Atoms,

Molecules,

and Ions

Chapter 2

Atoms, Molecules,

and Ions

Chemistry, The Central Science, 10th edition

Theodore L. Brown; H. Eugene LeMay, Jr.;

and Bruce E. Bursten

Atoms,

Molecules,

and Ions

Atomic Theory of Matter

The theory that atoms

are the fundamental

building blocks of

matter reemerged in

the early 19th century,

championed by John

Dalton.

Atoms,

Molecules,

and Ions

Dalton’s Postulates

1. Each element is composed of

extremely small particles called atoms.

Atoms,

Molecules,

and Ions

Dalton’s Postulates

2. All atoms of a given element are identical to one another in mass and other properties, but the atoms of one element are different from the atoms of all other elements.

Atoms,

Molecules,

and Ions

Dalton’s Postulates

3. Atoms of an element are not changed into atoms of a different element by chemical reactions; atoms are neither created nor destroyed in chemical reactions.

Atoms,

Molecules,

and Ions

Dalton’s Postulates

4. Compounds are formed when atoms of more than one element combine; a given compound always has the same relative number and kind of atoms.

Atoms,

Molecules,

and Ions

Law of Constant Composition Joseph Proust (1754–1826)

• Also known as the law of definite

proportions.

• The elemental composition of a pure

substance never varies.

Atoms,

Molecules,

and Ions

Law of Multiple Proportions • In chemisty the law of multiple proportions is one of the basic

laws and a major tool of chemical measurement (stoichiometry)

• It states that when elements combine they do so in a ratio of

small whole numbers. For example, carbon and oxygen react to

form CO or CO2, but not CO1.8.

Atoms,

Molecules,

and Ions

Atoms,

Molecules,

and Ions

Law of Conservation of Mass

The total mass of substances present at

the end of a chemical process is the

same as the mass of substances

present before the process took place.

Atoms,

Molecules,

and Ions

Atomic Structure

• Discovery of Electrons:

J J Thomson ( in 1897)

He gave the charge to mass ratio of

electrons.

He also showed that the nature of the

cathode ray did not depend on the

material of the cathode.

Atoms,

Molecules,

and Ions

Atoms,

Molecules,

and Ions

Conclusions drawn so far:

1. Cathode ray consists of negatively

charged particles and electrons are

constituents of all matter.

2. The charge on electrons is found to be

1.602 x 10 -19 coulombs.

Atoms,

Molecules,

and Ions

Millikan Oil Drop Experiment

Once the charge/mass

ratio of the electron

was known,

determination of either

the charge or the mass

of an electron would

yield the other.

Atoms,

Molecules,

and Ions

Millikan Oil Drop Experiment

Robert Millikan

(University of Chicago)

determined the charge

on the electron in

1909.

Atoms,

Molecules,

and Ions

• Now since a negative particle was

discovered it was definite that the atom

would also have an equal positive

charge.

• Then at the time the most reasonable

explanation seemed to be a plum

pudding model

Atoms,

Molecules,

and Ions

Atoms,

Molecules,

and Ions

• Rutherford explained the existence of a

focused positively charged nucleus in

the atom.

Atoms,

Molecules,

and Ions

Atoms,

Molecules,

and Ions

Atoms,

Molecules,

and Ions

The Nuclear Atom

• Rutherford postulated a very small, dense nucleus with the electrons around the outside of the atom.

• Most of the volume of the atom is empty space.

Atoms,

Molecules,

and Ions

Radioactivity:

• The spontaneous emission of radiation

by an atom.

• First observed by Henri Becquerel.

• Also studied by Marie and Pierre Curie.

Atoms,

Molecules,

and Ions

Radioactivity

• Three types of radiation were discovered by

Ernest Rutherford:

particles

particles

rays

Atoms,

Molecules,

and Ions

• Dalton Atomic theory

• J J Thomson Electrons and their charge to mass ratio

• Millikan Charge on the electron and later

the mass

• Henry Becquerel Radioactivity

• Rutherford α β and γ radiation

Gold leaf experiment to show the presence

of nucleus and coined the word proton

• James Chadwick Neutrons

Atoms,

Molecules,

and Ions

A. particles are scattered equally across a range of

deflection angles due to the high density of the foil

nuclei.

B. Most particles pass through the foil without being

deflected, because most of the volume of the atoms that

comprise the foil is empty space.

