Chemistry ChapterChemistry Chapter 44Atoms: Atoms:

The Building The Building Blocks of Matter Blocks of Matter

Law of Conservation of MassLaw of Conservation of Mass

Total mass of reactants =

Total mass of products

Antoine Lavoisier

Mass is neither created nor destroyed during chemical or physical reactions.

http://www.greatscientists.net/antoine-lavoisier/

Proust’s Law of Definite Proust’s Law of Definite ProportionsProportions

A given compound always contains the same proportions (by mass)of elements regardless of the sourceFor example water H2O must Always have 8 g oxygenCombining with 1 g Hydrogen

Hydrogen Peroxide H2O2 mustHave 16 g Oxygen combining with1 g Hydrogen

Law of Multiple ProportionsLaw of Multiple ProportionsIn compounds atoms combine in simple whole number ratios. The mass ratios will be different fordifferent compounds

Law of Definite Proportions

H2O2 atoms H to 1 atom O2 gram H to 8 gram O20% Hydrogen by mass and80% Oxygen by mass

Law of Multiple ProportionsH2O2 atoms H to 1 atom O2 gram H to 8 gram O

H2O2 2 atoms H to 2 atoms O2 gram H to 32 grams O

• If it takes 1.000 g of S for every 1.188 g F to make a compound SF what must be the mass ratio

to make the compound SF2 ?

A: 1.000 g S to 2.376 g F

b) What must be the mass ratio for SF3 ?

A: 1.000 g S to 3.564 g F

If it takes 14.000g N to combine with 16.000g O to form NO, what is the mass ratio for NO2 ?

A: 14.000g N to 32.000 g O

• It takes 24.000g C to combine with 4.000g H to form C2H4 what must be the mass of Hydrogen to combine with 72.000g Carbon?

• A; 12.000g H

• Hydrogen sulfide (H2S) is composed of two elements: hydrogen and sulfur. In an experiment, 6.500 g of hydrogen sulfide is fully decomposed into its elements. If 0.384 g of hydrogen is obtained in this experiment, how many grams of sulfur must be obtained?– What law of chemical behavior does this

experiment demonstrate?– A: 6.500g- 0.384g= 6.116g S– Law of conservation of mass

• Assume that we used 5.000g of Iron to heat up with 10.000 g sulfur to make our pyrite (Fool’S gold). What is the mass of pyrite made?

• A; 15.000 grams pyrite• What law does this illustrate?• Law of conservation of mass

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Dalton’s Atomic Theory Dalton’s Atomic Theory (1808)(1808)

Atoms cannot be subdivided, created, or destroyed Atoms of different elements combine in simple whole-number ratios to form chemical compounds In chemical reactions, atoms are combined, separated, or rearranged

All matter is composed of extremely small particles called atoms Atoms of a given element are identical in size, mass, and other properties; atoms of different elements differ in size, mass, and other properties

John Dalton

Discovery of the ElectronDiscovery of the ElectronIn 1897, J.J. Thomson used a cathode ray tube to deduce that the electrons are the subatomic negatively charged particles carrying electricity in a cathode ray tube.

Cathode ray tubes pass electricity through a gas that is contained at a very low

pressure.

Thompson measured the mass of cathode rays, showing they were made of particles that were around 1800 times lighter than the lightest atom, Hydrogen

Some ModernSome ModernCCathode athode RRay ay TTubesubes

Conclusions from the Study Conclusions from the Study of the Electronof the Electron

Cathode rays have identical properties regardless of the element used to produce them. All elements must contain identically charged electrons.Atoms are neutral, so there must be positive particles in the atom to balance the negative charge of the electrons Electrons have so little mass that atoms must contain other particles that account for most of the mass

Thomson’s Atomic Thomson’s Atomic ModelModel

Thomson believed that the electrons were like plums embedded in a positively charged “pudding,” thus it was called the “plum pudding” model.

Rutherford’s Gold Foil Rutherford’s Gold Foil ExperimentExperiment

Alpha particles are helium nuclei Particles were fired at a thin sheet of gold foil Particle hits on the detecting screen (film) are recordedhttp://www.youtube.com/watch?v=5pZj0u_XMb

Try it Yourself!Try it Yourself!In the following pictures, there is a target hidden by a cloud. To figure out the shape of the target, we shot some beams into the cloud and recorded where the beams came out. Can you figure out the shape of the target?

The AnswersThe Answers

Target #1 Target #2

Rutherford’s FindingsRutherford’s Findings

The nucleus size is small compared to the atomic size The nucleus is dense The nucleus is positively charged

Most of the particles passed right through A few particles were deflected VERY FEW were greatly deflected

“Like bullets bouncing off of tissue paper!”

Conclusions:

The Atomic The Atomic ScaleScale

Most of the mass of the atom is in the nucleus (protons and neutrons) Electrons are found outside of the nucleus (the electron cloud) Most of the volume of the atom is empty space

“q” is a particle called a “quark”

Atomic Mass ScaleAtomic Mass Scale1 atomic mass unit (u) has a mass of 1/12 of the mass of carbon-12 atom or 1.66054 *10-24g(1g= 6.02214*1023 u)Particle Charge Mass (u)

Proton Positive(1+)

1.0073

Neutron None(neutral)

1.0087

Electron Negative(1-)

5.486*10-4

Atomic NumberAtomic NumberAtomic number (Z) of an element is the number of protons in the nucleus of each atom of that element.

Element # of protons Atomic # (Z)

Carbon 6 6

Phosphorus 15 15

Gold 79 79

Mass NumberMass NumberMass number is the number of protons and neutrons in the nucleus of an isotope.Mass # = p+ + n0

Nuclide p+ n0 e- Mass #

Oxygen - 10

- 33 42

- 31 15

8 8 1818

Arsenic 75 33 75

Phosphorus 15 3116

IsotopeIsotopess

Elements occur in nature as mixtures of isotopes.Isotopes are atoms of the same element that differ in the number of neutrons

• THERE ARE TWO WAYS TO REPRESENT THE

• DIFFERENT TYPES OF ISOTOPES

Atomic number

Mass number

Or H-1

Mass number

011H

Charge(is included for ionsCharged atoms and is notIncluded for neutral atoms

• An atom becomes an ion when it loses or gains electrons. Now the electrons and protons are note balanced.

Al2713

32713 Al

13p13p

13e

-3e-

13p

10e

Modern Atomic TheoryModern Atomic TheorySeveral changes have been made to Dalton’s theory.

Dalton said:

Atoms of a given element are identical in size, mass, and other properties; atoms of different elements differ in size, mass, and other properties

Modern theory states:Atoms of an element have a

characteristic average mass which is unique to that element.

Average Atomic Mass (Atomic Average Atomic Mass (Atomic Weight)Weight)

• Average atomic mass is the average of all the naturally isotopes of that element

Atomic mass= ∑ (mass number ∙ % abundance)

ExampleExample

Isotope Symbol Composition of the nucleus

% in nature

Carbon-12 12C 6 protons6 neutrons

98.89%

Carbon-13 13C 6 protons7 neutrons

1.11%

Carbon-14 14C 6 protons8 neutrons

<0.01%

Find the average atomic mass of Carbon.

AAM (Carbon)= 12.011

AAM= (.9889*12)+ (.0111*13)+ (.0001*14)=

Modern Atomic Theory #2Modern Atomic Theory #2

Dalton said:

Modern theory states:

Atoms cannot be subdivided, created, or destroyed

Atoms cannot be subdivided, created, or destroyed in ordinary chemical reactions. However, these changes CAN occur in nuclear reactions!

Mass spectrometerMass spectrometer

• The MS works by ionizing chemical compounds to generate charged molecules or molecule fragments and measurement of their mass to charge ratios