3.1.3.4 Bonding and physical properties- boiling/melting point Flashcards
why the boiling point of methanol is much higher than that of oxygen
van der Waals’ forces between oxygen molecules
Hydrogen bonding between methanol molecules
H-B stronger than van der Waals’ O
R stronger IMF in methanol
the trend in melting point of the Group II elements Ca–Ba.
Trend: Decreases
Increase in size of ion/atom / more shells / decrease in charge density / decrease in charge size ratio
Weaker attraction for delocalised/free/sea of electrons / weaker metallic bonding
the trend in the melting points of the Period 3 metals Na, Mg and Al
trend: increases
more protons / higher charge on cation / more delocalised e– / smaller atomic/ionic radius
stronger attraction between (cat)ions and delocalised/free/mobile e–
OR stronger metallic bonding
why magnesium has a higher melting point than sodium
more protons ( (or Mg2+ more charge than Na+ ) attracts delocalised (or bonding) electrons more strongly more delocalised electrons Attacks positive ions more
Why diamond and graphite both have high melting points
macromolecular
(or giant molecule etc) covalent
strong covalent bonds
Change that occurs to the motion of the ions in sodium chloride when it is heated from room temperature to a temperature below its melting point
vibrate faster
why the boiling point of AsH3 is lower than that of NH3
(Only) weak Van der Waals forces between molecules /AsH3 has weaker IMF /ammonia has hydrogen bonding/ more energy needed to break IMF’s in ammonia/ Van der Waals weaker than H bonds;
Predict the type of bonding in a crystal of sodium azide. Suggest why its melting point is high.
Ionic
Oppositely charged ions / Na+ and N3 – ions
Strong attraction between (oppositely charged) ions / lots of energy needed to overcome (strong) attractions (between ions)
why nickel has a high melting point
Contains positive (metal) ions or protons or nuclei and delocalised / mobile / free / sea of electrons Strong attraction between them or strong metallic bonds
State the type of bonding in lithium fluoride. Explain why a lot of energy is needed to melt a sample of solid lithium fluoride.
Ionic
Strong or many or lots of (electrostatic) attractions (between ions)
Between + and − ions / between Li+ and F− ions / oppositely charged ions
why graphene has a high melting point
Covalent bonds
Many /strong / hard to break / need a lot of energy to break
why titanium has a high melting point
Nucleus / protons / positive ions and delocalised electrons (are attracted)
Strong attraction
the type of crystal structure in magnesium oxide and suggest why its melting point is high
(giant) Ionic
Between + and – ions / oppositely charged ions or Mg2+ and O2–
Strong attraction
why the melting point of sodium chloride is high
Strong (electrostatic) attraction
Between oppositely charged ions / particles
why the melting point of sodium iodide is lower than the melting point of sodium bromide
Iodide / I– bigger (ion) (so less attraction to the Na+ ion)
why KBrF4 has a high melting point
Ionic or (forces of) attraction between ions / bonds between ions Strong (electrostatic) attraction / strong bonds / lots of energy needed to break bonds Between K+ and BrF4 – ions/oppositely charged ions / + and – ions
why the melting point of carbon is high
Macromolecular / giant molecular / giant atomic
Covalent bonds in the structure
Strong (covalent) bonds must be broken or overcome / (covalent) bonds need a lot of energy to break
the type of bonding in sodium sulfide (Na2S) and explain why its melting point is high
Ionic
oppositely charged ions/+ and – ions or particles
ions attract strongly OR strong/many (ionic) bonds must be broken
why sodium has a lower melting point than magnesium
Na fewer protons/smaller nuclear charge/ fewer delocalised electrons
Na is a bigger ion/ atom
Smaller attraction between nucleus and delocalised electrons
Melting point of ice compared to sodium chloride
Attraction between ions in sodium chloride is very strong
Covalent bonds in ice are very strong
Hydrogen bonds between water molecules in ice are much weaker
Consequently, less energy is required to break the hydrogen bonds in ice to form separate water molecules than to break the ionic bonds in sodium chloride and make separate ions
The melting point of sodium chloride is much higher than that of sodium metal. What can be deduced from this information
the ionic bonding in NaCl is stronger/requires more energy to break than the metallic bonding in Na
why magnesium has a higher melting point than sodium
more protons attracts delocalised (or bonding) electrons more strongly
Why diamond and graphite both have high melting points
Macromolecular
Covalent
strong covalent bonds
bonds require much energy to break
why the heat energy required to melt sodium chloride is large
Ionic
Strong forces between ions
lots of energy required to break bonds
