Chapter 2 - Chemical Level of Organization Flashcards
Chemical Elements
Matter exists in three states: solid, liquid, and gas. Solids, such as teeth and bones, are compact and have a definite shape and volume. Liquids, such as blood plasma, take up the volume of their container. Gases, such as oxygen, have no shape or volume.
Chemical Elements in the Body
There are 26 types of elements. The major elements, which constitute 96.5% of the body’s mass, include oxygen, carbon, hydrogen, and nitrogen. The lesser eight elements (3.6%) are calcium, potassium, sulfur, chlorine, magnesium, and iron. There are an additional 14 trace elements, which are present in small amounts and make up the remaining 0.45%.
Structure of Atoms
Each element is made up of an atom, which is composed of subatomic particles: protons, neutrons, and electrons around a nucleus.
Electron Shells
- Shell 1 can hold a maximum of 2 electrons
- Shell 2 can hold a maximum of 8 electrons
- Shell 3 can hold a maximum of 18 electrons
- Shell 4 can hold a maximum of 32 electrons
- Shell 5 can hold a maximum of 50 electrons
Valence Shell
The outermost electron shell of an atom is called the valence shell. The electrons in the valence shell are involved in chemical bonding and interactions with other atoms.
Atomic Number/Mass Number/Atomic Mass
The atomic number is the number of protons in an atom. The mass number is the number of protons and neutrons in an atom. The atomic mass is the average mass of stable atoms of a given element.
Isotopes
Atoms of an element that have different numbers of neutrons, and therefore different mass numbers.
Radioactive isotopes
An unstable isotope that undergoes radioactive decay, emitting radiation in the process.
Ions
Electrically charged particles that are formed when atoms gain or lose electrons. For example, a sodium ion is formed when a sodium atom loses one electron, resulting in a positive charge.
Molecules
Groups of atoms held together by chemical bonds. For example, the H2O molecule is made up of two hydrogen atoms bonded to one oxygen atom.
Compounds
Substances composed of two or more different elements chemically combined. For example, CO2 is a compound made up of one carbon and two oxygen atoms.
Free Radical
A free radical is a highly reactive molecule or atom with an unpaired electron. It can damage cells and cause health issues by stealing electrons from other molecules. Antioxidants help neutralize free radicals to protect against damage.
Chemical Bonds
The forces that hold together the atoms of a molecule or a compound are chemical bonds. The likelihood that an atom will form a chemical bond with another atom depends on the number of electrons in its outermost shell, also called the valence shell.
Octet Rule
Atoms of most biologically important elements do not have eight electrons in their valence shells. Under the right conditions, two or more atoms can interact in ways that produce a chemically stable arrangement of eight valence electrons for each atom. This rule helps explain why atoms interact in predictable ways.
Ionic Bonds
When atoms lose or gain one or more valence electrons, it is called an ion. Positive and negatively charged ions are attracted to one another - opposites attract. This attraction creates a force that holds ions together.
Covalent Bonds
When a covalent bond forms, two or more atoms share electrons rather than gaining or losing them. Atoms form a covalently bonded molecule by sharing one, two, or three pairs of valence electrons. The larger the number of electron pairs shared between two atoms, the stronger the covalent bond. Covalent bonds may form between atoms of the same element or between two different atoms. They are the most common chemical bonds in the body, and the compounds that result from them form most of the body’s structure.
Single and Double Covalent Bonds
A single covalent bond results when two atoms share one electron pair. A molecule of hydrogen forms when two hydrogen atoms share their single valence electrons, allowing both atoms to have a full valence shell at least part of the time. A double covalent bond results when two atoms share two pairs of electrons, as in oxygen molecules. A triple covalent bond occurs when two atoms share three pairs of electrons, as in a molecule of nitrogen.
Polar Covalent Bonds
Polar covalent bonds are formed between two atoms that share electrons unequally. One atom has a higher electronegativity, resulting in a partial negative charge on that atom, and the other atom has lower electronegativity, resulting in a partial positive charge. This creates a separation of charges within the molecule.
Non-covalent Bonds
A type of chemical bond formed between two atoms that share electrons equally. The electronegativity of the atoms involved in the bond is similar, resulting in an even distribution of charge across the molecule. This creates a balanced electron sharing, making the molecule non-polar.
Hydrogen Bonds
Weak attractions between a hydrogen atom and an electronegative atom like oxygen or nitrogen. They contribute to the unique properties of water and play a crucial role in maintaining the structure of biological molecules such as proteins and nucleic acids.
Forms of Energy and Chemical Reactions
- Thermal energy: The random motion of particles supplied or released during chemical reactions as heat.
- Potential energy: Stored energy to be converted as bonds are broken and formed.
- Electrical energy: The transfer of electrons can result in the generation of electrical energy.
- Light energy: Electromagnetic radiation can be released during certain chemical reactions.
- Kinetic energy: Associated motion of particles. During a chemical reaction, the rearrangement of atoms and molecules can result in an increase or decrease in kinetic energy.
Energy Transfer in Chemical Reactions
Chemical bonds represent stored chemical energy, and chemical reactions occur when new bonds are formed or old bonds are broken between atoms. The overall reaction may either release energy or absorb energy.
Activation Energy
Because particles of matter such as atoms, ions, and molecules have kinetic energy, they are continuously moving and colliding with one another. A sufficiently forceful collision can disrupt the movement of valence electrons, causing an existing chemical bond to break or a new one to form. The collision energy needed to break the chemical bonds of the reactions is called the activation energy of the reaction.
Concentration and Temperature’s Effect on Chemical Reactions
Concentration: More particles of matter present in a confined space increase the chances of a collision. The concentration of particles increases when more are added to a given space or when the pressure on the space increases, forcing the particles closer together and causing them to collide more often.
Temperature: As temperature rises, particles of matter move about more rapidly. Thus, the higher the temperature of matter, the more forcefully particles will collide and the greater the chance that a collision will produce a reaction.
