principles of chemistry i chem 1211 chapter 2 dr. augustine ofori agyeman assistant professor of...

PRINCIPLES OF CHEMISTRY I

CHEM 1211

CHAPTER 2

DR. AUGUSTINE OFORI AGYEMANAssistant professor of chemistryDepartment of natural sciences

Clayton state university

CHAPTER 2

ATOMS, MOLECULES, AND IONS

THE ATOMIC THEORY OF MATTER

Law of Constant Composition- The relative numbers and kinds of atoms are constant in a given compound

- All samples of a given chemical compound have the same elemental composition

Example- Water (H2O) always contains 1 g of H for every 8 g of O

Law of Conservation of Mass (Matter)- The total mass of materials after a chemical reaction is equal to the total mass

before the chemical reaction


Law of Multiple Proportions- When two or more elements combine to form a compound, their masses in that

compound are in a fixed and definite ratio

- Elements combine in a ratio of small whole numbers

- If two elements form more than one compound, the ratios of the masses of the second element combined with a fixed mass of the first element will be in ratios

of small whole numbers


Law of Multiple Proportions

- C and O can combine to form CO and CO2

CO1.33 g O combine with 1.00 g C

CO2

2.66 g O combine with 1.00 g C

- Ratio of O is 2.66 g : 1.33 g = 2 : 1


Dalton’s Atomic Theory

1. All matter (every element) is made up of very small particles called atoms

- Atoms are indivisible and indestructible

2. All atoms of a given element are identical in mass and properties

- Atoms of a given element are different from atoms of all other elements


Dalton’s Atomic Theory

3. Compounds are formed from a combination of two or more different kinds of atoms

- A given compound always has the same relative number and kind of atoms

4. A chemical reaction is a rearrangement of atoms - Atoms are neither created nor destroyed in a chemical reaction


Modern atomic theory is more involved but based on Dalton’s theory

- Atoms can be destroyed by nuclear reactions but not by chemical reactions

- There are different kinds of atoms within an element (isotopes - different masses, same properties)


HomeworkRead about the following and summarize all in one page

(double spaced)

- Gas discharge tubes (cathode rays)- Antoine Lavoisier

- J. J. Thompson- Robert A. Millikan (oil drop experiment)

- Ernest Rutherford- James Chadwick

THE ATOMIC STRUCTURE

Atom - Is the smallest particle of an element that retains the chemical

identity of the element- Is the basic building block of ordinary matter

- Made up of smaller particles (the building blocks of an atom) called subatomic particles

Three Types of Subatomic ParticlesElectron: possesses a negative (-) electrical chargeProton: possesses a positive (+) electrical charge

Neutron: has no charge (it is neutral)


Electronic Charge equals 1.602177 x 10-19 C(C = coulombs)

- Charges are usually expressed as multiples of the electronic charge

Charge of an electron = -1.602177 x 10-19 C = -1

Charge of a proton = +1.602177 x 10-19 C = +1

Atoms have no net electrical charge since they have equal number of electrons and protons


- Protons and neutrons have very large masses (about 2000 x) as compared to electrons

- Atoms generally have extremely small masses- Atomic Mass Unit (u) is used to express such small masses

1 u = 1.66054 x 10-24 g or 1 g = 6.02212 x 1023 u

Charge

Negative (-1)Positive (+1)Neutral (0)

Particle

ElectronProtonNeutron

Mass (g)

9.109 x 10-28

1.673 x 10-24

1.675 x 10-24

Mass (u)

5.486 x 10-4

1.00731.0087

Relative Mass

118371839


- The center of an atom is small, dense, and positively chargedcalled the nucleus

- The nucleus contains all protons and neutrons and are referred to as necleons

- The nucleus is, therefore, positively charged and contributes about 99.9% of the mass of an atom


- The electrons move rapidly around the nucleus

- Outer region called the extranuclear region

- Account for most of the volume of an atom

Electron Cloud - Volume occupied by electrons

- Negatively charged

ATOMIC NUMBER (Z)

- The number of protons in the nucleus of an atom- determines the identity of the element

