atom,elements, molecules and compounds.pdf

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ATOMS, ELEMENTS, MOLECULES AND COMPOUNDS

Modern Atomic Theory and the Laws That Led to It

Modern Atomic Theory comes from;i. The law of Conservation of Mass

ii. The law of Definite Propotions

iii. The law of Multiple Propotions

Law of Conservation of Mass

Total mass of the materials you have before the reaction must equal the total mass of thematerials you have at the end

total mass of reactants = total mass of products (Antoine Lavoisier, 1743-1794)Reaction of Sodium with Chlorine to Make Sodium Chloride

7.7 g Na + 11.9 g Cl2 19.6 g NaCl

Law of Definite Proportions

All samples of a given compound, regardless of their source or how they were prepared, havethe same proportions of their constituent elements (Joseph Proust 1754-1826).

Proportions in Sodium Chloride

A 100.0 g sample of sodium chloride contains 39.3

g of sodium and 60.7 g of chlorine

A 200.0 g sample of sodium chloride contains 78.6

g of sodium and 121.4 g of chlorine

A 58.44 g sample of sodium chloride contains

22.99 g of sodium and 35.44 g of chlorine


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Law of Multiple Proportions

When two elements (call them A and B) form two different compounds, the masses of B thatcombine with 1 g of A can be expressed as a ratio of small, whole numbers (John Dalton 1766-

1844).

Oxides of Carbon

Carbon combines with oxygen to form two different compounds, carbon monoxide and carbondioxide

Carbon monoxide contains 1.33 g of oxygen for every 1.00 g of carbon Carbon dioxide contains 2.67 g of oxygen for every 1.00 g of carbon Because there are twice as many oxygen atoms per carbon atom in carbon dioxide of in

carbon monoxide, the oxygen mass ratio should be 2

Daltons Atomic Theory (1808)

1. Each element is composed of tiny, indestructible particles calledatoms2. All atoms of a given element have the same mass and other properties that distinguish them

from atoms of other elements

3. Atoms combine in simple, whole-number ratios to form molecules ofcompounds4. In a chemical reaction, atoms of one element cannot change into atoms of another element

PracticeDecide if each statement is correct according to Daltons model of the atom

1. Copper atoms can combine with zinc atoms to make gold atoms2. Water is composed of many identical molecules that have one oxygen atom and two hydrogen

atoms

3. Some carbon atoms weigh more than other carbon atoms4. Because the mass ratio of Fe:O in wsite is 1.5 times larger than the Fe:O ratio in hematite,

there must be 1.5 Fe atoms in a unit of wsite and 1 Fe atom in a unit of hematite

Solution

1. Copper atoms can combine with zinc atoms to make gold atoms incorrect; according toDalton, atoms of one element cannot turn into atoms of another element by a chemical

reaction. He knew this because if atoms could change it would change the total mass and

violate the Law of Conservation of Mass.

2.

Water is composed of many identical molecules that have one oxygen atom and two hydrogenatoms correct; according to Dalton, atoms combine together in compounds in small whole-

number ratios, so that you could describe a compound by describing the number of atoms of

each element in a molecule. He used this idea to explain why compounds obey the Law of

Definite Proportion


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3. Some carbon atoms weigh more than other carbon atoms incorrect; according to Dalton, allatoms of an element are identical.

4. Because the mass ratio of Fe:O in wsite is 1.5 times larger than the Fe:O ratio in hematite,there must be 1.5 Fe atoms in a unit of wsite and 1 Fe atom in a unit of hematite incorrect;

according to Dalton, atoms must combine in small whole-number ratios. If you could combine

fractions of atoms, that would mean the atom is breakable and Daltons first premise would be

incorrect.

Rutherfords Interpretation the Nuclear Model

1. The atom contains a tiny dense center called the nucleus2. The nucleus has essentially the entire mass of the atom3. The nucleus is positively charged4. The electrons are dispersed in the empty space of the atom surrounding the nucleusStructure of the Nucleus

Rutherford proposed that the nucleus had a particle that had the same amount of charge asan electron but opposite sign these particles are called protons

based on measurements of the nuclear charge of the elements protons are subatomic particles found in the nucleus with a charge = +1.60 x 1019 C and a

mass = 1.67262 x 1024

g

Because protons and electrons have the same amount of charge, for theatom to be neutralthere must be equal numbers of protons and electrons


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Neon

Charged Atoms When atoms gain or lose electrons, they acquire a charge Charged atoms or groups of atoms are called ions When atoms gain electrons, they become negatively charged ions, called anions When atoms lose electrons, they become positively charged ions, calledcations