C. Most particles are scattered at acute angles as they

pass close to the foil nuclei.

D. Most particles are deflected in a backwards direction

from the foil due to the high density of the foil atom

nuclei.

Atoms,

Molecules,

and Ions

Subatomic Particles

• Protons and electrons are particles that have a

charge.

• Protons and neutrons have essentially the same

mass.

• The mass of an electron is so small we ignore it.

Atoms,

Molecules,

and Ions

Symbols of Elements

Elements are symbolized by one or two

letters.

Atoms,

Molecules,

and Ions

Atomic Number

All atoms of the same element have the same

number of protons:

The atomic number (Z)

Atoms,

Molecules,

and Ions

Atomic Mass

The mass of an atom in atomic mass units

(amu) is the total number of protons and

neutrons in the atom.

Atoms,

Molecules,

and Ions

Isotopes:

• Atoms of the same element with different masses.

• Isotopes have different numbers of neutrons.

11

6 C 12

6 C 13

6 C 14

6 C

Atoms,

Molecules,

and Ions

Isotopes of Hydrogen

Atoms,

Molecules,

and Ions

Question:

Which among the following represent a set of isotopes? Atomic nuclei

containing

I. 20 protons and 20 neutrons.

II. 21 protons and 19 neutrons.

III. 22 neutrons and 18 protons.

IV. 20 protons and 22 neutrons.

V. 21 protons and 20 neutrons.

Answer

A) I, II, III

B) III, IV

C) I, V

D) I, IV and II, V

E) No isotopes are indicated.

Atoms,

Molecules,

and Ions

138Ba atom has :

(a) 56 protons, 56 electrons, and 82 neutrons

(b)56 protons, 82electrons, and 82 neutrons

(c) 82 protons, 56 electrons, and 82 neutrons

(d)56 protons, 56 electrons, and 56 neutrons

Atoms,

Molecules,

and Ions

Average Mass

• The unit for atomic mass is amu

• Because in the real world we use large

amounts of atoms and molecules, we

use average masses in calculations.

• Average mass is calculated from the

isotopes of an element weighted by

their relative abundances.

Atoms,

Molecules,

and Ions

Naturally occurring chlorine is 75.78% 35Cl, which has an atomic mass of

34.969 amu, and 24.22% 37Cl, which has an atomic mass of 36.966 amu.

Calculate the average atomic mass (that is, the atomic weight) of chlorine

75.78% = 0.7578 and 24.22% = 0.2422,

Average atomic mass = (0.7578)(34.969 amu) + (0.2422)(36.966 amu)

= 26.50 amu + 8.953 amu

= 35.45 amu

Three isotopes of silicon occur in nature: 28Si (92.23%), which has an

atomic mass of 27.97693 amu; 29Si (4.68%), which has an atomic mass of

28.97649 amu; and 30Si (3.09%), which has an atomic mass of 29.97377

amu. Calculate the atomic weight of silicon.

Answer: 28.09 amu

Atoms,

Molecules,

and Ions

Atoms,

Molecules,

and Ions

The extra mass of 0.0989436 u represents

the mass converted into energy when the

fundamental particles combine in forming

the atom.

This energy, called the binding energy,

can be calculated with Einstein’s equation,

E = mc2, where m is the mass

converted into energy, and c is the speed

of light in a vacuum.

Atoms,

Molecules,

and Ions

Modern Periodic Table

• A systematic

catalog of

elements.

• Elements are

arranged in order

of atomic number.

Atoms,

Molecules,

and Ions

Mendeleev’s table as published in 1869, with many gaps

and uncertainties

Atoms,

Molecules,

and Ions

Atoms,

Molecules,

and Ions

Periodicity

When one looks at the chemical properties of

elements, one notices a repeating pattern of

reactivities.

Atoms,

Molecules,

and Ions

Periodic Table

• The rows on the

periodic chart are

called periods.

• Columns are called

groups.

• Elements in the same

group have similar

chemical properties.

Atoms,

Molecules,

and Ions

Groups

These five groups are known by their names.

Atoms,

Molecules,

and Ions

Periodic Table

Nonmetals are on

the right side of the

periodic table (with

the exception of H).

Atoms,

Molecules,

and Ions

Periodic Table

Metalloids border

the stair-step line

(with the exception

of Al and Po).

