Biology Basic Chemistry

Biology is the scientific study of life.
Living things are composed of the same chemical elements as nonliving things.
Living things obey the same physical and chemical laws that govern everything in the universe.

Living things are organized, from atom to biosphere.
Life requires materials and energy, with the sun being the source of energy and metabolism referring to all chemical reactions in a cell.
Living things maintain homeostasis, which is the maintenance of internal conditions.
Living things respond to stimuli, reproduce and develop, and have adaptations that may lead to evolution.

Matter refers to anything that has mass and occupies space.
Matter exists in four states: solid, liquid, gas, and plasma.
All matter, both living and nonliving, is composed of basic substances called elements.
An element is a substance that cannot be broken down into simpler substances by ordinary chemical means.
Each element has its own unique properties, such as density, solubility, melting point, and reactivity.
Ninety-two elements are naturally occurring, and six elements (CHNOPS) make up 95% of the body weight of organisms.

An atom is the smallest part of an element that displays the property of the element.
Atoms are composed of subatomic particles: protons, neutrons, and electrons.
The central nucleus of an atom contains protons and neutrons.
Protons are positively charged, neutrons have no charge, and electrons are negatively charged.
Electrons revolve around the nucleus in energy shells.

The atomic number is equal to the number of protons in each atom of an element.
The mass number of an atom is equal to the sum of the number of protons and neutrons in the atom's nucleus.
The atomic mass is approximately equal to the mass number.

The periodic table is a table of elements arranged horizontally by increasing atomic number in rows called periods.
Atoms of an element are arranged in vertical columns called groups.
The atomic number increases by 1 from left to right in a period.
Atoms within the same group share the same chemical binding characteristics.
Group VIII are the noble gases and are inert.

The Bohr model is a useful way to visualize electron location.
Electrons revolve around the nucleus in energy shells.
The first energy shell can hold up to 2 electrons, and each additional shell can hold up to 8 electrons.
Each lower shell is filled first before electrons are placed in the next shell.

The outermost energy shell of any atom is called the valence shell.
The valence shell determines many of an atom's chemical properties.
The octet rule states that the outermost shell is most stable when it has eight electrons.

Chemical bonds contain energy.
Organisms are directly dependent on chemical-bond energy.
Bonds between atoms are caused by the interactions between electrons in outermost energy shells.
The process of bond formation is called a chemical reaction.

Ionic bonds form when electrons are transferred from one atom to another.
Covalent bonds result when two atoms share electrons.
In a nonpolar covalent bond, electrons are shared equally between atoms.
In a polar covalent bond, electrons are shared unequally.
Electronegativity is the ability of an atom to attract electrons towards itself in a chemical bond.

Water is a polar molecule.
The shape of a water molecule and its polarity make hydrogen bonding possible.
Hydrogen bonds are weak attractions between a slightly positive hydrogen atom and a slightly negative atom.
Hydrogen bonds help maintain the proper structure and function of complex molecules.

pH is a measure of hydrogen ion concentration in a solution.
Acids are substances that dissociate in water, releasing hydrogen ions.
Bases are substances that either take up hydrogen ions or release hydroxide ions.
The pH scale is used to indicate the acidity or basicity of a solution.
Buffers are chemicals or combinations of chemicals that keep pH within normal limits.