4.1/4.2: VSEPR, Hybridization, Chemical Bonding & Polarity

Question 1

What is covalent bonding?

Answer 1

• non-metal bonded with non-metal
• non-metal atoms (except metalloids) have valence shells that are more than half-filled and can form filled shells most effectively by sharing electrons
• shared electrons constitute a covalent bond

Question 2

What are molecular crystals/solids?

Answer 2

• nonmetals
• other than large hydrocarbons & polymers
• not hard & non-conductors
• packed as close as the shape allows
• bonded by London dispersion force, dipole-dipole, h-bonding

Question 3

What are ionic crystals/solids?

Answer 3

• metal + non-metal
• crystal-like shape, hard but brittle
• conduct electricity when liquid and when dissolved in water, not solids
• high MP; held together by simultaneous attractions of an ion by surrounding ions of opposite charges (electrostatic)

Question 4

Why do substances form bonds?

Answer 4

to achieve a more stable, lower-energy state

Question 5

What are covalent network solids?

Answer 5

• a substance in which all atoms are covalently bonded together in a continuous two or three-dimensional array; no natural beginning or end exists
• high melting points, insoluble, non-conductors

Question 6

What are allotropes?

Answer 6

• one of two or more compounds consisting of the same element but having different physical properties (ex. pure carbon)
• pure carbon can be found as diamond and as graphite
• covalent bonds can form among many carbon atoms in a variety of patterns

Question 7

Why are metals able to conduct electricity?

Answer 7

their valence electrons are free to move from one atom to another

~ if a potential difference is applied to the ends of a piece of metal, the electrons are drawn towards the positive end and repelled from the negative end

Question 8

How to tell if a molecule is polar or non-polar based on molecular shape?

Answer 8

• the symmetry of the molecule makes it none-polar despite the bonds being polar
• each of the base VSEPR shapes are also symmetrical and will give non-polar molecules unless a non-bonding pair or different ligand alters the symmetry

Question 9

Why is diamond so hard?

Answer 9

• each carbon in diamond is perfectly tetrahedral; this gives them their strength
• the three-dimensional array of covalently bound carbon atoms makes diamond the hardest naturally occurring substance known
• there are strong, rigid, interconnected covalent bonds between each carbon atom in a tetrahedral structure

Question 10

What is metallic bonding?

Answer 10

• metal bonded to metal
• metal atoms have valence shells that are less than half-filled so two metal atoms cannot combine to form a filled shell or contribute to each other to form a filled shell
  ~ instead, a “sea” of valence electrons of many metal atoms move freely among the atoms; the positively charged ions are all attracted simultaneously to many electrons

Question 11

What does VSEPR stand for?

Answer 11

valence shell electron pair repulsion theory

Question 12

What are metallic crystals/solids?

Answer 12

• metals
• good conductors of heat and electricity
• variety from 1) soft to hard 2) melting point: low to high
• closely packing together structures: bonding is a result of fixed “(t)” nuclei & loosely held valence electrons
• flexibility comes from nondirectional bonds (planes of atoms can slide over each other while remaining bonded)

Question 13

What is ionic bonding?

Answer 13

• metal bonded to non-metal
• metal atoms lose their electrons and become positive ions & non-metal atoms gain the electrons and become negative ions.
• oppositely charged ions attract one another

Question 14

How does the bonding in graphite give it its unique properties?

Answer 14

• the carbon atoms in graphite have three short bonds with other carbon atoms; this array forms layers. the fourth bond on each carbon is longer and not as strong
• as a result, this bond can easily be broken and reformed with another atom, allowing the layers to slide past each other
  ex. as you push the pencil across paper, the layers slide off the pencil and onto the paper

Question 15

What are alloys?

Answer 15

• a solid mixture of two or more different types of metal atoms
• if the metal atoms are similar in size, they form a substitutional alloy, in which atoms of the second metal take the place of atoms in a pure metal
• if atoms of the second metal are much smaller than those of the first metal, they will fit into the spaces between the larger atoms; these are interstitial alloys
• electron “sea” model: the electrons of the “sea” can attract any kind of positive metal ion, so ions of different metals can be held in the same “sea”