9. Structures and properties of substances

Question 1

definition of the structure of a substance

Answer 1

a description of its constituent particles and how they are arranged or packed together

Question 2

molecular structure consists of _________

Answer 2

isolable units

Question 3

giant structure

Answer 3

all particles are bond to each other

Question 4

molecular structures include 2 types

Answer 4

simple molecular structures e.g. He, Co2

macromolecular structures e.g. protein, starch

Question 5

giant structure include 3 types

Answer 5

giant ionic structures e.g. NaCl, K2O
giant covalent structures e.g. diamond, graphite
giant matellic structures e.g. Cu, Fe, Ag

Question 6

intermolecular forces increase with ________ and ______

Answer 6

molecular size and number of electrons in molecules

Question 7

definition of giant structure

Answer 7

all particles in the substance are bond together by strong chemical bonds, include strong ionic, covalent and matellic bond

Question 8

bondings in simple molecular structures

Answer 8

strong covalent bonds within the molecule

weak van der Waal’s forces between molecules

Question 9

properties of simple molecular structures

Answer 9

1. low melting point and boiling point;
   because molecules are held by weak van der Waal’s forces, little heat energy is needed to separate the molecules, thus they are either a gas, a volatile liquid or a solid with low melting point
2. simple molecular solids are usually soft;
   because the weak van der Waal’s forces between molecules are easy to break when stress is applied to it
3. they do not conduct electricity in any states;
   because they are no mobile ions or electrons
4. they are usually insoluble in water but soluble in non-aqueous solvents;
   because in aqueous solvent like water, the attractive forces between water molecules are strong while the attractive forces between simple molecule and water are weak, the interaction formed cannot compensate for the interaction broken
   in non-aqueous solvent like oil, both the attractive forces between non-aqueous solvent molecules and simple molecule are weak, the two forces are comparable in strength, the interaction formed and compensate the interaction broken

Question 10

some simple molecular substances are soluble in water and the aqueous solutions can conduct electricity, what are some examples?

Answer 10

Cl2, HCl, I2, CO2, SO2 and NH3

Question 11

will melting or boiling break the covalent bond in a simple molecular substance?

Answer 11

no, the strong covalent bonds within molecules are preserved

Question 12

Do all covalent substances have giant structure?

Answer 12

No, only a few have like carbon (diamond or graphite) and quartz (silicon dioxide, SiO2)

Question 13

allotropes

Answer 13

allotropes are pure crystalline forms of an element (with two or more forms). The atoms or molecules inside are arranges in different ways

Question 14

describe and draw the structure of diamond

Answer 14

each carbon atom is surrounded by 4 carbon atoms under strong C-C covalent bonds;
it forms a 3D giant network with tetrahedrons