The Components of Matter

The Components of Matter

Chapter 2

Overview of the Atomic Theory

The early civilizations had an idea of the composition of matter.

Egyptian: “kēme” (earth) Al-kimia: “The art of transformation” History? --> No single, straight history. ORIGINS: Possibly the advent of fire and

burning Leading to pottery, metal-works (metallurgy),

ancient structure-making


Matter was seen as continuous, as the four Greek elements were.

No distinct divisions between fire, water, earth, air

Mixtures of the four gave the properties of being hot or cold, moist, or dry

The early civilizations had an idea of the composition of matter. LEUCIPPUS: “There

must be tiny particles of water that could not be subdivided.” Observe the SAND.

DEMOCRITUS: Referred to these particles as atomos; Each atom was distinct in size and shape (eg. Water as round balls, Fire as sharp)


ARISTOTLE: Matter was continuous, not atomistic

Metallurgy and Alchemy was also common practice in ancient civilizations.Metallurgy Fire led to purification and material creation (eg.

Glass and metals) ALLOYS -> Bronze Age (ca.3000-1200BCE) Alloys and lasting metals (eg. gold) were precious

Metallurgy and Alchemy was also common practice in ancient civilizations.

Need: more stable materials like gold Hypothesis: Perhaps there is a way of

converting other materials to gold (philosopher’s stone)

MORE THAN GOLD: An early philosphical and spiritual discipline linking all things “Solve et coagula”- “Separate and join

together” Al-kimia: the art of transformation

Aim to improve life: Elixir of life Problems: Non-systematic, vague

language and concepts, pseudoscience angle, fraudulence 14th Century weakening

Alchemy

Finally in 1661, Robert Boyle re-worked the hypothesis of atoms. “The Sceptical Chymist or

Chymico-Physical Doubts & Paradoxes” by Robert Boyle in 1661

Thesis: “Matter consisted of atoms and clusters of atoms in motion and that every phenomenon was the result of collisions of particles in motion”

Appeal to EXPERIMENT! Chemistry should stop being

subservient to medicine and alchemy and establish itself as a separate science

According to Boyle, substances are made of elements which are in turn composed of “simple bodies” = atom.Element - the simplest type of substance with unique physical and chemical properties. An element consists of only one type of atom. It cannot be broken down into any simpler substances by physical or chemical means.Molecule - a structure that consists of two or more atoms that are chemically bound together and thus behaves as an independent unit.

Compound - a substance composed of two or more elements which are chemically combined.

Mixture - a group of two or more elements and/or compounds that are physically intermingled.

According to Boyle, substances are made of elements which are in turn composed of “simple bodies” = atom.

According to Boyle, substances are made of elements which are in turn composed of “simple bodies” = atom.

In the 18th century, several experiments led to the different LAWS we know of today. Antoine Laurent Lavoisier 1789- “When a chemical

reaction is carried out in a closed system, the total mass of the system is not changed.”

Red mercuric oxide Mercury + OXYGEN

1st to use systematic names; 1st chem bk. ; “father”

Experiments with burning coal (combustion), and breathing guinea pigs (respiration).

LAW: Matter is neither created nor destroyed in a chemical change. The total mass of the reaction products is always equal to the total mass of the reactants

We cannot create from nothing. Chemistry is about transformation.

In the 18th century, several experiments led to the different LAWS we know of today.

The total mass of substances does not change during a chemical reaction.

reactant 1 + reactant 2

product

total mass total mass

=

calcium oxide + carbon dioxide

calcium carbonate

CaO + CO2

CaCO3

56.08g + 44.00g

100.08g

Law of Mass Conservation:

In the 18th century, several experiments led to the different LAWS we know of today. Law of Mass

Conservation:

In the 18th century, several experiments led to the different LAWS we know of today. Joseph Louis Proust: Copper carbonate

always had the same composition LAW OF DEFINITE PROPORTIONS or

CONSTANT COMPOSITION: A compound always contains the same elements in certain definite proportions and in no other combinations.

