Atomic Theory

Unit 1

5-1

What is Matter?

Anything that has ____________, takes up _____________, composed of atoms.

Atomic Theory

Who was Aristotle?

Atomic Theory

Who first suggested the idea of atoms? What were his beliefs?

Democritus – Discontinuous Theory

Matter was composed of tiny _________ particles called ____________________. Atoms were indivisible, indestructible, fundamental units of matter

Atomic Theory

Scientist Year Experiment Knowledge GainedLavoisier 1743 Massed reactants and products of

reactions

Proust 1799 Massed reactions to determine the composition of compounds found that a compound always has the same elements in the same mass %.

Dalton 1803 Experimented with different compounds that contain the same elements

J.J. Thompson 1897

Goldstein 1886 Found the CRT to have a charge going in the opposite direction of the CR

Atomic Theory

Scientist Year Experiment Knowledge Gained

Chadwick 1932 Transmutations of one element into another element-nuclear chemistry

Rutherford

1911 Atom has a dense center of [ositive charges called the

Bohr 1913 Flame Tests

Atomic Theory

What is Dalton’s Atomic Theory (1803)?

All elements are composed of submicroscopic indivisible particles called atoms.

Atoms of the same element are ___________

Atoms of different elements can _______ mix together or ___________ combine in simple whole number ________ to form compounds.

Chemical reactions occur when atoms are __________, ___________, or ____________

Pictured as a small hard sphere.

Atomic Theory

J.J. Thomson (1856 – 1940)

The Thomson model suggested ______________ were embedded in a ______________ sphere.

He Received the Nobel Prize in Physics for his discovery of the ____________________ in 1897.

Atomic Theory

Ernest Rutherford (1871 – 1937)

Gold Foil Experiment

Atom was mostly ______________space.

Dense, positively charged center. (_________________)

Electrons outside the ________________________

Named the _________________________

Atomic Theory

Neils Bohr (1885 – 1962)

Bohr’s model showed

______________________ moving around the _____________

In _____________________ orbits.

Atomic Theory

Erwin Schrodinger (1887 – 1961)

Mathematical model demonstrated that the ___________________ position could be _________________, but not the pinpointed ___________________________.

Atomic Theory

James Chadwick (1891 – 1974)

English Physicist

Discovered the ________________________

Chemistry Unit 1

Density

Density

D = M V

Density

Which is heavier, a pound of lead or a pound of feathers?

Density

The density of an object factors in both the mass and volume of the substance. Density can be measured in many different

units as long as the top unit is ____________ and the bottom unit is ___________________.

Ex: g/mL, g/cm3, kg/m3…..

Density

Why do ice cubes float in your drink?

They are _________________________ dense than the liquid.

Density Column

Calculations

To indicate the __________________ of a number, scientists must round their final answer to the correct number of

______________________________________-

CalculationsSignificant Figures Rules

1. _______________________ numbers are significant. (Ex: numbers 1 – 9)

2. Zeros __________________ tow non-zero numbers are significant. (Ex: 4003 has 4 significant figures)

3. Zeros at the end of a number that includes a ________________________ are significant. (Ex: 6,700 has 4 significant figures.)

4. Zeros at the __________________of a number are not significant. (Ex: 0.007899 has 4 significant figures.)

Calculations, Significant Figures

How many significant figures are in the following numbers?

1. 0.002322

2. 1.00499

3. 6800

4. 9149

5. 5.92300

Calculations involving Significant Figures

Round _________________ your final answers to the correct number of significant figures for full credit!!!!!

Significant Figure Calculation Rules

ADDITION AND SUBTRACTION Round your answer to the same number of

__________________ as the measurement with the least number of decimal places.

MULTIPLICATION AND DIVISION Round your answer to the same number

of significant figures as the measurement with the _____________of significant figures.

Significant Figures Example

12.52m + 349.0m + 8.24 m = ?