Atoms,

Molecules,

and Ions

Periodic Table

Metals are on the left side of the chart.

Note that there are more metals than nonmetals

Atoms,

Molecules,

and Ions

The element __________ is the most similar to strontium (Sr) in chemical

and physical properties.

A) Li B) At C) Cs D) Rb E) Ba

Atoms,

Molecules,

and Ions

Chemical Formulas

H2O, CO2, CO, CH4,

H2O2,O2

The subscript to the right

of the symbol of an

element tells the number

of atoms of that element

in one molecule of the

compound.

Atoms,

Molecules,

and Ions

Molecular Compounds

Molecular compounds

are composed of

molecules and almost

always contain only

nonmetals.

Atoms,

Molecules,

and Ions

Diatomic Molecules

These seven elements occur naturally as

molecules containing two atoms.

Atoms,

Molecules,

and Ions

Allotropes

• Many elements like C, O and S exist in

more than one form in nature.

Oxygen :

dioxygen O2 - colorless

ozone O3 - blue

Atoms,

Molecules,

and Ions

Carbon:

• Diamond - an extremely hard, transparent crystal, with the carbon atoms arranged in a tetrahedral lattice. A poor electrical conductor. An excellent thermal conductor.

• Graphite - a soft, black, flaky solid, a moderate electrical conductor. The C atoms are bonded in flat hexagonal lattices, which are then layered in sheets.

• amorphous carbon

• fullerenes including "buckyballs", such as C60, and carbon nanotubes

Atoms,

Molecules,

and Ions

• Carbon Nanotube

Atoms,

Molecules,

and Ions

Phosphorus:

White phosphorus - crystalline solid P4

Red phosphorus - polymeric solid

Atoms,

Molecules,

and Ions

Sulfur

• Plastic (amorphous) sulfur - polymeric solid

• Rhombic sulfur - large crystals composed of

S8 molecules

• Monoclinic sulfur - fine needle-like crystals

• Other ring molecules such as S7 and S12

Atoms,

Molecules,

and Ions

Types of Formulas

• Molecular formulas give the exact

number of atoms of each element in

a compound.

• Empirical formulas give the lowest

whole-number ratio of atoms of each

element in a compound.

Atoms,

Molecules,

and Ions

__________ are found uncombined, as monatomic species in nature.

A) Noble gases

B) Halogens

C) Alkali metals

D) Alkaline earth metals

E) Chalcogens

Atoms,

Molecules,

and Ions

Types of Formulas

• Structural formulas show the

order in which atoms are

bonded.

• Perspective drawings also

show the three-dimensional

array of atoms in a

compound.

Atoms,

Molecules,

and Ions

Ions

• When atoms lose or gain electrons, they

become ions.

Cations are positive and are formed by elements

on the left side of the periodic chart.

Anions are negative and are formed by elements

on the right side of the periodic chart.

Atoms,

Molecules,

and Ions

Beryllium

• The chemistry of Beryllium is

dominated by its tendency to lose an

electron to form Be2+. As this ion is so

small it is highly polarizing to the

neighboring atom, to the extent that its

compounds are mostly covalent.

Atoms,

Molecules,

and Ions

• Polyatomic ions

• The ions that contain more than one

atom. These can be cations or anions

• NH4+ , CO3

2-

• Within the polyatomic ion the elements

are covalently linked. But they have an

overall charge.

Atoms,

Molecules,

and Ions

Poly atomic ions:

1. Only two cations:

NH4+ and H3O

+

2. Anions are many

In most chemical reactions the polyatomic

ions will move as a whole.

Atoms,

Molecules,

and Ions

Ionic Bonds

Ionic compounds (such as NaCl) are

generally formed between metals and

nonmetals.

Atoms,

Molecules,

and Ions

Atoms,

Molecules,

and Ions

______ form ions with a 2+ charge when

they react with nonmetals.

A) Alkali metals

B) Alkaline earth metals

C) Halogens

D) Noble gases

E) None of these choices

Atoms,

Molecules,

and Ions

All ionic compounds are crystalline

solids with high melting points.

Atoms,

Molecules,

and Ions

Writing Formulas

• Because compounds are electrically neutral,

one can determine the formula of a

compound this way:

The charge on the cation becomes the subscript

on the anion.

The charge on the anion becomes the subscript

on the cation.

If these subscripts are not in the lowest whole-

number ratio, divide them by the greatest common

factor.

