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Chemistry > Periodicity > Flashcards

Periodicity Flashcards

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1
Q

How are elements arranged in the Periodic Table?

A

In order of increasing atomic number - the number of protons in the nucleus.

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2
Q

Why do chemists find the Periodic Table useful?

A

They can make predictions about the properties of an element based on its position in the table.

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3
Q

Why are elements in the same group similar?

A

They share the same number of electrons in their outer shell.

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4
Q

Definition of periodicity?

A

A repeating pattern.

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5
Q

How are elements in periods organised?

A

In order of increasing atomic number, showing the increasing number of outer electrons. They also move from metallic to non-metallic characteristics.

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6
Q

Name three elements with metallic bonding and structure.

A

Li, Be, Na, Mg, Al, K, Ca

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7
Q

Name three elements with covalent molecular structure.

A

H2, N2, O2, F2, Cl2, P4, S8 and fullerenes (eg C60)

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8
Q

Name three elements with covalent network structure.

A

B, C (diamond, graphite), Si

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9
Q

Name three elements with monatomic structure.

A

Noble gases - He, Ne, Ar

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10
Q

What group are the noble gases?

A

Group 0/8

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11
Q

What does monatomic mean?

A

The molecules exist as individual atoms.

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12
Q

Why are noble gases unreactive?

A

They have a full outer energy level.

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13
Q

What are London dispersion forces (LDFs)?

A

They are very weak forces of attraction caused by the continual movement of electrons in an atom which causes a temporary uneven distribution of charge known as a temporary dipole. This induces a temporary dipole in a neighbouring atom and forming a force of attraction between them.

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14
Q

What is a temporary dipole?

A

Caused by the continual movement of electrons in an atom which causes a temporary uneven distribution of charge at opposite sides of the atom -this makes one side of an atom slightly negative 𝛿- and one side slightly positive 𝛿+.

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15
Q

How do LDFs change going down a group?

A

Although very weak, the more electrons, the bigger the LDFs, increasing the MPs and BPs as more energy is needed to separate them.

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16
Q

What is the difference between intermolecular and intramolecular forces?

A 
INTER = between separate molecules
INTRA = between atoms inside a molecule
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17
Q

Name the diatomic molecules.

A

H2, O2, F2, Br2, I2, N2, Cl2

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18
Q

What are diatomic molecules?

A

They exist as two atoms covalently bonded.

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19
Q

What force of attraction holds noble gases together?

A

LDFs

20
Q

Why are most diatomic molecules gases at room temperature?

A

The forces between them (LDFs) are so small that there is enough energy at room temperature to overcome the weak force of attraction and separate the molecules from each other.

21
Q

Name the halogens and their group number.

A

Group 7 - F2, Cl2, Br2, I2, At

22
Q

How do phosphorus and sulfur exist?

A

P4 and S8. They are solids at room temperature with low melting and boiling points.

23
Q

What bonds hold together P4 and S8?

A

The atoms which make up the molecules are held together by covalent bonds and the molecules are held together by LDFs.

24
Q

How can carbon exist?

A

As covalent networks - graphite and diamond, and as covalent molecules - fullerene (C60).

25
Q

Describe fullerene’s shape.

A

A series of carbons arranged in hexagons and pentagons are joined to form a ball shape. It can also exit as tube shapes called nanotubes.

26
Q

How is fullerene held together?

A

By LDFs but because of its size it requires a lot more energy to separate.

27
Q

What’s one thing that a high melting and boiling point indicates?

A

There are other forces holding the molecules together, apart from just LDFs.

28
Q

Give three points about diamond.

A
  • Each carbon atom is covalently bonded to four other carbons in a tetrahedral shape.
  • All the outer electrons of each carbon are used to make single covalent bonds with neighbouring atoms, hence the giant covalent network.
  • No individual molecules or unbonded (delocalised) electrons, so diamond does not conduct electricity.
29
Q

Give three points on graphite.

A
  • Any one carbon is only bonded to three other carbons, making the fourth electron in its outer shell delocalised, and therefore can conduct electricity.
  • Atoms form hexagonal plates held together by weak LDFs.
  • The plates are able to slide over each other, explaining why powdered graphite can be used as a lubricant.
30
Q

Why do covalent networks have such high melting and boiling points?

A

The strong covalent bonds need to be broken requiring a lot of energy.

31
Q

What’s unusual about graphite and diamond?

A

When heated to high temperatures, rather than melt they sublime; meaning they go straight from solid to gas.

32
Q

Describe silicon.

A

Silicon is similar to diamond in that it forms covalent bonds with four other silicon atoms and makes a covalent network. It has a very high melting point, is extremely hard, and is a poor conductor.

33
Q

Describe boron.

A

Boron is similar to carbon as it forms a stable covalent network. It is a very hard, black material with a very high melting point.

34
Q

What is the covalent radius?

A

The measure of the size of an atom. Taken by half the distance between the nuclei of two atoms joined by a single covalent bond.

35
Q

Explain what happens to the covalent radius going down a group.

A

INCREASES (atoms get bigger) - due to the increasing atomic number, there are more protons in the nucleus and more electrons in each energy level. As the energy levels increase there is shielding of the full pull of the positive nucleus allowing the outermost electrons to move further away.

36
Q

Explain what happens to the covalent radius going across a period.

A

DECREASES (atoms get smaller) - the atomic number increases by one each time, meaning the atom gains a proton while also gaining an electron in the same energy shell. Thus there is no shielding effect from the inner levels and so the outer electrons are more strongly attracted to the nucleus pulling them closer together.

37
Q

What is ionisation energy?

A

The energy required to remove one mole of electrons from one mole of atoms in the gaseous state.

38
Q

What unit is ionisation energy measured in?

A

kJ mol-1

39
Q

What does first and second ionisation energy mean?

A

The first ionisation energy is the energy required to remove one mole. The second is the energy required to remove two moles.

40
Q

Why are second ionisation energy values always higher than the first?

A

Although electrons are being removed, the number of protons in the nucleus stays the same increasing the pull on the remaining electrons.

41
Q

Describe what happens to ionisation energy as you go down a group.

A

DECREASES (less energy required) - because the covalent radius has increased and the outer electrons are shielded from the full pull of the nucleus, it is easier to remove an outer electron.

42
Q

Describe what happens to ionisation energy as you go across a period.

A

INCREASES (more energy required) - although electrons are being added, it is to the same energy level which increases the nuclear charge, holding the electrons closer together. This makes it harder to remove an outer electron.

43
Q

What is electronegativity?

A

The attraction an atom, involved in a bond, has for the electrons of the bond.

44
Q

What elements are the most and least electronegative?

A 
MOST = Fluorine (4.0)
LEAST = Caesium (0.8)
45
Q

What does electronegativity help indicate?

A

The difference in electronegativity within a bond helps indicate the type of bonding that primarily exists between them.

46
Q

Describe what happens to electronegativity going down a group.

A

DECREASES (less attraction) - the covalent radius increases and outer electrons are further from the nucleus and are also shielded from the full pull of the nucleus, combining to result in the nucleus having less of an attraction for the bonding electrons.

47
Q

Describe electronegativity going across a period.

A

INCREASES (more attraction) - the covalent radius decreases and the number of outer levels stay the same, so the nucleus’s attraction for bonding electrons increases.

Chemistry (15 decks)

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