Download Chapter 4 Notes

Chapter 4 Notes
CHAPTER 4
Atomic Structure
4.1 Atoms
• Democritus first suggested the idea of atoms
• Indivisible & Indestructible
• 460 B.C. – 370 B.C.
Dalton’s Atomic Theory
1. All elements are composed of submicroscopic indivisible particles called atoms
• Every sodium atom in the universe is the same…
• Every magnesium atom in the universe is thesame…
2. Atoms of the same element are identical. The atoms of any one element are different from those of any other element.
3. Atoms of different elements can physically mix together or can chemically combine with one another in simple whole­number ratios to form compounds.
1
Chapter 4 Notes
4. Chemical reactions occur when atoms are separated, joined, or rearranged. However, atoms of one element are never changed into atoms of another element as a result of a chemical reaction.
Atom
• The smallest particle of an element that retains the properties of that element.
• Have a size ranging from:
(5 x 10­11 m) – (2 x 10­10 m)
• Protons
• Electrons
• Neutrons
Parts of an atom
Do not have unique properties!
Scanning Tunneling Microscope
• The protons, electrons, and neutrons in one atom are the same as in any other atom.
• The number of protons, electrons, and neutrons is what makes each atom unique.
Atoms of Copper and Iron
Visualizes individual atoms and makes it possible to see them as a 3D image on a monitor.
2
Chapter 4 Notes
4.2 The Structure of the Nuclear Atom
Atoms can be broken down into more fundamental particles. In Chemistry we will learn about protons, electrons, and neutrons.
Electrons
• Negatively charged subatomic particle
• 1/1840 the mass of 1 proton
• Millikan: discovered that an electron carries one unit of negative charge
Electrons being repelled by magnet...
Electrons
• Discovered by Thomson using the Cathode ray tube experiment
Protons
• Positively charged subatomic particles
• Carries a one positive charge
3
Chapter 4 Notes
Neutrons
• Subatomic particle with no charge
• Discovered by Chadwick
• Mass equals that of a proton
The Atomic Nucleus
• The central core of an atom, composed of protons and neutrons
• Responsible for almost all the mass of an atom
Protons
Neutrons
• The nucleus has a positive charge, and it occupies a very small part of the volume of an atom.
Nucleus & Energy Levels
Nucleus
Energy Level
•
•
•
•
•
99.99% of the mass of an atom
Contains Protons and Neutrons
Overall positive charge
Very little volume of the atom
Proton Number defines the atom
Proton
Neutron
•
•
•
•
•
Contains only electrons
0% of the mass of an atom
Overall negative charge
Most of the volume of an atom
Determines the properties of an atom
4
Chapter 4 Notes
• The negatively charged electrons in an atom occupy most of the volume of the atom.
The Rutherford atomic model is known as the nuclear atom.
• The protons are located in the nucleus
• The electrons are around the nucleus
• The electrons occupy most of the volume of the atom
4.3 Atomic Number
Electrons: determine the properties of every atoms.
Protons: define what each atoms is.
• Differences among elements result from differences in the numbers of protons in their atoms.
• How are atoms of one element different from those of another element?
Atomic Number
• The number of protons in the nucleus of the atom of that element.
• Example: The atomic number of Oxygen is 8
5
Chapter 4 Notes
• Remember that atoms are electrically neutral. Thus the number of protons in the nucleus of an atom must equal the number of electrons around its nucleus.
• The periodic table gives the atomic number of each element.
Nucleons: protons & neutrons Mass Number
because they are in the nucleus.
s, p, d, f: sub­shells where electrons are found
• You can determine the composition of an atom of any element from its atomic number and its mass number.
Example:
• Beryllium: atomic number 4
mass number 9
# p = 4 # e = 4 # n = 5
• Mass number is the total number of protons and neutrons in the nucleus of an atom.
Aluminum ­ Al Palladium ­ Pd Atomic Number = Atomic Number = Mass Number = Mass Number = Proton Number = Proton Number = Electron Number = Electron Number= Neutron Number= Neutron Number =
Mass of Electrons =
Mass of Electrons = 6
Chapter 4 Notes
Shorthand Notation
• The atomic number is written as a subscript. The mass number is written as a superscript.
• Example: Be
9
4
Al
27
13
What can change in an atom?
• Protons: can never change
• Electrons: if the number changes, then an ion forms.
• Neutrons: if the number changes, then an isotope forms.
Al
If the proton number changes….
If the neutron number changes….
• Then the entire atom changes.
• If oxygen gains a proton, it becomes fluorine.
• If oxygen loses a proton, it becomes nitrogen.
• Then a different version of the same atom forms.
• Oxygen­16 has 8 neutrons.
• Oxygen­17 has 9 neutrons.
• Oxygen­18 has 10 neutrons
Isotopes of Elements
• The nuclei of the atoms of a given element must all contain the same number of protons, but the number of neutrons may vary.
Isotopes vs. Allotropes
Isotopes: atoms of the same element with different numbers of neutrons
Allotropes: different forms of an element, usually when the same atoms are joined as compound.