- Since atoms have no net electrical chargenumber of protons = number of electrons

Z = number of protons = number of electrons

MASS NUMBER (A)

- The sum of the number of protons and the number of neutrons in the nucleus of an atom

-The total number of subatomic particles in the nucleus of an atom

- The number of nucleons of an atom

A = number of protons + number of neutrons

number of neutrons = mass number - atomic number = A - Z

ATOMIC AND MASS NUMBERSMASS NUMBER

ATOMIC NUMBERCHEMICAL SYMBOL

SYMBOLA

Z

C12

6O

16

8Ca

40

20

Mass number is the superscript to the leftAtomic number is the subscript to the left

An atom has an atomic number of 56 and a mass number of 138.What are the numbers of protons, electrons, and neutrons presentin the atom? What is the number of subatomic particles present

in the nucleus of the atom?

Number of protons = atomic number = 56Number of electrons = atomic number = 56

Number of neutrons = mass number – atomic number = 138-56 = 82Number of subatomic particles in the nucleus = mass number = 138

ATOMIC AND MASS NUMBERS

CHEMICAL PROPERTIES OF ATOMS

- The number of protons (the atomic number) characterizes an atom

- Electrons determine the chemical properties of an atom

- Atoms with the same atomic number have the same chemical properties

- Atoms with the same atomic number are atoms of the same element

CHEMICAL PROPERTIES OF ATOMS

Chapter 1 definition of An Element - Is a pure substance that cannot be reduced to a simpler substance

by normal chemical means

Chapter 2 definition of An Element- Is a pure substance in which all atoms present have the same

atomic number

ISOTOPES

- Atoms of an element with the same atomic number but different mass numbers

- Atoms of an element with the same number of protons and the same number of electrons but different numbers of neutrons

- Isotopes of an element have the same chemical propertiesbut slightly different physical properties

- The atomic number is usually omitted since it is the same for isotopes of a given element

ISOTOPES

12

6C

6 66

11 13 14

H1 2 3

1 1 1

Si28 29 30

14 14 14

Most abundant is carbon-12

Most abundant is silicon-28

Most abundant is hydrogen-1

C C C

H H

Si Si

AVERAGE ATOMIC MASS

- Determined by using the masses of an element’s various isotopes and their respective natural abundances

Units 1 u = 1.66054 x 10-24 g or 1 g = 6.02214 x 1023 u

u (amu): atomic mass unit

u is defined by assigning a mass of exactly 12 u to an atom of carbin-12 (reference point)

For an element with n isotopes which have atomic masses in u (m1, m2, m3,….., mn) and

natural abundances expressed as fractions (x1, x2, x3,……,xn)

Average Atomic Mass = m1x1 + m2x2 + m3x3 +….+ mnxn

The natural abundance is usually expressed as a percentage

Divide by 100 to convert to the decimal form (fractional abundance)

AVERAGE ATOMIC MASS

The mass spectrometer is an instrument used to measurethe masses and relative (natural) abundances of the

isotopes present in a sample of an element

HomeworkDescribe the operation and uses of the mass spectrometer

One page maximum and double spaced

AVERAGE ATOMIC MASS

Naturally occurring copper is 69.09% 63Cu, which has a relative mass of 62.93 u, and 30.91% 65Cu, which has a relative mass of

64.93 u. Calculate the average atomic mass of copper.

63Cunatural abundance = 69.09%

fractional abundance = 69.09/100 = 0.6909

65Cunatural abundance = 30.91%

fractional abundance = 30.91/100 = 0.3091

Average Atomic Mass = (62.93)(0.6909) + (64.93)(0.3091) = 63.5478 = 63.55 u

AVERAGE ATOMIC MASS

PERIODIC TABLE OF ELEMENTS

- 117 known elements- 92 naturally occurring elements

- 25 are not found in nature but made in the laboratory

Periodic Table- Elements are arranged in a tabular form (called the periodic

table) in order of increasing atomic number such that elements with similar chemical properties are positioned in vertical columns

