Daltons Postulates

1
Daltons Postulates

• Each element is composed of extremely small
  particles called atoms.

2
Daltons Postulates

• 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.

3
Daltons Postulates

• 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.

4
Daltons Postulates

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

5
Law of Constant CompositionJoseph Proust
(17541826)

• Also known as the law of definite proportions.
• The elemental composition of a pure substance
  never varies.

6
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.

7
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.

8
The Components of Atoms
Atoms contain negatively charged electrons and a
positively charged nucleus.
Atoms can be broken up into simpler components by
the application of large amounts of energy. Two
types of particles are formed electrons and a
nucleus
9
The Components of Atoms

• An atom is held together by electrostatic forces
  of attraction between the electrons and the
  nucleus.
• Opposing this attraction is the repulsive forces
  between individual electrons in the atom.
• The balance of these two types of forces
  determines the size of each atom.
• The nucleus and 18 electrons of an argon atom can
  be represented

10
Subatomic Particles

• Protons and electrons are the only particles that
  have a charge.
• Protons and neutrons have essentially the same
  mass.
• The mass of an electron is so small we ignore it.

11
Symbols of Elements

• Elements are symbolized by one or two letters.

12
Atomic Number

• All atoms of the same element have the same
  number of protons
• The atomic number (Z)

13
Atomic Mass

• The mass of an atom in atomic mass units (amu)
  is the total number of protons and neutrons in
  the atom.

14
Isotopes

• Atoms of the same element with different masses.
• Isotopes have different numbers of neutrons.

15
Average Mass

• 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.

16
Periodic Table

• A systematic catalog of elements.
• Elements are arranged in order of atomic number.

17
The Periodic Table Elements Grouped by Similar
Properties
Each group of the periodic table consists of
elements that behave similarly.
In the 19th century, a Russian chemist, Dimitri
Mendeleev was the first to construct a modern
periodic table by listing elements in increasing
order based on their mass and in columns based on
their chemical properties. In doing so, he had
to leave room for elements unknown at that time.
He was able to predict the properties of the
unknown elements, which were subsequently
discovered, thus providing verification to his
theory.
18
Periodicity

• When one looks at the chemical properties of
  elements, one notices a repeating pattern of
  reactivities.

19
Periodic Table

• The rows on the periodic chart are periods.
• Columns are groups.
• Elements in the same group have similar chemical
  properties.

20
Periodic Table

• Nonmetals are on the right side of the periodic
  table (with the exception of H).

21
Periodic Table

• Metalloids border the stair-step line (with the
  exception of Al and Po).

22
Periodic Table

• Metals are on the left side of the chart.

23
The Periodic Table Elements Grouped by Similar
Properties
A partial periodic table.

• Each column in the periodic table is called a
  group.
• Each row in the periodic table is called a
  period.
• Elements in the same group have similar chemical
  properties.
• Elements in the same row increase their numbers
  of electrons by one as you move from left to
  right.

24
Groups

• These five groups are known by their names.

25
The Periodic Table Elements Grouped by Similar
Properties

• Group VIIIA are the inert gases.
• 8 valence electrons
• Group VIIA are the halogens.
• 7 valence electrons
• Group IA are the alkali metals.
• 1 valence electron
• Group IIA are the alkaline earths.
• 2 valence electrons
• All elements in the same group or column have the
  same number of valence electrons.

26
The Periodic Table Elements Grouped by Similar
Properties
The chemical properties of an atom are largely
determined by its valence shell of electrons.

• Elements having the same numbers of valence
  electrons will behave in a similar chemical way.
• Strontium can replace calcium (both alkaline
  earth elements) in bones.
• In the event of a nuclear accident, radioactive
  strontium can be released into the atmosphere
  from which it settles out on the ground and
  enters the food chain.
• Eventually the strontium reaches the human food
  chain (milk) and is deposited in our bones where
  it remains causing radiation related diseases.

27
The Components of Atoms
28
Covalent Bonding and the Formation of Molecules
A hydrogen molecule is held together by the
sharing of electrons.
When two unbonded hydrogen atoms form a H2
molecule, their electrons are said to form a
bonding pair. The two electrons travel about
both nuclei. This sharing of two electrons is
called a covalent chemical bond.
H3 or H4 molecules do not form because the outer
or valence shell of each hydrogen atom is already
full in H2.
29
Chemical Formulas

• 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.

30
Molecular Compounds

• Molecular compounds are composed of molecules
  and almost always contain only nonmetals.

31
Diatomic Molecules

• These seven elements occur naturally as
  molecules containing two atoms.

32
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.

33
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.

