3.2.1 Periodicity

Question 1

The periodic table is arranged by ____ _____

Answer 1

Atomic number

Question 2

Name the blocks

Answer 2

Question 3

Elements within a period have same number of _____ ___

Answer 3

electron shells

Question 4

Using the periodic table, write the electron configuration for phosphorus

Answer 4

Question 5

Using the periodic table, write the electron configuration for cobalt

Answer 5

Question 6

Atomic Radius _____ across a Period

Answer 6

decreases

Question 7

Why does atomic radius decreases across a period?

Answer 7

• As number of proton increases, positive charge of nucleus increases
• Increased attraction between nucleus and electrons
• Similar shielding in each period
  
  • As electrons added to same outer shell

Question 8

Why don’t the extra electrons that element gains across period provide extra shielding?

Answer 8

• Extra electrons are added to outer energy level
• (Shielding is mainly provided by electrons in inner shells)

Question 9

As you go across period 3, from sodium to magnesium to aluminium, why does melting and boiling points increase?

Answer 9

• ∵ metal-metal bonds get stronger
• Get stronger ∵ metal ions have increasing positive charge = increasing number of delocalised electrons and decreasing radius

Question 10

Why does silicon have such a high melting point?

Answer 10

• Silicon is macromolecular (tetrahedral structure) = many strong covalent bonds
• Lot of energy needed to break these bonds

Question 11

Why does phosphorus, sulfur and chlorine have low melting points?

Answer 11

• They’re molecular substances so melting points depend upon strength of van der Waals forces between molecules
• Van der Waals forces are weak and easily overcome

Question 12

Why does sulfur have a higher melting point than phosphorus or chlorine? (2)

Answer 12

• Sulfur is the biggest molecule (largest M_r)
• Stronger van der Waals forces between molecules (they’re stronger with larger M_r)

Question 13

Why does argon have a very low melting point?

Answer 13

∵ exists as individual atoms = weak van der Waals forces

Question 14

Ionisation energy generally ______ across a period

Answer 14

increases

Question 15

Why does ionisation energy generally increases across a period (4)

Answer 15

• As number of proton increases, positive charge of nucleus increases
• Increased attraction between nucleus and electrons
• Similar shielding in each period
  
  • As electrons added to same outer shell
• More energy needed to remove electron

Question 16

Predict the element in Period 3 that has the highest second ionisation energy. Give a reason for your answer. (2)

Answer 16

• Sodium / Na
• Electron (removed) from the 2nd shell / 2p (orbital)

Question 17

Explain why the ionisation energy of every element is endothermic (1)

Answer 17

Energy needed to overcome attraction between nucleus and electron