UNIT I The Atom CHEMISTRY Matter A History

UNIT I The Atom

CHEMISTRY: ** Matter:

A. History of the Atom 1. Democritus (460 – 370 B. C. ) a. “Atomos” b. Nature of Matter - Ignis - Aer - Terra - Aqua

2. John Dalton’s Atomic Theory (1803) a. All elements are composed of hard and indivisible spheres called atoms.

b. All atoms of a given element are identical. c. Atoms of different elements are different; that is, they have different masses.

d. Compounds are formed by the combination of atoms of different elements.

3. J. J. Thomson (1890’s) a. Cathode ray tube experiment b. identified the electron c. “plum pudding model” 1) 2)

-Experiment passes an electric current through a gas -Sealed the gas in a glass tube with metal disks (electrodes) -Electrodes are connected to a source of electricity. -One electrode, the anode, became positively charged. -The cathode, became negatively charged. -The result was a glowing beam, or cathode ray, that traveled from cathode to anode

Electrical/ Magnetic Field Cathode ray is deflected (repelled) by a metal plate that has a negative charge and attracted to a metal plate that has a positive charge. * Opposite charges attract and like charges repel

“Plum pudding model” 1) Atoms contain small, negatively, charged particles called electrons. 2) Electrons were seen as being randomly distributed in a sphere of positive charge.

4. Ernest Rutherford (1909) “gold foil experiment” a. Rutherford’s observation b. Rutherford’s proposal c. Rutherford’s conclusion

Rutherford’s observation 1) Alpha particles passed through gold foil with slight deflections (bounced back).

Rutherford’s proposal & conclusion 2) The atom is mostly empty space. 3) The atom has a dense central core called a nucleus. **NUCLEUS:

(write this under nucleus) i. 3 Parts of the Atom a. proton: b. neutron: c. electron:

Subatomic Particles Particle Charge Mass Location Symbol Proton +1 1 amu Nucleus - Neutron 0 1 amu Nucleus - Electron -1 1/1840 amu Outside -

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ii. Definitions a. ATOMIC NUMBER: ** The number of protons equals the number of electrons.

Element Helium Oxygen Sodium Argon Atomic # Protons Electrons

iii. Mass Number: MASS NUMBER = # PROTONS + # NEUTRONS # OF NEUTRONS = MASS NUMBER – ATOMIC NUMBER (Why? )

MASS NUMBER = # PROTONS + # NEUTRONS # OF NEUTRONS = MASS NUMBER – ATOMIC NUMBER Element Atomic # Protons Neutrons Lithium 3 Carbon 6 Potassium Fluorine 2 7 6 20 9 Mass # 10 39 Electrons

Representing the composition of an atom Isotopic Notation 197 79 Au Top #: Mass number Bottom #: Atomic number If you subtract the bottom # from the top #, what number do you get? Standard notation: Gold - 197.

12 6 C 1. What is the standard notation? 2. What is the mass number? 3. How many protons? 4. How many neutrons? 5. How many electrons?

Practice How many protons, electrons and neutrons are in each atom? 4 Be 1. 9 2. 20 10 Ne

iv. Isotopes:

Diamonds are a naturally occurring form of elemental carbon. Two stable isotopes of carbon are carbon - 12 and carbon – 13. Carbon - 12 # of Protons # of Neutrons # of Electrons Chemical Symbol Top: Mass # Bottom: Atomic # Carbon - 13

42 Mass # Atomic # # of Protons # of Neutrons # of Electrons Standard Notation 20 Ca 44 20 Ca

v. Atomic Mass:

Examine the table of student test scores for 5 tests, and calculate their average grades. Test Student A Student B 1 95 76 2 74 88 3 82 90 4 92 81 5 81 72 Average Grade

If you know the student’s average grade, can you tell what the student’s individual test scores were? Explain Test Student A Student B 1 95 76 2 74 88 3 82 90 4 92 81 5 81 72 Average Grade 84. 8 81. 4

Suppose student C had an average of 83%. On each of his five tests he scored either 65% or 95%. Which score occurred more often? Explain. • Find the average of 95 and 65. • Is 83% greater than this average? • Which score occurred more often?

What if the teacher decided that test five would count for 40% of the final grade and test four would count for 30% of the final grade and each of the other tests would count for 10%. Calculate the new average for each student. Note: this is called the weighted average. Test Student A Student B 1 95 x 10% = 76 x 10% = 2 74 x 10% = 88 x 10% = 3 82 x 10% = 90 x 10% = 4 92 x 30% = 81 x 30% = 5 81 x 40% = 72 x 40% = **Weighted Average

Solve for the weighted average for student A - Solve for the weighted average for student B -

A sample of cesium is 75% 133 Cs, 20% 132 Cs and 5% 134 Cs. What is the average atomic mass? 0. 75 x 133 = 99. 75 0. 20 x 132 = 26. 4 0. 05 x 134 = 6. 7_______ Total = 132. 85 amu = average atomic mass WHICH ISOTOPE OF CESIUM IS THE MOST ABUNDANT?

