10. PHYSICAL PERIODICITY Flashcards

1
Q

How is the covalent radius of an atom found

A
  • the distance between the two nuclei of the same type of atom in a covalent bond can be determined
  • this can be divided by two to arrive at the single covalent radius
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2
Q

Why are mainly covalent radii used

A
  • can be obtained for most elements

- so provide the best data for comparison purposes

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3
Q

Why do the noble gases in Group 18 not have a covalent radius

A

because they do not form bonds with each other

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4
Q

How are the van der Waals’ radii found

A
  • the distance between the nuclei of two neighbouring touching atoms that are not chemically bonded together can be found
  • this can be divided by two to arrive at the van der Waals’ radius
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5
Q

Why is the value of the van der Waals’ radius higher than the single covalent radius of any element

A

because there is no overlap of electron clouds in van der Waals’ radii

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6
Q

What property of SO2 enables it to act as a food preservative

A
  • reducing agent

- kills bacteria

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7
Q

What is the periodic pattern of atomic radii

A

atomic radii decrease across the period

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8
Q

Why do atomic radii decrease across a period

A
  • across the period, the nuclear charge increase as the number of protons increases
  • the extra electron is added to the same principal quantum shell
  • the shielding effect remains roughly constant
  • the greater attractive force exerted by the increasing positive nuclear charge on the outer electrons pulls them in closer to the nucleus
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9
Q

Explain the difference in size between the cations and their corresponding atoms

A
  • cation contains fewer electrons than corresponding atom
  • decreased shielding effect on outer electrons
  • increased attraction by nucleus
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10
Q

Variation in ionic radii from Na+ to Si4+

A
  • ionic radii decrease
  • the greater attractive force exerted by the increasing nuclear charge on the valence electrons pulls them in closer to the nucleus
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11
Q

Variation in ionic radii from P3- to Cl-

A
  • ionic radii decrease
  • the greater attractive forces exerted by the increasing nuclear charge on the valence electrons pulls them in towards the nucleus
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12
Q

Explain the difference in size between the anions and their corresponding atoms

A
  • anion contains more electrons than corresponding atom
  • increased repulsion between the electrons
  • nuclear charge remains constant
  • decreased nuclear attraction
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13
Q

Why does melting point increase in the metals across a period

A
  • the bonding is metallic
  • the strength of the bonding increases/ the electrostatic forces of attraction between the ions increases
  • as the number of delocalised electrons increases
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14
Q

Why does electrical conductivity increase in the metals across a period

A
  • the number of delocalised electrons increases

- more electrons are available to drift through the structure when a potential difference is applied

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15
Q

Why does silicon have the highest melting point in the period

A
  • silicon has a giant covalent structure
  • the Si atoms are bonded to each other with strong covalent bonds
  • the covalent bonds require a large amount of energy to break
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16
Q

Why does silicon not conduct electricity

A
  • it has a giant covalent structure
  • Si atoms are bonded to each other with covalent bonds
  • no free delocalised electrons to to move around and conduct charges
17
Q

Sulfur exists as

A

S8 molecules (solid)

18
Q

Phosphorus exists as

A

P4 molecules (solid)

19
Q

Explain the variation in melting points from P to Ar

A
  • van der Waals’ forces decrease as size of molecule decreases
  • sulfur has greatest melting point
  • highest number of electrons in S8 molecule
20
Q

What is the general trend in first ionisation energies from Na to Ar

A
  • the first ionisation energies increase
  • the nuclear charge increases
  • the distance between the nucleus and outer electrons remains reasonably constant
  • shielding effect remains roughly constant
  • increased attractive force by nucleus
21
Q

Why is there a rapid decrease in ionisation energies from the end of one period to the next

A
  • the distance between the nucleus and other electrons increases
  • the shielding by inner shells increases
  • these factors outweigh the increased nuclear charge
22
Q

Why is there a decrease from s to p subshells

A
  • electronic structure
  • the 3p subshell is further away from the nucleus than the 3s subshell
  • the shielding by inner shells increases
  • these outweigh the increased nuclear charge