Atoms of different elements have different masses. Since atoms are so small it is very difficult to...

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Transcript of Atoms of different elements have different masses. Since atoms are so small it is very difficult to...

Page 1: Atoms of different elements have different masses. Since atoms are so small it is very difficult to measure their mass. One way is to bombard a sample.
Page 2: Atoms of different elements have different masses. Since atoms are so small it is very difficult to measure their mass. One way is to bombard a sample.

Atoms of different elements have different masses. Since atoms are so small it is very difficult to measure their mass. One way is to bombard a sample of an element’s atoms with electrons. This knocks electrons off these atoms and leaves them with a positive charge.

Page 3: Atoms of different elements have different masses. Since atoms are so small it is very difficult to measure their mass. One way is to bombard a sample.

The positive ions are then fired through a magnetic field. The less massive ions are deflected more than the more massive ions. By comparing the amount of deflection a relative mass can be determined.

Page 4: Atoms of different elements have different masses. Since atoms are so small it is very difficult to measure their mass. One way is to bombard a sample.
Page 5: Atoms of different elements have different masses. Since atoms are so small it is very difficult to measure their mass. One way is to bombard a sample.
Page 6: Atoms of different elements have different masses. Since atoms are so small it is very difficult to measure their mass. One way is to bombard a sample.

The more massive the _______(more/less) it is deflected.

less

Page 7: Atoms of different elements have different masses. Since atoms are so small it is very difficult to measure their mass. One way is to bombard a sample.

Any atom’s relative mass can be determined using this method called mass spectrometry.

A scale based on the mass of a C-12 atom was arbitrarily established. The standard is defined as 1/12 the mass of a C-12 atom.

1 = 1/12 mass of a C-12 atom

The average mass of all isotopes of a given element are listed on the periodic table.

Page 8: Atoms of different elements have different masses. Since atoms are so small it is very difficult to measure their mass. One way is to bombard a sample.

This value is based on the relative abundances of all natural isotopes for any given element.

For example the element chlorine consists of a mixture of 75.53% Cl-35 and 24.47% Cl-37. Any sample of chlorine from any source will consist of these two isotopes in this proportion. The average mass of a chlorine atom is calculated by

(0.7553 X 35 ) + (0.2447 x 37 ) = 35.49 Try pg. 166 # 10,11 in the Nelson Textbook

Page 9: Atoms of different elements have different masses. Since atoms are so small it is very difficult to measure their mass. One way is to bombard a sample.

In the real world single atoms are too small to concern us. However if the mass of 1 oxygen atom is 16 and the mass of 1 hydrogen atom is 1 then the mass of 100 atoms of O is 1600 , the mass of 100 atoms of H is 100 Regardless of the number of O and H atoms if an equal number of each is compared the ratio of O to H is always16 to 1.This can be turned around to get a more valuable statement.

Page 10: Atoms of different elements have different masses. Since atoms are so small it is very difficult to measure their mass. One way is to bombard a sample.

If samples of oxygen and hydrogen in a mass ratio of 16 to 1 are taken there are an equal number of atoms in each sample, regardless of the units used. Thus 16 lb of oxygen contains the same number of atoms as 1 lb of hydrogen.If grams (g) are used for atomic masses instead of the number of atoms involved is called Avogadro’s Number.12.011 g of C has Avogadro’s number of atoms as does 14 g of N, or 4 g of He, or 19 g of F, or 26.98 g of Al, or 6.94 g of Li.

Page 11: Atoms of different elements have different masses. Since atoms are so small it is very difficult to measure their mass. One way is to bombard a sample.

Oxygen atoms Hydrogen atoms

Equal numbers of oxygen and hydrogen atomsoxygen is 16x’s more massive

Page 12: Atoms of different elements have different masses. Since atoms are so small it is very difficult to measure their mass. One way is to bombard a sample.

The quantity of an element having a weight in grams numerically equal to that element’s atomic mass always contains Avogadro’s number of atoms. The value of Avogadro’s number has been determined by crystallographic and electrochemical techniques as 6.023 x 1023.The magnitude of this number is difficult to imagine. If Avogadro’s number of 1 cm3 ice cubes were spread out over all of Canada it would cover the entire country to a depth of more than 30 km.

Page 13: Atoms of different elements have different masses. Since atoms are so small it is very difficult to measure their mass. One way is to bombard a sample.

Here is Avogadro’s Number

602 300 000 000 000 000 000 000.

This quantity is also called a mole

Page 14: Atoms of different elements have different masses. Since atoms are so small it is very difficult to measure their mass. One way is to bombard a sample.

The quantity of a substance that contains Avogadro’s number of the units indicated by the formula of the substance is called a mole. (mol)The term can be applied to a variety of items: collections of atoms, ions, electrons, molecules or chemical bonds.A mole of calcium chloride, CaCl2 for instance, contains1 mol of Ca, 2 mol of Cl; the mass of 1 mol of CaCl2 can be calculated as:40.078 g + (35.4527 g x 2) = 110.983 g

Page 15: Atoms of different elements have different masses. Since atoms are so small it is very difficult to measure their mass. One way is to bombard a sample.

Calculate the molar mass ofmagnesium sulfate1 mol of MgSO4 contains1 mol of Mg1 mol of S4 mol of O(1 x 24.305 g + 1 x 32.066 g + 4 x 15.9994 g) =

120.369 g

Page 16: Atoms of different elements have different masses. Since atoms are so small it is very difficult to measure their mass. One way is to bombard a sample.

Calculate the molar mass ofbarium phosphite1 mol of Ba3(PO3)2 contains3 mol of Ba2 mol of P6 mol of O(3 x 137.33 g + 2 x 30.974 g + 6 x 15.9994 g) =

569.93 g

Page 17: Atoms of different elements have different masses. Since atoms are so small it is very difficult to measure their mass. One way is to bombard a sample.

If 1.0 mole of barium phosphite has a mass of 569.93 g how many moles are there in 1139.86 g of Ba3(PO3)2?1139.86 g / 569.9 g/mol = 2.0 molThis approach gives us a simple formula to use when calculating the number of moles of a substance.

Number of moles

=mass

Molar mass

n =m

M

Page 18: Atoms of different elements have different masses. Since atoms are so small it is very difficult to measure their mass. One way is to bombard a sample.

How many moles are there in 40 g of hydrogen fluoride? The formula is HF

n =m

M

n =40 g

1 g/mol + 19 g/mol

40 g

20 g/mol =

= 2.0 mol

Page 19: Atoms of different elements have different masses. Since atoms are so small it is very difficult to measure their mass. One way is to bombard a sample.

What is the mass of 2.5 mol of carbon dioxide? The formula is CO2

n =m

M

To find mget rid of the fractionmultiply both sides by the bottom of the fraction, M

MM

m = n x M

m = 2.5 mol x 44 g/mol

m = 1.1 x 102 g

Page 20: Atoms of different elements have different masses. Since atoms are so small it is very difficult to measure their mass. One way is to bombard a sample.

If 4.5 mol of a substance has a mass of 207 g what is this substance’s molar mass?

n =m

M

get rid of the fractionmultiply both sides by the bottom of the fraction, M

MM

m = n x M To solve for M divide both sides by n

nnM = 207 g / 4.5 mol

= 46 g/mol


Finding aid for the Owen W. Bombard Interviews series, 1951-1961

Finding aid for the Owen W. Bombard Interviews series, 1951-1961

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