Question

1. A(n) ___________ forms when atoms share one or more pairs of electrons.

Answer 1

1.COVALENT BOND   [c]                                                                                         2. Ionic bond                [d]                                                                                         3. Ionic bond             [d]                                                                                             4. a reaction where energy is released [b]                                                                5. 2FE2C03=4FE=3CO2 [a]                                                                                     6. The mass of reactant must be equal to  the number of mass of the product            [a]                                                                                                         7. Valence electrons [a]                                                                                             8. Atomic number [a]                                                                                                9. combustion  [c]                                                                                                      10. More nitrogen in the nitrogen cycle [a]

Answer 2

Answer:

1) c. Covalent Bond

2) d. Ionic bond

3) d. Ionic bond

4) b. a reaction where energy is released

5) a. 2 Fe2O3 + 3C ---> 4Fe + 3CO2

6) a. The mass of reactants must equal the mass of products.

7) a. valence electrons

8) a. atomic number

9) c. Combustion

10) d. increase in average temperature on Earth

Explanation:

1)

In a metallic bond, metals receive or gain electrons to achieve stability.

A molecule is a substance formed by two or more atoms, and the bond between atoms can be metallic, covalent or ionic.

In the covalent bond, the atoms share electrons of their last level until the electronic configuration of the nearest noble gas is achieved in the periodic table,this means that their last level of energy must be complete (with all electrons).

In ionic bonds there is a transfer of electrons from one atom to another.

So, the correct answer is covalent bond.

2)

A metal bond occurs between metal atoms.

A molecule is produced between atoms that can be metallic or nonmetallic.

A covalent bond occurs between nonmetallic atoms.

An ionic bond occurs between metals and nonmetals.

So, the correct answer is ionic bond.

3)

An element from Group 2 is a metal, and an element from Group 16 is a nonmetal. An ionic bond occurs between metals and nonmetals.

So, the correct answer is ionic bond.

4)

The exothermic reaction is that reaction where energy is released, this means that the energy of the molecules of the products is less than the energy of the molecules of the reagents.

In an endothermic reaction energy is absorbed, this means that the energy of the molecules of the products is greater than the energy of the molecules of the reagents.

5)

To balance an equation, you need the same number of each kind of element on both sides. For that, you have to look at the subscripts next to each atom to find the number of atoms in the equation.

For example, in this case, you have 2  irons and 3 oxygen in Fe2O3 and 1 C in the left side.

You must start balancing the oxygen.  Add a coefficient to the molecule CO2 on the right of the equation to balance it with oxygen atoms in Fe2O3 on the left of the equation. And vice versa.

So, for that reason, you put a 2 on Fe2O3 and a 3 on CO2. Now you have 6 atoms of oxygen in boths sides (In the left side, when you multiply the coefficient 2 times by the subscript 3, you end up with 6 oxygens. You can do the same in the right side and you have 6 oxygens). And it's balanced.

Now, when you multiply the coefficient 2 times by the subscript 2, you end up with 4 irons in the left side. You need 4 irons on the other side, so you put a 4 in that element.

And finally you balance the carbon in the same way.

6)

The mass of reactants must equal the mass of products is a statement FALSE because you need the same number of each kind of element on both sides (the same amount of elements).  This does not mean that the mass must be the same.

7)

Electrons involved in bonding between atoms are  valence electrons because these are the electrons that are less attracted to the nucleus of the atom.

8)

Protons are found only in the nucleus of the atom. The atomic number is the total number of protons that each atom has. So, you can say that the number of protons in the nucleus of an atom of that element is atomic number.

9)

Photosynthesis occurs in plants. Respiration is something biological of living beings.

As for a combustion, which is a chemical oxidation process, a fuel (gas) is needed, the correct answer is c.

10)

CO2 is the most important gas for controlling Earth’s temperature.  

Carbon dioxide absorbs a lot of energy, and part of it returns to Earth. If there is much of this gas, the atmosphere maintains its elevated temperature.