J.J.Berzelius: Prepared an extensive list of atomic weights; Lead sulfide experiments

Henry Cavendish: 1783; Hydrogen gas + Oxygen gas Water

1800: Volta designed a powerful battery W.Nicholson and A.Carlisle would use to separate water into its elements.

In the 18th century, several experiments led to the different LAWS we know of today.

No matter the source, a particular compound is composed of the same elements in the same parts (fractions) by mass.

Analysis by Mass(grams/20.0g)

Mass Fraction(parts/1.00 part)

Percent by Mass(parts/100 parts)

8.0 g calcium2.4 g carbon9.6 g oxygen

20.0 g

40% calcium12% carbon48% oxygen

100% by mass

0.40 calcium0.12 carbon0.48 oxygen

1.00 part by mass

Law of Definite Composition:

In the 18th century, several experiments led to the different LAWS we know of today. Elements could combine

in in more than one set of proportions.

If elements A and B react to form two different compounds, the masses of B combined with a fixed mass of A, can be expressed as a ratio of small whole numbers

In the 18th century, several experiments led to the different LAWS we know of today.Law of Multiple

Proportions: Example: Carbon Oxides A & B

Carbon Oxide I : 57.1% oxygen and 42.9% carbonCarbon Oxide II : 72.7% oxygen and 27.3% carbon

Assume that you have 100g of each compound. In 100 g of each compound: g O = 57.1 g for oxide I & 72.7 g for oxide IIg C = 42.9 g for oxide I & 27.3 g for oxide II

2

g Og C =

57.142.9 = 1.33

= g Og C

72.727.3 = 2.66

2.66 g O/g C in II1.33 g O/g C in I

21

=

Finally in 1808, John Dalton presented the atomic theory of matter.

1. All matter consists of atoms.

2. Atoms of one element cannot be converted into atoms of another element.

3. Atoms of an element are identical in mass and other properties and are different from atoms of any other element.4. Compounds result from the chemical combination of

a specific ratio of atoms of different elements.

Dalton’s Atomic THEORY:

Dalton’s Atomic Theory explained the different mass laws that were established before.Mass conservationAtoms cannot be created or destroyedor converted into other types of atoms.

postulate 1postulate 2Since every atom has a fixed

mass,during a chemical reaction atoms are combined differently and therefore there is no mass change overall.

postulate 3

Dalton’s Atomic Theory explained the different mass laws that were established before.

Definite compositionAtoms are combined in

compounds in specific ratiosand each atom has a specific mass.So each element has a fixed fraction of the total mass in a compound.

postulate 3postulate 4

Dalton’s Atomic Theory explained the different mass laws that were established before.

Multiple proportionsAtoms of an element have the same massand atoms are indivisible.

So when different numbers of atoms of elements combine, they must do so in ratios of small, whole numbers.

postulate 3postulate 1

However, Dalton’s Atomic theory did not fully explain why atoms bond as they do

or how charged particles arise in experiments.

In the 19th century Cathode rays were studied to learn more about electricity.

+ -CathodeAnode

CATHODE RAY!

Evacuated tube

Phosphor coated plate detects position of the CATHODE RAY

Power Supply

S


+ -CathodeAnode

1. Magnetic Field bends the cathode ray!

N

+


+ -CathodeAnode

2. In Electric field, ray bends toward the (+) plate

-


+ -CathodeAnode

3. Changing the metal in the cathode doesn’t matter.


1. Ray bends in magnetic field.

2. Ray bends towards positive plate in electric field.

consists of charged particles consists of negative

particles3. Ray is identical for any cathode.

particles found in all matter

In 1897, J. J. Thompson measured the mass-to-charge ratio of this cathode ray particle…

MASS OF PARTICLE <<<<<< MASS OF HYDROGENTHERE IS SOMETHING SMALLER

THAN THE SMALLEST ELEMENT?!?!

