Unit Three: Bonding/Nomenclature

1
Unit Three Bonding/Nomenclature
GPS SC1 Students will analyze the nature of
matter and its classifications.
2
Classification of Matter
3
Forming Chemical Bonds

• Chemical bond force that holds 2 atoms together
  (holds compounds together)
• Valence electrons are involved in the formation
  of chemical bonds between atoms.

4
Illustrating Chemical Bonds

• Electron configurations, electron dot diagrams,
  and orbital diagrams are useful in visually
  illustrating how bonds form.
• Patterns on the periodic table are important in
  understanding why the bonds form.

5
Periodic Trends

• Ionization energy
• Electron affinity

6
Why do bonds/compounds form?

• All atoms have valence electrons.
• Noble gases have eight valence electrons. They
  are unreactivemeaning they dont form bonds or
  compounds.
• Eight valence electrons is important in the
  stability of atoms.

7
Octet Rule

• Octet Rule atoms tend to gain, lose, or share
  electrons in order to acquire a full set of 8
  valence electrons.
• All atoms want to have eight valence electronsto
  be stable.

8
Forming a Ion

• How does a positive ion form?
• Positive ions are formed by losing electrons.
  Atoms lose electrons in order to achieve noble
  gas configuration or the octet rule.
• Remember, low ionization energy is best for
  losing electrons. Where are the elements that
  are most likely to lose electrons?
• On the left sidemetals! Metals form ions.

9
Stability of Ion

• A positive ion is called a cation.
• Consider stability. Which is more stable a
  neutral Na atom or a Na ion? Hint Which has
  an electron configuration or a number of valence
  electrons closer to the noble gases?
• The sodium ion is more stable.

10
Forming - Ions

• Remember, electron affinity involves attracting
  electrons, and a negative ion is formed by
  gaining electrons.
• A high electron affinity is helpful in forming a
  negative ion. Where are elements found that are
  most likely to gain an electron forming a
  negative ion?
• On the right side of the tablenonmetals!
  Nonmetals form ions.

11
Stability of Ion

• What is more stable a neutral chlorine atom or a
  Cl-?
• The chlorine ion has an electron configuration
  similar to a noble gas.
• SIMPLE All atoms want an electron configuration
  ending with p6. They will gain or lose electrons
  until they do.

12
Formation and Nature of Ionic Bonds

• Opposites _____________________.
• Lets look at a reaction between sodium and
  chlorine.
• Sodium likes to lose electrons to become a
  cation. Chlorine likes to gain electrons to
  become an anion.
• A bond forms between the ions called an ionic
  bond.

13
Opposites Attract!
14
Ionic Bond

• Ionic bond the electrostatic force that holds
  oppositely charged particles together in an
  ionic compound
• Compounds that contain ionic bonds are called
  ionic compounds.
• Ionic compounds form between metals and nonmetals.

15
Properties of Ionic Compounds

• The compounds that you built are simplified.
  They are called formula units.
• Formula units give the proportions and identities
  of atoms that come together to form unit cells of
  ionic compounds.
• Unit cells are order arrangements of ions that
  minimize repulsive forces.

16
Unit cells form beautiful crystalsIonic
compounds are crystals!
17
Metallic Bonds

• Metals are made up of closely packed cations
  rather than neutral atoms
• The cations are surrounded by freely floating
  valence electrons.
• Metallic bonds attraction of the free-floating
  valence electrons for the positively charged
  metal ions forces of attraction that hold metals
  together

18
Metallic Bonds Properties

• Conduct electricity
• Mobility of electrons
• Malleable
• Cations slide easily on the sea of electrons
• Ductile
• Cations slide easily on the sea of electrons
• Crystalline
• Closest packing

19
Covalent Bonding
20
Why do atoms bond?

• Remember that ionic compounds form by gaining and
  losing electrons.
• Covalent compounds form when 2 atoms both need to
  gain electrons.
• They can both achieve the full octet by sharing
  electrons.

21
What is a covalent bond?

• Covalent bond chemical bond that results from
  sharing electrons
• Covalent bonding generally occurs when elements
  are relatively close together on the periodic
  table.
• The majority of covalent bonds form between
  nonmetallic elementsoften groups 4A to 7A.

22
Formation of a Covalent Bond

• Molecules form because the atoms are more stable
  as a compound than individually.
• Facts and forces for formation
• Repulsive force exists between electrons of the
  individual atoms and the protons of the
  individual atoms
• Attractive force exists between protons of one
  and electrons of the other
• As atoms move closer, attractive forces are
  maximizedTHIS IS THE MOST STABLE POSITION.
• At this point, atoms can share electrons of their
  valence shells.

23
Single Covalent Bonds

• Single bonds are formed when two atoms share a
  pair of electrons.
• A single bond contains two electrons or a single
  pair.
• Single bonds are easy to see in drawings of
  covalent compounds called Lewis structures.

24
Lewis Structures

• Lewis structures use electron-dot diagrams to
  show how electrons are arranged in molecules
• Draw electron dot diagrams for atoms showing ONLY
  valence electrons.
• Notice that the atoms can fit together like a
  puzzle to complete the octets of two or more of
  the atoms.
• Dashes represent bonding pairs and dots
  represent lone pairs.

25
Lewis Structures

• Tips
• Hydrogen is always on an end of the atom. (In
  other words, not at the center)
• The atom farthest to the left on the table is
  usually in the centerwith the exception of
  hydrogen.

26
Lewis Structures

• Rules
• Find the total of valence electrons in the
  atoms of the molecule.
• Divide this number by 2. This is the number of
  bonding pairs.
• Place one of these pairs between the central atom
  and all the terminal atoms.
• Place the remaining pairs around the terminal
  atomsif they need more electrons. Put the rest
  around the central atom.
• Check to be sure that multiple bonds dont exist.

27
Formation of a Single Bond

• Group 7A elements need only one more electron to
  attain a full octet.
• Therefore, the elements form a single covalent
  bond.
• Examples F2, Cl2, Br2, I2, and compounds with
  carbon

28
Formation of More Single Bonds

• Group 6A elements need 2 electrons to form 2
  covalent bonds.
• Oxygen is a part of group 6A. Consider that
  water consists of 1 oxygen and 2 hydrogen. Each
  hydrogen atom attains the full octet by sharing
  one electron with the oxygen. Oxygen attains a
  full octet by sharing one electron with each
  hydrogen atom.

29
More Single Covalent Bonds

• Group 5A and 4A elements form three and four
  covalent bonds, respectively.
• Examples Group 5A NH3, Group 4A CH4

30
Multiple Covalent Bonds

• Some atoms form a full octet by sharing more than
  one pair of electrons between two atoms, forming
  a multiple covalent bond.
• Atoms of the elements carbon, nitrogen, oxygen,
  and sulfur most often form multiple bonds.
• The number of valence electrons of an element is
  associated with the number of shared electron
  pairs needed to complete the octet and gives a
  clue as to the number of covalent bonds that form.

31
Multiple Covalent Bonds

• Double and triple bonds are examples of multiple
  covalent bonds.
• Double bonds sharing 2 pairs of electrons
• Triple bonds sharing 3 pairs of electrons
• Diatomic oxygen and nitrogen have multiple
  covalent bonds.