Atoms, Molecules and Ions

Chapter 23 Lectures

Copyright © The McGraw-Hill Companies, Inc.  Permission required for reproduction or display.

Chapter 2 Topics

Dr. Ali Bumajdad

• Chemical laws1) Law of Conservation of mass2) Law of definite Proportion3) Law of Multiple Proportions•Dalton’s Atomic Theory•Early Atom Characterization•Atomic number, mass number & Isotopes•Introduction to periodic Table •Molecules and Ions•Chemical Formulas•Chemical nomenclature •Introduction to Organic Compounds

Atoms, Molecules and Ions

Chemical laws

1) Law of Conservation of massIn any chemical reaction mass neither created nor destroyed

balancing chemical equation

Mg + O2 MgO

What about the second O !!!

•What is the benefit of this law?

Dr. Ali Bumajdad

2) Law of definite ProportionDifferent pure samples of a compound always contain the same elements in the same proportion by mass

5 grams of waterH:O mass ratio 1:8

50000 grams of waterH:O mass ratio 1:8

e.g. In a sample of H2O that have 3.00 g of H it should have 24.0 g of O because:

•What is the benefit of this law?

8

1

24

3

e.g. If I have 3.00 g of H and 8.00 g of O and they react, does the reaction proceeds until all chemicals react?

No, 2.00 g of H remain unreacted

Q) A sample of NaCl contains 23.0 g of Na and 35.5 g of Cl, In a different sample of NaCl, how many grams of Na would be combined with 71.0 g of Cl.

Mass of Na = 46.0 g

3) Law of Multiple ProportionsWhen two elements, A and B, form more than one compound, If the masses of one element are the same in the two samples, then the

masses of the other element are in a ratio of small whole numbers.

Dr. Ali Bumajdad

Q)In a sample of 2.33 g of CO we find 1.33 g of O combined with 1.00 g of C

In a sample of 3.66 g of CO2 we find

2.66 g of O combined with 1.00 g of C

Show that the data support the law of Multiple proportions

1

2

33.1

66.2 A ratio of small whole numbers

•What is the benefit of this law?

Dr. Ali Bumajdad

Q) (Not very Important)What is the ratio of masses of O that are combined with 1.00 g of N in the compounds NO and N2O3

Here we need to use both law of definite proportion and law of multiple proportions

2

3

0.1

5.1

14.1

71.1

71.10.28

0.48

1

?

14.10.14

0.16

1

?

32

g

g

OofgNg

Og

Ng

OgONin

OofgNg

Og

Ng

OgNOin

Dr. Ali Bumajdad

Dalton’s Atomic Theory(1808)

Dr. Ali Bumajdad

Dalton’s Atomic Theory(1808)

1. Elements are composed of extremely small particles called atoms. All atoms of a given element are identical, having the same size, mass and chemical properties.

2. Compounds are composed of atoms of more than one element. The relative number of atoms of each element in a given compound is always the same.

3. Chemical reactions only involve the rearrangement of atoms. Atoms are not created or destroyed in chemical reactions.

Dr. Ali Bumajdad

Early Atom Characterization

The electron discovery

•J.J. Thomson (English physicist, 1856-1940) •Studied the electrical discharges in evacuated tubes called ‘Cathode-ray tubes’•1906 Nobel Prize in Physics

Dr. Ali Bumajdad

Cathode Ray TubeGlass tube evacuated from air

Cathode

-Anode

+

High Voltage

He Found particles transfer from Cathode to Anode it must be negative particles

• In 1897 He measured mass/charge of e- and found it to be -1.76 × 108 C/g using

e/m = E / B L (not Important)

E

B

L

• Thomson said ‘since e- can be produced from different metals then all atoms must contains e-’

• It is known that atoms are neutral. Because of that Thomson assumed that atoms also contain positive charges. He assumes atoms as a cloud of +ve charge with – ve electrons dispersed in it.