34
Ionic Bonds

• Ionic compounds (such as NaCl) are generally
  formed between metals and nonmetals.

35
Ions and Ionic Bonding
Ionic compounds need not have a 11 ratio of
atoms.
All cations do not have a charge of 1 and all
anions do not have a charge of -1. Any salt
composed of cations and anions must be
electrically neutral, however. This fact enables
us to deduce the formula for the compound formed
from the combination of any cation and any anion.
36
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.

37
Ions and Ionic Bonding
The following examples are all electrically
neutral salts Using Cations Na, Mg2,Al3
Anions Cl-, O2-, N3- NaCl 1x(1) 1x(-1)
0 Na2O 2x(1) 1x(-2) 0 Na3N 3x(1)
1x(-3) 0 MgCl2 1x(2) 2x(-1)
0 MgO 1x(2) 1x(-2) 0 Mg3N2 3x(2)
2x(-3) 0 AlCl3 1x(3) 3x(-1)
0 Al2O3 2x(3) 3x(-2) 0 AlN 1x(3)
1x(-3) 0
38
Common Cations
39
Common Anions
40
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.)

41
Nomenclature of Binary Compounds

• The ending on the more electronegative element is
  changed to -ide.
• CO2 carbon dioxide
• CCl4 carbon tetrachloride

42
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

43
Chemical Equations

• Concise representations of chemical reactions

44
Anatomy of a Chemical Equation

• CH4 (g) 2 O2 (g) CO2 (g) 2
  H2O (g)

45
Anatomy of a Chemical Equation

• CH4 (g) 2 O2 (g) CO2 (g) 2
  H2O (g)

• Reactants appear on the left side of the equation.

46
Anatomy of a Chemical Equation

• CH4 (g) 2 O2 (g) CO2 (g) 2
  H2O (g)

• Products appear on the right side of the equation.

47
Anatomy of a Chemical Equation

• CH4 (g) 2 O2 (g) CO2 (g) 2
  H2O (g)

• The states of the reactants and products are
  written in parentheses to the right of each
  compound.

48
Anatomy of a Chemical Equation

• CH4 (g) 2 O2 (g) CO2 (g) 2
  H2O (g)

• Coefficients are inserted to balance the equation.

49
Subscripts and Coefficients Give Different
Information

• Subscripts tell the number of atoms of each
  element in a molecule

50
Subscripts and Coefficients Give Different
Information

• Subscripts tell the number of atoms of each
  element in a molecule
• Coefficients tell the number of molecules

51
Reaction Types
52
Combination Reactions

• Two or more substances react to form one product

• Examples
• N2 (g) 3 H2 (g) ??? 2 NH3 (g)
• C3H6 (g) Br2 (l) ??? C3H6Br2 (l)
• 2 Mg (s) O2 (g) ??? 2 MgO (s)

53
2 Mg (s) O2 (g) ??? 2 MgO (s)
54
Decomposition Reactions

• One substance breaks down into two or more
  substances

• Examples
• CaCO3 (s) ??? CaO (s) CO2 (g)
• 2 KClO3 (s) ??? 2 KCl (s) O2 (g)
• 2 NaN3 (s) ??? 2 Na (s) 3 N2 (g)

55
Combustion Reactions

• Rapid reactions that produce a flame
• Most often involve hydrocarbons reacting with
  oxygen in the air

• Examples
• CH4 (g) 2 O2 (g) ??? CO2 (g) 2 H2O (g)
• C3H8 (g) 5 O2 (g) ??? 3 CO2 (g) 4 H2O (g)

56
Formula Weights
57
Formula Weight (FW)

• Sum of the atomic weights for the atoms in a
  chemical formula
• So, the formula weight of calcium chloride,
  CaCl2, would be
• Ca 1(40.1 amu)
• Cl 2(35.5 amu)
• 111.1 amu
• These are generally reported for ionic compounds

58
Molecular Weight (MW)

• Sum of the atomic weights of the atoms in a
  molecule
• For the molecule ethane, C2H6, the molecular
  weight would be

59
Moles
60
Avogadros Number

• 6.02 x 1023
• 1 mole of 12C has a mass of 12 g

61
Molar Mass

• By definition, these are the mass of 1 mol of a
  substance (i.e., g/mol)
• The molar mass of an element is the mass number
  for the element that we find on the periodic
  table
• The formula weight (in amus) will be the same
  number as the molar mass (in g/mol)

62
Mole Relationships

• One mole of atoms, ions, or molecules contains
  Avogadros number of those particles
• One mole of molecules or formula units contains
  Avogadros number times the number of atoms or
  ions of each element in the compound