice With Particles Complete each item with what can be known.

Use “?” for what cannot be known.

Practice With Particles 2

Isotopic Notation

Number of Protons

Number of Neutrons

Number of Electrons

15

7

K +

32 15 17

3617

2427 22

Complete each item with what can be known. Use “?” for what cannot be known.

Practice With Particles 2

Isotopic Notation

Number of Protons

Number of Neutrons

Number of Electrons

15

N7

7 8 7

?

K +

1919 ? 18

32

P2-

1515 17 17

3617Cl 17 19 17

5124Cr2+ 24 27 22

Complete each item with what can be known. Use “?” for what cannot be known.

Definite Ratios

How does the mass of one Oxygen (O2) balloon compare with the mass of one Hydrogen (H2) balloon?

What seems to be true regarding the Volume of a Gas and the Number of Gas Molecules? At same Temperature and Pressure, Equal Volumes of Gases contain Equal Number of Gas Molecules.

O2 = 15.9994 amu X 2 atoms/molecule = 32.00 amu

H2 = 1.00794 amu X 2 atoms/molecule = 2.02 amuFor a Simple Ratio: Set Smaller number equal to one, determine Larger value.

32.00 amu O2 2.02 amu H2

= __________mass O2

mass H21

xX = 32 x 1 ÷ 2.02 = 15.8

O2 Balloon is 15.8 times heavier than H2 Balloon.

What does this experiment demonstrate about the apparent increase in mass of product?Why did the water rise into the glass jar during the reaction?

What percentage of the original volume of air was taken up by the water after the reaction? Why?

Additional mass came from something in the air

Outside Air pressure pushes the water up against the weaker Inside Air pressure until all forces are balanced

If All the Oxygen in the air reacts, then approximately 21% of the volume will be water. Oxygen gas occupies much,

much more volume than Oxygen in solid phase as Tin Oxide

Percent Oxygen in Air