Dr. Ali Bumajdad

Millikank’s e- charge = -1.60 x 10-19 C

Thomson’s charge/mass of e- = -1.76 x 108 C/g

Millikank’s e- mass = 9.10 x 10-28 g

The electron charge and mass discoveryBritish

Dr. Ali Bumajdad

•R. A. Millikan (1868-1953) measured e- charge and mass of e-

•1923 Nobel Prize in Physics

•He sprayed oil with atomizer

• Some of these small drops fall dawn from the upper small hole

•He determine the mass of oil drop from its velocity

•Next he ionized the chamber gas using X-ray source

Dr. Ali Bumajdad

•Some of these charge adhere to the oil droplets by controlling the voltage across the plates, the negatively charge droplets slow down

• At certain voltage the oil drop can be suspended

• At this point m × g = q × E

•Now q can be found

•He found always q = n × small chargewhere n is an integer

• This small charge were found to be -1.60 × 10-19C

•He said this is the charge of e-

•Then he used e- × (m / e-) to find m

(e.g. Uranium: emit radiation spontaneously)

The discovery of radiation

Alpha, = particles with +2 charge (i.e. 2 ×1.60 x 10-19 C) Beta, = high speed e-

Gamma, = high energy light (no charge)

A.H. Becquerel (1845-1923)

Nobel Prize in 1901

French

Dr. Ali Bumajdad

The discovery proton and nucleus

New Zealand but did most of his

work in England• Rutherford (1871-1937) tested Thomson Model• He directed particles at a thin Sheet of metal a) If there were no big deflection then Thomson model correctb) If there were big deflection then Thomson model wrong

He found some particles not only deflected but even scattered or bounced back• So he assume a new model: - most of the atom are empty space - the atom’s +ve charge are concentrated in the center

Nobel prize 1908

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)

particle velocity ~ 1.4 x 107 m/s(~5% speed of light)

Rutherford’s Model of the Atom

- Atomic radius ~ 100 pm = 1 x 10-10 m

- nuclear radius ~ 5 x 10-3 pm = 5 x 10-15 m

- P + ve charge = e –ve charge = 1.6 × 10-19 C

- N are neutral and its mass mass of P 1.67 x 10-24 g

Mass of atom mass of nucleus

-Nucleus are very dense (a pea have a mass of 250 million tons) in chemistry e is more important that P

mass p = mass n = 1840 x mass e-

•Mass number (A) = number of protons + number of neutrons

= atomic number (Z) + number of neutrons

• Atomic number (Z) = number of protons in nucleus

XAZ

H11 H (D)2

1 H (T)31

U23592 U238

92

Mass Number

Atomic NumberElement Symbol

Atomic number, mass number & Isotopes

•Isotopes: atoms of the same element has the same number of P

but different numbers of N

Dr. Ali Bumajdad

6 protons, 8 (14 - 6) neutrons, 6 electrons

How many protons, neutrons, and electrons are in C14

6 ?Q)

6 protons, 5 (11 - 6) neutrons, 6 electrons

How many protons, neutrons, and electrons are in C11

6 ?Q)

Atom has an atomic number of 9 and a mass of 19. What is it symbol? How many e’s and N’s does it contain?

Sa. Ex. 2.2:

F, 9 electrons,10 (19 - 9) neutrons,

8 protons, 8 (16 - 8) neutrons, 10 electrons

How many protons, neutrons, and electrons are in O-216

?Q)

Dr. Ali Bumajdad

13 protons, 10 (13 – 3) electrons

34 protons, 36 (34 + 2) electrons

How many protons and electrons are in ?Al2713

3+

How many protons and electrons are in ?Se7834

2-

Q)

Q)

Period

Group

Alkali M

etal

Noble G

as

Halogen

Alkali E

arth Metal

Introduction to periodic Table

diatomic

monatomic

•Metals: Good conductor of heat and electricity, malleability (can be hammered), ductility (can be wired), shiny, tend to lose e- to form +ve ions, form ionic bond with non-metals

•Non-Metals: Poor conductor of heat and electricity, can not be hammered, can not be wired, not shiny, tend to gain e- to form -ve ions, form ionic bond with metals and covalent bond with nonmetal

•Metalloid: Intermediate properties between metals •and non-metals

•Groups: Vertical columns, element having similar physical and chemical properties

•Periods: Horizontal rows

A molecule is an aggregate of two or more atoms in a definite arrangement held together by chemical bonds

H2 H2O NH3 CH4

A diatomic molecule contains only two atomsH2, N2, O2, Br2, HCl, CO

A polyatomic molecule contains more than two atoms

O3, H2O, NH3, CH4

Molecules and Ions

A Covalent bond bond formed by sharing of e-( non-metalnon-metal)An Ionic bond bond formed by attraction between ions (metal non-metal) Dr. Ali Bumajdad

An ion is an atom, or group of atoms, that has a net positive or negative charge.

cation – ion with a positive chargeIf a neutral atom loses one or more electronsit becomes a cation.

anion – ion with a negative chargeIf a neutral atom gains one or more electronsit becomes an anion.

