Chemistry Notes

These notes were compiled while working through the Chinese High School Chemistry Reader, cross-referencing the corresponding Wikipedia entries
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[Pinned] Q & A

Q. How do we explain why the first ionization energy of helium, beryllium, neon, magnesium, nitrogen, and phosphorus is higher than that of their neighbouring elements?

A.

Helium, neon: the outermost shell is in a filled, stable state, so electrons are not easily lost.
Beryllium, magnesium: the s sublevel of the L shell is fully filled (aufbau principle).
Nitrogen, phosphorus: the p sublevel is in a half-filled state, which is relatively stable (aufbau principle).

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[Pinned] Chemical Equations

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• Complete Collection of High School Chemical Equations PDF DOC DOCX

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[Pinned] Downloadable Resources

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• Complete Collection of High School Chemical Equations PDF DOC DOCX
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• Complete Collection of High School Chemistry Formulas PDF DOC DOCX
• Categorized Summary of Knowledge Points from High School Chemistry Elective 4 PDF DOC
• High School Chemistry: Chemistry and Life, a Summary PDF DOC
• Analysis of the High School Chemistry Curriculum Standards (2017 Edition) PDF PPTX

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Silicon, Colloids

Group IV (Carbon Group) Elements

• Group IVA of the periodic table
• Carbon, silicon, germanium, tin, lead
• A middle-position group, easily forming covalent compounds
• Outermost electron configuration
• Properties shift down the group; the trend from nonmetallic to metallic character top to bottom is more pronounced than in the nitrogen group
• Electronegativity is lower than that of the halogen, oxygen, and nitrogen groups

1. The melting point and boiling point of the carbon group elements decrease as atomic mass increases. Carbon sublimes at 3825 °C.
2. The density and atomic radius of the carbon group elements increase as atomic mass increases.
3. Carbon’s crystal structure is hexagonal; under high temperature and high pressure it forms diamond. Silicon and germanium also have diamond-cubic crystal structures. Tin has a diamond structure at low temperature (below 13.2 °C) and becomes tetragonal at room temperature. Lead has a cubic crystal structure.

Silicon and Its Compounds

• No free elemental silicon exists in nature
• Combined-state silicon is almost entirely silicon dioxide and silicates
• Silicon is the main constituent element of minerals and rocks

Colloids

• Generally, colloidal particles of metal hydroxides and metal oxides adsorb cations and carry a positive charge; colloidal particles of nonmetal oxides and metal sulfides adsorb anions and carry a negative charge
• Colloidal particles are charged particles, so under the action of an electric field, they undergo directional migration, producing electrophoresis
• Main component of bittern: $MgCl2\cdot 6H2O$
• Gypsum: $CaSO4\cdot 2H2O$

Electrolyte Solutions

Strong and Weak Electrolytes

1. Strong electrolytes: ionic compounds and certain covalent compounds with polar bonds that fully ionize into particles in aqueous solution are called strong electrolytes (strong acids, strong bases, and most salts)
2. Weak electrolytes: certain covalent compounds with polar bonds reach an ionization equilibrium, only partially ionizing into ions

Degree of Ionization and Ionization Constant

• Generally, for the same weak electrolyte, the more dilute the solution, the greater the degree of ionization; the higher the temperature, the greater the degree of ionization
• When temperature is not stated, assume 25 °C
• Ionization constants

• The ionization constants K1, K2, K3 for successive ionization steps of a polyprotic weak acid generally differ by several orders of magnitude, so acidity is determined mainly by the first ionization step

Definition of pH

$$\operatorname{pH} = -\log_{10} \left[ \operatorname{H}^+ \right]= \log_{10} \frac{1}{\left[ \operatorname{H}^+ \right]}$$

Other

• $2NaOH+Cl_2=NaClO+NaCl+H_2O$