Chapter 3 Atoms: The Building Blocks of Matter

The Atomic Theory  Law of conservation of mass  Mass is neither destroyed nor created  Law of definite proportions  Compound is always composed of same proportion of elements  Law of multiple proportions  If two different compounds are composed of the same elements, the two elements form a ratio of small number  Law of conservation of mass  Mass is neither destroyed nor created  Law of definite proportions  Compound is always composed of same proportion of elements  Law of multiple proportions  If two different compounds are composed of the same elements, the two elements form a ratio of small number

Law of Conservation of Mass

Law of Multiple Proportions

Dalton  All matter is composed of atoms  Atoms of an element are identical in size, mass and other properties  Atoms cannot be subdivided, created, or destroyed  Atoms combine in simple whole-number ratios  Atoms are combined, separated, or rearranged in chemical reactions  All matter is composed of atoms  Atoms of an element are identical in size, mass and other properties  Atoms cannot be subdivided, created, or destroyed  Atoms combine in simple whole-number ratios  Atoms are combined, separated, or rearranged in chemical reactions

Modern Atomic Theory  All matter is composed of atoms  Atoms of one element differ in properties from atoms of another element  Atom - smallest particle of an element that retains the chemical properties of that element  All matter is composed of atoms  Atoms of one element differ in properties from atoms of another element  Atom - smallest particle of an element that retains the chemical properties of that element

Thompson  Current passed through cathode-ray tube  Current produced a stream of particles (cathode ray) that traveled towards the anode  Rays deflected from negatively charged object  Ratio of charge to mass of particles  Current passed through cathode-ray tube  Current produced a stream of particles (cathode ray) that traveled towards the anode  Rays deflected from negatively charged object  Ratio of charge to mass of particles

Milikan  Oil-drop experiment  Charge of electron determined  Calculated mass of electron using ratio of charge to mass  Oil-drop experiment  Charge of electron determined  Calculated mass of electron using ratio of charge to mass

The Electron  Mass of x kg  Atoms are neutral, so must contain same number of electrons and protons  Electrons mass has negligible effect on total mass of atom  Mass of x kg  Atoms are neutral, so must contain same number of electrons and protons  Electrons mass has negligible effect on total mass of atom

The Nucleus  Rutherford’s gold foil experiment  Thin, gold foil bombarded with  particles  Some  particles deflected  Caused by positively charged nucleus  Volume of nucleus small  Rutherford’s gold foil experiment  Thin, gold foil bombarded with  particles  Some  particles deflected  Caused by positively charged nucleus  Volume of nucleus small

Rutherford

The Nucleus  Composed of two particles  Protons  Neutrons  Protons mass = x kg  1826 times greater than e -  Nuclear strong force  Holds positive particles together  Composed of two particles  Protons  Neutrons  Protons mass = x kg  1826 times greater than e -  Nuclear strong force  Holds positive particles together

Atomic Number  Atoms of different elements have different number of protons  Atomic number (Z)  number of protons in the nucleus  Elements arranged in order of their atomic number on periodic table  Atoms of different elements have different number of protons  Atomic number (Z)  number of protons in the nucleus  Elements arranged in order of their atomic number on periodic table

Mass Number  Total number of protons and neutrons  Ex.Hydrogen Isotopes  Total number of protons and neutrons  Ex.Hydrogen Isotopes

Isotopes  Element may contain different number of neutrons  Isotopes have differing mass  Naming  Helium-4 (hyphen notation)  4 2 Helium (nuclear symbol)  Element may contain different number of neutrons  Isotopes have differing mass  Naming  Helium-4 (hyphen notation)  4 2 Helium (nuclear symbol)

Problems  How many protons, electrons, and neutrons are in an atom of carbon-13?  Write the nuclear symbol for oxygen- 16.  How many protons, electrons, and neutrons are in an atom of bromine-80?  Write the nuclear symbol for carbon-13.  Write the hyphen notation for the element that contains 15 electrons and 15 neutrons.  How many protons, electrons, and neutrons are in an atom of carbon-13?  Write the nuclear symbol for oxygen- 16.  How many protons, electrons, and neutrons are in an atom of bromine-80?  Write the nuclear symbol for carbon-13.  Write the hyphen notation for the element that contains 15 electrons and 15 neutrons.

