Chemistry Chapter 4: Molecules and Isotopes

General Chemistry

• Matter makes up everything in the universe, including living organisms
• An element is a pure substance that cannot be broken down
• An atom is the smallest particle of an element
• Atoms bond together to form molecules and compounds.

Organic Compounds

• Organic compounds are made up of C, H, O, and sometimes N
• These compounds make up 96% of the mass of living organisms
• The other 4% consists primarily of Ca, P, K, S, Na, Cl, and Mg

Atomic Structure

• Atoms are composed of three subatomic particles: protons, neutrons, and electrons

• Protons determine the identity of an atom

• An atomic mass is equal to the sum of protons and neutrons

• A proton has a positive charge (+), a neutron is neutral, and an electron is negative (-)

• Protons and neutrons are located in the nucleus

• Electrons are located in orbitals outside the nucleus

• The atomic number of an atom shows the number of protons

• The atomic mass of an atom shows the number of protons and neutrons

Isotopes and Radioisotopes

• Isotopes are atoms of the same element with the same number of protons but a different number of neutrons
• Isotopes behave the same way in chemical reactions because they have the same number of protons and electrons
• Radioisotopes are unstable isotopes that decay (break down)
• Radioisotopes are used to date fossils by comparing the ratio of 14C to 12C as the half-life of 14C is 5730 years.

Electron Arrangements

• Electrons are arranged in orbitals around the nucleus
• Electron orbitals are grouped into shells (energy levels)
• The first shell holds 2 electrons, the second 8, and the third 18
• Shells are designated by letters: 1s, 2s, 2p, 3s, and 3p
• The energy levels are further described by regions (s, p, d, f).

Chemical Bonds

• Ionic bonds form when atoms transfer electrons
• Covalent bonds form when atoms share electrons
• The strength of a covalent bond is determined by the electronegativity of the atoms involved
• Electronegativity is the measure of an atom's attraction for additional electrons

Polar Molecules

• Polar molecules have an uneven distribution of charge
• The more electronegative an atom, the more strongly it attracts electrons
• Electronegativity differences between the component atoms determine the polarity of a covalent molecule

Intermolecular Forces

• Intermolecular forces are forces of attraction between molecules
• Hydrogen bonds are a type of intermolecular force that involves a partially positively charged hydrogen atom and a partially negatively charged atom in another molecule
• Individual hydrogen bonds are weak but collectively strong and are important for the 3-D structure of biological molecules

Chemical Reactions of Biological Importance

• Condensation (dehydration) reactions combine monomers into polymers while removing water
• Hydrolysis reactions break polymers into monomers by adding water

Oxidation and Reduction (Redox) Reactions

• Oxidation → loss of electrons
• Reduction → gain of electrons
• In biological systems, these reactions must occur together

Properties of Water

• Water molecules associate via hydrogen bonding
• Water has a high specific heat capacity, meaning that it takes more energy to raise the temperature of water compared to other substances
• Water has a high capacity to absorb energy when it evaporates, making it useful in temperature regulation, such as sweating.

Aqueous Solutions

• Water is a solvent in many biological processes
• Polar or charged molecules, or hydrophilic (water loving) molecules dissolve easily in water
• Non-polar molecules, or hydrophobic (water fearing) molecules, do not readily dissolved in water

Water as a Solvent

• Water molecules surrounding and forming hydration spheres around molecules dissolve
• Small molecules (and ions) dissolve easily into water molecules

pH and Acids and Bases

• The pH scale measures acidity and basicity of a solution on a scale from 0 to 14.
• A pH < 7 is an acid; a pH > 7 is a base
• The concentration of H+ ions determines the acidity of a solution
• Buffers resist changes in pH

Carbon-Based Molecules

• Carbon atoms have 4 valence electrons → capable of forming 4 covalent bonds
• Carbon forms the backbone of most large biological molecules in living organisms
• The variety of carbon molecules is due to these bonds
• Many molecules important to living organisms are called biomolecules
• This includes carbohydrates, lipids, proteins, and nucleic acids.

Carbohydrates

• Monosaccharides are simple sugars (e.g., glucose, fructose, galactose)
• Disaccharides are formed by joining two monosaccharides (e.g., sucrose, lactose, maltose)
• Polysaccharides are long chains of monosaccharides (e.g., starch, glycogen, cellulose)

Lipids

• Fats store energy
• Phospholipids form the membranes that surround cells
• Steroids are important signalling molecules

Proteins

• Proteins are composed of amino acids
• Amino acids are the building blocks of proteins (20 common)
• Proteins carry out a variety of functions in cells

Nucleic Acids

• DNA stores genetic information
• RNA helps in protein synthesis

Cell Structures

• Organelles are internal, functional structures of cells (e.g. mitochondria, chloroplasts, nuclei)
• Cells contain components for metabolism, energy production, and reproduction

Cellular Respiration

• Breakdown of sugars (and other fuels) to produce ATP
• Aerobic respiration requires oxygen
• Anaerobic respiration does not require oxygen and typically produces less ATP
• The process of aerobic respiration occurs in 3 stages: glycolysis, pyruvate oxidation, and the citric acid cycle.
• In the electron transport chain, high energy electrons are transferred by carrier molecules along a protein chain; this process sets up an electrochemical gradient that drives ATP synthesis
• Fermentation occurs when there is no oxygen in respiration

Photosynthesis

• The process that plants use to produce food
• Photosynthesis occurs in chloroplasts
• CO2, water and light are the reactants; O2 and glucose are the products

Enzymes

• Biological catalysts
• Accelerate chemical reactions by lowering the activation energy required for a reaction.
• A suitable substrate molecule binds to the enzyme at its active site.
• The reaction occurs, then the enzyme allows the product to detach from the active site, where it can bind a new substrate.

The Nervous System and Hormone Regulation

• Receptors detect an environmental stimulus
• Nerve impulses carry information along neurons
• Nerve impulses involve a change in electrical potential across a nerve cell membrane
• Hormones are chemical messengers released into the bloodstream influencing specific target tissues

Other

• Homeostasis the maintenance of internal conditions within a tolerable range
• Negative feedback mechanisms regulate homeostasis
• Positive feedback causes a change to be amplified further (e.g., childbirth, blood clotting)

Test your knowledge on the molecular geometry of methane (CH4) and the characteristics of isotopes. This quiz covers key concepts including bond angles, electronegativity, and the applications of radioisotopes. Perfect for students aiming to solidify their understanding of basic chemistry principles.