refers to whether a substance commonly exists as atoms, ions, or molecules, or formula unit.
pure covalent (non-polar), when electronegativity difference is zero. polar covalent is when the electronegativity difference is more than zero but less that 1.67.
The percentage of the total mass of a compound by an element is the
percentage of that element in the compound.
Empirical Formula Definition
Empirical Formula gives the lowest whole number ratio of the elements in a compound.
When empirical and molecular formulas are not the same, the molecular formula is
a simple multiple of the empirical formula. the empirical formula is the simplest form, because it's the LOWEST whole number ratio.
First Quantitative information about atomic masses came from the work of
Dalton, Gay-Lussac, Lavoisier, Avogadro, Berzelius.
By observing the proportion sin which elements combine to form various comounds, nineteenth- century chemists calculated
relative atomic masses.
The modern system of atomic masses, instituted in __, is based on ____ as the standard.
1961; Carbon twelve, ¹²C
¹²C is assigned an atomic mass of exactly ___
12 atomic mass units (amu), and the masses of all other atoms are given at this standard.
Process of Mass Spectrometer: Atoms or molecules are passed into a beam of ___, which knock electrons off the atoms or molecules being analyzed and change them into ____. An applied electric field then ___ these ions into a magnetic field.
high speed electrons; positive ions; accelerates.
Because an accelerating ion produces it own magnetic field, an interaction with the applied magnetic field occurs, which _____
tends to change the path of the ion.
Process for Mass Spectrometry:
Put a substance in, in the gas phase, and it is ionized. The deflection that the resulting ion exhibits as it is accelerated through a magnetic field can be used for its mass.
It is difficult to use Mass Spectrometry with large molecules because:
they are difficult to vaporize because they have high boiling points.They decompose! Example: Proteins!!!!
Process for Matrix Assisted Laser Desorption or "The Flying Elephant"
Large "target" molecule is embedded in matrix of smaller molecules. The matrix is then placed in the mass spectrometer and blasted with a laser beam, which causes its disintegration. This frees the large molecule, and it is then swept into the mass spectrometer.
Technique of Matrix Assisted Laser Desorption allows scientists to ____
determine the mass of huge molecules. The most they have done is 350,000 daltons.
Matrix Assisted Laser Desorption could be
a revolutionary development in the characterization of biomolecules. DNA one day.
Deflection in Mass Spectrometry
The most massive ions are deflected the smallest amount-which causes the ions to separate. So the smallest ions are deflected the most!
Average Atomic Mass of an element (Look at the math in the book)
the weighted average of the masses of all naturally occurring isotopes of an element
Mass spectrometer is also used to determine the ___. Besides for finding accurate mass values for individual atoms.
isotopic composition of a natural element.
Mole (book example...pg 83)
the number equal to the number of carbon atoms in exactly 12 grams of pure ¹²C...12.01gC = 6.02x10²³ (same number of atoms)
Elephant Tusks-Mass spectrometer
Scientists analyze the ivory for relative amounts of ¹²C, ¹³C, ¹⁴N, ¹⁵N, ⁸⁶Sr, ⁸⁷Sr to determine the diet of the elephant and its place of origin. Grasses and trees have slightly different ¹³C/¹²C ratios because they use different photosynthetic pathways. Trees use more steps, so they have a smaller ratio.
Results of elephant tusk experiments!
Scientists have reported being able to distinguish between elephants living only about 100m apart! Must have isotopes for ivory trade restrictions because isotopes prove origin! Save the elephants!
2 common ways for describing composition of a compound:
1. In terms of the numbers of its constituent atoms.
2. in therms of the percentages (by mass) of its elements.
Compound by comparing mass of element in one mole of compound to the total mass of 1 mole of compound and multiplying by 100. (DUH, sounds so complicated. )
Device For the formula of a compound? (Read this part in the book for further understanding and look at the diagram, page 93)
Take a weighted sample of the compound and decompose it into its component elements (or react it with oxygen to produce CO₂, H₂O, or N₂--analyzing for Carbon and Hydrogen) which are then collected and weighed.