- A tool that chemists use for organizing and remembering chemical facts

SYMBOL

Atomic number

Atomic mass

Period- The horizontal row of elements in the periodic table- Labeled with Arabic numbers from top to bottom - First row is period 1, second row is period 2, etc

Group- The vertical column of elements in the periodic table

- May be labeled with Arabic numbers (1 through 18)

Arabic numbers with letters A or B (1A, 1B, 2A, 3B, etc)Roman numerals with letters A or B (IA, IB, IIA, IIIB, etc)


Groups With Special Names

Alkali Metals- Elements in Group 1A (excluding hydrogen)

Li, Na, K, Rb, Cs, and Fr- Properties: soft, shiny, react readily with water

- Reactivity increases down the group

Alkaline Earth Metals- Elements in Group 2A Be, Mg, Ca, Sr, Ba, Ra

- Properties: soft, shiny, react moderately with water



Chalcogens- Elements in Group 6A

O, S, Se, Te, Po- Properties: commonly found as minerals

Halogens (salt formers)- Elements in Group 7A

F, Cl, Br, I, At- Properties: reactive, colored, gas at room temperature

- Reactivity decreases down the group



Noble Gases (inert gases)- Elements in Group 8AHe, Ne, Ar, Kr, Xe, Rn

- Properties: unreactive gases


Classification by Physical Properties

Metals - Elements on the left block of the periodic table

Characteristics: - good conductors of heat and electricity

- ductile (capable of being shaped or drawn into wire) - malleable (capable of being rolled into sheets)

- high luster (shiny)- high melting points

- high density- solids at room temperature (except mercury)

(iron, aluminum, gold, silver, copper)



Nonmetals- Elements on the right block of the periodic table

Characteristics: - poor conductors of heat and electricity

- good insulators (except diamond)- no metallic luster

- nonductile- lower melting points

- lower density- solids, liquids or gases at room temperature

(oxygen, hydrogen, nitrogen, carbon, sulfur, bromine)



Metals and nonmetals on the periodic table are separated by a bold steplike line running from

Group 3A through Group 6A

Metalloids - Some elements that lie along the line separating

metals from nonmetals

Characteristics:- Properties fall between those of metals and nonmetals

- Semiconductors (weak conductors of electricity) (B, Si, Ge, As, Sb, Te)


- The attractive force that holds atoms together

- The result of interactions between electrons in the combining atoms

- Two types of chemical bonds covalent and ionic (electrovalent) bonds

CHEMICAL BOND

Covalent Bond - Formed through the sharing of one or more pairs of electrons

between two atoms - Always involve two nonmetals

(electron sharing)

Ionic Bond - Formed by attraction between two oppositely charged ions

- Formed as a result of the transfer of electron(s) from atom(s) toanother atom(s)

- Often formed between metal and nonmetal ions throughelectrostatic attraction

(electron transfer)

CHEMICAL BOND

- A substance consisting of two or more different elements chemically bonded together in a fixed proportion by mass

Two classes of chemical compounds molecular and ionic compounds

CHEMICAL COMPOUND

THE MOLECULE

- Two or more atoms tightly bound together and behaving as a single unit

- Basic structural unit of molecular compounds

- The molecule is the limit of physical subdivision (the smallest particle of a compound)

- The atom is the limit of chemical subdivision

THE MOLECULE

Homoatomic Molecule - All atoms present are of the same kind (element)

ExamplesH2, O2, N2, Cl2, S8

Heteroatomic Molecule- Two or more kinds of atoms are present (compound)

- Two or more elements are present

ExamplesH2O, CO2, CH4, HCl

THE MOLECULE

Diatomic molecule contains two atoms (HCl, H2, O2)

Triatomic molecule contains three atoms (H2O, CO2)

Tetratomic molecule contains four atoms (HNO2, SO3)

Pentatomic molecule contains five atoms (HNO3, CH4)

ETC.

