AS Chemistry Unit 1AS Chemistry Unit 1

Weighing and Counting Weighing and Counting AtomsAtoms

Atoms: The Building Atoms: The Building Blocks of MatterBlocks of Matter

DaltonDalton’’s Atomic Theory – English s Atomic Theory – English school teacher John Dalton was school teacher John Dalton was the first to recognize that these the first to recognize that these laws and many experimental laws and many experimental results could be explained by the results could be explained by the existence of atoms.existence of atoms.

Bell Work, 8/15/12Bell Work, 8/15/12

Answer Question # 1 on pg. 21.Answer Question # 1 on pg. 21.

Statements of the Atomic Statements of the Atomic Theory Theory

All matter is composed of extremely small All matter is composed of extremely small particle called atoms.particle called atoms.

Atoms of a given element are identical in size, Atoms of a given element are identical in size, mass and other properties; atoms of different mass and other properties; atoms of different elements differ in size, mass, and other elements differ in size, mass, and other properties.properties.

Atoms cannot be subdivided, created or Atoms cannot be subdivided, created or destroyed.destroyed.

Atoms of different elements can combine in Atoms of different elements can combine in simple, whole-number ratios to form chemical simple, whole-number ratios to form chemical compounds.compounds.

In chemical reactions, atoms are combined, In chemical reactions, atoms are combined, separated, or rearranged.separated, or rearranged.

DaltonDalton’’s Atomic Theory s Atomic Theory ContCont’’dd

DaltonDalton’’s theory has since been s theory has since been discarded it was the basis for discarded it was the basis for further experiments because it further experiments because it successfully explained the Law of successfully explained the Law of Conservation of Mass, Law of Conservation of Mass, Law of Definite Composition and other Definite Composition and other observations.observations.

Theory UpdatedTheory Updated

We now know that atoms are We now know that atoms are divisible.divisible.

We also know that an element can We also know that an element can have atoms with differing masses; have atoms with differing masses; these atoms are called these atoms are called isotopes.isotopes.

Theory LawsTheory Laws Law of Definite Composition by Mass Law of Definite Composition by Mass

states that a chemical compound contains states that a chemical compound contains the same elements in exactly the same the same elements in exactly the same proportions by mass regardless of the size proportions by mass regardless of the size of the sample.of the sample.

Law of Multiple Proportions states that If Law of Multiple Proportions states that If two or more different compounds are two or more different compounds are composed of the same two elements, the composed of the same two elements, the masses of the second element combined masses of the second element combined with a certain mass of the first element with a certain mass of the first element can be expressed as ratios of small whole can be expressed as ratios of small whole numbers.numbers.

Example: Example: Carbon Monoxide Carbon Monoxide COCO

Carbon DioxideCarbon Dioxide CO CO22

OxygenOxygen O O22

OzoneOzone O O33

Atomic Numbers and Mass Atomic Numbers and Mass NumbersNumbers

Atomic NumberAtomic Number – (Z) the number of – (Z) the number of protons in the nucleus of each atom protons in the nucleus of each atom of that element.of that element.

Mass NumberMass Number – total number of – total number of protons and neutrons in the protons and neutrons in the nucleus of an isotope.nucleus of an isotope.

NuclideNuclide – the general term for any – the general term for any isotope of any element.isotope of any element.

Average Atomic Masses of Average Atomic Masses of ElementsElements

Average Atomic MassAverage Atomic Mass – the weighted – the weighted average of the atomic masses of the average of the atomic masses of the naturally occurring isotopes of an element.naturally occurring isotopes of an element.

Example: Copper consists of Example: Copper consists of

69.17% Cu-63 atomic mass 62.939 598 69.17% Cu-63 atomic mass 62.939 598 uu

30.83% Cu-65 30.83% Cu-65 64.927 793 64.927 793 uu

(.6917)(62.939 598(.6917)(62.939 598uu) + (.3083)(64.927 793) + (.3083)(64.927 793uu))

= 63.55 = 63.55 uu (as seen on the periodic table) (as seen on the periodic table)

Average atomic mass Average atomic mass equationequation

aam = (faaam = (fa1)(m1) + (fa2)(m2) + etc……

aam – average atomic massaam – average atomic mass

fa – fraction abundance of that fa – fraction abundance of that specific isotopespecific isotope

m – mass of specific isotopem – mass of specific isotope

Atomic StructureAtomic Structure ProtonsProtons – subatomic particles that have a – subatomic particles that have a

positive charge equal in magnitude to the positive charge equal in magnitude to the negative charge of an electron and are present negative charge of an electron and are present in atomic nuclei. Protons have a mass of 1.673 in atomic nuclei. Protons have a mass of 1.673 x 10x 10-24-24..

