Physical Science Unit 3: Te Bonding Unit
Lewis Dot Structures (aka Electron Dot Diagrams or EDD)
Ions and Electron Dot Diagrams
Ionic Bonds and Compounds
VSEPR
Polar Covalent Bonds
Molecular Attractions
Metallic Bonds
Physical Science Unit 3: Te Bonding Unit
Lewis Dot Structures (aka Electron Dot Diagrams or EDD)
Ions and Electron Dot Diagrams
Ionic Bonds and Compounds
VSEPR
Polar Covalent Bonds
Molecular Attractions
Metallic Bonds
Amedeo Avogadro was one of the most brilliant scientists of the 19th century. He was born in Italy on August 9, 1776 and died on his 80th birthday on August 9, 1856. Avogadro studied the behavior of gasses and realized that the properties of a gas such as volume and pressure at a known temperature depended on the number of gas particles, not the type of gas molecule.
Avogadro proposed that the weight of a sample of gas at a known volume, pressure and temperature was related to the weight of the individual molecules of the gas.
In 1909, a French Physicist named Jean Perrin, proposed that a scaling factor could be found relating the weight of 1 molecule of a gas to its volume and suggested this scaling factor be named after his predecessor, Avogadro.
The value of this scaling factor could not be measured untill the 1950’s.
In the 1950’s, methods became available which allowed scientists to obtain extremely pure samples of Carbon-12. Using X-ray diffraction, exact measurements were made of the spacing of Carbon atoms in Graphite.
artists rendering of graphite crystal
X-Ray Diffraction pattern from single crystal graphite. The arrangement of the bright spots shows the hexagonal structure of the graphite crystal. The spacing of the bright spots can be related back to the spacing between individual atoms.
In the 1990’s new techniques such scanning-tunneling microscopy were developed which allow us to directly image the atoms on the surface of a crystal.
Notice the hexagonal arrangement of the Carbon atoms in graphite.
Knowing that Carbon 12 has 6 protons and 6 neutrons for a total of 12 Atomic Mass Units, scientists set about to make an ultra pure sample of Carbon-12, they measured out exactly 12.000…. grams and grew a single crystal of graphite. By measuring the volume of the crystal and knowing the exact spacing of the carbon atoms (from x-ray diffraction), they were able to determine the exact number of Carbon atoms in 12 grams of graphite. This number was calculated to be:
N = 6.022 x 10^23 and was the first accurate measurement of Avogadro’s number.
Avogadro’s number turned out to be a very useful number. The name mole (or mol) is used to denote the 1 molecular weight of a substance. The names mol and mole are used interchangeably.
For example, 1 mol of Carbon contains 6.022 x 10^23 atoms of Carbon and weighs 12 grams. 1 mol of water weighs 18 grams and contains 6.022 x 10^23 molecules of H2O.
If you know the weight of a sample and its chemical composition, you can find the number of moles in a sample.
Simply total up the elements in a compound, multiply each by their atomic weight to get the molecular weight of the compound.
Next divide the weight of the sample by the molecular weight of the molecule.
example: 18 grams of H2O is 1 mole
example 36 grams of H2O is 2 moles
(notice the relation between MOLEcular weight and the unit MOLE)
Find the weight of 1 mole of each of these chemicals.
Hint: Total up the molecular weights of each component.
H2
He
12C
H2O
Al2O3
Find the weight of 2 moles of each of these chemicals.
Hint: Total up the molecular weights of each component, multiply by 2.
H2
He
12C
H2O
Al2O3
This post contains a PHET model of molecular bond polarities including dipole, charge density and electronegativity. WE discuss diploes, dipole moments, hydrogen bonds, and the effect of dipole moment on boiling point. Continue reading Molecular Polarity and Boiling Points
This post is an introduction to VSEPR theory and provides an overview up to 4 domains.
Learning objective:understand basic molecular geometries and the relation of these shapes to Lewis Dot Structure. Continue reading The VSEPR Theory
Linus Pauling characterized an atom’s ability to pull an electron from another atom in terms of an “electronegativity” scale. He set this relative scale to 1.0 for Lithium in Group I up to 4.0 for Florine in Group VII. Continue reading Electronegativity
This post shows the relation of atoms to their charge states and the way in which an atoms size changes when it become ionized.
This post contains basic definitions, a chart of atomic and ionic radii, and a worksheet. Continue reading Ions and Ionic Radii
There are 4 basic types of chemical bonds. These are; ionic, covalent, metallic and hydrogen bonds. Each has specific properties and involves specific “groups” of elements. The type of bond between 2 atoms depends on whether they both give or take electrons or if one atom gives electrons while the other takes electrons.
Continue reading 3 (+1) Types of Chemical Bonds