Topic 3: Periodicity

Question 1

How do you find an effective nuclear charge?

Answer 1

Atomic number - number of shielding electrons

Question 2

How do you find number of shielding electrons/?

Answer 2

Atomic number minus valence electrons

Question 3

What is atomic radius?

Answer 3

It is measured as half the distance bweteen neighbouring nuclei

Question 4

What is the trend of atomic radius across a period?

Answer 4

Atomic radius decreases across a period

Question 5

Explain the trend of atomic radius across a period

Answer 5

It decreases, because nuclear charge increases across a period, meaning there are more valence electrons in atoms across a period. The number of shielding electrons remains constant, so with more protons than electrons, the attracting force between the valence electrons and nucleus decreases, decreasing atomic radius.

Question 6

Explain the trend of atomic radius down a group

Answer 6

It increases, because the number of occupied energy levels increases, and the number of shielding electrons increases. This weakens the attraction between the nucleus and valence electrons, increasing the distance, therefore increasing atomic radius.

Question 7

Explain the trend of ionic radius down a group

Answer 7

It increases due to the increasing number of energy shells, weakening the attraction between the electrons and nucleus.

Question 8

Explain the trend of ionic radius across a period

Answer 8

It decreases for positive ions due to their stronger attraction to the nucleus as a result of fewer valence electrons. It increases for negative ions, due to a weaker attraction to the nucleus as a result of more electrons. It then decreases again.

Question 9

What are isoelectric ions?

Answer 9

Ions with the same electron configuration but a different number of protons.

Question 10

What is the formula for first ionisation energy?

Answer 10

X(g) → X+(g) + e-

Question 11

What is the definition of first ionisation energy?

Answer 11

The energy required to remove one mole of electrons from one mole of gaseous atoms to form one mole of gaseous ions.

Question 12

What are first ionisation energies?

Answer 12

is the energy involved in removing one mole of electrons from one mole of atoms in the gaseous state

Question 13

Explain the trend of ionisation energy down a group

Answer 13

It decreases down a group because as the number of shielding electrons increases, the electrostatic attraction between the electrons and the nucleus weakens, requiring less energy to remove the valence electrons. Also, as the number of energy levels increases, the distance between the nucleus and outer electrons increases, also weakening attraction and decreasing ionisation energy.

Question 14

Explain the trend of ionisation energy across a period

Answer 14

It increases, because as the nuclear charge increases, so does the attraction between the protons and the outer electrons. The atomic radius decreases, strengthening the attraction between the nucleus and the outer electrons. This increases the energy needed to remove an electron from the outer shell, therefore increasing ionisation energy.

Question 15

What is electronegativity?

Answer 15

A measure of the ability of an atom to attract a bonding pair of electrons

Question 16

Explain the trend of electronegativity down a group

Answer 16

It decreases. The number of energy levels and shielding electrons increases, also increasing the atomic radius. This means the bonding electrons are further from the attraction of the nucleus, weakening their attraction to the bond.

Question 17

Explain the trend of electronegativity across a period

Answer 17

It increases across a period. The nuclear charge increases, strengthening the attraction between the bonding electron and the nucleus. The atomic radius decreases, also strengthening this attraction.

Question 18

What is first electron affinity?

Answer 18

The first electron affinity is the energy released when one mole of electrons is added to one mole of gaseous atoms to form one mole of 1- ions.

X(g) + e- → X-(g)

Question 19

What is second electron affinity?

Answer 19

The second electron affinity corresponds to the addition of one mole of electrons to one mole of gaseous 1- ions.

Question 20

Explain the trend of electron affinity down a group

Answer 20

It decreases, due to an increase in shielding electrons and atomic radius, weakening the attractive force between the nucleus and valence electrons, lessening the energy released when adding a valence electron, therefore decreasing electron affinity.

Question 21

Explain the trend of electron affinity across a period

Answer 21

It increases. An increase in nuclear charge leads to an increase in the attractive force between the nucleus and valence electrons, as does a decrease in atomic radius. Therefore, the energy released when adding an electron will increase, also increasing electron affinity.

Question 22

What is a melting point

Answer 22

The point at which materials turn from solid to liquid. Tightly packed molecules have higher melting points, as a strong attraction between molecules leads to a higher melting point.

Question 23

What are the physical properties of group 1 alkali metals?

Answer 23

• silver metals too reactive to be found in nature (stored in oil to prevent contact with air and water)
• extremely reactive
• first three elements:
  
  • good conductors of electricity
  • low densities
  • have shiny surfaces when cut

Question 24

What are the chemical properties of group 1?

Answer 24

• Reactivity increases down a group because ionisation energy decreases, and outer shell electron is more easily removed
• Alkali metals react with water to form hydrogen gas and metal hydroxide

Question 25

What is the trend of reactivity down group 1?

Answer 25

It increases because the number of shielding electrons/occupied energy levels increases, as well as the atomic radius. So the electrostatic force of attraction between the nucleus and the outer electron decreases. Therefore, the outer electron is lost more easily and the atoms react more easily

Question 26

Explain reaction of group 1 (alkali metals) with water

Answer 26

Alkali metals react with water to form metal hydroxide and hydrogen gas (Na + H2O —> NaOH + H2). The reaction with water becomes more vigorous down the group as ionisation energy decreases and positive ions are formed more readily

Question 27

Describe Lithium’s reaction with water

Answer 27

Reacts slowly, releases H2 but keeps its shape and floats

Question 28

Describe Sodium’s reaction with water

Answer 28

Vigorously releases H2 which releases enough heat to melt the remaining Na that floats on the surface

Question 29

Describe Potassium’s reaction with water

Answer 29

Reacts vigorously to produce enough to ignite H2 produced and creates a lilac flame which dances on the surface

Question 30

What are the physical properties of group 17 Halogens?

Answer 30

• coloured

- show gradual change from gases to liquids to solids

Question 31

What are the chemical properties of group 17 halogen?s

Answer 31

• very reactive
• reactivity decreases down group (atomic radius increases, which means more shielding electrons, therefore more difficult for negative electrons to be attracted to positive protons)
• they form ionic compounds with metals or covalent compounds with other non-metals

Question 32

Describe displacement reactions

Answer 32

The more reactive halogen displaces the halide ion of the less reactive halogen from the solution

Question 33

Describe basic oxides

Answer 33

• basic oxides dissolve in water to form a basic or alkaline solution due to the presence of hydroxide ions. They produce solutions with ph above 7 (basic)

Question 34

Example of basic oxide reaction with oxygen

Answer 34

4Na + O2 —> 2Na2O

Question 35

Acidic oxides

Answer 35

Write them down

Question 36

Amphoteric oxides

Answer 36

Can react to be either basic or acidic oxide

Question 37

Oxide reactions to remember

Answer 37

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