Atoms: The Building Blocks of Matter

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Atoms The Building Blocks of Matter

• Chapter 3

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Basic laws of chemical reactions

• Law of conservation of mass mass is neither
  created nor destroyed in ordinary reactions
• Law of definite proportions a chemical compound
  always contains the same elements in exactly the
  same proportions by mass regardless of the size
  of the sample or the source of the compound

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Daltons Atomic Theory

1. All matter is composed of extremely small
   particles called atoms.
2. Atoms of a given element are identical in size,
   mass, other properties.
3. Atoms cannot be subdivided, created, or
   destroyed.
4. Atoms of different elements combine in simple
   whole number ratios to form chemical compounds.
5. In chemical reactions, atoms are combined,
   separated, rearranged.

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The modern atomic theory has proven that atoms
are divisible into smaller particles that a
given element can have atoms with different
masses.
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The Atom

• Atom smallest particle of an element that
  retains the chemical properties of that element
• Contains 2 parts
• Nucleus located near the center of the atoms
• Electron cloud located in rings around the
  nucleus

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Subatomic Particles

• The atom contains 3 basic subatomic particles
• Proton positively charged particle located
  inside the nucleus
• Neutron neutrally charged particle located
  inside the nucleus
• Electron negatively charged particle located in
  the rings of the electron cloud

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Atomic Mass Number

• atomic number (Z) number of protons in the
  nucleus of each atom
• The atomic number identifies an element.
• mass number total number of protons neutrons
  in the nucleus
• Scientists use atomic mass units (amu) to
  measure the mass of atoms.

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Isotopes

• All atoms are composed of the same basic
  particles, but all atoms are not the same. Atoms
  of different elements have different number of
  protons.
• Isotope atoms of the same element that have
  different masses

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Contd

• Most elements occur naturally as a mixture of
  isotopes.
• Average atomic mass weighted average of the
  atomic masses of the naturally occurring isotopes
  of an element

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Problem

• Copper is a naturally occurring isotope. It
  consists of 69.17 copper-63 and 30.83
  copper-65. Calculate the average atomic mass of
  the naturally occurring copper if copper-63
  weighs 62.929598 amu and copper-65 weighs
  64.927793 amu.

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The Mole

• Mol SI unit for amount of substance
• Avogadros number number of particles in a mole,
  6.02x1023
• Molar mass mass of 1 mole of a pure substance
• Written in grams/mole (g/mol)
• Equal to the atomic mass number found on the
  periodic table

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Mole Conversions
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Problems

1. What is the mass in grams of 3.50 mol of the
   element copper?
2. A chemist produced 11.9 g of aluminum. How many
   moles of aluminum were produced?
3. How many moles of silver (Ag) are in 3.01x1023
   atoms of Ag?
4. What is the mass in grams of 1.20x108 atoms of
   copper?