Pure substances

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Pure substances
Element a substance that cannot be decomposed
into simpler substances by chemical means
composed of only one kind of atom Examples
copper, helium, sulfur, iron Currently there are
114 known elements, 90 of which are naturally
occurring. The chemical elements make up all
known substances. Compound a substance
composed of two or more elements in fixed
proportions Examples sodium chloride, sucrose,
ammonia, ethanol
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Periodic Table of the Elements
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Chemical Elements
Atomic weight
Atomic number
14
28.0855
Si
3540 1685
Symbol
2.33
Ne3s23p2
Additional data density melting point boiling
point oxidation states electronegativity electron
configuration etc.
Silicon
Name
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Chemical Elements
A chemical element consists of only one type of
atom
Scanning Electron Microscope Image of a Silicon
wafer cross-section
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Silicon surface image using Scanning Tunneling
Microscopy B.S. Swartzentruber, Sandia National
Laboratory
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Familiarize yourself with these elements
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Chemical Compounds
The simplest unit of a chemical compound is a
molecule or formula unit. Chemical compounds are
represented with chemical formulas. Each
chemical formula contains the symbols of each
constituent chemical element, followed by a
subscript to indicate the number of atoms of a
given element present in the molecule. An
example familiar to us all water Water is a
chemical compound, represented with the formula
H2O The formula indicates that the water
molecule contains two elements hydrogen (H) and
oxygen (O), and that there are two atoms of
hydrogen and one atom of oxygen.
Water molecule
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Chemical Compounds
Sodium chloride, NaCl consists of sodium atoms
and chloride atoms in exactly one to one
ratio Sucrose, C12H22O11 consists of
carbon, hydrogen, and oxygen atoms. commonly
known as table sugar
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Chemical Reactions
conditions
Reactant(s)
Product(s)
The chemical properties of the reactants are
different from the chemical properties of the
products. A chemical change occurs.
water
Example Nickel Hydrochloric
acid Hydrogen Nickel(II) chloride
water
Ni HCl H2
NiCl2
(chemical reactions will be visited in more
detail in Ch6)
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Which is a physical change?

• Boiling of liquid water to form steam (gaseous
  water)
• Combustion of gasoline to form carbon dioxide and
  water
• Electrolysis of water to form hydrogen and oxygen
• Neutralization of hydrochloric acid with sodium
  hydroxide to form water and sodium chloride

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Which is a physical change?

• Boiling of liquid water to form steam (gaseous
  water)
• Combustion of gasoline to form carbon dioxide and
  water
• Electrolysis of water to form hydrogen and oxygen
• Neutralization of hydrochloric acid with sodium
  hydroxide to form water and sodium chloride

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Which is a chemical change?

• Dissolution of solid potassium chloride in water
  to form aqueous potassium chloride
• Oxidation of copper metal to form copper(II)
  oxide
• Sublimation of dry ice (solid carbon dioxide) to
  form gaseous carbon dioxide
• Vaporization of liquid ammonia to form gaseous
  ammonia

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Which is a chemical change?

• Dissolution of solid potassium chloride in water
  to form aqueous potassium chloride
• Oxidation of copper metal to form copper(II)
  oxide
• Sublimation of dry ice (solid carbon dioxide) to
  form gaseous carbon dioxide
• Vaporization of liquid ammonia to form gaseous
  ammonia

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Butane has a melting point of 138.4oC and a
boiling point of 0.5oC. If room temperature is
25oC, butane is a

• gas.
• liquid.
• solid.
• Cant tell from the given information.

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Butane has a melting point of 138.4oC and a
boiling point of 0.5oC. At room temperature
(25oC) butane is a

• gas.
• liquid.
• solid.
• Cant tell from the given information.

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Give the symbol for the element silicon.

• S
• Sc
• Si
• Sn

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Give the symbol for the element silicon.

• S
• Sc
• Si
• Sn

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Give the symbol for the element sodium.

• Na
• S
• Si
• Sm

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Give the symbol for the element sodium.

• Na
• S
• Si
• Sm

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How many atoms of hydrogen are in one molecule of
isopropyl alcohol, (CH3)2CHOH?

• One
• Two
• Three
• Eight

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How many atoms of hydrogen are in one molecule of
isopropyl alcohol, (CH3)2CHOH?

• One
• Two
• Three
• Eight

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The element indicated in blue on the periodic
table is a

• metal.
• metalloid.
• mixture.
• nonmetal.

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The element indicated in blue on the periodic
table is a

• metal.
• metalloid.
• mixture.
• nonmetal.