Chem Problem Sets

Rosal People

Dahil meron sa inyong mga di nabigyan ng handouts sa chem last week at merong mga prob sets na binigay si Ma’m, eto yung mga problem sets

Please read about

1. Discovery of Radioactivity by Henri Becquerel

2. J.J. Thompson’s plum pudding model

3. Rutherford’s gold foil experiment

4. Millikan’s oil-drop experiment

5. Chadwick’s discovery of neutron

6. Bohr’s planetary model of atom

PROBLEM SET 1: Early Models of Atom (to be submitted on 1 whole pad paper)

1. Draw the model of atom according to

a. Dalton  

b. Thomson

c. Rutherford

d. Bohr

2. What are the postulates of Dalton’s Atomic Theory?

3. How does Dalton’s Atomic Theory explain chemical reactions? How does it support the Law of Conservation of Mass?

4. Review each postulate of Dalton.  Which of these is/are still applicable or acceptable today? Explain the        flaws of other postulates.

5. The gold foil used in the gold-foil scattering experiment was about 2000 atoms thick.  Why did most of the alpha particles pass straight through the foil?

6. What did Rutherford’s experiment prove about the atom? Is this still considered true today?

7. What was the significance of Robert Millikan’s Work?

8.  Answer the following:

a. Can isotopes of the same element have the same mass no.? The same atomic no.?

b. Can isotopes of different elements have the same mass no.? The same atomic no.?

c. Explain

9. Use Dalton’s Atomic Theory to answer this: can more than one compound be made from atoms of the same two elements? If yes, cite examples.  If no, explain your answer.

10. Compare the subatomic particles in terms of weight or mass, and charges.

11. Sulfur and fluorine form at least 2 compounds, SF₄ and SF₆.  How can these be explained using Dalton’s atomic theory?

12. What are the flaws of each model of the atom? (Explain what is wrong with each model.)

13. Fill up the table with correct numbers! Remember the relationships among atomic number, atomic mass, no. of electrons, no. of protons, and no. of neutrons? This table reviews what you learned in the first quarter.

SYMBOL	ATOMIC NO.	ATOMIC MASS	e-	p+	n0
K	19	39		19
Na+1	11				12
Cu		64	29
I-1		127	55
Ar				18	22
Mg+2	12				12

 

 

Please continue reading the textbooks and focus on these people and their contributions (their brief explanations are found below):

 

1. Max Planck (Quantum Theory)

2. Albert Einstein (Photoelectric Effect)

3. Louie de Broglie (Matter Waves)

4. Werner Heisenberg (Uncertainty Principle)

5. Erwin Schroerdinger (Equations to Wave Motion)

Also please study the idea of quarks…

Some Ideas to consider

Ø       MURRAY GELL-MANN AND GEORGE ZWEIG: started idea of quarks

Ø       Protons and neutrons are composites of quarks called up, down, or strange (u, d, s) with spin of ½ and electric charges 2/3, -1/3, -1/3, respectively

Ø       PROTON: made up of 2 up quarks and 1 down quark [2/3+2/3+(-1/3)]

Ø       NEUTRON: made up of 1 up quark and 2 down quarks [2/3+(-1/3)+(-1/3)]

 

PROBLEM SET 2: Quantum Mechanics

14. Explain why the spectral lines are discontinuous when the light from an elemental gas like sodium is seen through a spectroscope.

15. (For this time, never mind this question since this is based on an experiment we have never done yet.) Refer to the flame test activity: are the electrons in the gas in the nichrome wire in the ground state or in the excited state when it is not placed over the flame? Explain your answer.

16. The quantum mechanical model of the atom includes (explain your choice)

                a. all of the Bohr model

                b. part of the Bohr model

                c. no part of Bohr model

17. Which among the ff. are not quantized?

                a. shoelaces

                b. cars passing through NLEX tollgate

                c. droplets of water from defective faucet

                d. flow of a river in km³/hr

                e. the opening and closing of an automatic door (One which senses your presence)

18. What kind of light would be emitted by atoms if electron energy were not quantized? Why?

19. Comment on the common picture of the atom showing one or more electrons whirling around the nucleus of an atom.  To whom do we credit such atomic model?

