Forming Compounds

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Forming Compounds
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Framing Questions

• What is a compound?
• Why do compounds form?
• How can atoms bond? What kinds of compounds do
  these form?
• What are the properties of ionic compounds?
• What are the properties of molecular compounds?
• Define ionic charge, oxidation number, diatomic
  molecule and electrolyte.

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Why do Compounds Form?

• So we know that compounds are pure substances
  with two types of atoms bonded together.
• Bonds occur because of the Happy Atom Syndrome
  trying to become stable
• An atom may acquire a full valence shell in three
  ways
• An atom may give up electrons (becomes a cation
  )
• An atom may gain electrons (becomes an anion -)
• An atom may share electrons

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Why do Compounds Form?

• When atoms give up or take up electrons to form
  ions, they gain a charge ( or -). This charge
  causes them to attract the opposite charge and
  form a bond.
• When atoms share electrons, they also form a bond.

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How do Atoms Together?
"Stick"

• Bonding involves either a transfer or a sharing
  of electrons to form stable ions.
• There are 2 main types of bonds that hold
  compounds together
• 1. Ionic bonds (transfer electrons)
• 2. Covalent bonds (share electrons)

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Because anions and cations are electrically
attracted to each other (electronegativity), they
form compounds called Ionic Compounds (ionic bond
ionic compound)
Ionic Bonds
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Animations to ponder
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Ionic Charge and Oxidation Numbers

• To figure out which elements will form ionic
  bonds together, you must understand their ionic
  charge.
• An elements ionic charge is directly related to
  its number of valence electrons.
• If an element has less than 4 valence electrons,
  it will give them away and become positive. Its
  ionic charge is the of electrons it will give
  away and its charge ().
• If an element has more than 4 valence electrons,
  it will take more and become negative. Its
  ionic charge is the of electrons it will take
  and its charge (-).
• Its oxidation number is the same as its ionic
  charge.

Element of valence electrons Ionic charge Oxidation number
Na 1 Na 1
Mg 2 Mg2 2
P 5 P3- -3
O 6 O2- -2
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Covalent Bonds

• Covalent bonds are formed when atoms share
  electrons.
• A neutral (non-charged) particle that is made up
  of atoms joined by covalent bonds is called a
  molecule, so we have Molecular Compounds.

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Animations to ponder
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Diatomic Molecules

• Molecules containing two atoms are called
  diatomic. This means they have paired with
  themselves, sharing electrons (covalent bonds).
• Seven elements exist as diatomic molecules in the
  gaseous state
• Hydrogen
• Oxygen
• Nitrogen
• Flourine
• Chlorine
• Bromine
• Iodine

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Make sure you understand these next properties
for our upcoming lab
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Properties of Ionic Compounds

• Ionic compounds are usually bonds between metal
  cations and non-metal anions. These bonds form a
  regular, repeating pattern which forms a
  crystalline shape.
• Properties
• Strong bonds because the attraction between
  oppositely charged ions is strong
• Tend to have relatively high melting points
  because a large amount of energy is needed to
  break the strong bonds
• Conduct electricity when absorbed in water
  (electrolyte a substance that dissolves in
  water to produce a solution that conducts
  electricity)
• Not electrical conductors in a solid state

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Properties of Molecular Compounds

• Molecular compounds are formed when atoms of
  non-metals are joined by covalent bonds.
• Properties
• Strong bonds but weak forces of attraction
  between molecules (because no charges)
• Tend to have relatively low melting points
  because little energy is needed to break the
  forces of attraction between molecules
• Do not conduct electricity in solid or liquid
  state or when absorbed in water because they do
  not contain ions (no charges)

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Homework Answer

• Think about it
• Na can give away an electron and be happy, so
  its likely to form an ion and therefore an ionic
  bond
• If H gives away its electron, it doesnt have
  any, so its more likely to form a covalent bond
  and share it instead!