Relative Atomic Masses  Atomic mass unit (amu)  1/12 the mass of carbon-12  x kg  Hydrogen-1 = 1 amu  Average atomic mass  Weighted average of atomic masses of isotopes  Atomic mass unit (amu)  1/12 the mass of carbon-12  x kg  Hydrogen-1 = 1 amu  Average atomic mass  Weighted average of atomic masses of isotopes

Average Atomic Mass  Ex.  25% weigh 2.00 g  75% weigh 3.00 g  (2.00 g x 0.25) + (3.00 g x 0.75) = 2.75 g  Ex.  25% weigh 2.00 g  75% weigh 3.00 g  (2.00 g x 0.25) + (3.00 g x 0.75) = 2.75 g

Problem  What is the average atomic mass of copper which consists of 69.17% copper-63 ( amu), and copper-65 ( amu)?

Problems  Three isotopes of argon occur in nature - Ar-36, Ar-38, Ar-40. Calculate the average atomic mass of argon to two decimal places, given the following relative atomic masses and abundances of each of the isotopes: argon-36 (35.97 amu; 0.337%), argon-38 (37.96 amu; 0.063%), and argon-40 (39.96 amu; %).

The Mole  Amount of substance that contains as many particles as there are atoms in exactly 12 g of carbon-12  Counting unit like dozen  Dozen = 12  Mole = x  Avogadro’s number  x  Amount of substance that contains as many particles as there are atoms in exactly 12 g of carbon-12  Counting unit like dozen  Dozen = 12  Mole = x  Avogadro’s number  x 10 23

Molar Mass  Mass of one mole of pure substance  Units → g/mol  Molar mass = atomic mass in amu  Mass of one mole of pure substance  Units → g/mol  Molar mass = atomic mass in amu

Conversions

 1 mol/(6.022 x ) atoms  Molar mass/mol  1 mol/(6.022 x ) atoms  Molar mass/mol

Problems  What is the mass in grams of 3.6 mol of the element carbon, C?  What is the mass in grams of mol of the element chlorine, Cl?  How many moles of copper, Cu, are in 3.22 g of copper?  How many moles of lithium, Li, are in 2.72 x g of lithium?  What is the mass in grams of 3.6 mol of the element carbon, C?  What is the mass in grams of mol of the element chlorine, Cl?  How many moles of copper, Cu, are in 3.22 g of copper?  How many moles of lithium, Li, are in 2.72 x g of lithium?

Problems  How many moles of carbon, C, are in 2.25 x atoms of carbon?  How many moles of oxygen, O are in atoms of oxygen?  How many atoms of sodium, Na, are in 3.80 mol of sodium?  What is the mass in grams of 5.0 x 10 9 atoms of neon, Ne?  How many moles of carbon, C, are in 2.25 x atoms of carbon?  How many moles of oxygen, O are in atoms of oxygen?  How many atoms of sodium, Na, are in 3.80 mol of sodium?  What is the mass in grams of 5.0 x 10 9 atoms of neon, Ne?

Problems  How many atoms of carbon, C, are in g of carbon?  What mass of silver, Ag, contains the same number of atoms as 10.0 g of boron, B?  How many moles of CO 2 are in 66.0 g of dry ice, which is solid CO 2  How many atoms of carbon, C, are in g of carbon?  What mass of silver, Ag, contains the same number of atoms as 10.0 g of boron, B?  How many moles of CO 2 are in 66.0 g of dry ice, which is solid CO 2

Chapter Review  Pg. 89  1, 8, 11, 17, 18acd, 20, 21, 22ade, 23abcd  Pg. 89  1, 8, 11, 17, 18acd, 20, 21, 22ade, 23abcd