Chem - Bonding 2

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  • Created by: KTPL
  • Created on: 20-11-16 15:39
What is electronegativity?
The power of an atom to attract the pair of electrons in a covalent bond
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How does electronegativity change ACROSS a period?
Increases. (nuclear charge increases bc. more protons)
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How does electronegativity change DOWN a group?
Decrease. (atomic radius increases bc. no. of shells increases so more shielding)
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What is the most electronegative atom?
Fluorine (F)
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Why do noble gases not have electronegativity values?
They do not normally form covalent bonds
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When is a bond polar?
When there is an uneven distribution of electrons
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When is there a non-polar covalent bond?
When there is no or VERY small difference in electronegativity (All molecules of same element eg.Cl-Cl)
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When is there a polar covalent bond?
When there is a difference in electronegativity
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What is a polar covalent bond shown by?
delta +/-
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when is there an ionic bond?
When there is a large difference in electronegativity
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On which atom does the delta - go on?
The on closest to F on the periodic table
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What to elements should be considered to have the same electronegativity?
Carbon and Hydrogen
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In a polar molecule, what dipole is induced?
A permanent dipole
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Why are some molecules non-polar,in relation to their shape?
When they have lines of symmetry
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What are intermolecular forces?
Forces of attraction between MOLECULES
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What are the 3 types of intermolecular force?
Van Der Waal's forces; Permanent dipole-dipole forces; Hydrogen bonds
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What is the weakest intermolecular force?
Van Der Waal's forces
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What is the strongest intermolecular force?
Hydrogen bonds
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What are Van Der Waal's forces caused by?
Movement of electrons that unbalance the charge distribution. This creates an INSTANTANEOUS DIPOLE
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Which force is present in all molecules?
Van Der Waal's forces
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What results in stronger Van Der Waal's forces?
Bigger molecules (greater Mr) have more electrons, so the induced dipoles are larger
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What happens to the boiling points of the noble gases down the group?
Increase - increasing strengths of Van Der Waal's forces
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Where do permanent dipole-dipole forces occur?
Between molecules with a permanent dipole
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When do hydrogen bonds occur?
When the molecule contains a hydrogen atom bonded to either F/O/N
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What is a hydrogen bond formed between?
delta + H atom and a lone pair of electrons on N/O/F in a neighbouring molecule
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Which bond usually allows substances to dissolve in water?
Hydrogen bonds (they form hydrogen bonds with water)
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Why, when water freezes, does it become LESS dense than water?
Water molecules are held apart by hydrogen bonds in an OPEN TETRAHEDRAL STRUCTURE. When it is frozen, the hydrogen bonds freeze in place, trapping air.
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What can current be carried by?
Electrons or Ions
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What do ionic and polar substances dissolve in?
Polar solvents e.g. water
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What do non-polar substances dissolve in?
Non-polar solvents e.g. hexane
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What surrounds a single ion in a giant ionic lattice?
6 oppositely charged ions
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A Giant Ionic Lattice is held together by what?
Ionic Bonds
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Why do ionic compounds have high melting points?
Held together by strong ionic bonds that need a large amount of energy to break
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When do ionic compounds NOT conduct electricity, and why?
When they are solid - The ions only vibrate in a fixed position and are not free to move to carry the charge.
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When do ionic compounds conduct electricity, and why?
When dissolved/molten - The ions are free to move and can carry the current
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Why are ionic substances brittle?
When enough force is applied, the layers slide over each other; like charged are side by side, causing repulsion; the lattice structure breaks down
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High melting points in metals?
Metallic bonds are strong, needs large amount of energy
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Why do metals conduct electricity?
Delocalised electrons can flow through the structure, carrying the current
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Why are metals strong?
Metallic bonds are strong and extend throughout the giant metallic lattice.
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Why are metals malleable/ductile?
Layers of ions can slide over each other without disrupting the metallic bond
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What are the two main types pf covalent substances?
Simple molecular, giant covalent
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As a solid, covalent substances have low melting points because...
Van Der Waal forces between molecules are weak
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As a solid, covalent substances are generally insoluble in water because...
cannot form hydrogen bonds
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Covalent substances cannot conduct electricity because...
No charged particles that are free to move
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Other cards in this set

Card 2

Front

How does electronegativity change ACROSS a period?

Back

Increases. (nuclear charge increases bc. more protons)

Card 3

Front

How does electronegativity change DOWN a group?

Back

Preview of the front of card 3

Card 4

Front

What is the most electronegative atom?

Back

Preview of the front of card 4

Card 5

Front

Why do noble gases not have electronegativity values?

Back

Preview of the front of card 5
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