Significant Figures Example

74.626 m – 23.34 m = ?

Significant Figure Example

7.55 m x 0.34 m = ?

Significant Figure Example

2.4526 m + 8.4 = ?

Significant Figures

Apply what you know about significant figures and density to the following problems:

The density of silver at 20oC is 10.5 g/cm3. What is the volume of a 68 g bar of silver?

Significant Figure Example

Calculate the density of ice which weighs 0.5g and has the dimensions 10 mm x 0.0004 cm x 15 mm.

Important conversions: 100 cm = 1 m

1000 mL = 1 L.

Don’t forget about significant figures on your homework.

Solutions

A solution is a ____________ mixed with a ____________. Solute: The substance ___________dissolved Solvent: The substance ______________the

dissolving Example: Salt Water- Solute is _________

Solvent is__________

Solutions

In yesterday’s lab you made a solution of sugar water. Identify the solute and solvent in sugar water. Solute:__________________ Solvent:_________________

Solutions

Solutions may be classified as concentrated or dilute Concentrated solution:___________________

solute particles dissolved in the solvent. Dilute solution: _______________ solute particles

dissolved in the solvent

Solutions

Draw a picture of a concentrated and dilute solution below:

Dilute Concentrated

Solutions

There are two physical properties that influence density 1._____________________________ 2._____________________________

Explain how the density of water changes when the concentration of sugar increases. The density of water _____________________

Models

What is a model?

Models

Which scientist in the previous data table would you say contributed the following models of the atom?

A) c)

B) D)

Atomic Models

What technology led to the discovery of the

Electron

Nucleus

Cathode Ray Tube

A cathode ray tube is a vacuum. A high voltage was passed throughThe metal at the negative plate. A beam appeared that headed towardsThe positive plate. Thompson called this beam a cathode ray. To rpoveThe beam contained negative charges, he put up electrical fields in theApparatus. The cathode ray deflected away from the negative plate andAttracted to the positive plate. This happened no matter what the metal

Was He therefore concludedThe beam held negative charges called electrons. He also said all elements must have electrons.

Gold Foil Experiment

In the gold foil experiment, Rutherford used alpha radiation. Alpha particlesAre positive particles. He thought that the particles would go straight through the gold foil because Thomson suggested that the atom was a sphere of positive charge with negative particles floating inside. However,

Rutherford found that the alpha particles went through the gold atoms most of the time. OnRare occation the positive alpha particles Would be deflected back. He thus stated thatThe atom is most empty space, but there mustBe a small dense area of positive charge in the Center. Positive because it repelled the alphaParticles and small because the deflection wasSo rare.

Gold Foil Experiment

If the atom were the size of a football stadium, the nucleus would be the size of a marble.

Expected versus actual results.

Structure of the Nuclear AtomHow are the parts of an atom arranged?

Particle Location Charge Mass (g) Mass (amu)

Distinguishing Between Atoms

What can we learn about an atom from its subatomic particles?

Protons –

Electrons –

Distinguishing between Atoms

What is a cation?

What is an anion?

What is the symbol for Oxygen with 8 protons and 10 electrons?

Distinguishing Between Atoms

Neutrons -

Distinguishing Between Atoms

There are three known isotopes of hydrogen.Common Name

Mass Number

Proton

Neutrons

Electron

Atomic Number

Hydrogen 1

Hydrogen

Hydrogen 2

Deuterium

Hydrogen 3

Tritium

Writing Nuclei Symbols

An atom’s nuclei symbol tells us the number of subatomic particles found on one particular atom. It can tell us what isotope of a particular atom we are looking at or whether we haven an ion of that particular element.

Nuclear Symbols: The following format is generally used to look at the particle counts of atoms.

Nuclear Symbols

MN –

AN –

X –

Charge -

Nuclear Symbols Examples

A) 136C What element is this? Is it neutral, anion or

cation? Find Each Value:

Atomic Number = Mass Number = P+ = no = e- =

B) 35 Cl-1

17

C) Cobalt – 59

D) Write the nuclei symbol for the element that ahs 6 protons, 6 electrons, and 6 neutrons.