Ions and Compounds

Ions behave much differently than the neutral atoms e.g., the metal sodium, made of neutral Na atoms, is highly reactive and quite unstable;

however, the sodium cations, Na+, found in table salt are very nonreactive and stable

Because materials such as table salt are neutral, there must be equal amounts of charge fromcations and anions in them


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Atomic Structures of Ions

Nonmetals form anions For each negative charge, the ion has one more electron than the neutral atom

F = 9 p+ and 9 e, F = 9 p+ and 10 e P = 15 p+ and 15 e, P3 = 15 p+ and 18e

Anions are named by changing the ending of the name to -idefluorine F + 1e

F

fluoride ion

oxygen O + 2e

O2

oxide ion

Metals form cations For each positive charge, the ion has one less electron than the neutral atom

Na atom = 11 p+ and 11 e, Na+ ion = 11 p+ and 10 e Ca atom = 20 p+ and 20 e, Ca2+ ion = 20 p+ and 18e

Cations are named the same as the metalsodium Na Na

++ 1e

sodium ion

calcium Ca Ca2+

+ 2e

calcium ion

Practice Complete the table

The Modern Periodic Table

Elements with similar chemical and physical properties are in the same column Columns are called Groups or Families

designated by a number and letter at top Rows are called Periods Each period shows the pattern of properties repeated in the next period


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Practice What is the charge on each of the following ions?

potassium cation sulfide anion calcium cation bromide anion aluminum cation


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Mass Spectrum

A mass spectrum is a graph that gives the relative mass and relative abundance of each particle Relative mass of the particle is plotted in thex-axis Relative abundance of the particle is plotted in the y-axis

PracticeGa-69 with mass 68.9256 amu and abundance of 60.11% and Ga-71 with mass 70.9247 amu

and abundance of 39.89%. Calculate the atomic mass of gallium.

Chemical Bonds

Chemical bonds are forces of attraction between atoms The bonding attraction comes from attractions between protons and electrons

Bond Types

Two general types: ionic and covalent Ionic bonds result when electrons have been transferred between atoms, resulting in oppositely

charged ions that attract each other

generally found when metal atoms bond to nonmetal atoms Covalent bonds result when two atoms share some of their electrons

generally found when nonmetal atoms bond togetherChemical Formula

To represent the compounds

Types of Formula:Empirical Formula

An empirical formula gives the relative number of atoms of each elementin a compound The empirical formula for the ionic compound fluorspar is CaCl2.


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This means that there is 1 Ca2+ ion for every 2 Cl ions in the compound.Types of Formula:Molecular Formula

A molecular formula gives the actual number of atoms of each element in a molecule of acompound

The molecular formula is C2H2O4. This does not tell you that the carbon atoms are attachedtogether in the center of the molecule, and that each is attached to two oxygen atoms.

Types of Formula:Structural Formula

A structural formula uses lines to represent covalent bonds and shows how atoms in a moleculeare connected or bonded to each other

single line = two shared electrons, a single covalent bond double line = four shared electrons, a double covalent bond triple line = six shared electrons, a triple covalent bond

Structural Formula of Oxalic Acid

O C

O

C

O

O HH


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Classifying Elements & Compounds

Atomic elements = elements whose particles are single atoms Molecular elements = elements whose particles are multi-atom molecules Molecular compounds = compounds whose particles are molecules made of only nonmetals Ionic compounds = compounds whose particles are cations and anions

Classify Each of the Following as Either an Atomic Element, Molecular Element, Molecular Compound, or

Ionic Compound

Aluminum, Al

Aluminum chloride, AlCl3

Chlorine, Cl2

Acetone, C3H6O

Carbon monoxide, CO


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Cobalt, Co

Ionic Compounds

Compounds of metals with nonmetals are made of ions Have a 3-dimensional array of cations and anions made offormula units Many contain polyatomic ions

several atoms attached together by covalent bonds into one ion

Practice What are the formulas for compounds made from the following ions?