Determine the average atomic mass of the following mixtures of isotopes. 1. 50% 197 Au, 50% 198 Au 1. 15% 55 Fe, 85% 56 Fe 1. 98% 12 C, 2% 14 C 1. 95% 14 N, 3% 15 N, 2% 16 N 1. 99% 1 H, 0. 8% 2 H, 0. 2% 3 H

model” e. Niels Bohr (1915) “Bohr model or Planetary shells; orbits; Principle Energy Levels (n)

1) Orbit, shell, principle energy level: * Each level (n) can hold a specific # of electrons (2 n 2). Orbits PEL (n) Max e- (2 n 2) K L M N O P Q 1 2 3 4 5 6 7 2 8 18 32 50 72 98

a) Bohr’s atomic model (shell diagram) i) Electron shell (1 st) closest to nucleus contains least amount of energy. ii) Electron shell farthest from nucleus contains electrons with most amount of energy. iii) Electron configuration found in the periodic table shows the arrangement of electrons in these electron shells.

Oxygen Electron Configuration:

2) Ground State: **LOOK for an electron configuration that is same as on the Periodic Table for that atom:

Example: Find the ground state electron configuration for sodium and draw Bohr’s shell diagram. • • Symbol? Atomic #? Mass #? # of protons? # of neutrons? # of electrons? Electron configuration? Draw Bohr’s shell diagram

Practice # 1: Find the ground state electron configuration for HELIUM and draw Bohr’s shell diagram. • • Symbol? Atomic #? Mass #? # of protons? # of neutrons? # of electrons? Electron configuration? Draw Bohr’s shell diagram

Practice #2: Find the ground state electron configuration for LITHIUM and draw Bohr’s shell diagram. • • Symbol? Atomic #? Mass #? # of protons? # of neutrons? # of electrons? Electron configuration? Draw Bohr’s shell diagram

Practice # 3: Find the ground state electron configuration for Phosphorous and draw Bohr’s shell diagram. • • Symbol? Atomic #? Mass #? # of protons? # of neutrons? # of electrons? Electron configuration? Draw Bohr’s shell diagram

Practice # 4 1. What is the total number of electrons in the configuration 2 – 8 – 18 – 5? 2. How many electrons are in the fourth shell of an Iodine atom?

3) Excited State: a) Occurs when electrons are subjected to a stimuli (heat, light, electricity). b) An excited state – electron quickly returns to a lower available energy level, emitting (releasing) the same amount of energy. Example: Sodium in the excited state is 2 – 7 – 2

Excited state: LOOK for a configuration that has the same total number of electrons as of the element given, BUT, different arrangement on Periodic Table What is the ground state and excited state configuration for phosphorous? Ground state: Excited state:

Sulfur Selenium Ground state: Excited state:

Which is an excited state electron configuration for an atom with 16 protons and 18 neutrons? 1) 2 – 8 – 5 – 1 2) 2 – 8 – 6 3) 2 – 8 – 6 – 2 4) 2 – 8 – 7

4) Valence electrons: Example: How many valence electrons are in the element with the atomic number 15? Draw the electron – dot (Lewis) diagram.

Chlorine 1. Find the electron configuration. 2. Find the number of valence electrons 3. Draw the electron – dot diagram.

Draw the electron dot diagram for: 1. Oxygen 2. Helium

5) Ions: – Cations • Have a positive charge • Have lost electrons – Anions • Have a negative charge • Have gained electrons – Ion symbol • To write the ion symbol, you must write the element symbol with the net charge written on the top right. • Example: Ca 2+, Zn 2+, Ag 1+, Cl 1 -

sodium and sodium ion # of protons ____ # of electrons ____ net charge _____ cation # of protons ____ # of electrons __10__ net charge ____

chlorine and chlorine ion # of protons ____ # of electrons ____ net charge _____ anion # of protons ____ # of electrons ___18_ net charge ____

Determine the ions for these atoms. Potassium Cation # of protons ____ # of electrons __18__ net charge _____ Oxygen Anion # of protons ____ # of electrons __10__ net charge _____

f. Wave mechanical model (Schrödinger): “Quantum Theory” 1. Electron cloud:

electron. a. ) Quantum: The specific amount of energy absorbed by an b. ) Photons: A bundle of light being emitted as an electron jumps down to ground state.

c. ) Spectroscope: An instrument that separates light into its various wavelengths and displays them as colored lines of bands. d. ) Bright Line Spectrum: The particular set of colored bands produced by a given element.

Your Bright Line Spectrum 400 nm 500 nm 600 nm 700 nm

Which elements are present in this mixture?

Which elements are present in this mixture?

Below are the bright line spectra of four elements and the spectrum of an unknown gas. a) Which elements are in the unknown? b) Why are you able to exclude the other elements? c) Young stars are mostly hydrogen with a small abundance of helium and other elements. Is the unknown a likely spectrum for a young star?

