critical thinking questions
33. the most abundant elements in the foods and beverages you consume are oxygen, carbon, hydrogen, and nitrogen. why might having these elements in consumables be useful?
34. oxygen, whose atomic number is eight, has three stable isotopes: $^{16}o$, $^{17}o$, and $^{18}o$. explain what this means in terms of the number of protons and neutrons.
35. magnesium is an important element in the human body, especially in bones. magnesium’s atomic number is 12. is it stable or reactive? why? if it were to react with another atom, would it be more likely to accept or to donate one or more electrons?
36. explain why $ch_4$ is one of the most common molecules found in nature. are the bonds between the atoms ionic or covalent?
37. in a hurry one day, you merely rinse your lunch dishes with water. as you are drying your salad bowl, you notice that it still has an oily film. why was the water alone not effective in cleaning the bowl?

Question

Accepted Answer

### 33.
# Brief Explanations:
Oxygen is for respiration and energy - release, carbon is a building - block for organic molecules, hydrogen is involved in many biochemical reactions, and nitrogen is crucial for proteins and nucleic acids.
# Answer:
These elements are useful because oxygen is essential for cellular respiration to release energy, carbon is the backbone of organic compounds like carbohydrates, lipids, proteins, and nucleic acids. Hydrogen is involved in many biochemical reactions and is part of water and many organic molecules. Nitrogen is a key component of amino acids (building - blocks of proteins) and nucleic acids (DNA and RNA).

### 34.
# Brief Explanations:
The atomic number is the number of protons. Isotopes have the same number of protons but different numbers of neutrons. Calculate neutrons as mass - number minus atomic number.
# Answer:
Oxygen has an atomic number of 8, so the number of protons is 8. For $^{16}O$, the number of neutrons is $16 - 8=8$; for $^{17}O$, the number of neutrons is $17 - 8 = 9$; for $^{18}O$, the number of neutrons is $18 - 8=10$.

### 35.
# Brief Explanations:
Magnesium has 12 electrons with an electron - configuration of 2, 8, 2. It will lose 2 electrons to achieve a stable octet.
# Answer:
Magnesium is reactive. Its atomic number is 12, so it has 12 electrons. Its electron - configuration is 2, 8, 2. To achieve a stable electron configuration (a full outer shell, similar to noble gases), it will donate 2 electrons.

### 36.
# Brief Explanations:
Carbon can form 4 covalent bonds, and hydrogen can form 1 covalent bond. $CH_4$ has covalent bonds due to electron - sharing.
# Answer:
$CH_4$ is common because carbon can form four covalent bonds and hydrogen can form one covalent bond, allowing for the stable formation of the molecule. The bonds between the atoms in $CH_4$ are covalent bonds as the electrons are shared between the carbon and hydrogen atoms.

### 37.
# Brief Explanations:
Water is a polar molecule and oil is non - polar. Polar and non - polar substances do not mix.
# Answer:
Water alone is not effective in cleaning the bowl because water is a polar molecule and oil is a non - polar substance. According to the principle "like dissolves like", polar water molecules do not interact well with non - polar oil molecules, so the oil does not dissolve in water.

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Explanation:

33.

Answer:

34.