Chemical Foundations: Elements, Atoms and Ions

1
Chapter 4

• Chemical Foundations Elements, Atoms and Ions

2
(No Transcript)
3
Law of Constant Proportion

• Most natural material are mixtures of pure
  substances
• Pure substances are either elements or
  combinations of elements called compounds
• A given compound always has the same proportions
  of elements by mass

4
Daltons Atomic Theory

• Elements are made of tiny particles called atoms
• All atoms of a given substance are identical
• The atoms of a given element are different from
  those of any other element
• Atoms of one element can combine with atoms of
  other elements to form compounds. A given
  compound always has the same relative numbers
  and types of atoms
• Atoms are indivisible in chemical processes.
  Atoms cant be created or destroyed in a chemical
  reaction

5
Formulas of Compounds

• Each atom present is represented by its element
  symbol
• The number of each type of atom is indicated by a
  subscript to the right of the element symbol
• When only one atom of a given type is present,
  the subscript 1 is not written

6
Examples

• Each molecule of a compound that is responsible
  for acid rain contains one atom of sulfur and
  three atoms of oxygen
• A compound contains two atoms of nitrogen and
  five atoms of oxygen
• Glucose contains six atoms of carbon, twelve
  atoms of hydrogen and six atoms of oxygen.

7
Answers

• SO3
• N2O5
• C6H12O6

8
Structure of the atom

• JJ Thompson discovered electrons
• William Thomson aka Lord Kelvin proposed plum
  pudding model of atom
• Ernest Rutherford used alpha particles
• Gold foil experiment

9
(No Transcript)
10
(No Transcript)
11
(No Transcript)
12
Results

• Most alpha particles traveled straight through as
  expected
• Some were deflected at minor or major angles
• Some were completely deflected

13
Conclusions?

• Not consistent with plum pudding model of atom
• Large deflection could only be caused by a center
  of positive charge
• Called a nucleus with all of the positive charge
  located at the center of the atom
• Surrounded by mostly empty space where electrons
  are located

14
Introduction to the Modern Concept of Atomic
Structure
15
Isotopes

• Same number of protons (atomic number)
• Different number of neutrons
• Results in different atomic mass

A is mass number
X
A
Z is number of protons
Z
16
Interpreting Symbols for Isotopes

• 12C
• 14C
• 23Na

17
Introduction to the Periodic Table

• Arranged in rows and columns
• Uses chemical symbols
• Lists A and Z for each element
• A is an average of all isotopes that occur in
  nature
• First arranged by Dmitri Mendeleev 1869

18
(No Transcript)
19
Groups

• Metals
• Non-metals
• Metalloids
• Columns forms groups

20
Groups

• Alkali metals
• Alkaline earth metals
• Transitition metals
• Halogens
• Noble gases
• Lanthanides
• Actinides

21
Physical Properties of Metals

• Efficient conduction of heat and electricity
• Malleability (sheets)
• Ductility (Wires)
• Lustrous

22
Natural States of Elements

• Gases
• Seven diatomic elements
• H2
• N2
• O2
• F2
• Cl2
• Br2
• I2

23
Ions

• Charged particles
• Elements are neutral
• Can be positive or negative
• Positive lost an electron
• Negative gained an electron
• Protons and neutrons stay the same

24
Group Ions

• Group 1 forms ions with a 1 charge
• Group 2 forms ions with a 2 charge
• MOST of group 3 forms ions with a 3 charge
• Group 6 forms ions with a 2 charge
• Group 7 forms ions with a 1 charge
• Group 8 rarely form ions

25
Compounds That Contain Ions

• Pure water does not conduct electricity
• Pure NaCl does not conduct electricity
• A mixture of salt and water is a good conductor

26
Compounds

• Compounds have no net charge
• Ionic compounds have negatively and positively
  charged ions
• Equal in charge to equal zero overall
• Na and Cl- ? NaCl equal zero overall
• Mg2 and 2 Cl- ? MgCl2 equal zero overall