Question 1

Which group of elements is referred to as the 'SPONCH' elements, and why are they significant in biology?

Accepted Answer

Sulfur, Phosphorus, Oxygen, Nitrogen, Carbon, Hydrogen; they make up about 98% of the body weight in living organisms.

Question 2

An atom of carbon has an atomic number of 6 and a mass number of 12. How many neutrons does it have?

Accepted Answer

$$12 - 6 = 6$$ neutrons

Question 3

Which statement best describes the relationship between atomic number and the number of electrons in a neutral atom?

Accepted Answer

The atomic number equals the number of electrons in a neutral atom.

Question 4

Why do atoms with incomplete outer (valence) shells tend to be chemically reactive?

Accepted Answer

They seek to fill their valence shell to achieve stability, often by forming chemical bonds.

Question 5

Which of the following best explains why neon (Ne) is chemically inert?

Accepted Answer

Neon's valence shell is full, so it does not tend to gain or lose electrons.

Question 6

Which of the following elements has the highest electronegativity, and what is the biological significance of this property?

Accepted Answer

Fluorine; its high electronegativity allows it to attract electrons strongly in chemical bonds.

Question 7

A water molecule ($$H_2O) is $$polar because:

Accepted Answer

Oxygen is more electronegative than hydrogen, creating partial charges and a dipole.

Question 8

Which type of bond is the strongest among the following, and what is the energy required to break it?

Accepted Answer

Triple covalent bond; $$200$$ kcal/mol

Question 9

What happens to the potential energy of an electron when it moves from the first shell to the third shell in an atom?

Accepted Answer

The electron absorbs energy and its potential energy increases.

Question 10

Which of the following best describes an ionic bond?

Accepted Answer

It is formed by the transfer of electrons from one atom to another, resulting in oppositely charged ions.

Question 11

Why are ionic bonds generally weaker in water than in air?

Accepted Answer

Water molecules surround and stabilize ions, reducing the electrostatic attraction between them.

Question 12

Which of the following is a trace element in the human body, and what is its biological role?

Accepted Answer

Iron (Fe); it is essential for oxygen transport in hemoglobin.

Question 13

Which statement best explains the difference between polar and nonpolar covalent bonds?

Accepted Answer

Polar covalent bonds have unequal sharing of electrons due to differences in electronegativity; nonpolar covalent bonds share electrons equally.

Question 14

A sodium atom ($$Na) $$loses one electron to become a sodium ion ($$Na^+). $$What is the resulting charge and why?

Accepted Answer

Positive; losing an electron leaves more protons than electrons.

Question 15

Which of the following best describes a hydrogen bond?

Accepted Answer

A weak attraction between a hydrogen atom in one molecule and an electronegative atom in another molecule.

Question 16

In a water molecule, which atom carries a partial negative charge and why?

Accepted Answer

Oxygen; it is more electronegative and attracts shared electrons.

Question 17

Which of the following scenarios best illustrates the concept of electron shells and energy levels?

Accepted Answer

A ball bouncing up a flight of stairs, where each step represents a higher energy level.

Question 18

Which of the following is true about van der Waals interactions?

Accepted Answer

They are weak forces that occur between nonpolar molecules due to temporary dipoles.

Question 19

If an atom has 11 protons, 12 neutrons, and 11 electrons, what is its atomic number and mass number?

Accepted Answer

Atomic number: $$11$$; Mass number: $$11 + 12 = 23$$

Chapter 2: The Chemical Context of Life – Essential Elements and Atomic Structure

Study Guide - Practice Questions