O.o >_< x_x

Atoms are divisible! ^___^

In 1909, Robert Millikan measured the charge and mass of this small particle (later called electrons)

In 1909, Robert Millikan measured the charge and mass of this small particle (later called electrons)

mass of electron =

masscharg

e

X charge

= (-5.686x10-12 kg/C) X (-1.602x10-19C)

determined by J.J. Thomson and others

= 9.109x10-31kg = 9.109x10-28g

If matter is electrically neutral, atoms must have a positively charged part to counter act the electrons…

Before the turn of the century, Becquerel discovered radioactivity, (a term which was coined by Marie Sklodowska) the spontaneous emission of radiation from unstable elements.•MARIE SKLODOWSKA

married PIERRE CURIE, a French Physicist and discover radioactive polonium and radium•1903 Nobel in Physics (Becquerel, Curie, Curie)•Marie Curie: 2nd Nobel prize in 1911

Ernest Rutherford named the radioactive emissions as alpha (+), beta (-) and gamma

In 1910, Rutherford (and his colleagues Hans Geiger and Ernest Marsden) discovered that the positive part of the atom is not dispersed but rather concentrated at the center.

1. atoms positive charge is concentrated in the nucleus2. proton (p) has opposite (+) charge of electron (-)3. mass of p is 1840 x mass of e- (1.67 x 10-24 g)

In 1910, Rutherford (and his colleagues Hans Geiger and Ernest Marsden) discovered that the positive part of the atom is not dispersed but rather concentrated at the center. RUTHERFORD: The smallest positive-ray

particle is the unit of positive charge in the nucleus. This is the PROTON, with a charge equal in magnitude to a an electron, and nearly the same mass as a hydrogen atom

In 1932, James Chadwick measured the mass of He vs. mass of H.

H atoms - 1 p; He atoms - 2 pmass He/mass H should = 2measured mass He/mass H = 4

neutron (n) is neutral (charge = 0)n mass ~ p mass = 1.67 x 10-24 g

JAMES CHADWICK and the NEUTRON

Revisiting the model:

atomic radius ~ 100 pm = 1 x 10-10 mnuclear radius ~ 5 x 10-3 pm = 5 x 10-15 mIf the atom were the blue eagle gym, the

nucleus would be a microscopic speck of dust in the center, but weighing millions of tons.

Properties of the Three Key Subatomic Particles

Charge

MassRelative

1+

0

1-

Absolute (C)*

+1.60218 x 10-19

0

-1.60218 x 10-19

Relative (amu)†

1.00727

1.00866

0.00054858

Absolute (g)

1.67262 x 10-24

1.67493 x 10-24

9.10939 x 10-28

Location in the Atom

Nucleus

Outside Nucleus

Nucleus

Name (Symbol)

Electron (e-)

Neutron (n0)

Proton (p+)

Table 2.2

* The coulomb (C) is the SI unit of charge.† The atomic mass unit (amu) equals 1.66054 x 10-24 g.

Figure 2.8

Atomic Symbols, Isotopes, Numbers

X = atomic symbol of the element

A = mass number; A = Z + N

Isotopes = atoms of an element with the same number of protons, but a different number of neutrons

AZ

Z = atomic number (the number of protons in the nucleus)

N = number of neutrons in the nucleus

XThe Symbol of the Atom or Isotope

Determining the Number of Subatomic Particles in the Isotopes of an Element

PROBLEM: Silicon (Si) is essential to the computer industry as a major component of semiconductor chips. It has three naturally occurring isotopes: 28Si, 29Si, and 30Si. Determine the number of protons, neutrons, and electrons in each silicon isotope.

PLAN:

We have to use the atomic number and atomic masses.

SOLUTION:

The atomic number of silicon is 14. Therefore,28Si has 14p+, 14e- and 14n0 (28 - 14)29Si has 14p+, 14e- and 15n0 (29 - 14)30Si has 14p+, 14e- and 16n0 (30 - 14)

Sample Problem 2.4

Calculating the Atomic Mass of an Element

PLAN:

We have to find the weighted average of the isotopic masses, so we multiply each isotopic mass by its fractional abundance and then sum those isotopic portions.