Below are the bright line spectra of four elements and the spectrum of an unknown gas. a) Which elements are in the unknown? Hydrogen and Helium b) Why are you able to exclude the other elements? Because only hydrogen and helium give out bands of light in those wavelengths similar to the unknown. c) Young stars are mostly hydrogen with a small abundance of helium and other elements. Is the unknown a likely spectrum for a young star? Yes, because the unknown has hydrogen and helium.

g. Werner Heisenberg Uncertainty Principle:

scientist ideas model diagram Dalton “Plum. Pudding” Thomson Rutherford A dense nucleus at center and empty space surrounding it Planetary model Bohr Schrodinger Wave Mechanical Model Cloud Model problems

1. The atomic number tells you the number of ______ in one atom of an element. It also tells you the number of _______ in a neutral atom of that element. 2. The ________ of an element is the total number of protons & neutrons in the _____ of the atom.

1. The atomic number tells you the number of protons in one atom of an element. It also tells you the number of electrons in a neutral atom of that element. 2. The mass number of an element is the total number of protons & neutrons in the nucleus of the atom.

2. Quantum Numbers A. Principle Quantum Number (n): * Each PEL contains sublevels

Principal Energy Level Type of Sublevel 1 s 1 1 2 s p 1 3 4 3 s p d 1 3 5 4 s p d f 1 3 5 7 Level n n types (n=1, 2, 3, …) (s, p, d, f, etc. ) # of Orbitals in Total Orbitals a Sublevel per level 9 Max # of electrons 2 (2 electrons) 2 6 (8 electrons) 2 6 10 (18 electrons) 16 2 6 10 14 (32 electrons) n 2 orbitals 2 n 2 electrons

In the 1 st Principle Energy LEVEL, there is one sub-LEVEL, it’s name is “s”, which has 1 orbital with two electrons of opposite spin.

In the 2 nd Principle Energy LEVEL, there are 2 sub -LEVELs, whose names are “s” and “p”. S has 1 orbital, which holds 2 electrons. P has 3 orbitals, which holds 2 electrons each.

B. Electron Configuration: 4 Principal Energy 3 p Level Type of sublevel Number of electrons in sublevel

Rules for filling sublevels 1. Each added electron is placed in the sublevel of lowest energy available (*Aufbau Principle). 2. No more than 2 electrons, with opposite spins can placed in any orbital (*Pauli Exclusion). 3. Before a second electron can be placed in any orbital, all the orbitals of that sublevel must contain at least one electron with same spin (*Hunds Rule). 4. No more than four orbitals (one s and three p orbitals) can be occupied in the outermost principle energy level. The next electron must enter the next principle energy level.

Write the electron configurations for: (and draw the orbital filling diagram) 1. Neon 2. Aluminum 3. Titanium 4. Gallium

Practice 1. What is the total number of electrons needed to complete fill all the orbitals in an atom's second principal energy level? (1) 16 (2) 2 (3) 8 (4) 4 2. What is the total number of sublevels in the fourth principal energy level? (1) 1 (2) 2 (3) 3 (4) 4 3. Which sublevel contains a total of five orbitals? (1) s (2) p (3) d (4) f

Practice 1. What is the total number of electrons needed to complete fill all the orbitals in an atom's second principal energy level? (1) 16 (2) 2 (3) 8 (4) 4 2. What is the total number of sublevels in the fourth principal energy level? (1) 1 (2) 2 (3) 3 (4) 4 3. Which sublevel contains a total of five orbitals? (1) s (2) p (3) d (4) f

Practice 4. What is the maximum number of electrons that can occupy the fourth principal energy level of an atom? (1) 6 (2) 8 (3) 18 (4) 32 5. Which of the following sublevels has the highest energy? (1) 2 p (2) 3 p (3) 2 s (4) 3 s 6. What is the maximum number of electrons in an orbital of any atom? (1) 1 (2) 2 (3) 6 (4) 10

Practice 4. What is the maximum number of electrons that can occupy the fourth principal energy level of an atom? (1) 6 (2) 8 (3) 18 (4) 32 5. Which of the following sublevels has the highest energy? (1) 2 p (2) 3 p (3) 2 s (4) 3 s 3. What is the maximum number of electrons in an orbital of any atom? (1) 1 (2) 2 (3) 6 (4) 10

Practice 1. 2. 3. 4. 1 s 2 2 s 22 p 6 3 s 23 p 63 d 104 s 24 p 5 In this electron configuration, what do the coefficients represent? Letters? Exponents? How many energy levels are shown? What is the atomic number of this element? What would this electron configuration look like in the excited state?

Answers 1 s 2 2 s 22 p 6 3 s 23 p 63 d 104 s 24 p 5 1. Coefficients represent principal energy levels 1. Letters represent sublevels 2. Exponents represent number of electrons 2. Four energy levels are shown 3. Atomic Number for this element is 35 (Bromine) 4. 1 s 2 2 s 22 p 6 3 s 23 p 63 d 104 s 24 p 4 4 d 1

g. Werner Heisenberg Uncertainty Principle: