Unit 1 Atomic Theory

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Asher Mosley
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1 Unit 1 Atomic Theory 1.0 You are expected to be already familiar with. Ionic nomenclature (binary, polyatomic, multivalency) Covalent nomenclature Writing chemical formulas for ionic and covalent compounds 1 Gu 2017

ways to describe atoms: Example: Write the symbol for a neutral Fluorine 19 atom Write the symbol for a Barium

2 1.1 Nuclear Notation (WB P.60, 63 64, ) Atomic number: equals to Mass number: Atomic mass: Isotope: Nuclear Notation: There are two ways to describe atoms: Example: Write the symbol for a neutral Fluorine 19 atom Write the symbol for a Barium 137 atom that has had 2 electrons removed Write the symbol for neutral Carbon 13 Symbol # protons # electrons # neutrons Atomic number Atomic mass Charge Gu 2017

3 1.2 Bohr Model (WB P.61, 63 64) Practice: Draw the Bohr diagram for the following atoms: a) Na b) N c) N ion d) Mg ion e) Lithium fluoride f) CH 4 g) NH 3 h) oxygen gas 3 Gu 2017

4 1.3 Lewis Structures (WB P.62 64) Drawing atoms element symbol represents nucleus + core electrons dots represent valence electrons dots are drawn in pairs as a reminder that electrons are paired in orbitals Example: Draw the Lewis structure for the following atoms Li Be B C N O F Ne Drawing Covalent Molecules octet rule predicts bonding arrangement: bonded non metallic atoms have 8 electrons in their outermost energy levels (exception can only have 2) molecules tend to be symmetrical covalent and polar covalent bonds are represented by pairs of dots between two atoms number of dots you draw must equal the sum of the valence electrons of all atoms in the molecule pairs of electrons forming covalent bonds can be represented by a line Example: Draw the Lewis structure for the following molecules a) CCl 4 b) NH 3 c) C 2 H 6 d) CO 2 4 Gu 2017

5 Example: Draw the Lewis structure of HCN Example: Draw the Lewis structure of calcium chloride. 1.4 Shrӧdinger and Heisenberg Atomic Model (FS) Bohr s model of the atom was famous because it could explain the. Activity: A spectroscope is a tool that separates light into its individual components. Use a spectroscope to see what is in white light from the sun, versus what is in light produced by energized elements. Light Source What I Observe sunlight 5 Gu 2017

6 The spectrum of white light is continuous: it shows all the colours of the rainbow. The spectrum of energized gas is discontinuous, it shows discrete bands. Summarize how the bright line spectrum supports Bohr s atomic model: Bohr s model is significantly wrong in two ways: Gu 2017

7 Schrödinger s model describes the of where to find an electron in an atom Orbital: the around a nucleus where an electron can be found orbitals are described by quantum numbers. Quantum Number 1 st or principal quantum number (n) 2 nd quantum number (l): 3 rd quantum number (m l ): 4 th quantum number (m s ): Symbols What does it Mean? 7 Gu 2017

8 Each energy level has a specific set of orbitals and each one represents where a maximum of electrons can be found. Orbital Type Begins at n= # of Orbitals in a Subshell s 1 p 2 d 3 f 4 Maximum # of Electrons in a Subshell Instead of representing atoms with the Bohr diagram, we can represent them with the more accurate energy level diagram. Rules to follow when filling orbitals: 1. Fill orbitals from lowest to highest energy (Aufbau Principle) 2. Place one electron in each orbital of a sub shell 3. When each orbital of a sub shell has one electron, go back and pair the electrons (Hund s Rule) 4. If two electrons are in an orbital, they must have opposite spin (Pauli Exclusion Principle) These rules ensure that the electron configuration gives the lowest energy, most stable atom by reducing. 8 Gu 2017

9 Example: Fill the orbitals with He electrons Example: Fill the orbitals with Na electrons Example: Fill the orbitals with Al electrons How many electrons are in He? How many electrons are in Na? How many electrons are in Al? How many shells have electrons? How many sub shells have electrons? How many orbitals have a single electron? How many orbitals have paired electrons? How many shells have electrons? How many sub shells have electrons? How many orbitals have a single electron? How many orbitals have paired electrons? How many shells have electrons? How many sub shells have electrons? How many orbitals have a single electron? How many orbitals have paired electrons? What is the electron configuration? What is the electron configuration? What is the electron configuration? 9 Gu 2017

The periodic table is a tool to obtain the electron configuration of elements quickly. Simply write the orbitals as they appear on the period table above, going left to right, row by row.