Na 11 protons11 electrons Na+ 11 protons

10 electrons

Cl 17 protons17 electrons Cl-

17 protons18 electrons

Dr. Ali Bumajdad

A monatomic ion contains only one atom

A polyatomic ion contains more than one atom

Na+, Cl-, Ca2+, O2-, Al3+, N3-

OH-, CN-, NH4+, NO3

-

Some Common Polyatomic Ions

Name Symbol Charge

bicarbonate (or hydrogen carbonate)

HCO3- (e.g. NaHCO3) -1

bisulfate (or hydrogen sulfate) HSO4- (e.g. NaHSO4) -1 

chlorate ClO3- (e.g. NaClO3) -1

cyanide CN- (e.g. NaCN) -1

dihydrogen phosphate H2PO4- (e.g. NaH2PO4) -1 

hydroxide OH- (e.g. NaOH) -1 

Nitrate NO3- (e.g. NaNO3) -1 

nitrite NO2- (e.g. NaNO2) -1 

perchlorate ClO4- (e.g. NaClO4) -1 

permanganate MnO4- (e.g. KMnO4) -1 

carbonate CO32- (e.g. Na2CO3) -2

hydrogen phosphate HPO42- (e.g. Na2HPO4) -2 

peroxide O22- (e.g. H2O2) -2

sulfate SO42- (e.g. H2SO4) -2

sulfite SO32- (e.g. H2SO3) -2

phosphate PO43- (e.g. H3PO4) -3

ionic compounds consist of a combination of cations and an anions

• The sum of the charges on the cation(s) and anion(s) in each formula unit must equal zero

The ionic compound NaCl

Formula of Ionic Compounds

Al2O3

2 x +3 = +6 3 x -2 = -6

Al3+ O2-

CaBr2

1 x +2 = +2 2 x -1 = -2

Ca2+ Br-

Na2CO3

2 x +1 = +2 1 x -2 = -2

Na+ CO32-

Chemical Formulas

Molecular FormulaEmpirical Formula Structural Formula

Show exact numberShow simplest-whole number ratio

Show :1) Exact number2) How atoms are bonded to one another

H2O H2O

C6H12O6CH2O

O3O

N2H4NH2

Dr. Ali Bumajdad

- Chemical nomenclature: the naming of chemical compounds.

- We must first distinguish between organic and inorganic compounds.

- Organic compounds contain carbon (C), usually in combination with elements

such as hydrogen (H), oxygen (O), nitrogen (N), and sulfur (S).

- All other compounds are classified as inorganic compounds.

For convenience, some carbon-containing compounds such as: carbon monoxide

(CO), carbon dioxide (CO2), carbon disulfide (CS2), cyanide group (CN-), carbonate

(CO32-) and bicarbonate (HCO3

-) groups are considered to be inorganic

compounds.

- We can divide inorganic compounds into four categories:

1. ionic compounds, 2. molecular compounds, 3. acids and bases, and

4. hydrates

Chemical Nomenclature: Ionic Compounds

- Ionic Compounds are:

1. Often a metal (+ve - start) and a nonmetal (-ve - end)

2. Anion (nonmetal), add “-ide” to element name

3. Many ionic compounds are binary compounds: compounds formed from just two elements e.g. NaCl.

4. Some ionic compounds are ternary compounds: compounds consist of three elements e.g. LiOH.

BaCl2

Metal Nonmetal + ide

barium chloride

K2O potassium oxide

Mg(OH)2 magnesium hydroxide

KNO3 potassium nitrate

- Transition metal (can have multiple charges) ionic compounds:

1. indicate charge on metal with Roman numerals (I, II, III, IV, V, VI, VII)

FeCl2 2 Cl- -2 so Fe is +2 iron(II) chloride

FeCl3 3 Cl- -3 so Fe is +3 iron(III) chloride

Cr2S3 3 S-2 -6 so Cr is +3 (6/2) chromium(III) sulfide

Ionic CompoundsThe cation (+ve): Transition metal

Look at the charge!

