CHEM1011 Lecture Notes - Lecture 8: Chemical Formula, Empirical Formula, Sodium Chloride
24 May 2018
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Lecture 8: Molecules and ions
Molecular vs Network Solids
- Coalet oded sustaes aye oleular or etork aterials
- E.g. the elements iodine and carbon
Weak non-covalent forces can be broken easily but they are preserved when turned into gas
(black substance at bottom)
Properties
- Molecular materials are:
Soft when solid (e.g. wax) with a low melting point
May also be gases or liquids at room temperature (e.g.
CO2)
- Network materials are:
Hard solids with a high melting point
Covalent bonds broken when solid melts (e.g. SiO2)
Types of formula
Empirical formula: Lowest ratio of atoms of different types present
- Ionic compounds e.g. NaCl, K2O
- Molecular compounds e.g. glucose CH2O
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Document Summary
Co(cid:448)ale(cid:374)t (cid:271)o(cid:374)ded su(cid:271)sta(cid:374)(cid:272)es (cid:373)ay(cid:271)e (cid:858)(cid:373)ole(cid:272)ular(cid:859) or (cid:858)(cid:374)et(cid:449)ork(cid:859) (cid:373)aterials. Weak non-covalent forces can be broken easily but they are preserved when turned into gas (black substance at bottom) Soft when solid (e. g. wax) with a low melting point. May also be gases or liquids at room temperature (e. g. co2) Hard solids with a high melting point. Covalent bonds broken when solid melts (e. g. sio2) Empirical formula: lowest ratio of atoms of different types present. Elements (do not have a ratio) always used except for molecular elements e. g. h2, n2, Actual number of atoms of each type in molecule e. g. glucose has a molecular formula. Always a simple multiple of empirical formula. The element with the lower group number called by the element name. The name of the other is derived from the ele(cid:373)e(cid:374)t (cid:374)a(cid:373)e a(cid:374)d e(cid:374)ds i(cid:374) ide. Covalent bonds between identical atoms have electrons shared equally.
