(2009? Ningde) (1) is expressed in chemical terms: 2 oxygen atoms _ _ _ _ _ _; Calcium ion _ _ _ _ _; The main component of natural gas is _ _ _ _. (2) The picture on the right.

(1) According to the representation method of atoms, an atom is represented by an element symbol, and a number is added before the element symbol. Therefore, two oxygen atoms are represented as: 2O; ?

According to the expression method of ions: in the upper right corner of the symbol of elements representing ions, mark the number of positive and negative charges carried by ions. When the number comes first and the positive and negative signs come last, 1 should be omitted, so calcium ion is expressed as Ca2+;

The main component of natural gas is methane, which can be expressed as: CH4；;

(2)① As can be seen from the figure, the element 15 is phosphorus, and the atomic group of phosphorus is stone, so it belongs to non-metallic elements;

(2) As can be seen from the figure, aluminum is 13, and the outermost layer has three electrons, so it is easy to lose three electrons in chemical reaction, so its valence is+3;

(3) Boron is element No.5 and has two electron shells, so the second shell has three electrons;

(3)① From the chemical formula of shikimic acid as C2H2O5, it can be seen that shikimic acid is composed of hydrocarbon and oxygen, so the answer is: 3;

② The chemical formula of shikimic acid is C2H2O5, which shows that shikimic acid is a carbon-containing compound, so it belongs to organic matter.

③ The mass ratio of elements is equal to the sum of atomic weights, and the mass ratio of hydrogen and oxygen in shikimic acid is1× 2:16× 5 =1:40.

(4) The chemical properties of a substance refer to the properties shown by chemical changes, so the chemical properties are: D.

So the answer is: (1) 2O; ? Ca2+； CH4(2)① nonmetal; ②+3; ③ 1:40; (3)①3; ② Organic matter; ③ 1:40; ④D；