Ionic CompoundsThe Anion (-ve)

Name the following compounds:

(a)Cu(NO3)2

contain both metal and nonmetal atoms, copper(II) nitrate

(b) KH2PO4

contain both metal and nonmetal atoms, potassium dihydrogen phosphate

(c) NH4ClO3

ammonium group, which bears a positive charge. So NH4ClO3 is also an ionic compound, ammonium chlorate

Strategy Note that the compounds in (a) and (b) contain both metal and nonmetal atoms, so we expect them to be ionic compounds.

There are no metal atoms in (c) but there is an ammonium group, which bears a positive charge. So NH4ClO3 is also an

ionic compound.

Our reference for the names of cations and anions is Table 2.3.

Keep in mind that if a metal atom can form cations of different charges (see Figure 2.11), we need to use the Stock system.

Solution

(a)The nitrate ion ( ) bears one negative charge, so the copper ion must have two positive charges. Because copper forms both Cu+ and Cu2+ ions, we need to use the Stock system and call the compound copper(II) nitrate.

(b)The cation is K+ and the anion is (dihydrogen phosphate). Because potassium only forms one type of ion (K+), there is no need to use potassium(I) in the name. The compound is potassium dihydrogen phosphate.

(c) The cation is (ammonium ion) and the anion is . The compound is ammonium chlorate.

Write chemical formulas for the following compounds:

(a)mercury(I) nitrite Hg2(NO2)2

(b)cesium sulfide Cs2S

(c)calcium phosphate Ca3(PO4)2

Strategy

We refer to Table 2.3 for the formulas of cations and anions.

Recall that the Roman numerals in the Stock system provide useful information about the charges of the cation.

Solution

(a)The Roman numeral shows that the mercury ion bears a +1 charge. According to Table 2.3, however, the mercury(I) ion is diatomic (that is, ) and the nitrite ion is . Therefore, the formula is Hg2(NO2)2.

(b)Each sulfide ion bears two negative charges, and each cesium ion bears one positive charge (cesium is in Group 1A, as is sodium). Therefore, the formula is Cs2S.

(c) Each calcium ion (Ca2+) bears two positive charges, and each phosphate ion ( ) bears three negative charges.

To make the sum of the charges equal zero, we must adjust the numbers of cations and anions:

3(+2) + 2(−3) = 0

Thus, the formula is Ca3(PO4)2.

- Molecular compounds: Nonmetals or nonmetals +

metalloids

1. Common examples: H2O, NH3, CH4

2. Element furthest to the left in a period and

closest to the bottom of a group on periodic

table is placed first in formula

3. If more than one compound can be formed from

the same elements, use prefixes to indicate

number of each kind of atom

4. Last element name ends in -ide

Chemical Nomenclature: Molecular compounds

HI hydrogen iodide

NF3 nitrogen trifluoride

SO2 sulfur dioxide

N2Cl4 dinitrogen tetrachloride

NO2 nitrogen dioxide

N2O dinitrogen monoxide

Chemical Nomenclature: Molecular compounds

- Exceptions to the use of Greek prefixes are molecular compounds containing

hydrogen.

- Traditionally, many of these compounds are called either by their common,

nonsystematic names or by names that do not specifically indicate the number

of H atoms present:

Name the following molecular compounds:

(a) SiCl4 silicon tetrachloride

(b) P4O10 tetraphosphorus decoxide

Strategy

We refer to Table 2.4 for prefixes.

In (a) there is only one Si atom so we do not use the prefix “mono.”

Solution

(a)Because there are four chlorine atoms present, the compound is silicon tetrachloride.

(b)There are four phosphorus atoms and ten oxygen atoms present, so the compound is tetraphosphorus decoxide. Note that the “a” is omitted in “deca.”

Write chemical formulas for the following molecular compounds:

(a)carbon disulfide CS2

(b) disilicon hexabromide Si2Br6

Strategy

Here we need to convert prefixes to numbers of atoms (see Table 2.4).