PROBLEM: Silver (Ag: Z = 47) has 46 known isotopes, but only two occur naturally, 107Ag and 109Ag. Given the following mass spectrometric data, calculate the atomic mass of Ag:Isotop

eMass (amu)

Abundance (%)107Ag

109Ag106.90509108.90476

51.8448.16

Sample Problem 2.5

Calculating the Atomic Mass of an Element

SOLUTION:mass portion from 107Ag = 106.90509 amu x 0.5184 = 55.42 amu mass portion from 109Ag = 108.90476 amu x 0.4816 = 52.45 amu atomic mass of Ag = 55.42 amu + 52.45 amu = 107.87 amu

Sample Problem 2.5

continued

The Modern Reassessment of the Atomic Theory

1. All matter is composed of atoms. The atom is the smallest body that retains the unique identity of the element.

2. Atoms of one element cannot be converted into atoms of another element in a chemical reaction. Elements can only be converted into other elements in nuclear reactions.

3. All atoms of an element have the same number of protons and electrons, which determines the chemical behavior of the element. Isotopes of an element differ in the number of neutrons, and thus in mass number. A sample of the element is treated as though its atoms have an average mass.

4. Compounds are formed by the chemical combination of two or more elements in specific ratios.

As instruments became sophisticated, more and more elements were discovered. There came a need to organize elements.

Compounds: Introduction to

Bonding

Electrons of atoms interact to form chemical bonds COMPOUNDS. Electrons of atoms can interact in two ways:

1. An atom can transfer an electron to another atom forming ions. Oppositely charged ions are attracted to each other forming Ionic Compounds

Na+ Cl-

Cations• positive charges• Usually form from metals that lose electrons

Anions• Negative charges• Usually form from nonmetals that gain electrons


The resulting ions aggregate (due to electrostatic forces of attraction) and form a regular pattern of stable solids.

Electrons of atoms interact to form chemical bonds COMPOUNDS. Electrons of atoms can interact in two ways:How many electrons are lost or

gained?

Electrons of atoms interact to form chemical bonds COMPOUNDS. Electrons of atoms can interact in two ways:What affects attraction between

ions?

€

Force∝ charge 1 x charge 2distance2

Ca2+ Calcium is a metal in Group 2A(2). It loses two electrons to have the same number of electrons as 18Ar.

Predicting the Ion an Element Forms

PROBLEM: What monatomic ions do the following elements form?

PLAN:

Use Z to find the element. Find its relationship to the nearest noble gas. Elements occurring before the noble gas gain electrons and elements following lose electrons.

SOLUTION:

(a) Iodine (Z = 53)

(b) Calcium (Z = 20)

(c) Aluminum (Z = 13)

I- Iodine is a nonmetal in Group 7A(17). It gains one electron to have the same number of electrons as 54Xe.

Al3+ Aluminum is a metal in Group 3A(13). It loses three electrons to have the same number of electrons as 10Ne.

Sample Problem 2.6


1. An atom can transfer an electron to another atom forming ions. Oppositely charged ions are attracted to each other forming Ionic Compounds

2. An atom can also share its electron with another atom to form Covalent Compounds


Some elements occur as diatomic (or polyatomic) molecules


Compounds arise when two different atoms share electrons

Polyatomic ions are made up of covalently bonded atoms

Compounds: Formulas, Naming

and Masses

A chemical formula shows the type and number of each atom present in the smallest unit of the substance.

1. The empirical formula shows the relative number of atoms of each element in the compound.

2. The molecular formula shows the actual number of atoms of each element in the compound

3. A structural formula shows the number of atoms and the bonds between them; that is, the relative placement and connectinos of atoms in the molecule.

NAMING IONIC COMPOUNDS1. All ionic compounds are named by

giving the cation first and then the anion

2. For Cations, Ion charge is usually equal group number (there are many exceptions). For Anions, ion charge = group number – 8.

3. Cations usually end with –ium, while anions are named by taking the root name and changing the end with -ide

NAMING IONIC COMPOUNDS

PROBLEM: Name the ionic compound formed from the following pairs of elements:

PLAN:

(a) Magnesium and nitrogen

SOLUTION:

Use the periodic table to decide which element is the metal and which is the nonmetal. The metal (cation) is named first and we use the -ide suffix on the nonmetal name root.

