Elements, Compounds, Bonds

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Elements, Compounds, Bonds

• Matter
• How is it organized?

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Elements, Atoms Compounds

• Element simplest type of matter with unique
  chemical properties
• 92 elements occur naturally
• Atom Smallest particle of an element that has
  the chemical characteristics of that element
• Compound Substance containing two or more
  elements in a fixed ratio

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Atoms

• Composed of three subatomic particles
• protons () neutrons (0) make up the nucleus
• electrons (-, e-) in orbitals (clouds)

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Periodic Table
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Atoms

• Mass of atom summed mass of its protons and
  neutrons
• 1 proton 1 atomic mass unit or amu
• 1 neutron 1 amu
• Mass Atomic weight

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Approximate atom
Pea nucleus
electron (-)
proton ()
nucleus
neutron (0)
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Atoms

• Stable atoms always have same protons.
  protons atomic
• Carbon C 6
• Atoms can have differing s of neutrons.
  protons neutrons Atomic weight (mass
  number)
• 12C has 6 protons and 6 neutrons
• 13C has 6 protons and 7 neutrons

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Periodic Table
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Importance (by weight)
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Valence and reactivity
2 electrons

• Remember electrons are arranged in valence
  shells or energy levels that orbit the nucleus.
• of electrons in atoms influence their
  reactivity, relative to other atoms.

2 electrons
8 electrons
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Atoms with unfilled electron shells are reactive

• Atoms are greedy (want full e- orbitals) and
  lazy (dont want to work hard to achieve them)
• Results in formation of chemical bonds
• Three types of bonds
• Ionic bonds
• Covalent bonds
• Hydrogen bonds

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Ionic bonds

• Ionic bonds form between anions (atoms that
  stripped an e- from another atom) and cations
  (atoms that lost an e-)
• Salts form by ionic bonding
• Basically, a strong electrostatic attraction

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Covalent bonds

• Covalent bonds form when atoms share e-.
• Single or double
• H-H (H2)
• OCO (CO2)
• of bonds formed of e- needed to fill outer
  shell

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Non-polar Covalent bonds

• Equal sharing of e-
• Nuclei of similar size have similar
  elecronegativity pull on shared electrons in a
  covalent bond

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Polar Covalent bonds

• Form due to unequal sharing of e-
• Relative size and electrical attraction of nuclei
  differ
• Partial and partial sides of molecule result

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Hydrogen bonds

• Weak attraction between opposite charged poles of
  polar molecules
• IMPORTANT bond
• determines structure of large, complex molecules
• Produces cohesion (water droplets)

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Hydrogen bonds give H20 its amazing properties
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Structural bonds

• Responsible for secondary structure of proteins
• ?-helix
• ?-pleated sheet

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Allow water transport

• H-bonding creates surface tension between water
  molecules
• As H20 evaporates, it pulls attached H20
  molecules along with it

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Ionic covalent bonds form

• Molecules atoms held together by covalent bonds
• H20, O2, H2, CO2
• Compounds chemical substance made of atoms of 2
  or more elements, regardless of type of bond
  joining them.
• H20, NaCl, CO2.

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Concept Check
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• The reactive properties or chemical behavior of
  an atom mostly depend on the number of
• the electrons in each electron shell of the atom.
• the neutrons found in the nucleus.
• the filled electron shells.
• the electrons in the outer electron shell of the
  atom.

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Answer
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• The reactive properties or chemical behavior of
  an atom mostly depend on the number of
• the electrons in the outer electron shell of the
  atom.

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Concept Check
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• Water molecules form hydrogen bonds because
• the water molecule is polar.
• the oxygen molecule is positively charged.
• the water molecule forms a tetrahedron.
• the hydrogen atoms are negatively charged.

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Answer
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• Water molecules form hydrogen bonds because
• the water molecule is polar.