Nuclear Symbols

Element Atomic Number

Mass Number

Protons Electrons Neutrons

Be 4 9

Ne 10 20

Na 11 23

52

6

17 35

S

Ca2+

7 10

Ag+

Nuclear Symbols

Three isotopes of chromium are chromium-50, chromium-52, and chromium-53. How many neutrons are in each isotope, given that chromium always has an atomic number of 24?

The Atom

Reflect back on Dalton’s original postulates. What two postulates no longer hold true today?

Dalton was limited by the fact that he did not have the devices needed to discover these particles.

Nuclear Chemistry

What is radioactivity?

When the _________________ of unstable isotopes(________________) gain stability by emitting large amounts of energy called ____________________________.

___________________________Dalton’s idea of indivisible atoms.

Nuclear reactions are not affected by changes in ________________, pressure, or _____________________

Like regular chemical reactions are.

Three types of radiation

Types Particle Type Types of Nuclear Decay

ALPHA Nuclei with atomic numbers > 83 are very heavy and have too many p* & no and therefore they emit an alpha particle which _________ the neutron-proton ratio

BETA Beta Decay – too many ___________ causing a neutron to turn into a proton by releasing a beta particle from the nucleus

GAMMA Have no mass and no charge therefore are released along with beta and alpha particles

Nuclear Stability

The _____________________ of a nucleus depends on its ____________ratio. Atomic Number _______, the ratio of stability is ______

Ex: Carbon-12 and Nitrogen-14

Atomic Number _______, the ratio of stability reaches _______ for heavy elements (A.N. 83 and up) Ex: Lead-206

Band of Stability

Understand how to read this diagram!

Half-Life Section 28.2

Half-Life is: The time required for _________________________ of the

nuclei of a radioisotope sample to decay to products.

After one half life, _____________________________________ radioactive atoms have decayed into atoms of a new element.

How long is one half-life?

Half-lives _______________________________________for radioisotopes Some are as short as a fraction of a second or as long as

billions of years.

Half-Life Examples

Nitrogen-13 emits beta radiation and decays to carbon-13 with a half life of 10 minutes. Assuming a starting mass of 2.00g of nitrogen-13 A. How long is three half-lives?

B. How many grams of the isotope will still be present at the end of three half-lives?

Half-Life Example

Manganese-56 is a beta emitter with a half life of 2.6 hours. What is the mass of manganese-56 in a 1.0 mg sample of the isotope at the end of 10.4 hours?

Half Life Example

A sample of thorium-234 has a half life of 25 days. Will all the thorium undergo radioactive decay in 50 days? Explain.

Half-Life Example

A sample initially contains 50.0g of cobalt-60. After 2.00 years, the sample contains 38.4g of cobalt-60. Calculate the half-life of cobalt-60. What is the amount of cobalt-60 at t = 8.00 years?

Transmutation Reactions

The conversion of an _________________ of one element to an __________________________ of another element Occurs in 2 ways

________________________________________________ When __________________________________________

bombarded the nucleus of an atom (ex. Protons, neutrons, or alpha particles).

Examples

Al + He Si + ___________

Bi He + __________

Si e + __________

Cu Zn + __________

Write nuclear equations for these conversions

P to Si

C to C

I to Xe

Honors Chemistry Question

The complete decay of 241Am involves successively alpha, alpha, beta, alpha, alpha, beta, alpha, alpha, alpha, beta, alpha, and beta production. What is the final stable nucleus produced in this decay series?

Predict whether each of the following nuclides is stable or unstable (radioactive). If the nuclide is unstable, predict the type of radioactivity you would expect it to exhibit, 45K, 50Fe, 20Na or 194Ti.

*******complete problem on back of homework worksheet.