Bio Chapter 2 Study Guide

What is an element? 

1. An element is any substance that cannot be reduced to any simpler set of constituent substances through chemical means. Each element is defined by the number of protons in its nucleus.

What is an atom? 

1. An atom is the fundamental unit of matter that retains the properties of an element. It consists of protons, neutrons, and electrons. ​

A proton? 

1. A proton is a positively charged particle found in the nucleus of an atom.

A neutron? 

1. A neutron is a neutrally charged particle found in the nucleus of an atom. 

An electron?

1. An electron is a negatively charged particle that orbits the nucleus of an atom.

What is an atom’s atomic number? From this information, be able to calculate the number of protons and electrons in an atom of a specific element.

1. The atomic number of an element is the number of protons in its nucleus. It can be used to calculate the number of protons and electrons in an atom of a specific element since the number of electrons equals the number of protons in a neutral atom. 

What is an atom’s atomic weight? From this information and the atomic number, be able to calculate the number of neutrons in an atom of a specific element.

1. The atomic weight (or mass number) is the total number of protons and neutrons in an atom's nucleus. To calculate the number of neutrons, subtract the atomic number from the atomic weight.​

What is an isotope?

1. Isotopes are different forms of the same element that have the same number of protons but different numbers of neutrons.

Which particles allow atoms to interact with each other to form bonds?

1. Electrons, specifically those in the outermost shell (valence electrons), allow atoms to interact with each other to form bonds.

What is the valence shell of an atom?

1. The valence shell is the outermost electron shell of an atom. The number of unpaired electrons needed to complete the atom’s outermost shell is called the atom’s valence. 

What is an ion?

1. An ion is a charged atom that has lost or gained electrons. A positively charged ion is called a cation, and a negatively charged ion is called an anion.

What is a molecule?

1. A molecule is formed when two or more atoms bond together.

What is a covalent bond?

1. A covalent bond involves the sharing of electron pairs between atoms. It can be single, double, or triple based on the number of shared electron pairs.

What is electronegativity?

1. Electronegativity is the attraction of a particular atom for the electrons of a covalent bond.

What does hydrophilic mean? What molecules are hydrophilic?

1. Hydrophilic means "water-loving." Molecules that are hydrophilic typically dissolve well in water.

What does hydrophobic mean?

1. Hydrophobic means "water-fearing." Molecules that are hydrophobic do not dissolve well in water.

What is an ionic bond?

1. An ionic bond results from the attraction between ions with opposite charges (cation-anion). 

What is a hydrogen bond?

1. A hydrogen bond forms when a hydrogen atom that is covalently bonded to an electronegative atom is attracted to another electronegative atom.

Compare covalent, ionic, and hydrogen bonds. Which is strongest?  Weakest?

1. Covalent bonds are generally the strongest, followed by ionic bonds, and then hydrogen bonds. Covalent bonds are crucial for forming molecules, ionic bonds are important for forming compounds, and hydrogen bonds are significant in biological processes like DNA structure and water properties.

Why are hydrogen bonds important?

1. Hydrogen bonds are significant in biological processes like DNA structure and water properties.

What are the main properties of water? List them.

1. Water has unique properties such as high specific heat, cohesion, adhesion, high surface tension, and the ability to dissolve many substances. It expands when it freezes due to the formation of a crystalline structure. 

What types of substances does water dissolve?

1. Water is known as a universal solvent because it can dissolve many substances. It primarily dissolves:

   1. Ionic compounds: such as salts (e.g., sodium chloride).

   2. Polar covalent compounds: such as sugars and alcohols.

   3. Gases: like oxygen and carbon dioxide, to some extent.

Unlike nearly all other liquids, water expands when it freezes. Why does this happen?

1. It expands when it freezes due to the formation of a crystalline structure. 

How are cohesion and adhesion different?

Cohesion refers to the attraction between molecules of the same substance (essentially pulling the other molecules)  while adhesion refers to the attraction between molecules of different substances. 

What is pH?

1. pH is a measure of the hydrogen ion concentration in a solution. It is calculated as pH = -log [H⁺].

What is a buffer?

1. Buffers are substances that reduce changes in the concentration of H⁺ and OH⁻ in a solution by accepting H⁺ when they are in high concentration and donating H⁺ when their concentration drops.