111 - Chapter 2

7/27/2019 111 - Chapter 2

1/55

Chapter 2

Atoms, Molecules, and Ions

Dr. Garland Crawford

7/27/2019 111 - Chapter 2

2/55

John Dalton and the Atomic Theory of Matter

Elements are composed of

extremely small, particles calledatoms.

All atoms of a given element areidentical, having the same size,mass, and chemical properties.

The atoms of one element aredifferent from the atoms of otherelements.

Compounds are atoms of different

elements united in fixed proportions(AB, AB2, A2B3)

In a chemical reaction, no atoms arecreated, destroyed, or broken apartbut rearranged to produce new

compounds

7/27/2019 111 - Chapter 2

3/55

The Atomic Theory

All the oxygen molecules are identical

CO2 forms when carbon atoms combine with two oxygen atoms

All atoms present before the reaction are present after the

reaction

7/27/2019 111 - Chapter 2

4/55

The Atomic Theory

Law of def in i te prop ort ions

Joseph Proust - all samplesof a compound contain the same elements in the same

mass ratio

Sample Mass of O (g) Mass of C (g) Ratio (g O : g C)

123 g carbon dioxide 89.4 33.6 2.66:1

50.5 g carbon dioxide 36.7 13.8 2.66:1

88.6 g carbon dioxide 64.4 24.2 2.66:1

7/27/2019 111 - Chapter 2

5/55

The Atomic Theory

Law of mul t ip le proport ions- If two elements

form more than one compound between them, thenthe ratios of the masses of the second element

which combine with a fixed mass of the first

element will be ratios of small whole numbers

7/27/2019 111 - Chapter 2

6/55

The Atomic Theory

1

2=

O to C ratio in CO

O to C ratio in CO2

7/27/2019 111 - Chapter 2

7/55

The Structure of the Atom

Is the Dalton atom divisible?

7/27/2019 111 - Chapter 2

8/55


When metal plates are connected to a high-voltage source, the

negatively charged plate, orcathode, emits a ray.

The cathode ray is drawn to the anode.

Cathode(-)

Anode(+)

7/27/2019 111 - Chapter 2

9/55


Cathode rays

Deflected by magnetic or electric fields

Mass/Charge Ratio determined by J.J. Thompson

Composed of electrons - negatively charged particles

7/27/2019 111 - Chapter 2

10/55


R. A. Millikan measured the charge of an electron with great precision.

1928

8

charge 1.6022 10 Cmass of an electron = = = 9.10 10 g

charge / mass 1.76 10 C/g

7/27/2019 111 - Chapter 2

11/55

Early Model of the Atom

Atoms containnegatively chargedelectrons

Atoms are neutral How is the positive

charge evenlydistributed?

7/27/2019 111 - Chapter 2

12/55


Radioactive decay:

Alpha () rays- positively charged

Beta () rays - negatively charge

Gamma () rays- no charge; very high energy waves

7/27/2019 111 - Chapter 2

13/55


Ernest Rutherford

Used particles to study the

atoms in gold foil

7/27/2019 111 - Chapter 2

14/55


Rutherfords new model for the

atom the Planetary Model:

Positive charge is

concentrated in the nucleus

The nucleus accounts for most

of an atoms mass

A typical atomic radius is about

100 pm (1 Angstrom)

A typical nucleus has a radius

of about 5 x 103 pm

7/27/2019 111 - Chapter 2

15/55


Protons- positively chargedparticles in the nucleus

Neutrons- electronically neutral

particles in the nucleus

Electronsnegatively charged,

distributed around the nucleus

7/27/2019 111 - Chapter 2

16/55

Understanding the Atom

The basics of atomic structure

What do we know about subatomic particles (protons,neutrons, electrons)?

What do we know about electrons?

How do we know about the structure of the atom? Whyis it important?

7/27/2019 111 - Chapter 2

17/55

John Dalton and the Atomic Theory of Matter

Elements are composed ofextremely small, particles calledatoms.

All atoms of a given element areidentical, having the same size,mass, and chemical properties.

The atoms of one element aredifferent from the atoms of otherelements.

