What is a Chemical Bond?

1
What is a Chemical Bond?

• A chemical bond is a force holding two or more
  atoms together to form a molecule.

2
Why do atoms form chemical bonds?

• Atoms tend to form chemical bonds to satisfy the
  octet rule
• Atoms share or transfer their valence electrons
  to fill their outermost energy level either 2
  (for hydrogen) or 8 electrons.

3
There are three types of chemical bonds we will
study

• Ionic bonds
• Covalent bonds
• Hydrogen bonds

4
Ionic Bonds Give Take

• Ionic bonds form when atoms transfer (lose or
  gain) electrons with other atoms.
• Atoms with 5, 6,or 7 valence electrons tend to
  gain electrons to fill their outer shells .
  Gaining electrons makes the atom a negative ion .
• Atoms with 1, 2 or 3 valence electrons tend to
  lose electrons . Losing electrons makes the atom
  a positive ion.

5
Examples of Ionic Bonds

• Ionic bonds form easily between the group 1
  metals and the group 17 non-metals
• These new ionic compounds are known as metallic
  salts.
• Sodium Chloride is a good example of an Ionic
  Compound

6
Sodium Chloride is an Ionic Compound

• Sodium (Na) has 1 valence electron in its third
  energy orbital
• Chlorine (Cl) has 7 valence electrons in its
  third energy level
• They form an ionic compound when Sodiums
  electron is transferred to Chlorine
• Now Sodium is a 1 ion and Chlorine is a 1- ion.
  Their opposite charges keep them attracted to
  each other
• Overall, the compound is electrically neutral.
• Other examples of Ionic Compounds include rust,
  baking soda and limestone

7
Properties of Ionic Compounds

• Crystal Shaped Solids
• High Melting Points
• Electrical Conductivity

8
Covalent Bonds Good at Sharing

• Covalent bonds are formed when 2 or more atoms
  SHARE their valence electrons
• Usually formed between two non-metals oxygen,
  carbon and nitrogen like to form covalent bonds
• Atoms with exactly half ( 1 or 4 electrons) of
  their valence electrons like to form covalent
  bonds.

9
Drawing a covalent bond

• Draw a molecule of methane.
• Start with 1 carbon atom (in middle)
• Add the correct number of hydrogen atoms needed
  to form covalent bonds that satisfy the octet
  rule.

10
Properties of Covalently Bonded Molecules

• Low melting point
• Poor Conductors of electricity
• Typically form organic compounds like fats,
  proteins carbohydrates

11
Polar vs Non-polar Covalent BondsOil Water
dont mix

• Some atoms tend to pull harder on the shared
  electrons in a covalently bonded molecule.
• This creates a positive side and a negative side
  of the molecule.
• We call these kinds of molecules polar, because
  the electrons are shared unequally, creating a
  molecule with positively charged pole and a
  negatively charged pole
• Water is a good example of a polar molecule. Many
  molecules important to living things are polar
  and dissolve easily in water.

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12
Hydrogen Bonds Opposites attract

• Hydrogen bonds form between two nearby water
  molecules
• The negatively charged oxygen end of one water
  molecule is attracted to the positively charged
  hydrogen end of another.
• Hydrogen bonds cause many unique properties of
  water its stickiness to itself, its ability
  to dissolve all other polar substances easily,
  its ability to remain a liquid at a wide range of
  temperatures.

13
Non-polar molecules

• Molecules which share their electrons equally are
  non-polar.
• Oils and fats are non-polar. Their molecules
  dont have an overall charge.
• Thats why oil water dont mix. Theyre not
  attracted to each other.

14
So How does soap clean?
Soap has a polar head and a non-polar
tail The polar head is attracted to water
the non-polar tail is attracted to dirty
oils Each oil molecule is surrounded by a ring
of soap molecules When the water is washed away,
it carries an oil molecule with it