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Chemistry -Unit 1 > Chemical Bonding > Flashcards

Chemical Bonding Flashcards

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1
Q

What is a cation?

A

A positive metal ion

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2
Q

What is an anion?

A

A negative ion

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3
Q

What is 6:6 coordination?

A

When the positive ion is surrounded by six negative ions and vice versa

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4
Q

When might you find a face-centred cubic arrangement

A

When the anion is somewhat bigger than the cation

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5
Q

What is the optimum arrangement in an ionic lattice?

A

A compromise between maximum attraction of oppositely charged ions and minimal repulsion of ions of the same charge

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6
Q

When would you find 8:8 co-ordination?

A

When the two oppositely charged ions are of similar size

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7
Q

Why are metals good conductors?

A

Because of the mobile electrons in the metal lattice

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8
Q

What are superconductors?

A

Materials which conduct electricity with no resistance

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9
Q

What ability does a superconductor have?

A

It can carry a current infinitely without losing any energy

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10
Q

Why are superconductors often unrealistic to use for practical applications?

A

Because achieving temperatures near absolute zero is very difficult and costly

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11
Q

What are 1-2-3 superconductors known as?

A

Ceramic supercondtucors

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12
Q

Why are ceramics hard to form wires with?

A

Because they are less ductile than metals.

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13
Q

What usually happens to electrons in a metal?

A

They repel each other and are scattered throughout the lattice which resists their movement to some extent

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14
Q

What usually happens when an electron moves through the lattice?

A

The positive ions are attracted to the electron and move slightly towards it, once the electron has passed the ions quickly spring back into their original position.

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15
Q

What happens differently at low temperatures when the electron moves through the lattice?

A

The positive ions do not return to their original positions so quickly and momentarily a positively charged local region is created.

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16
Q

What is the result of the momentary positively charged region?

A

A second electron is attracted to this positive region and in this way follows the first electron through the lattice.

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17
Q

Why don’t the pair of electrons meet resistance?

A

Because they are no longer scattered

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18
Q

Why do superconductors resist a magnetic field? (diamagnetic)

A

Because they have no unpaired electrons

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19
Q

Why can magnets levitate above the surface of a superconductor?

A

When a magnet approaches the superconductor it will induces a current in the superconductor, the current will flow continuously because there is no resistance and thus it induces its own magnetic field which will repel the magnet.

20
Q

Give a use of superconductors

A

magnetic resonance imaging

21
Q

What is the most commercially valuable property of a superconductor?

A

Their electrical conductivity increases with a n increase in temperature

22
Q

What is the unit of conductivity?

A

Siemens (the reciprocal of ohms)

23
Q

What is formed when molecular orbitals formed have very smiler energies?

A

They form a virtually continuous band covering a range or energies

24
Q

What does the total width of the energy band depend on?

A

The strength of interaction between neighbouring atoms

25
Q

Which electrons are free to move and conduct electricity?

A

Only electrons in partially filled bands

26
Q

Why are metals good conductors of electricity?

A

The highest band occupied by electrons is only partially filled.

27
Q

What is the structure of the bands in semiconductors and

insulators?

A

The bands are either completely filled or completely empty

28
Q

What needs to happen for a semi-conductor to conduct?

A

An electron needs to be excited into a higher unfilled band to create a partially filled band

29
Q

Why might a material not conduct?

A

If the band gap is too big

30
Q

Because of the small band gaps in semiconductors what is the movement of the electrons?

A

Some electrons will have enough energy to move from the highest occupied band (valence band) into the lowest unfilled band (conduction band).

31
Q

How can the temperature increase the conductivity of the semiconductor?

A

If more energy is provided, more electrons can move into he higher band and the conductivity will increase.

32
Q

Which two elements can be used for semiconductors?

A

silicon and gremanium

33
Q

What is the effect of light on a semiconductor?

A

When the semiconductor absorbs photons of light electrons can be promoted into the lowest unfilled band leaving vacancies in the highest occupied band

34
Q

What happens when a voltage is applied to a semiconductor?

A

Negative electrons and positive holes move through the lattice.

35
Q

How can the number of charge carriers in a semiconductor be increased?

A

By doping the metal

36
Q

What properties does a dopant have?

A

It will have a different number of outer electrons than the parent element

37
Q

What happens to the extra electron of the arsenic doping agent?

A

The extra electron occupies the lowest unfilled band or conduction and makes the silicon a better conductor.

38
Q

What semiconductor uses negative electron as the charge carriers?

A

N-type

39
Q

What does the element boron produce when using it as a doping agent?

A

Positive holes

40
Q

How does a p-type junction conduct?

A

By movement of positive holes in the highest occupied band

41
Q

What creates the separation of charges on each side of the junction.

A

The movement of electrons from the n-type to the p-type material

42
Q

What happens when light is incident on the p-n junction?

A

Electron-hole pairs are formed

43
Q

What happens to the charge carriers?

A

They migrate to their corresponding semiconductor

44
Q

What is the effect of the migration of the newly formed electron hole pairs?

A

The n-type region will achieve a negative potential relative to the p-type region

45
Q

What is useful about the potential difference created?

A

It means an electric current will flow through an external circuit from the top layer to the bottom layer as long as light is hitting the junction

46
Q

What effectively has the solar cell achieved?

A

To convert light energy into electrical energy.

Chemistry -Unit 1 (7 decks)

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