请选出正确答案，共10题，每题10分，满分100分：

1. Which of the following best describes the octet rule?

The valence shell of an atom likes to be empty.

Atoms like to have their electrons in shells with higher energy.

The valence shell of an atom likes to be full with eight electrons.

The valence shell of an atom likes to lose electrons once it becomes full with eight electrons.

2. 2.At STP, fluorine is a gas and bromine is a liquid because, compared to fluorine, bromine has:

stronger covalent bonds

stronger intermolecular forces

weaker covalent bonds

weaker intermolecular forces

3. Silicon nitride is a very hard, high-temperature-resistant ceramic used as a component of turbine blades in jet engines. It is prepared according to the following equation:
3Si (s) + 2N2 (g) →Si3N4 (s)
When this reaction is carried out in the atmosphere with 2.000 g Si, what is the reaction yield if we obtain 2.750 g of Si3N4?
Atomic weights (g/mol): Si 28.085, N 14.007

27.53%

72.73%

137.50%

82.61%

4. Ammonia (NH3) acts as a weak base in aqueous solution. What is the acid that reacts with this base when ammonia is dissolved in water?

none, there are no acids in pure water

H2O

NH4+

trick question, because no acids are present, ammonia cannot act as a base

5. The teeth are the hardest substances in the human body. Besides being essential for chewing, the teeth play an important role in speech. The uppermost part of the teeth is enamel; measuring 4–8 μm in diameter, formally called an enamel prism, is a tightly packed mass of hydroxyapatite crystals Ca5(PO4)3(OH) in an organized pattern. From an electrostatic interaction perspective, which structure would you expect to form among different atoms or groups of atoms, Ca2+, PO43-, and OH-?

Figure 1. Enamel structure showing the organization of hydroxyapatite rods in humans, and a cross-section of rods found in mouse teeth.[Reference: Pandya M, Diekwisch TG. Enamel biomimetics—fiction or future of dentistry. International journal of oral science. 2019 Jan 5;11(1):8.]

6. In Rutherford scattering experiment, it was first expected that the alpha particles would penetrate the gold foil without any deflection because

the mass of gold atom is high and alpha particle is positively charged

the velocity of alpha particle is high and the mass of alpha particle is low

the positive charge density of gold atom is low and the mass of electron is low

the net charge of gold atom is neutral

7. In a first-order reaction, a linear relation exists between time and

the natural logarithm of concentration of the reactant

the reciprocal of concentration of the reactant

the square root of concentration of the reactant

the concentration of the reactant

8. According to the molecular orbital theory, which of the following substance does NOT exist？

A. He2+

B. Li2

C. Be2

D. B2

9. A chemical reaction is spontaneous when

A. the enthalpy change is negative

B. the internal energy change is negative

C. the entropy change is positive

D. the Gibbs free energy change is negative

10. A reversible reaction proceeds towards the forward reaction when

A. the reaction quotient is greater than the equilibrium constant

B. the reaction quotient is smaller than the equilibrium constant

C. the reaction quotient equals the equilibrium constant

D. it depends on the temperature and pressure

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