Chemical Formula

- Tells which elements and how many of those elementsmake up a compound

ExampleThe chemical formula of sulfuric acid is H2SO4

Conveys the information that a sulfuric acid molecule contains - 3 different elements: hydrogen (H), sulfur (S), oxygen (O)- 7 atoms: 2 hydrogen atoms, 1 sulfur atom, 4 oxygen atoms

- When a particular atom is 1 (as in S above) the subscript is not written

THE MOLECULE

Chemical Formula

- Note the difference between CoCl2 and COCl2

CoCl2

- 2 different elements: cobalt (Co) and chlorine (Cl)- 3 atoms: 1 Co atom and 2 Cl atoms

COCl2

- 3 different elements: carbon (C), oxygen (O), and chlorine (Cl)- 4 atoms: 1 C atom, 1 O atom, and 2 Cl atoms

THE MOLECULE

MOLECULAR COMPOUNDS

- Compounds composed of molecules- Contain more than one type of atom

- Atoms are joined through covalent bonds -Generally composed of nonmetals only

(H2O, CO2, CH4, NH3)

Physical Properties - low melting points

- poor conductors of electricity- can be solids, liquids, or gases at room temperature

- low solubility in water

Empirical Formula- Chemical formula indicating the relative number of atoms

of each type in a molecule- Indicates the smallest possible whole number ratios

Molecular Formula

- Chemical formula indicating the actual numbers and types of atoms in a molecule

- Identifies multiples of the smallest whole number ratios

MOLECULAR COMPOUNDS

Substance

WaterHydrogen PeroxideMethaneBenzeneHexane

Molecular Formula

H2OH2O2

CH4

C6H6

C6H14

Empirical Formula

H2OHOCH4

CHC3H7

MOLECULAR COMPOUNDS

Structural Formula- Shows how atoms are arranged (connected)

- Shows chemical bonding within the molecule (which atom is bonded or attached to which)

- Graphical representation of molecular formula

H

O

H

O O

H

H

C

H

H H

H

Water Hydrogen Peroxide Methane

MOLECULAR COMPOUNDS

1. Molecular (condensed) formula

2. Structural formula

3. Perspective drawing - Depicts three dimensional shape

4. Ball-and-stick model - Shows atoms as spheres and bonds as sticks- Shows angles at which bonds are attached

5. Space-filling model - Shows relative sizes of atoms

MOLECULAR COMPOUNDS

- Positively or negatively charged particles - Result from loss (positive) or gain (negative) of electrons

- Basic structural units of ionic compounds- Charges are represented by superscripts

- Two types of ions

Cation- An ion with a positive charge (loss of electrons)

(H+, Na+, Al3+, Ca2+)

Anion- An ion with a negative charge (gain of electrons)

(O2-, Cl-, Br-, I-)

IONS

Generally, metals form cations whereas nonmetals form anions

- Chemical properties of ions are different from those of the atoms from which they were derived

- Atoms lose or gain electrons to attain the same number of electrons as the noble gas (Group 8A element) closest to it

GenerallyGroup 1A elements form 1+ ionsGroup 2A elements form 2+ ionsGroup 6A elements form 2- ionsGroup 7A elements form 1- ions

IONS

Monatomic Ion - An ion composed of one atom

(Br-, Na+, Mg2+, Al3+, O2-)

Polyatomic Ion- An ion (charged particle) composed of two or more atoms

covalently bonded together- behave as a single unit

(OH-, NH4+, SO4

2-, CO32-, HCO3

-)

IONS

- Compounds in which ionic bonds are present- Contain both positively and negatively charged ions

- Generally composed of metals (positive ions) and nonmetals (negative ions)

(NaCl, KCl, CaBr2, Na2O)

Physical Properties- High melting and boiling points

- High hardness- Brittle (easily cracked or fractured)

- Good conductors of electricity when molten (electrolytes)- Solid at room temperature and pressure

- High solubility in water

IONIC COMPOUNDS

- Ionic compounds do not contain discrete molecules but ordered arrays of positive and negative ions

NaCl for example- The formula unit indicates combining ratio (empirical formula)

- A given sodium ion has six immediate chloride ion neighbors

- A given chloride ion has six immediate sodium ion neighbors

IONIC COMPOUNDS

- The charges of ions can be used to depict the empirical formula for ionic compounds

