Chapter 2 Atoms, Molecules and Ions

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Chapter 2 Atoms, Molecules and Ions
Atomic Force Microscope
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Atoms and Molecules

• 18 ml of H2O ?6.02 x 1023 molecules of H2O
• If one H2O was a marshmellow, this would cover
  the US 600 miles deep
• There are more atoms in you than cells in all
  animals since the beginning of time
• You are full of these tiny bits and they are
  involved in everything you do
• Can we see atoms?? If so, how?

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The Idea of Models in Science

• Model Activity
• The word model has many meanings in the English
  language. What are some of them?
• What is the purpose of a model?
• What makes a good model?
• Give one specific example of a model to support
  your thinking.
• Be prepared to share!!

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Atomic Theory of Matter John Dalton (1766-1844)

• Each element is composed of atoms
• All atoms of an element are identical
• In chemical reactions, the atoms are not changed
• Compounds are formed when atoms of more than one
  element combine

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Law of Conservation of Mass
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Law of Conservation of Mass
The total mass of the reactants in any chemical
reaction is exactly equal to the total mass of
the products
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Conceptual Question
Which of the following product mixtures (b-d)
is consistent with the law of conservation of
mass?
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Law of Definite Proportions

• Law of Definite Proportions
• For every pure compound the mass ratios of its
• constituent elements are constant
• (water is always H2O)

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Law of Multiple Proportions
Elements can combine in different ways to form
different substances.
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The Structure of Atoms

• Group Activity Draw a representation of an atom
• What are the parts of an atom?
• How are the parts arranged?
• Be creative!

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Atomic Structure

• History How did scientists learn about atomic
  structure?
• What experiments lead to our current
  understanding of atomic structure?
• Lets look at electrons first!

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Thomsons Cathode Ray Tubes and Atomic Structure
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Millikan Oil Drop Experiment and Atomic Structure

In 1909 Robert Millikan succeeded in determining
the charge of an electron, which allowed him to
calculate the mass of an electron Electron mass
9.10 x 10-28 g
Oil-drop Animation
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Atomic Structure

• Why dont atoms fly a part?
• Where are the subatomic particles located?

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Plum Pudding Model

• From the separation of radiation we conclude that
  the atom consists of neutral, positively, and
  negatively charged entities.
• Thomson assumed all these charged species were
  found in a sphere.

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Rutherfords Experiment
Rutherfords Animation
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The Nuclear Atom
Rutherford modified Thomsons model by assuming
the atom is spherical but the positive charge
must be located at the center, with a diffuse
negative charge surrounding it.
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Basic Atomic Structure
1840 x mass of e-
Neutrons
-neutral charge
-Mass 1.67493 x 10-24 g
mass of proton
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Atomic Structure
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Mass and Atomic Numbers

• Mass number the sum of the number of protons
  plus neutrons in the nucleus of an atom
• Atomic number the number of protons in the
  nucleus of an atom

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Atomic Number (Z)
Z ?
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Mass Number and Isotopes
Mass (A) Protons neutrons
A ?
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Isotopes

• Isotopes atoms with the same number of protons
  but a different number of neutrons

• carbon-12 has 6 protons and 6 neutrons
• carbon-13 has 6 protons and 7 neutrons
• carbon-14 has 6 protons and 8 neutrons

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Carbon Dating
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Representing Atomic and Mass Number
Lets Practice See Handout
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Atomic Mass

• Atomic mass the weighted average of the masses
  in amu of the isotopes of an element found in
  nature

• example chlorine is 75.77 chlorine-35
• and 24.23 chlorine-37

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Compounds

• To form water, there must always be twice as much
  hydrogen gas as oxygen gas.
• Pure substances that cannot be decomposed are
  elements.

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Mixtures

• Heterogeneous mixtures are not uniform throughout
• Oil and water
• Sulfur and iron
• Homogeneous mixtures are uniform throughout
• called solutions
• Salt water

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Conceptual Question
Which drawing represents a collection of Sulfur
dioxide Molecules? Which drawing represents a
Mixture?
Red O Yellow S
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Molecules

• Molecules are assemblies of two or more atoms
  bonded together by covalent bonds
• Each molecule has a chemical formula
• which atoms are found in the molecule
• what proportion

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Representing Molecules
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Diatomic Molecules

• Molecules that contain two atoms bonded together
  
• are called diatomic molecules.
• Some elements exist as diatomic molecules! Know
• these!!

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Conceptual Question
Give the molecular formula for each of the
following. Red O Gray C Blue N White H
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Ions

• Cation
• Positively charged ion
• When an atom or molecule loses electrons, it
  becomes positively charged

cation
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• Anion
• negatively charged ion
• When an atom or molecule gains electrons, it
  becomes negatively charged

anion
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Predicting Ionic Charge
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Ionic Compounds (Ionic Bonding)

• The majority of chemistry involves the transfer
  of electrons between species.
• Ionic bonds exist between a metal and a non-metal
• Example

Loses an e-
The Na and Cl- ions are attracted to form an
ionic NaCl lattice
Na
Na
Gains an e-
Cl
Cl-
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3-D NaCl
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Predicting Ionic Compounds

• What is the formula for an ionic compound
  composed of Na and O?
• What is the formula for and ionic compound
  composed of Ca and P?

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Nomenclature

• Learn Polyatomic Ions!
• Sample Problems
• Practice, Practice, Practice!!!

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Nomenclature Problems

• Write the formula
• Sulfur difluoride
• Lithium nitride
• Chromium (II) carbonate
• Tin (II) fluoride
• Mercury (I) chloride
• Sodium hydride
• Cobalt (III) nitrate

SF2
Li3N
CrCO3
SnF2
HgCl
NaH
Co(NO3)3
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Nomenclature

• Name each of these Compounds
• CsF
• SiF4
• V2O5
• ZnS
• FeSO4
• HNO3
• HNO2
• N2F4
• Ru(NO3)3

Cesium fluoride
Silicon tetrafluoride
Vanadium (V) pentoxide
Zinc(II) sulfide
Iron (II) sulfate
Nitric acid
Nitrous acid
Dinitrogen tetrafluoride
Ruthenium(III) Nitrate