Atoms and Atomic Theory

1
Atoms and Atomic Theory

• Overview
• Atomic Structure (protons, electrons, neutrons)
• Isotopes
• Electron shells, energy levels
• Periodic table

2
Characteristics of Atoms

• Atoms possess mass
• Atoms contain positive nuclei
• Atoms contain electrons
• Atoms occupy volume
• Atoms have various properties
• Atoms attract one another
• Atoms can combine with one another to form
  molecules

3
Atomic Structure

• Atom
• Nucleus protons () and neutrons (0)
• Electrons ()
• Protons
• All atoms of same element have same number of
  protons
• Number of protons in the nucleus defines the
  element
• Atomic number (A) nuclear charge

4
Atomic Number
Symbol and atomic number signify same thing.
5
Mass Number

• Protons and neutrons in the nucleus
• Sum of p n mass number (Z)
• Number of neutrons can vary within a given
  element
• Variations are called isotopes

C
12C 6 p 6 n
13C 6 p 7 n
14C 6 p 8 n
11C 6 p 5 n
6
Problem 1

• Complete the following table of isotopes

7
Problem 1

• Complete the following table of isotopes

13
13
13
26
86
86 37 49
37
Rb
17 18 35
35Cl
17
8
Atomic Weight

• Weighted average of all naturally occurring
  isotopes
• Mass number n p, whole number, particular
  isotope
• Atomic weight, decimal,
• combination of all isotopes naturally found
• experimental number

9
Atomic Weight
7
N
99.63 14N 14.00307 amu 0.37 15N 15.00011
amu
14.01
0.9963(14.00307) 0.0037(15.00011) 14.0067
14.01 amu
10
Problem 2

• Magnesium has three naturally occurring isotopes
  with the following masses and abundances
• 23.99 amu 78.99
• 24.99 amu 10.00
• 25.98 amu 11.01
• Calculate the atomic weight of magnesium.

11
Problem 2

• (23.99 amu)(0.7899)
• (24.99 amu)(0.1000)
• (25.98 amu)(0.1101)
• 24.31 amu
• amu correlation to grams

12
The Mole

• Chemists use moles as a way to count atoms
  which are so tiny
• Industry analogs
• Atomic weight (molar mass) connects gram amount
  to atomic mass units (which is related to
  proton/neutron mass)
• Avogadros number 6.02 x 1023
• Numerically correlated
• 24.31amu ? 24.31g/mol
• Know grams ? know atoms

13
Periodic Table

• Electronic structure
• Bohr Model flawed but functional
• Electronic energy levels
• How do scientists (chemists) use models?

14
Models

• Useful to simplify complex or confusing systems
• Understand behavior of aspects of universe
• Limitations, oversimplification
• Atomic models vs. atomic theory

15
Law versus Theory

• Discuss each of the following terms (as is
  typically done in society). Give an example of
  each.
• Law
• Theory

16
Scientific Perspective

• Law generalization based upon observation
  (measurement) to which there are no exceptions
• Law of gravity
• Gas Laws
• Newtons Laws of Motion
• No theoretical framework, empirically based

17
Scientific Perspective

• Theory model that describes underlying cause of
  physical behavior (law)
• Predictive
• Goes beyond laws from which formulated
• Testable (experiment)
• Examples
• Kinetic Molecular Theory
• Atomic Theory
• How do models fit?

18
Atomic Theory

• Atomic Theory and Quantum Mechanical model of the
  atom developed through interaction of matter with
  light (electromagnetic radiation)

19
Electromagnetic Spectrum
20
Visible Spectrum
21
Bohr Model

• Line spectra
• Light through a prism ? continuous spectrum

Ordinary white light
22
Bohr Model

• Line spectra
• Light from gas-discharge tube
• through a prism ? line spectrum

H2 discharge tube
23
Line Spectra (emission)

• White light

H
He
Ne
24
Line Spectra (absorption)
Gas-filled tube
Light source
25
Electronic Energy Levels

• n electronic energy level
• n 1 2 electrons (H, He)
• n 2 8 electrons (Li ? Ne)

NOT orbits, energy levels
2e
8e
26
Electronic Energy Levels

• n main electronic energy level
• Sublevels s, p, d, f
• n 1, s only 2 electrons maximum
• n 2, s p 2 electrons in s, 6 electrons in p
• n 3, s, p d 2 electrons in s, 6 electrons in
  p, 10 electrons in d
• n 4, s, p, d, f s-2, p-6. d-10, f has 14
• Filling order is unexpected

27
Electronic Energy Levels

• Filling order

1s 2s 2p 3s 3p 3d 4s 4p 4d 4f 5s 5p 5d 5f 5g 6s 6p
6d 7s 7p
28
Electronic Energy Levels
Periodic table can be derived from energy levels

• n electronic energy level
• Sublevels s, p, d, f
• n 3 s and p fill first 8 electrons (Na ? Ar)
• n 4
• 4s fills before 3d (K, Ca)
• but 3d fills before 4p (Sc ? Zn)
• 4p (Ga ? Kr)

2e
8e
8e
29
Periodic Table (p. 293)
n 1
n 2
n 3
n 4
30
Electronic Energy Levels

• Inner shell versus outer shell electrons
• Inner shell not involved in formation of
  chemical bonds
• Outer shell involved in formation of chemical
  bonds
• Outer shell ? valence electrons

31
Valence Electrons
n 1
n 2
n 3
32
Problem 3

• Draw the electron configurations for each of the
  following elements according to the Bohr model.
  Indicate which electrons are valence electrons.
• S
• Na
• C

33
Problem 3

• a) S, 16 electrons

34
Problem 3

• a) S, 16 electrons

35
Problem 3

• b) Na, 11 electrons

36
Problem 3

• b) Na, 11 electrons

37
Problem 3

• c) C, 6 electrons

38
Problem 3

• c) C, 6 electrons

39
Probability Density Functions(Beyond the Bohr
Model)
Link to Ron Rineharts page

• ? energy
• ?2 probability density function
• s, p, d, f, g
• 1s

3s
2s
Node area of 0 electron density
40
Probability Density Functions

• 2p

Node area of 0 electron density
nodes
Link to Ron Rineharts page
41
Ions and Ionic Compounds

• Ion gained or lost electrons to be a charged
  species (NEVER PROTONS!)
• Cl e ? Cl

anion -chg
17 p 18 e
17 p 17 e
Na ? Na e
cation chg
Na with Cl NaCl
11 p 11 e
11 p 10 e
42
Problem 4

• Complete the following table of ions

43
Problem 4

• Complete the following table of ions

13
10
35
36
2
S
2
Mg