Atoms,

Molecules,

and Ions

Common Cations

Atoms,

Molecules,

and Ions

Common Anions

Atoms,

Molecules,

and Ions

Inorganic Nomenclature

• Write the name of the cation.

• If the anion is an element, change its

ending to -ide; if the anion is a

polyatomic ion, simply write the name of

the polyatomic ion.

Atoms,

Molecules,

and Ions

If the cation can have more than one possible charge,

write the charge as a Roman numeral in

parentheses.

This happens in the case of transition metals.

The other metals will have only a fixed charge.

Atoms,

Molecules,

and Ions

The 7th group elements are called

A) Alkali metals

B) Alkaline earth metals

C) Halogens

D) Noble gases

E) None of these choices

Atoms,

Molecules,

and Ions

Atoms,

Molecules,

and Ions

Which of the following is a transition metal and will have more than

one kind of ion.

A. Na

B. F

C. Fe

D. Al

E. Cs

Atoms,

Molecules,

and Ions

Patterns in Oxyanion Nomenclature

• When there are two oxyanions involving

the same element:

The one with fewer oxygens ends in -ite

• NO2− : nitrite; SO3

2− : sulfite

The one with more oxygens ends in -ate

• NO3− : nitrate; SO4

2− : sulfate

Atoms,

Molecules,

and Ions

indicating that a chemical compound contains a high proportion of a specified element: peroxide ; perchloride. indicating that a chemical element is in a higher than usual state of oxidation: permanganate ; perchlorate

Atoms,

Molecules,

and Ions

•

ClO − : hypochlorite

ClO2− : chlorite

ClO3− : chlorate

ClO4− : perchlorate

Atoms,

Molecules,

and Ions

Anions derived by adding H+ to the oxy

anion:

• CO32- and HCO3

-

Carbonate and hydrogen carbonate

• PO43- , H2PO4

-

Phosphate and dihydrogen phosphate

Atoms,

Molecules,

and Ions

Acid Nomenclature

• If the anion in the acid

ends in -ide, change

the ending to -ic acid

and add the prefix

hydro- :

HCl: hydrochloric acid

HBr: hydrobromic acid

HI: hydroiodic acid

Atoms,

Molecules,

and Ions

Acid Nomenclature

• If the anion in the acid

ends in -ate, change

the ending to -ic acid:

HClO3: chloric acid

HClO4: perchloric acid

Atoms,

Molecules,

and Ions

Acid Nomenclature

• If the anion in the acid

ends in -ite, change

the ending to -ous

acid:

HClO: hypochlorous

acid

HClO2: chlorous acid

Atoms,

Molecules,

and Ions

Other than this you need to know the names of

Acetic acid,

phosphoric acid,

chlorous acid and

hypochlorous acid for now

Atoms,

Molecules,

and Ions

When a metal and a nonmetal react, the __________ tends to lose

electrons and the __________

tends to gain electrons.

A) metal, nonmetal

B) nonmetal, metal

C) nonmetal, nonmetal

D) metal, metal

E) None of the above, these elements share electrons .

Atoms,

Molecules,

and Ions

Covalent Compounds

• Covalent compounds are formed

between two nonmetals.

• Covalent compounds can be solids,

liquids or gases at room temperature.

Atoms,

Molecules,

and Ions

Nomenclature of Binary

Compounds

• The less electronegative atom is usually listed first.

• A prefix is used to denote the number of atoms of each element in the compound (mono- is not used on the first element listed, however.)

Atoms,

Molecules,

and Ions

Nomenclature of Binary

Compounds

• The ending on the more

electronegative element is

changed to -ide.

CO2: carbon dioxide

CCl4: carbon tetrachloride

Atoms,

Molecules,

and Ions

Nomenclature of Binary

Compounds

If the prefix ends with a or o and the name of the element begins with a vowel, the two successive vowels are often elided into one:

N2O5: dinitrogen pentoxide

Atoms,

Molecules,

and Ions

The correct name for N2O5 is __________.

A) nitric oxide

B) nitrogen pentoxide

C) nitrogen oxide

D) nitrous oxide

E) dinitrogen pentoxide

Atoms,

Molecules,

and Ions

The correct name for CaH2 is

A) calcium hydride

B) hydrocalcium

C) calcium dihydride

D) calcium dihydroxide

E) calcium hydroxide