20. Explain what you think of that common picture.  What is wrong with it?

21. A ______is made up of 1 up quark and 2 down quarks, while a _______is made up of 2 up quarks and 1 down quark

 

PROBLEM SET 3: Quantum Mechanical Model of the atom (some may have questions; some may only have information)

1. PLANCK’S QUANTUM THEORY

Energy can be released (or absorbed) by atoms only in discrete “chunks” of some minimum amount, called QUANTUM that can be emitted or absorbed as electromagnetic radiation.  He proposed that energy or E of a single quantum varies directly to its frequency (v).  If we used this as an equation:

E=h*v where equals h is Planck’s constant (6.63 * 10^-34 Joule-second)

a. If Planck’s theory were correct, why aren’t its effect more obvious in our daily lives?

b. Why is it that in most situations, energy changes seem continuous and not discrete, or quantized?

2. EINSTEIN’S PHOTOELECTRIC EFFECT

Experiments show the light shining on a clean metal surface causes the surface to emit electrons.  For each metal, there is a minimum frequency of light below which no electrons are emitted.  For example, light with a frequency of 4.60 * 10¹⁴/s or higher will cause cesium metals to emit electrons.  If the frequency is lower, no electron is emitted.  Einstein assumed that the radiant energy striking the metal surface is a stream of tiny energy packets, called photons.

a. To emit electrons from sodium metal, a photon with a minimum energy of 4.41 * 10^-19 J is needed.  What is the minimum frequency of light necessary to emit electrons from sodium through photoelectric effect?

b. What is the wavelength of light?

c. If sodium is irradiated with light of 439 nm, what is the maximum kinetic energy of the emitted electrons?

d. What is the maximum number of electrons that can be freed by a burst of light whose total energy is 1.00 μJ?

3. DE BROGLIE’S MATTER WAVES

If light, under appropriate conditions, behave as though it were a stream of particles, could matter, also under appropriate conditions, possibly show the behavior or properties of a wave? If the electron which orbits around the nucleus could be thought of as a wave, then, as De Broglie suggested, it follows that electron has particular wavelength associated with it.  The characteristic wavelength of the electron or of any other particle depends on its mass, m, and velocity, u.  Thus

λ (wavelength) = h/(m*u) (m*u is the object’s momentum). 

De Broglie called these wave characteristics MATTER WAVES.

Find λ of the following objects

a. a 55 kg student skating at 40 km/hr

b. a Lithium atom moving at 2.5 * 10⁵ m/s

4. WERNER HEISENBERG’S UNCERTAINTY PRINCIPLE

Can you determine electron’s position, direction of motion, and speed at any time, that shows wave properties? A wave extends in space, and its location is not precisely defined.  Heisenberg concluded that wave characteristic of matter puts a fundamental limitation on how precisely we can know both the location and momentum of any object. 

UNCERTAINTY PRINCILE: states that it is impossible for us to determine the exact position and momentum of an electron at the same time. 

It also showed the flaw of Bohr’s model which described the electron of H atom in a well-defined orbit around the nucleus.

5. ERWIN SCHRÖDINGER’S WAVE EQUATION

(Solutions are not discussed in the high school chemistry)

His wave equation describes behavior of Hydrogen’s electron. 

WAVE FUNCTIONS: solutions to the wave equation; predict the allowed energy states of an electron and the probability of finding that electron in a given location

6. QUANTUM NUMBERS, ENERGY LEVELS, AND ORBITALS

ORBITAL: region where electron can be found

PRINCIPAL QUANTUM NUMBER, n: measures the most probable distance of the electron from the nucleus, not the radius of the well –defined orbit

                Values: 1, 2, 3, 4, …

SECOND QUANTUM NUM, / (or azimuthal quantum number): defines the shape of orbital

                Values: 0 to n-1

THIRD QUANTUM NUM, m (magnetic quantum number): orientation of orbital in space

                Values: between / and -/, including 0

ELECTRON SHELL: collection of orbitals

All n=2 orbitals are said to be in the second shell

SUBSHELL: refers to the set of orbitals which have the same n and / values

n squared: total number of orbitals in a shell

EVERY ORBITAL: can have maximum no. of 2 electrons

What is the difference between Bohr’s orbit and the quantum mechanical model’s orbital?

Chem HW2

Do these in your notebook:

on pp.236-248..

Do nos :

25-29 (257)

30-32 (257)

1-9(256)

Chem HW!

Given the Balanced Chemical Equation:

NaOH + HCl —-> H2O + NaCl

100g           100g

 

1. Find the Limiting Reactant

2. How much (in g) is in excess?

3. How much H₂O is produced?