Unit 1 Atomic Theory

1 Gu 2017

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

2 Gu 2017

1.1 ‐ Nuclear Notation (WB P.60, 63‐64, 123‐124)

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

56 54 83

18 16 32.1

19 39.1 1+

92 241 0

3 Gu 2017

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) CH4

g) NH3

h) oxygen gas

4 Gu 2017

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) CCl4 b) NH3

c) C2H6 d) CO2

5 Gu 2017

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

6 Gu 2017

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:

1. _____________________________________________________________________________________

2. _____________________________________________________________________________________

7 Gu 2017

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 Symbols What does it Mean?

1st or principal quantum number (n)

2nd quantum number (l):

3rd quantum number (ml):

4th quantum number (ms):

8 Gu 2017

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 Maximum # of Electrons

in a Subshell

s 1

p 2

d 3

f 4

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

__________________________________________________.

9 Gu 2017

Example: Fill the orbitals with He electrons

How many electrons are in He? ______

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?

Example: Fill the orbitals with Na electrons

How many electrons are in Na? ______






Example: Fill the orbitals with Al electrons

How many electrons are in Al? ______






10 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. 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: _______________________

11 Gu 2017

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? __________________________

12 Gu 2017

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 O2‐

b) Ca and Ca2+

13 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 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

14 Gu 2017

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)

CO2

CH2O

H2O

NH3

CH4

CH2F2

15 Gu 2017

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

2 2 0 Linear

3 3 0 Trigonal planar

4

4 0 Tetrahedral

3 1 Trigonal pyramidal

2 2 Bent or Angular

16 Gu 2017

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

17 Gu 2017

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) CH4

b) H2O

c) NH3

18 Gu 2017

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 H2O H2S HF

19 Gu 2017

Example: Which would you expect to have a higher melting point, CCl4 or CHCl3?

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Unit 1 Atomic Theory