Chapter 2 Reading Guide: The Chemical Context of Life

Practice flashcards covering basic chemical concepts, atomic structure, bonding, water properties, pH, and ocean acidification from Chapter 2.

How is matter defined in Chapter 2?

Matter is defined as anything that takes up space and has mass.

What is an element?

An element is a substance that cannot be broken down by chemical reactions.

How is a compound defined?

A compound consists of two or more different elements in a fixed ratio.

Which four elements make up $96\%$ of all living matter?

$C$, $H$, $O$, and $N$.

What is the difference between an essential element and a trace element?

Essential elements are needed to be healthy and reproduce; trace elements are needed only in minute amounts, such as iron ($Fe$).

What are the atomic number and atomic mass of helium?

Helium has an atomic number of $2$ and an atomic mass of $4$.

What are the definitions of a neutron, proton, and electron?

A neutron is a subatomic particle with no charge, a proton has a positive charge, and an electron has a negative charge.

How are atomic mass and atomic number defined?

Atomic mass is the total number of protons and neutrons in the nucleus; atomic number is equal to the number of protons.

What are electron shells, and how is energy defined?

Electron shells represent the distance of electrons to the nucleus (each with different energy levels); energy is defined as the capacity to do work.

What are the atomic mass, atomic number, number of electrons, and number of neutrons for carbon?

Carbon has an atomic mass of $12$, an atomic number of $6$, $6$ electrons, and $6$ neutrons.

What are isotopes, using carbon as an example?

Isotopes are forms of atoms that vary in their number of neutrons, such as Carbon 12, 13, and 14, which each have $6$ protons, but have $6$, $7$, or $8$ neutrons respectively.

What is a radioactive isotope and how is it used in medicine?

A radioactive isotope has a nucleus that decays spontaneously, giving off particles and energy, and can become a different element. It is used as a diagnostic tool in medicine, such as monitoring kidney function by the amount excreted in urine.

What is potential energy, and which has more potential energy between water and glucose?

Potential energy is energy that matter possesses because of its location. Glucose has more potential energy than water.

Which subatomic particle is directly involved in chemical reactions between atoms?

Electrons.

How is a molecule defined?

A molecule is two or more atoms held together by covalent bonds.

What type of bond is seen in $O_2$ and what does it mean?

$O_2$ has a double covalent bond, which means sharing two electrons.

What is electronegativity?

Electronegativity is the attraction of a particular atom for the electron in a covalent bond.

What is the difference between a nonpolar covalent bond and a polar covalent bond?

In a nonpolar covalent bond, electrons are shared equally. In a polar covalent bond, electrons are not shared equally, causing temporary charges on the molecule.

What occurs during the formation of an ionic bond between $Na$ and $Cl$?

One electron from $Na$ is transferred to $Cl$, resulting in opposite charges that attract ($Na^+$ and $Cl^-$).

What is a hydrogen bond?

A hydrogen bond is a non-covalent attraction between $H$ and an electronegative atom.

Why is molecular shape crucial in biological systems, using morphine and endorphins as an example?

Biological molecules recognize and bind with specificity. Natural endorphins have receptors in the brain that also bind to morphine and cause similar pain relief.

In the chemical shorthand equation for photosynthesis, how many molecules of carbon dioxide, molecules of glucose, and elements in glucose are present?

There are $6$ molecules of carbon dioxide, $1$ molecule of glucose, and $3$ elements in glucose.

Why is water considered a polar molecule?

Water is a polar molecule because its overall charge is unequally distributed, where $O$ is $\delta^-$ and $H$ is $\delta^+$.

How many hydrogen bonds can a single water molecule form?

A single water molecule can form $4$ hydrogen bonds.

What is the difference between cohesion and adhesion?

Cohesion holds substances together, whereas adhesion is the attraction of one substance to another.

Which property of water explains the ability of a water strider to walk on water?

Surface tension.

How is a calorie defined?

A calorie is the amount of heat it takes to raise $1\,\text{g}$ of $H_2O$ by $1^\circ\text{C}$.

How does hydrogen bonding contribute to water's high specific heat?

When increasing temperature, absorbed energy goes into breaking hydrogen bonds. Energy is released when hydrogen bonds form during a temperature decrease.

What is heat of vaporization and what are two effects of this property on living organisms?

Heat of vaporization is the quantity of heat $1\,\text{g}$ of liquid absorbs to convert to a gas. Two effects are evaporative cooling in animals via sweating and plant leaf transpiration.

Why does ice float, and why is $4^\circ\text{C}$ a critical temperature for water?

Hydrogen bonds hold the molecules far enough apart to make ice less dense as a solid than liquid water. The temperature $4^\circ\text{C}$ is critical because it is the temperature of water with the greatest density.

How are solvent, solution, and solute defined?

A solvent is the dissolving agent in a solution, a solution is a mixture of two or more substances, and a solute is the substance being dissolved.

In coffee with added sugar, which substance is the solvent and which is the solute?

Coffee is the solvent and sugar is the solute.

What two ions form when water dissociates, and what is their concentration in pure water at $25^\circ\text{C}$?

$H_3O^+$ and $OH^-$ form, each with a concentration of $1 \times 10^{-7}\,\text{M}$ in pure water at $25^\circ\text{C}$.

How is water assigned a pH of $7$?

Water has a $H^+$ concentration of $1 \times 10^{-7}\,\text{M}$ at $25^\circ\text{C}$, giving $\text{pH} = -\log_{10}(10^{-7}) = 7$.

What is the difference between an acid and a base?

An acid is a substance that increases the $H^+$ concentration of a solution, while a base reduces the $H^+$ concentration of a solution.

How do buffers moderate pH changes?

Buffers moderate pH changes by accepting $H^+$ when they are in excess and donating $OH^-$ when they are depleted.

How do $CO_2$ emissions affect marine life and ecosystems?

$CO_2$ dissolves in $H_2O$ and acidifies it, forming carbonic acid and causing a pH $0.1$\,pH lower than any time in the past $420,000$ years, which makes it difficult for marine animals to form shells and skeletons.