Compounds are atoms of different

elements united in fixed proportions(AB, AB2, A2B3)

In a chemical reaction, no atoms arecreated, destroyed, or broken apartbut rearranged to produce new

compounds

7/27/2019 111 - Chapter 2

18/55

Atomic Number and Mass Number

Elemental symbol

Atoms are identified by the number of protons and neutrons

they contain

Elemental symbol Abbreviation for element

Atomic number (Z) - the number of protons in the nucleus

Mass number (A) - the total number of protons and neutrons

Mass number

(number of protons + neutrons)

Atomic number

(number of protons)

XZ

A

7/27/2019 111 - Chapter 2

19/55

Isotopes!

Isotopes of an element have the same atomic number, butdifferent mass numbers

7/27/2019 111 - Chapter 2

20/55

Atomic Number, Mass Number, and Isotopes

Most elements have two or more isotopes

hydrogen

1 proton

0 neutrons

deuterium

1 proton

1 neutron

tritium

1 proton

2 neutrons

1

1H

3

1H

2

1H

Isotopes of the same element exhibit similar chemical properties

7/27/2019 111 - Chapter 2

21/55

How many neutrons are in the

following atom?

17Cl

35

7/27/2019 111 - Chapter 2

22/55

The Atomic Mass Scale and Average Atomic Mass

Molecular mass is measured in a mass spectrometer

7/27/2019 111 - Chapter 2

23/55


7/27/2019 111 - Chapter 2

24/55

Atomic mass is the mass of an atom in atomic mass units (amu).

1 amu = 1/12 the mass of a carbon-12 atom

The atomic weight on the periodic table represents the average mass of the

naturally occurring mixture of isotopes.

Average mass (C) = (0.9893)(12.00000 amu) + (0.0107)(13.003355 amu)

Average mass (C) = 12.01 amu

IsotopeIsotopic mass

(amu)

Natural

abundance (%)

12C 12.00000 98.93

13C 13.003355 1.07


7/27/2019 111 - Chapter 2

25/55

The atomic mass and natural abundances of the two stable isotopes of

copper are given below. Calculate the average atomic mass.

IsotopeIsotopic

mass (amu)

Natural

abundance

(%)

63Cu 62.929599 69.17

65Cu 64.927793 30.83


7/27/2019 111 - Chapter 2

26/55

The Periodic Table

Elements with similar chemical and physical properties are

grouped together

7/27/2019 111 - Chapter 2

27/55

Elements can be categorized as metals, nonmentals or metalloids.

Metals- good conductors

of heat and electricity

Nonmetals- poor

conductors of heat or

electricity

Metalloids- have

intermediate properties

The Periodic Table

7/27/2019 111 - Chapter 2

28/55

The Periodic Table

Horizontal rows are called periods

Vertical columns are called groups orfamilies

7/27/2019 111 - Chapter 2

29/55

The Periodic Table

7/27/2019 111 - Chapter 2

30/55

Compounds

Molecular Compounds

Ionic Compounds

7/27/2019 111 - Chapter 2

31/55

Molecules and Molecular Compounds

Molecule - a combination of at least two atoms held together by

chemical bonds

May be an elementor a compound

Diatomic molecules - contain two atoms and may be either

heteronuclear orhomonuclear.

Polyatomicmolecules - contain more than two atoms.

7/27/2019 111 - Chapter 2

32/55

Chemical formula denotes the

composition of a substance

Molecular formula denotes the

exact number of atoms of each

element in a molecule

Structural formula shows the

elemental composition and the

general arrangements


7/27/2019 111 - Chapter 2

33/55


Binarymo lecular compounds

Nomenclature:

1) Name the first element that appears in the formula

2) Name the second element that appears in the formula,

changing its ending to ide.

Examples:

HCl hydrogen chloride

HI hydrogen iodide.

7/27/2019 111 - Chapter 2

34/55


Greek prefixes denote the number of atoms of each element present

Examples:

SO2 sulfur dioxide

CO carbon monoxide

The prefix mono- is generally omitted for the first element.

N2O5 dinitrogen pentoxide

7/27/2019 111 - Chapter 2

35/55


Name the following binary molecular compounds:

(a) Cl2O

(b) SiCl4

7/27/2019 111 - Chapter 2

36/55


Write the formula for the following compounds

(a) carbon disulfide

(b) dinitrogen trioxide

7/27/2019 111 - Chapter 2

37/55


Acid- a substance that produces hydrogen ions (H+) when

dissolved in water

HCl is an example

To name these types of acids:

1) remove thegen ending from hydrogen

2) change theide ending on the second element toic.

hydrogen chloride +icacid hydrochloric acid

7/27/2019 111 - Chapter 2

38/55


Acid- a substance that produces hydrogen ions (H+) when

dissolved in water

Examples:

HF hydrofluoric acid

HCl hydrochloric acid

HBr hydrobromic acid

HI hydroiodic acid

7/27/2019 111 - Chapter 2

39/55


Organic compounds

contain carbon andhydrogen, sometimes in

combination with other

atoms

Hydrocarbons contain only

carbon and hydrogen

7/27/2019 111 - Chapter 2

40/55


Molecular formulas give the exact number of each type ofelement in a compound.