10 The periodic table is a tool to obtain the electron configuration of elements quickly. Simply write the orbitals as they appear on the period table above, going left to right, row by row. Each element space counts as one electron. Example: Write the electron configuration for the following atoms. a) Ar b) Ga c) Ag d) *Rn Core notation: It sure is annoying to write super long electron configurations! the shortcut: look for the closest previous noble gas element to the element you are writing the configuration for and start there useful because we aren t interested in the core electrons anyways (they don t participate in chemical reactions) to write core notation for a noble gas, use the previous noble gas Example: Write the electron configuration for Ga using core notation. Closest previous noble gas element: Core notation: 10 Gu 2017

11 Practice: Write the electron configuration in core notation for the following elements. a) Zn b) K c) Kr 1.5 Atomic Trends: Atomic Radii (FS) Ponder This: What do you suppose happens to the size of an atom as you a) Move from left to right across the periodic table? b) Move down a family on the periodic table? c) Add electrons to create an anion? d) Remove electrons to create a cation? 11 Gu 2017

12 Consider This: Which has a larger effect on atomic radii, a change in the number of protons, or a change in the number of electrons? Example: Consider the following pairs of atoms. Which atom has the larger atomic radius? a) O and O 2 b) Ca and Ca Gu 2017

1.6 Atomic Trends: Electronegativity (FS) Electronegativity: an atom s ability to attract electrons towards itself Ponder This: How does electronegativity change as we a) Move left to right across

13 1.6 Atomic Trends: Electronegativity (FS) Electronegativity: an atom s ability to attract electrons towards itself Ponder This: How does electronegativity change as we a) Move left to right across the periodic table? b) Move down a family on the periodic table? Apply Knowledge: Use what you have learned to explain the reactivity trend of the alkali metals. The reaction occurs when the metal atom donates its valence electrons to water. Summary of Trends 13 Gu 2017

14 1.7 Valence Shell Electron Repulsion Theory (VSEPR) (FS) Visit MolView at molview.org and use the molecular model sets to complete the following. 1. On the left panel, use MolView tools to draw the Lewis structures of the molecules below. 2. Click 2D to 3D and MolView will generate the 3D structure that you can rotate around. Sketch it. Molecule Lewis Structure (2D) Sketch the VSEPR Structure (3D) CO 2 CH 2 O H 2 O NH 3 CH 4 CH 2 F 2 14 Gu 2017

15 Think: Why are the shapes the way they are? What determines what shape molecules take? Summary # Repelling Items Atoms Bonded to Central Atom Lone Pairs of Electrons Bonded to Central Atom Name Shape Example (Lewis Structure) VSEPR Structure Linear Trigonal planar 4 0 Tetrahedral Trigonal pyramidal 2 2 Bent or Angular 15 Gu 2017

16 1.8 What are Intermolecular Forces? (FS) Ponder This: Why is water in liquid form in the room, whereas oxygen gas is not? Draw a picture of water and oxygen gas at the molecular level in the room to help you think it through. Water Oxygen Gas Visit MolView. 1. Model > Jmol 2. Draw oxygen gas in the left panel then hit 2D to 3D 3. Jmol > MEP Surface lucent then make some observations of the result in the right panel 4. Hit the trashcan button to clear the left field 5. Repeat the above for water 16 Gu 2017

17 Critical Thinking: What do you suppose the different colours mean? Using MolView and the table of electronegativities, can you come up with an explanation for why water molecules stick together, but oxygen ones don t? 1.9 Intermolecular Forces: Dipole Dipole (FS) In order for molecules to be able to form dipole dipole interactions, the molecule must be polar so that a side of one molecule is attracted to the + side of another. Practice: Which of the following molecules are polar? Which can form dipole dipole interactions? a) CH 4 b) H 2 O c) NH 3 17 Gu 2017

18 How molecules arrange themselves when there are dipole dipole interactions: 1.10 Intermolecular Forces: Hydrogen Bonds (FS) A hydrogen bond is essentially a dipole dipole interaction, but occurs at a much stronger level. It occurs when a molecule contains an H atom bonded to an especially electronegative atom (,, ) Ponder This: Why are H bonds so strong? Practice: Which of the following molecules can hydrogen bond? HCN H 2 O H 2 S HF 18 Gu 2017

19 Example: Which would you expect to have a higher melting point, CCl 4 or CHCl 3? 19 Gu 2017

Chapter 10: Modern Atomic Theory and the Periodic Table. How does atomic structure relate to the periodic table? 10.1 Electromagnetic Radiation

Chapter 10: Modern Atomic Theory and the Periodic Table How does atomic structure relate to the periodic table? 10.1 Electromagnetic Radiation Electromagnetic (EM) radiation is a form of energy that exhibits