Chemistry 2nd Quarter

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Amica !

Chemistry 2nd

Quarter

I. Empirical and Molecular Formula Empirical Formula

- Shows the simplest number ratio for theelements in a compound

Molecular Formula- Shows the number of elements of each kind in a

compound- Multiples of the Empirical FormulaMultiply Divide

Mass(grams) molar mass Mole Avogadros Moles

(g/mole) Number Atoms

Particles

Divide Multiply

II. Stoichiometry- The study of the amounts of material consumed

and produced in chemical reactions

-

Greek: Stoichion (Element); Metron (measure)

aA + bB cC to solve for number of moles

1. Write the balanced equation2. Calculate the available moles of each reactant3. Determine the mole ratio (using the balanced

equation) of the reactants in the chemical reaction

4. Compare; limiting = smaller amount; excess = largeramount

Limiting reactant- Reactant in a chemical reaction that limits the

amount of product that can be formed

- Completely consumed Excess Reactant

- Reactant in a chemical reaction that remainswhen a reaction stops (when limiting reactant is

completely consumed)

III. Pecent Yield1. Write the balanced equation2. Do stoichiomety (get the limiting reactant)3. Limiting reactant is the Theoretical Yield4. Actual Yield__ x 100 = Percent Yield

Theoretical Yield

IV. History Of Atomic Structurea. Leucippus and Democritus

- A material can be broken down into smallerpieces

- Atomos (Greek for indivisible)b. Aristotle

- Rejected the atomic//particulate view- Matter is made up of 4 elements (Fire, Air, Wind,

Earth); continuous all of one piece

Particle Theory

a. Robert Boyle- Postulates that gasses are composed of discrete

particles separated by a void

b. Isaac Newton- God formed matter in solid, massy, hard,

impenetrable movable particles

Daltons Atomic Theory

1808 a new system of chemical philosophy1. All matter is composed of indestructible atoms.2. The atoms of a given element are identical, but

different from other elements and are

unchangeable.

3. Compounds are formed by the combination of theatoms of two or more elements forming molecules.

They combine in definite ratios of small whole

numbers (Law of Definite Composition Proust).

4. Chemical reactants involve only the separation andor union of atoms. They are only rearranged; areneither created nor destroyed.

Foundations of Discovery of Electrons

a. Thales- Amber when rubbed attracted small fibers

b. Sir William Gilbert- Materials rubbed = charge

Elektron (Greek for Amber) Polarization neutrally charged objects interacting

with charged objects

c. Charles Coulomb- Force is inversely proportional to the square of

the distance to the charged bodies

Coulomb (C) amount of charge that passes througha circuit if a current of one ampere passes for one

second

Discovery of Electrons

(Before Thompson)

a. Sir Humphry Davy- When electric current is passed through molten

compounds of metals resulted in the

decomposition of compounds to produce the

metals

b. Michael Faraday- Mass of the element formed is proportional to the

quantity of electricity passed

c. George J. Stoney


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- suggested the name electron for the particle ofelectricity

d. Heinrich Geissler- was able to device a method of producing a good

vacuum in glass tubes

e. Julius Plucker- sealed two metal pieces into a Geissler tube and

applied a high voltage across the electrodes and

observe a greenish luminescence emanating from

the negative electrode, the cathode- cathode ray is drawn to the positively charged

plate, called the anode

f. Eugene Goldstein- proposed that the luminescence observed by

Plucker is cathode ray (later on identified as

electron by Thomson)

g. William Crookes- Cathode ray travelled in a straight line and objects

placed in its path cast a shadow at the opposite

side of the tube

Cathode Ray Tube

No external fields straight Magnetic field applied up ( ) Electric field applied down ( + ) Electromagnetic Theory

- a moving charged body behaves like a magnet andcan interact with electric and magnetic fields

though which it passes

-

attracted by + and repelled by Ray travels form cathode to anode Actual ray is invisible but seen as green because of

Zinc Sulfide

Thompsons Experiment

Passing an electric current makes a beam appear tomove from the negative to the positive end

By adding an electric field he found that the movingpieces were negative

JJ Thompson- measured the charge mass ratio of electron thus

providing a way of identifying it

- e/m = 1.76 x 108 C/g- made the cathode ray tube- found that metals emit these same particles when

light of appropriate wavelength shines on them

Thompsons model- Atoms were made of small negatively charged

particles

- larger part of atom ispositively charged with small

electrons scattered in it

- plum puddingMilikans Experiment

Robert Millikan- determine the charge of a particle ( + -) and

magnitude of electric charge

- observed that the electrical charge was always awhole-number multiple of a smallest charge,

which he called the unit charge

Oil Drop Experiment- oil drops atomizer speed- As oil droplet falls through the air, it may acquire

a positive or negative charge due to friction

- value of the unit charge is 1.60 x 10-19 coulomb- balanced state will be shown by the state of the

particle; it will remain suspended in the mid-air

Radioactivity

Wilhelm Roentgen- noticed that cathode rays caused glass and metalsto emit unusual rays

Radioactivity (by Marie Curie)- spontaneous emission of particles and or

radiation

- A. Alpha rays ( ) consist of positively chargedparticles called alpha particles and therefore are

deflected by the positively charged plate.

- B. Beta rays ( ) or beta particles are electronsand deflected by negatively charged plate

- C. Gamma rays ( ) have no charged and are notaffected by an external electric field or magnetic

field

Rutherfords Experiment

Ernest Rutherford- Conducted an experiment to isolate the positive

particles in an atom

- knew that atoms had positive and negativeparticles, didnt know how they were arranged

- Hans Geiger (associate)- Alpha particles are found to be helium atoms with

their electrons removed (x2500 electron)

Gold Foil Experiment- Expected: alpha particles to pass through without

changing direction very much (he thought the

mass was evenly distributed in the atom)

- Atom consists of a very small nucleus surroundedby electrons

- Nucleus contains most of the mass of the atomand all of its positive charge.

- Alpha particles are deflectedby nucleus it if they get close

enough with each other


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Modern Atomic Theory

1. All matter is composed of atoms2. Atoms of one element cannot be converted into

atoms of another element in a chemical reaction

3. All atoms of an element have the same number ofprotons , which determines the chemical behaviour

of the element

4. Compounds are formed by the chemicalcombination of two or more elements in specific

ratios

Electron Cloud Model

Bohrs Model

- Electrons move in circular orbits around thenucleus

- Energies are quantized (Planck)3 Postulates :

Only orbits of certain radii, corresponding to certainenergies, are permitted for electrons in an atom.

An electron in a permitted orbit has a specific energyand is in an allowed energy state. Electron will not

radiate energy.

Energy is only emitted or absorbed by an electron asit changes from one allowed energy state to another.

This energy is emitted or absorbed as a photon.

V. Nuclear Chemistry Nuclear Reactions

- Changes in matter originating from the nucleus ofan atom

- Elements are converted; involves epn;absorption/release of a lot of energy; not affected

temp

Chemical Reactions- Atoms rearranged; only electrons;

absorption/release of small energy; affected by

temp, prssr

Radioactive- When a nuclei change spontaneously, emitting

energy

Nucleons- Particles in the nucleus

Radionuclide- Radioactive nucleus

Radioisotopes- Atoms containing radionuclide

Mode of Decay:

1. High n/p ratio (too many neutrons; lie above band ofstability) --- undergoes beta decay

2. Low n/p ratio (neutron poor; lie below band ofstability) --- positron decay or electron capture

3. Heavy nuclides ( Z > 83) --- alpha decay Half-life

- Indicates the rate at which a radionuclide decays Mass Defect

- mass difference due to the release of energy Nuclear binding energy (BE)

- is the energy required to break up a nucleus intoits component protons and neutrons

Nuclear chain reaction- is a self-sustaining sequence of nuclear fissionreactions

Positron- Positive Electron

Emission- Product side; decay

Capture- Reactant side

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Chemistry 2nd Quarter