- For equal magnitude of charges on cation and anion the subscript on each ion is 1

NaCl: Na+ and Cl-

KBr: K+ and Br-

MgO: Mg2+ and O2-

IONIC COMPOUNDS


- For unequal magnitude of charges the charge on one ion is the subscript on the other ion

(without the positive or negative sign)

AlCl3: Al3+ and Cl-

CaCl2: Ca2+ and Cl- Na2S: Na+ and S2-

Fe2O3: Fe3+ and O2-

IONIC COMPOUNDS


- For polyatomic ionseach ion is considered as one unit

NH4NO3: NH4+ and NO3

-

(NH4)2CO3 : NH4+ and CO3

2- Na2CO3: Na+ and CO3

2-

Sr3(PO4)2: Sr2+ and PO43-

Ca(OH)2: Ca2+ and OH-

IONIC COMPOUNDS

- Only two elements are present

- Any number of atoms of the two elements may be present

Examples NaCl, H2O, CaCl2, NH3, Al2O3

BINARY COMPOUNDS

Binary Ionic Compounds- One of the two elements is a metal (cation)

and the other is a nonmetal (anion)

ExamplesAl2S3, NaCl, KCl, KBr

Binary Molecular Compounds- Both elements are nonmetals

ExamplesH2O, CO2, NO2, SO2, HCl, NH3

BINARY COMPOUNDS

FORMULA MASS

- The sum of atomic masses of all the atoms present in the chemical formula of a substance

- Relative mass based on the carbon-12 relative-mass scale

- It is advisable to use two decimal places for atomic masses

For molecular compounds- Formula mass is obtained from the molecular formula

- Also known as molecular mass

For ionic compounds- Formula mass is obtained from the empirical formula

Calculate the formula mass of H2SO4

H: 2 x 1.01 u = 2.02 uS: 1 x 32.06 u = 32.06 uO: 4 x 16.00 u = 64.00 u

Formula mass = (2.02 + 32.06 + 64.00) u = 98.08 u

FORMULA MASS

Calculate the formula mass of H2OH: 2 x 1.01 u = 2.02 u

O: 1 x 16.00 u = 16.00 uFormula mass = (2.02 + 16.00) u = 18.02 u

Calculate the formula mass of Fe2(SO4)3

Fe: 2 x 55.85 u = 111.70 uS: 3 x 32.07 u = 96.21 u

O: 12 x 16.00 u = 192.00 uFormula mass = (111.70 + 96.21 + 192.00) u = 399.91 u

FORMULA MASS

Calculate the formula mass of CaCO3

Ca: 1 x 40.08 u = 40.08 uC: 1 x 12.01 u = 12.01 uO: 3 x 16.00 u = 48.00 u

Formula mass = (40.08 + 12.01 + 48.00) u = 100.09 u

Positive Ions (Cations)

- Cations have the same name as the metal atom from which they were formed

Na+: sodium ionAl3+: aluminum ionK+: potassium ion

NAMING SIMPLE COMPOUNDS


- The positive charge is indicated by a Roman numeral (in parenthesis) if the metal can form different cations

- Usually seen in transition metals

Fe2+: iron(II) ion Fe3+: iron(III) ionPb2+: lead(II) ion Pb4+: lead(IV) ionSn2+: tin(II) ion Sn4+: tin(IV) ion

Cu+: copper(I) ion Cu2+: copper(II) ion



- Older method for naming differently charged ions of the same metal

Fe2+: ferrous ion Fe3+: ferric ionPb2+: plumbous ion Pb4+: plumbic ionSn2+: stannous ion Sn4+: stannic ionCu+: cuprous ion Cu2+: cupric ion



- If you have any doubt whether a metal forms more than one cation, just use the Roman numeral (never wrong to do so)

- The charge on the nonmetal and charge neutrality can be used to identify the charge on the metal

- Cations formed from nonmetal atoms end in -ium (polyatomic ions)

