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Chemical Foundations: Elements, Atoms and Ions

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Most natural material are mixtures of pure substances ... Ductility (Wires) Lustrous. Natural States of Elements. Gases. Seven diatomic elements ... – PowerPoint PPT presentation

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Title: Chemical Foundations: Elements, Atoms and Ions


1
Chapter 4
  • Chemical Foundations Elements, Atoms and Ions

2
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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
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10
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11
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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
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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
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