(b) Iodine and cadmium(c) Strontium and fluorine (d) Sulfur and cesium

(a) Magnesium nitride(b) Cadmium iodide

(c) Strontium fluoride(d) Cesium sulfide


Ionic compounds are formed by an array of alternation cations and anions. There is no sodium chloride “molecule” to speak of. Instead we use formula unit -> similar to an empirical formula

EXCEPTIONS: PEROXIDES and MERCURY (I) ions

(a) Magnesium nitride(b) Cadmium iodide

(c) Strontium fluoride(d) Cesium sulfide

Mg2+ and N3-

Ca2+ and I-

Na+ and F-

Cs+ and S2-


Some metals form more than one ion (usually transition metals)


1. Some ions contain more than one atom (polyatomic)

2. There are some naming conventions for oxoanions (an ion with a nonmetal bonded to one or more oxygens).

Determining Names and Formulas of Ionic Compounds of Elements That Form More Than One Ion

PLAN:

SOLUTION:

Compounds are neutral. We find the smallest number of each ion which will produce a neutral formula. Use subscripts to the right of the element symbol.

PROBLEM: Give the systematic names for the formulas or the formulas for the names of the following compounds:

(a) tin(II) fluoride

(b) CrI3(c) ferric oxide (d) CoS

(a) Tin(II) is Sn2+; fluoride is F-; so the formula is SnF2.(b) The anion I is iodide (I-); 3I- means that chromium is Cr3+. CrI3 is chromium(III) iodide.(c) Ferric is a common name for Fe3+; oxide is O2-, therefore the formula is Fe2O3.(d) Co is cobalt; the anion S is sulfide (2-); the compound is cobalt(II) sulfide.

Sample Problem 2.9


Some ionic compounds have water associated to them and are called hydrates

MgSO4 * 7H2O

CuSO4 * 5H2O

Determining Names and Formulas of Ionic Compounds Containing Polyatomic Ions

PLAN:

SOLUTION:

Note that polyatomic ions have an overall charge so when writing a formula with more than one polyatomic unit, place the ion in a set of parentheses.

PROBLEM: Give the systematic names for the formula or the formulas for the names of the following compounds:

(a) Fe(ClO4)2

(b) Sodium sulfite

(a) ClO4- is perchlorate; iron must have a 2+ charge.

This is iron(II) perchlorate.(b) Sodium is Na+ ; the anion sulfite is SO3

2- . You need 2 sodium ions per sulfite. The formula is Na2SO3.(c) Barium is a 2+ ion while the hydroxide is OH-. When water is included in the formula, we use the term “hydrate” and a prefix which indicates the number of waters. So the name is barium hydroxide octahydrate.

(c) Ba(OH)2 8H2O

Sample Problem 2.10

Recognizing Incorrect Names and Formulas of Ionic Compounds

SOLUTION:

PROBLEM: Something is wrong with the second part of each statement. Provide the correct name or formula.

(a) Ba(C2H3O2)2 is called barium diacetate.(b) Sodium sulfide has the formula (Na)2SO3.

(a) Barium is always a 2+ ion and acetate is 1-. The “di-” is unnecessary. The correct name is barium acetate.(b) An ion of a single element does not need parentheses. Sulfide is S2-, not SO3

2-. The correct formula is Na2S.(c) Since sulfate has a 2- charge, only 1 Fe2+ is needed. The formula should be FeSO4.(d) Since only one carbonate is needed in this formula, the parentheses are unnecessary. The correct formula is Cs2CO3.

(c) Iron(II) sulfate has the formula Fe2(SO4)3.(d) Cesium carbonate has the formula Cs2(CO3).