Because there is no prefix for carbon in (a), it means that there is only one carbon atom present.

Solution

(a)Because there are two sulfur atoms and one carbon atom present, the formula is CS2.

(b) There are two silicon atoms and six bromine atoms present, so the formula is Si2Br6.

- An acid: a substance that yields (produces) hydrogen ions (H+) when dissolved

in water. Formulas for acids contain one or more hydrogen atoms as well as an

anionic group. Anions whose names end in “-ide” form acids with a “hydro-”

prefix and an “-ic” ending, as shown in Table 2.5 .

-For example: HCl gas and HCl in water, dissolved in water (H3O+ and Cl−),

hydrochloric acid

Chemical Nomenclature: acids

- Oxoacids: are acids that contain hydrogen, oxygen, and another element (the

central element).

- The formulas of oxoacids are usually written with the H first, followed by the

central element and then O. We use the following five common acids as our

references in naming oxoacids:

-Often two or more oxoacids have the same central atom but a different

number of O atoms.

- Starting with our reference oxoacids whose names all end with “-ic,” we use

the following rules to name these compounds.

1. Addition of one O atom to the “-ic” acid: The acid is called “per . . . -ic” acid.

Thus, adding an O atom to HClO3 changes chloric acid to perchloric acid, HClO4.

2. Removal of one O atom from the “-ic” acid: The acid is called “-ous” acid. Thus,

nitric acid, HNO3, becomes nitrous acid, HNO2.

3. Removal of two O atoms from the “-ic” acid: The acid is called “hypo . . . -ous”

acid. Thus, when HBrO3 is converted to HBrO, the acid is called hypobromous

acid.

Naming oxoacids and oxoanions.

The rules for naming oxoanions, anions of oxoacids, are as follows:

1. When all the H ions are removed from the “-ic” acid, the anion’s name ends with

“-ate.” For example, the anion CO32- derived from H2CO3 is called carbonate.

2. When all the H ions are removed from the “-ous” acid, the anion’s name ends

with “-ite.” Thus, the anion ClO2- derived from HClO2 is called chlorite.

3. The names of anions in which one or more but not all the hydrogen ions have

been removed must indicate the number of H ions present. For example, consider

the anions derived from phosphoric acid:

Table 2.6 gives the names of the oxoacids and oxoanions that contain chlorine.

Name the following oxoacid and oxoanion:

(a)H3PO3 reference acid, phosphoric acid (H3PO4). This is

phosphorous acid

(b) The parent acid is HIO4. has one more O atom than our reference iodic acid (HIO3), it is called periodic acid. Therefore, the anion derived from HIO4 is called periodate.

Strategy To name the acid in (a), we first identify the reference acid, whose name ends with “ic,” as shown in Figure 2.15.

In (b), we need to convert the anion to its parent acid shown in Table 2.6.

Solution

(a)We start with our reference acid, phosphoric acid (H3PO4). Because H3PO3 has one fewer O atom, it is called phosphorous acid.

(b)The parent acid is HIO4. Because the acid has one more O atom than our reference iodic acid (HIO3), it is called periodic acid. Therefore, the anion derived from HIO4 is called periodate.

Naming Bases

A base: a substance that yields hydroxide ions (OH-) when dissolved in water. Some

examples are:

Ammonia (NH3), a molecular compound in the gaseous or pure liquid state, isalso classifi ed as a common base.

- Hydrates: are compounds that have a specific number of water molecules

attached to them.

Hydrates

- For example, in its normal state, each unit of copper(II) sulfate has five

water molecules. The systematic name for this compound is copper(II) sulfate

pentahydrate, and its formula is written as:

CuSO4.5H2O.

Organic chemistry: is the branch of chemistry that deals with carbon compounds

Table 2.8 shows the names, formulas, and molecular models of the first ten

straight-chain alkanes, in which the carbon chains have no branches. Note that

all the names end with - ane .

- The chemistry of organic compounds is largely

determined by the functional groups. For example,

when an H atom in methane is replaced by a hydroxyl

group (-OH), an amino group (-NH2), and a carboxyl group

(-COOH).

- All will be discussed in chapter 24