Potassium ion with a nitride ion Calcium ion with a bromide ion Aluminum ion with a sulfide ion

Naming Metal Cations Metals with variable Charges

metals whose ions can have more than one possible charge


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Naming Metal Cations

Metals with invariant charge metals whose ions can only have one possible charge


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Naming Monatomic Nonmetal Anion

To name anion, change ending on the element name toide1. KCl

2. MgBr2

3. Al2S3

potassium chloride

magnesium bromide

aluminum sulfide


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Practice Find the charge on the cation

1. TiCl4

2. CrO3

3. Fe3N2

4 Cl = 4, Ti = 4+

3 O = 6, Cr = 6+

2 N = 6, 3 Fe = 6+, Fe = 2+

Example: Naming binary ionic with variable charge metal CuF21. Identify cation and anion

F = F

because it is Group 7

Cu = Cu2+

to balance the two () charges from 2 F

2. Name the cation

Cu2+

= copper(II)

3. Name the anion

F

= fluoride

5. Write the cation name first, then the anion namecopper(II) fluoride

Name the following compounds

1. TiCl4

2. CrO3

3. Fe3N2


copper(II) ion with a nitride ion

iron(III) ion with a bromide ion

Compounds Containing Polyatomic Ions

Polyatomic ions are single ions that contain more than one atom Often identified by parentheses around ion in formula Name and charge of polyatomic ion do not change Name any ionic compound by naming cation first and then anion


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Periodic Pattern of Polyatomic Ions -ate groups

Name the Following Compounds

1. NH4Cl

2. Ca(C2H3O2)2

3. Cu(NO3)2

Example Writing formula for ionic compounds containing polyatomic ion

Iron(III) phosphate

1. Write the symbol for the cation and its charge

2. Write the symbol for the anion and its charge

3. Charge (without sign) becomes subscript for other ion

4. Reduce subscripts to smallest whole number ratio

5. Check that the total charge of the cations cancels the total

charge of the anions

Fe3+

PO43

Fe3+

PO43

Fe3(PO4)3 FePO4

Fe = (1)(3+) = +3

PO4= (1)(3) = 3


aluminum ion with a sulfate ion

chromium(II) with hydrogen carbonate

Hydrates are ionic compounds containing a specific number of

waters for each formula unit

o CoCl26H2O = cobalt (II) chloride hexahydrateo CaSO4H2O = calcium sulfate hemihydrateo MgSO47H2O = magnesium sulfate heptahydrateo NiCl26H2O = nickel (II) chloride hexahydrate


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Example: Naming binary molecular BF3

1. Name the first element2. Name the second element with an ide3. Add a prefix to each name to indicate the subscript4. Write the first element with prefix, then the second element with prefixa) drop prefix mono from first element

boron

fluorine fluoride

monoboron, trifluoride

boron trifluoride

Name the Following

NO2

PCl5

I2F7

Example: Binary Molecular

dinitrogen pentoxide

Identify the symbols of the elements Write the formula using prefix number for subscript

N2O5

nitrogen = N, oxide = oxygen = O

di = 2, penta = 5

Write Formulas for the Following

dinitrogen tetroxide

sulfur hexafluoride

diarsenic trisulfide

Example: Naming binary acids HCl(aq)

1. Identify the anion

2. Name the anion with anicsuffix

3. Add a hydro- prefix to the anion name

4. Add the word acidto the end

Cl = Cl

, chloride because Group 7A

Cl

= chloride chloric

Hydrochloric

hydrochloric acid


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Example: Naming oxyacids H2SO4(aq)


2. If the anion hasate suffix, change it toic. If

the anion hasite suffix, change it to -ous

3. Write the name of the anion followed by the

word acid

SO4 = SO42

= sulfate

SO42

= sulfate sulfuric

sulfuric acid

(kind of an exception, to make it sound

nicer!)

Example: Naming oxyacids H2SO3(aq)


2. If the anion hasate suffix, change it toic. If

the anion hasite suffix, change it to -ous

3. Write the name of the anion followed by the

word acid

SO3 = SO32

= sulfite

SO32

= sulfite sulfurous

sulfurous acid

Name the Following

H2S

HClO3

HNO2

Writing Formulas for Acids

When name ends in acid, formulas starts with H Write formulas as if ionic, even though it is molecular Hydro prefix means it is binary acid, no prefix means it is an oxyacid For oxyacid, if ending is ic, polyatomic ion ends in ate; if ending is ous, polyatomic ion ends in

ous


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Example: Oxyacids - sulfurous acid

1. Write the symbol for the cation and its charge

2. Write the symbol for the anion and its charge

3. Charge (without sign) becomes subscript for

other ion

4. Add (aq) to indicate dissolved in water

5. Check that the total charge of the cations

cancels the total charge of the anions

H+

SO32

H+

SO32

H2SO3

H2SO3(aq)

H = (2)(1+) = +2

SO3= (1)(2) = 2

Practice What are the formulas for the following acids?

chlorous acid

phosphoric acid

hydrobromic acid

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