NH4+: ammonium ion H3O+: hydronium ion


Negative Ions (Anions)

- Monatomic anions are formed by replacing the ending of the name of the element with -ide

Br-: bromide ionCl-: chloride ionO2-: oxide ionS2-: sulfide ion


Negative Ions (Anions)

- Some polyatomic anions also end in -ide

OH-: hydroxide ionCN-: cyanide ionO2

2-: peroxide ion


- Polyatomic anions containing oxygen end in -ate or -ite- The -ite ion has one less oxygen atom than the -ate ion

- The pair carry the same charge

SO42-: sulfate ion SO3

2-: sulfite ionNO3

-: nitrate ion NO2-: nitrite ion

ClO3-: chlorate ion ClO2

-: chlorite ionPO4

3-: phosphate ion


- Prefix is used in some cases

per- indicates one more O atom than the -ate (ClO3

-: chlorate; ClO4-: perchlorate)

hypo- indicates one less O atom than the -ite (ClO2

-: chlorite; ClO-: hypochlorite

- Some pairs differ by the presence of hydrogen

CO32- (carbonate) and HCO3

- (hydrogen carbonate or bicarbonate)


Ionic Compounds- Names consist of the cation name followed by the anion name

NaCl: sodium chlorideKOH: potassium hydroxideNH4Br: ammonium bromideCaCO3: calcium carbonate

- Parenthesis are used for compounds containing two or more polyatomic ions

Mg(OH)2: magnesium hydroxidePb(NO3)2: lead(II) nitrate


Acids- Hydrogen containing compounds

- Substance whose molecules yield hydrogen ions (H+) when dissolved in water

A 1) names ending in -ide change to -ic

2) the prefix hydro- is added to the anion 3) the word acid follows

HCl: anion is chloride; hydrochloric acidHBr : anion is bromide; hydrobromic acidHCN : anion is cyanide; hydrocyanic acid


Acids- Hydrogen containing compounds

- Substance whose molecules yield hydrogen ions (H+) when dissolved in water

B 1) names ending in -ate change to -ic and -ite change to -ous

2) the word acid follows

HNO3: anion is nitrate: nitric acid HNO2: nitrous acidH2SO4: anion is sulfate: sulfuric acid H2SO3: sulfurous acid

H3PO4: anion is phosphate: phosphoric acid


Binary Molecular Compounds

- Compounds with two elements but any number of atoms

- Some molecular compounds with nonsystematic common namesH2O: water

NH3: ammoniaCH4: methane



- The name of the element farther to the left in the periodic table is usually written first (oxygen is an exception)

- For elements in the same group of the periodic table the one with higher atomic number (to the bottom) is named first

- The name of the second element ends in -ide



- The number of atoms of each element is indicated by Greek prefixes

- The prefix mono- is not written for first elements

- If the element begins with a vowel, the a or o of prefix is not written



CO2: carbon dioxidePCl3: phosphorus trichloride

PCl5: phosphorus pentachlorideSF6: sulfur hexafluoride

P4O10: tetraphosphorus decoxideO2F2: dioxygen difluoride

CO: carbon monoxideN2O4: dinitrogen tetroxideN2O5: dinitrogen pentoxideCBr4: carbon tetrabromideIF7: iodine heptafluoride


Organic Compounds- Compounds containing carbon and hydrogen, and in combination with oxygen, nitrogen and other elements

Hydrocarbons - Contain only carbon and hydrogen

- Each carbon is bonded to four other atoms

AlkanesOne carbon atom: methaneTwo carbon atoms: ethane

Three carbon atoms: propaneFour carbon atoms: butaneFive carbon atoms: pentane


Alcohols - When one H atom is replaced by an -OH group

One carbon atom: methanolTwo carbon atoms: ethanol

Three carbon atoms: propanolFour carbon atoms: butanolFive carbon atoms: pentanol

etc.

The position of the -OH group can be specified(2-pentanol, 2-butanol, 1-pentanol, 1-propanol)


principles of chemistry i chem 1211 chapter 2 dr. augustine ofori agyeman assistant professor of...

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