Question

The four most abundant elements by mass in the human body are oxygen, carbon, hydrogen, and nitrogen. These four elements make up about \(96 \%\) of the human body. The next four most abundant elements are calcium, phosphorus, magnesium, and potassium. Excluding hydrogen, which of these elements would have the smallest size? largest size? smallest first ionization energy? largest first ionization energy?

Short answer

Based on the analysis of the periodic table and understanding the trends in atomic size and ionization energy, the smallest size belongs to oxygen and the largest size belongs to potassium. The smallest first ionization energy belongs to potassium, and the largest first ionization energy belongs to oxygen.

Step-by-step solution

Identify the position of each element in the periodic table #

Locate the positions of the given elements in the periodic table. Oxygen, carbon, and nitrogen are located in the second period; calcium, phosphorus, magnesium, and potassium are in the third period. It's essential to know the positions to understand the trends in atomic size and ionization energy.

Compare atomic sizes #

Based on the periodic trend, atomic size decreases as we move from left to right across a period and increases as we move down a group. Comparing the given elements: - Oxygen: 2nd period, 16th group - Carbon: 2nd period, 14th group - Nitrogen: 2nd period, 15th group - Calcium: 4th period, 2nd group - Phosphorus: 3rd period, 15th group - Magnesium: 3rd period, 2nd group - Potassium: 4th period, 1st group From their positions, we can conclude that the smallest size belongs to oxygen, and the largest size belongs to potassium.

Compare first ionization energies #

Based on the periodic trend, the first ionization energy increases as we move from left to right across a period and decreases as we move down a group. Comparing the given elements: - Oxygen: 2nd period, 16th group - Carbon: 2nd period, 14th group - Nitrogen: 2nd period, 15th group - Calcium: 4th period, 2nd group - Phosphorus: 3rd period, 15th group - Magnesium: 3rd period, 2nd group - Potassium: 4th period, 1st group From their positions, we can conclude that the smallest first ionization energy belongs to potassium and the largest first ionization energy belongs to oxygen.

Key concepts

Atomic Size

Understanding atomic size is vital for exploring the properties of elements and their interactions. Atomic size refers to the distance from an element’s nucleus to the outer boundary of its electrons. Generally, the atomic size increases moving down a group in the periodic table because each successive period adds a new electron shell. Conversely, the atomic size decreases across a period from left to right due to the increase in positive charge in the nucleus, which pulls the electron shells closer.

For instance, in the exercise, potassium has a larger atomic size than oxygen because potassium’s electrons are found in a higher period, meaning they are located further from the nucleus. This understanding is essential, especially when studying the physical and chemical properties of elements as they engage in different reactions.

First Ionization Energy

First ionization energy is another fundamental concept in chemistry that influences how elements react. It is the energy required to remove the most loosely held electron from an atom to form a cation. This energy reflects an element's tendency to lose an electron and is affected by several factors including atomic size and nuclear charge.

Within the periodic table, first ionization energy generally increases across a period from left to right due to a stronger attraction between the increasing positive nuclear charge and the electrons. It typically decreases down a group because the outer electrons are farther from the nucleus and more shielded by inner electrons. In our exercise, oxygen has a higher first ionization energy than potassium, indicating oxygen's greater hold on its electrons.

Periodic Table

The periodic table is a well-organized chart that displays all known chemical elements in an informative arrangement. Elements are organized by increasing atomic number, electron configuration, and recurring chemical properties. Periodic trends, such as changes in atomic size and ionization energy across the table, stem from this arrangement.

Elements are sorted into groups (columns) and periods (rows) which help predict behavior and characteristics. For example, elements in the same group typically exhibit similar chemical reactivity. The exercise provided uses the periodic table's structure to compare elements effectively and illustrates the importance of its layout in understanding elemental properties.

Elemental Abundance in Human Body

The human body is composed of many different elements, with a few occurring in significantly higher proportions. Oxygen, carbon, hydrogen, and nitrogen make up approximately 96% of the body's mass, playing crucial roles in biological molecules and processes.

Oxygen is vital for respiration and is a component of water, which is essential for life. Carbon serves as the backbone of organic molecules. Hydrogen is a component of water and organic compounds, and nitrogen is critical for the structure of amino acids and nucleic acids. Elements like calcium, phosphorus, potassium, and magnesium, while less abundant, are crucial in bone structure, energy transfer, muscle function, and many physiological processes. Understanding the distribution and role of elements underscores their significance in biological chemistry and health sciences.