Neutrons are electrically neutral subatomic Neutrons are electrically neutral subatomic particles found in atomic nuclei. The mass of a particles found in atomic nuclei. The mass of a neutron is 1.675 x 10neutron is 1.675 x 10-24-24 g. g.

Physicists have also found many other Physicists have also found many other subatomic particles. However particles other subatomic particles. However particles other than electrons, protons, and neutrons play little than electrons, protons, and neutrons play little role in the properties of matter that are of role in the properties of matter that are of interest in chemistry.interest in chemistry.

ScientistsScientists

Look up the following Scientists in Look up the following Scientists in your textbook and write what they your textbook and write what they were responsible for discovering and were responsible for discovering and how they did it.how they did it. Ernest RutherfordErnest Rutherford Sir John Joseph ThomsonSir John Joseph Thomson Robert Millikan (Oil Drop Experiment)Robert Millikan (Oil Drop Experiment)

Atomic massAtomic mass – the relative – the relative atomic mass of atoms of atomic mass of atoms of

that nuclide.that nuclide. The Mole, AvogadroThe Mole, Avogadro’’s Number, and Molar s Number, and Molar

MassMass mole mole – the amount of a substance that – the amount of a substance that

contains the same number of particles as the contains the same number of particles as the number of atoms in exactly 12 g of carbon-12. number of atoms in exactly 12 g of carbon-12. Abbreviation is mol. Abbreviation is mol.

AvogadroAvogadro’’s numbers number – 6.022 x 10 – 6.022 x 102323 – the – the number of particles in exactly one mole of a number of particles in exactly one mole of a pure substance.pure substance.

Molar massMolar mass – the mass in grams of one mole – the mass in grams of one mole of a pure substance. of a pure substance.

Molecules and IonsMolecules and Ions

MoleculeMolecule – a collection of atoms held – a collection of atoms held together by forces called covalent together by forces called covalent chemical bonds.chemical bonds.

Covalent chemical bondsCovalent chemical bonds – caused by – caused by sharingsharing electrons between atoms. electrons between atoms.

Chemical formulaChemical formula – a method of using – a method of using symbols and subscripts to represent symbols and subscripts to represent molecules.molecules.

Structural formulaStructural formula – symbols and lines are – symbols and lines are used to represent the shape of molecules used to represent the shape of molecules

IonsIons

Ions – an atom or groups of atoms Ions – an atom or groups of atoms that have a net positive or negative that have a net positive or negative charge. charge.

CationCation – positively charged ion. – positively charged ion. AnionAnion – negatively charged ion. – negatively charged ion.

Ionic bondingIonic bonding – force of attraction – force of attraction between oppositely charged ions.between oppositely charged ions.

Copy the following Copy the following questions and answer. questions and answer.

Turn in at the end of classTurn in at the end of class1.1. The element Boron, has an atomic The element Boron, has an atomic

mass of 10.81 u according to the mass of 10.81 u according to the periodic table. However, no single periodic table. However, no single atom of boron has a mass of exactly atom of boron has a mass of exactly 10.81 u. How can you explain the 10.81 u. How can you explain the difference?difference?

2.2. How did the outcome of RutherforHow did the outcome of Rutherfordd ’’s gold-foil experiment indicate the s gold-foil experiment indicate the existence of a nucleus?existence of a nucleus?

Bell Work, 8/16/12Bell Work, 8/16/12

Complete the Average Atomic Mass Complete the Average Atomic Mass Worksheet for a grade.Worksheet for a grade.

3.3. List the number of protons, electrons List the number of protons, electrons and neutrons in the followingand neutrons in the following

a. Si-30a. Si-30

b. Cr-52b. Cr-52

c. Sr – 88c. Sr – 88

d. Be-11d. Be-11

4.4. FeO, FeFeO, Fe22OO3, 3, FeFe33OO44, represent what Law , represent what Law of matter?of matter?

5.5. Tell which of DaltonTell which of Dalton’’s principles of his s principles of his Atomic Theory have been changed and Atomic Theory have been changed and why.why.

6.6. Convert the following to gramsConvert the following to gramsa.a. 1.22 mol sodium1.22 mol sodium

b.b. 14.5 mol copper14.5 mol copper

c.c. 1.204 x101.204 x102424 atoms lithium atoms lithium

d.d. 6.046 x 106.046 x 102323 atoms bismuth atoms bismuth

7.7. Convert the following to atomsConvert the following to atoms

a. 64.1 grams aluminuma. 64.1 grams aluminum

b. 0.255 g sulfurb. 0.255 g sulfur

c. 0.366 mol zincc. 0.366 mol zinc

d. 9.37 x 10d. 9.37 x 10-3-3 mol magnesium mol magnesium

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Work on Exam style question 2 on Work on Exam style question 2 on pages 21 and 22.pages 21 and 22.