The way atoms are arranged
Carbon exhibits both…
• Isotopes: Carbon­12, Carbon­13, Carbon­14
• Allotropes: graphite, diamond, and fullerenes
7
Chapter 4 Notes
Isotopes
• Atoms that have the same number of protons but different numbers of neutrons
Hydrogen
• Hydrogen has three known isotopes:
• Hydrogen­1 (one proton, no neutrons)
• Protium
• Because isotopes of an element have different numbers of neutrons, they also have different mass numbers.
• Isotopes are chemically alike because they have identical numbers of protons and electrons.
Atomic Mass
• The masses of atoms are too small to work with so we use Carbon as the comparative atom.
• Deuterium
• An Atomic Mass Unit (amu) is defined as one­twelfth the mass of a carbon­12 atom.
• Tritium
• Proton=1­amu, Neutron=1­amu, electrons=0­amu
• Hydrogen­2 (one proton, one neutron)
• Hydrogen­3 (one proton, two neutrons)
Atomic Mass
• The atomic mass of an element is a weighted average mass of the atoms in a naturally occurring sample of the element.
Atomic Mass vs. Mass Number
• There is a difference!!
• Average Atomic Mass is the mass on the periodic Table
• Mass Number is the actual mass of a given atom.
8
Chapter 4 Notes
• The weighted average mass reflects both the mass and the relative abundance of the isotopes as they occur in nature.
Chlorine­35
Isotopes
Chlorine­36
(54%)
Relative Abundance
(46%)
Calculating the Atomic Mass of an Element
You must know:
• The number of stable isotopes of that element
• The mass of each isotope
• The natural percent abundance of each isotope
Average Atomic Mass of Carbon
• Carbon­12: 12 x 0.917 = 11.004
• Carbon­13: 13 x 0.069 = 0.897
• Carbon­14: 14 x 0.014 = 0.196
• Add together products together • 12.097 (Avg. atomic mass)
Determining Average Atomic Mass
of a "New" element
Isotope Percentage Fontainium ­ 41 87.3 % Fontainium ­ 43 9.8 % Fontainium ­ 44 2.9 % Write the following in shorthand notation...
Oxygen ­ 15
Isotope or Common
Oxygen ­ 16
Isotope or Common
Oxygen ­ 17
Isotope or Common
Show Work Average Atomic Mass 9
Chapter 4 Notes
States of Atoms
Energy Levels of an Atom
Ground State: electrons are at their lowest possible energy level
Excited State: electrons have absorbed Nucleus energy and jumped to a higher energy level
If an atom gains electrons, then….
• Then a negatively charged version of the same atom forms.
• If oxygen gains 2 electrons, it has 10 electrons and 8 protons.
• It now has a “2­” charge
If an atom loses electrons, then….
• Then a positively charged version of the same atom forms.
• If calcium lost 2 electrons, it has 18 electrons and 20 protons.
• It now has a “2+” charge.
10
Chapter 4 Notes
Cation vs. Anion
Examples of Ions
Sulfur
Neutral Version
Gain or Loss
Chlorine
P=16
P=12
P=3
P=17
E=16
E=12
E=3
E=17
Gain 2 electrons
New electron number
Lithium
Magnesium
E=18
S2­
Charge
Lose 1 electron
Lose 2 electrons
Atomic
Number
Protons
Gain 1 electron
E=10
E=2
E=18
2+
Mg Li +
Cl ­
Electrons
• Cation: Positive Ion
More protons than electrons
I am “Positive” I love my Cat.
• Anion: Negative Ion
More electrons than protons
Mass
Number
Neutrons
Al 3+
Atomic
Number
Al 3+
Protons
Electrons
Neutrons
Mass
Number
13
13
10
14
27
Hydrogen – 1
Hydrogen – 1
1
1
1
0
1
Hydrogen – 3
Hydrogen – 3
1
1
1
2
3
1
1
0
0
1
8
8
16
H +
H +
Oxygen – 16
Oxygen – 16
8
8
Oxygen – 14
Oxygen – 14
O 2­
8
8
8
6
14
O 2­
8
8
10
8
16
Element
Atomic
#
Neutral = Periodic Table Version
Element
Atomic #
Protons
Number
Electron
Number
Neutron
Number
Mass
Number
Ion, Isotope, or Neutral
Protons
Number
Electron Neutron
Number Number
Ion, Isotope, or Mass
Number
Neutral
Fluorine
9
9
9
10
19
Fluorine
9
9
9
10
19
Neutral &
Common
Chromium
24
24
24
32
56
Chromium
24
24
24
32
56
Isotope
Calcium
20
20
18
20
40
Calcium
20
20
18
20
40
Cation
Iodine
53
53
54
74
127
Iodine
53
53
54
74
127
Anion
Polonium
84
84
84
131
215
Polonium
84
84
84
131
215
Isotope
11
Chapter 4 Notes
The Periodic Table: A Preview
• The Periodic Table allows you to compare properties of one element
to another element
• Period
• Group
12