Sample Problem 2.11

1) Binary acid solutions form when certain gaseous compounds dissolve in water. For example, when gaseous hydrogen chloride (HCl) dissolves in water, it forms a solution called hydrochloric acid. Prefix hydro- + anion nonmetal root + suffix -ic + the word acid - hydrochloric acid

2) Oxoacid names are similar to those of the oxoanions, except for two suffix changes:

Anion “-ate” suffix becomes an “-ic” suffix in the acid. Anion “-ite” suffix becomes an “-ous” suffix in the acid.

The oxoanion prefixes “hypo-” and “per-” are retained. Thus, BrO4

- is perbromate, and HBrO4 is perbromic acid; IO2

- is iodite, and HIO2 is iodous acid.

NAMING ACIDS

Determining Names and Formulas of Anions and Acids

SOLUTION:

PROBLEM: Name the following anions and give the names and formulas of the acids derived from them:

(a) Br - (b) IO3

-(c) CN -

(d) SO4

2-(e) NO2

-

(a) The anion is bromide; the acid is hydrobromic acid, HBr.(b) The anion is iodate; the acid is iodic acid, HIO3.

(c) The anion is cyanide; the acid is hydrocyanic acid, HCN.(d) The anion is sulfate; the acid is sulfuric acid, H2SO4.

(e) The anion is nitrite; the acid is nitrous acid, HNO2.

Sample Problem 2.12

1) The element with lower group number is the first word in the name (EXCEPTION: When compounds have both oxygen and halogen, halogen is named first)

2) IF both elements are of the same group, higher period is named first

3) Use of prefixes to indicate number of atoms

NAMING BINARY COVELENT (nonmetal – nonmetal) COMPOUNDS

Determining Names and Formulas of Binary Covalent Compounds

SOLUTION:

PROBLEM: (a) What is the formula of carbon disulfide?

(c) Give the name and formula of the compound whose molecules each consist of two N atoms and four O atoms.

(b) What is the name of PCl5?

(a) Carbon is C, sulfide is sulfur S and di- means 2. The formula is CS2.(b) P is phosphorous, Cl is chloride, the prefix for 5 is penta-. The name of PCl5 is phosphorous pentachloride.(c) N is nitrogen and is in a lower group number than O (oxygen). Therefore the formula is N2O4. Its name is dinitrogen tetraoxide.

Sample Problem 2.13

Recognizing Incorrect Names and Formulas of Binary Covalent Compounds

SOLUTION:

(a) SF4 is monosulfur pentafluoride.

(c) N2O3 is dinitrotrioxide.(b) Dichlorine heptaoxide is Cl2O6.

(a) The prefix mono- is not needed for one atom of the first element; the prefix for four is tetra-. So the name is sulfur tetrafluoride.(b) Hepta- means 7; the formula should be Cl2O7.(c) The first element is given its elemental name so N2O3 is dinitrogen trioxide.

PROBLEM: Explain what is wrong with the name of formula in the second part of each statement and correct it:

Sample Problem 2.14

1) The molecular mass is the sum of all the atomic masses in a given compound

2) For ionic compounds, the molecular mass is calculated as the “formula” mass – use of the lowest integer relationships between each component.

MOLECULAR MASS

(a) Tetraphosphorous trisulfide

(b) Ammonium nitrate

CALCULATE THE MOLECULAR WEIGHT OF THE FOLLOWING:

MOLECULAR MODELS

Using Molecular Depictions to Determine Formula, Name, and Mass

PROBLEM: Each circle contains a representation of a binary compound. Determine its formula, name, and molecular (formula) mass.

Sample Problem 2.16

Physically mixed, therefore can be separated by physical means; in this case by a magnet.

Allowed to react chemically, therefore cannot be separated by physical means.

MIXTURES are combinations of two or more elements or compounds that can be separated by physical means

Heterogeneous mixtures: has one or more visible boundaries between the components.

Homogeneous mixtures: has no visible boundaries because the components are mixed as individual atoms, ions, and molecules.

Solutions: A homogeneous mixture is also called a solution. Solutions in water are called aqueous solutions, and are very important in chemistry. Although we normally think of solutions as liquids, they can exist in all three physical states.

MIXTURES are combinations of two or more elements or compounds that can be separated by physical means

The Components of Matter

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