Molecular Compounds and Ions

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• Atoms can attain a more stable arrangement of
  electrons in their outermost shell by interacting
  with one another.
• An ionic bond is formed when electrons are
  transferred from one atom to the other. A
  covalent bond is formed when electrons are shared
  between atoms.

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Molecular Compounds and Ions

• 1. What does it mean to say that an atom is
  neutral?
• contains equal number of protons and electrons
• 2. What would happen to the charge on an atom if
  an electron
• were removed? If an electron were added?
• have a positive charge, have a negative charge
• 3. What is the name for an atom that has a
  charge?
• an ion
• 4. What is a molecule?
• A particle that contains more than one atom
• 5. How do the molecules of elements and compounds
  differ?
• the molecules of a compound contain atoms from
  more than one element

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With the exception of the noble gases, which
exist as isolated atoms, most elements found in
nature form molecules

• Molecule smallest electrically neutral unit of
  a substance that still has the properties of the
  substance. A molecule is made up of two or more
  atoms that act as a unit
• Examples
• H2O
• O3
• CO2

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• Compounds Atoms of different elements can
  combine chemically to form compounds. Compounds
  composed of molecules are called molecular
  compounds Compounds composed of ions are called
  ionic compounds
• Molecular Compounds
• tend to have relatively low melting and boiling
  points
• exist as gases or liquids at room temperature
• most molecules of molecular compounds are
  composed of the atoms of two or more nonmetals
• Ions not all compounds are molecular, many are
  composed of particles called ions. Ions are atoms
  or groups of atoms that have a positive or
  negative charge. An ion forms when an atom or
  group of atoms loses or gains electrons

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Ions

• EXAMPLE NaCl
• net charge on a sodium atom is zero 11(-11)
  0
• in forming a chemical compound, an atom of sodium
  tends to lose one of its electrons, making its
  number of electrons no longer equal to the number
  of protons
• the atom of sodium becomes an ion, because there
  are more positive charges (protons) than negative
  charges (electrons), the sodium ion has a
  positive charge

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NaCl
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• Cation atoms or groups of atoms that have a
  positive charge
• atoms of metallic elements tend to form cations
  by losing one or more electrons
• cations have fewer electrons than the
  electrically neutral atom from which it is formed
• an ionic charge is written as a number followed
  by a sign
• What is the charge of a sodium cation?
• 1 (11 protons, 10 electrons) Na or Na1
• What is the charge on a magnesium ion?
• 2 12 protons, 10 electrons) Mg2
• How many electrons does an Aluminum atom lose to
  form an aluminum cation?
• (3 electrons)

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Ions vs. Atoms

• There are many differences between the metal and
  its respective cation
• Example
• Sodium metal reacts violently with water, but
  sodium cations are quite unreactive

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Anion atoms or groups of atoms that have a
negative charge

• atoms of nonmetallic elements tend to form anions
  by gaining one or more electrons
• anions have more electrons than the electrically
  neutral atom from which it is formed
• the name of an anion of a nonmetallic element is
  not the same as the element name. Anions
  typically end in -ide

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EXAMPLE NaCl

• net charge on the chlorine atom is zero 17
  (-17) 0
• in forming a chemical bond, a nonmetal tends to
  gain electrons to form an anion
• the chloride anion has 17 protons and 18
  electrons, it has an ionic charge of 1-
• written as Cl-
• Common anions
• Oxide ion, oxygen atom gains 2 electrons, giving
  it an ionic charge of 2-, written as O2-

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Examples

• Cations are givers (positive)
• Anions are takers (negative)
• sulfur forms a _________ anion
• Sulfide S2-
• bromine forms a __________ anion
• Bromide Br-

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Cations Anions Activity
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Ionic Compounds compounds composed of cations
and anions

• ionic compounds are usually composed of metal
  cations and nonmetal anions
• Ionic compounds, even though they are composed of
  ions that are electrically charged, the total
  positive charge equals the total negative charge.
  The overall compound is electrically neutral
• Usually solid crystals at room temperature, melt
  at high temperatures

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Examples

• NaCl - sodium cation chloride anion
• CaO (lime) calcium cations oxide anions

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Characteristics of Molecular and Ionic Compounds Characteristics of Molecular and Ionic Compounds Characteristics of Molecular and Ionic Compounds
Characteristic Molecular Compound Ionic Compound
Representative unit Molecule Formula unit (balance of oppositely charge ions)
Type of elements Nonmetallic Metallic combined with nonmetallic
Physical state Solid, liquid, or gas Solid
Melting point Low (usually below 300C) High (usually above 300C)
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Review Questions- Molecular Compounds Ions

• Give the name and symbol of the ion formed when
• a sulfur atom gains two electrons
• sulfide ion S2-
• an aluminum atom loses three electrons
• aluminum ion Al3
• a calcium atom loses two electrons
• calcium ion Ca2

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Review Questions- Molecular Compounds Ions

• How many electrons are lost or gained in forming
  each ion?
• Ba2
• 2 lost
• As3-
• 3 gained
• Cu2
• 2 lost

• What is the symbol and name for the cation formed
  when
• a potassium atom loses one electron
• K
• a zinc atom loses two electrons
• Zn2

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Review Questions- Molecular Compounds Ions

• Write the symbol and name for the anion formed
  when
• a fluorine atom gains one electron
• F-
• a sulfur atom gains two electrons
• S2-