Empirical formulas give the simplest ratio of elements in a

compound.

7/27/2019 111 - Chapter 2

41/55


7/27/2019 111 - Chapter 2

42/55


Write the empirical formula for the following compound:

C8H10N4O2

A) C8H10N4O2B)C4H5N2O1

C)C6

H5

N4

O1

D)C4H10N2O2

7/27/2019 111 - Chapter 2

43/55

Compounds

Molecular Compounds

Ionic Compounds

7/27/2019 111 - Chapter 2

44/55

Ions and Ionic Compounds

An atomic ion ormonatomic ion - consists of just one atom

with a positive or negative charge.

Na Atom Na+ Ion

11 protons 11 protons

11 electrons 10 electrons

Cl Atom Cl Ion



7/27/2019 111 - Chapter 2

45/55


Cations formed by the loss of one or more electrons from

an atom

Cations have a positive charge.

Na Atom Na+ Ion



7/27/2019 111 - Chapter 2

46/55


Anions formed by the gain of one or more electrons to anatom

Anions have a negative charge

Cl Atom Cl Ion



7/27/2019 111 - Chapter 2

47/55


Atoms can lose or gain more than one electron.

7/27/2019 111 - Chapter 2

48/55


A monatomic anion is named by changing the ending of the

elements name to ide.

Cl is chloride O2 is oxide

Some metals can form cations of more than one possiblecharge.

Fe2+ : ferrous ion [Fe(II)]

Fe3+

: ferric ion [Fe(III)]

Mn2+ : manganese(II) ion

Mn3+ : manganese(III) ion

Mn4+ : manganese(IV) ion

I d I i C d

7/27/2019 111 - Chapter 2

49/55


Polyatom ic ions-consist of a combination

of two or more atoms

You need to know table2.9 in your text:

- Name

- Formula

- Charge

7/27/2019 111 - Chapter 2

50/55


Formulas for ionic compounds are generally empirical formulas.

Ionic compounds are electronically neutral.

7/27/2019 111 - Chapter 2

51/55


Al3+ O2

Al2O3

The sum of the charges on the cation and anion in each

formula must be zero.

Aluminum oxide:

Sum of charges: 2(+3) + 2(3) = 0

7/27/2019 111 - Chapter 2

52/55


To name ionic compounds:

1) Name the cation.

omit the word ion

use a Roman numeral if the cation can have more

than one charge2) Name the anion

omit the word ion

Examples:

NaCN sodium cyanide

FeCl2 iron(II) chloride

FeCl3 iron(III) chloride

7/27/2019 111 - Chapter 2

53/55


Oxoanions- polyatomic anions that contain one or more

oxygen atoms and one atom of another element.

Starting with the oxoanions whose names end inate, the

following can be used to name other oxoanions in the same

family:

1) The ion with one more O atom than theate ion is

called per . . . ate ion. (ClO3- is chlorate; ClO4

- is perchlorate)

2) The ion with one less O atom than theate anion is

called theite ion. (ClO2- is chlorite)

3) The ion with two fewer O atoms than theate ion is

called the hypo . . . ite ion (ClO- is hypochlorite)

7/27/2019 111 - Chapter 2

54/55


Oxoacidsare acids that contain oxoanions.

1) An acid based on theate ion is called . . . icacid

HClO3 is chloric acid

2) An acid based on the ite ion is called . . . ous acid

HClO2 is chlorous acid

3) Prefixes in oxoanion names are retained in the name

of the acid.

HClO4 is perchloric acid

HClO is hypochlorous acid

I d I i C d

7/27/2019 111 - Chapter 2

55/55


Hydrates- compounds with a specific number of water

molecules within their solid structure.CuSO4 5 H2O copper(II) sulfate pentahydrate

Documents

111 - Chapter 2