AP Bio ch 2

Matter

Anything that takes up space and has mass; everything around us.

Element

Substance that cannot be broken down into other substances by chemical reactions.

Compound

Substance of two or more different elements combined in a fixed ratio.

Essential Elements

Carbon, oxygen, nitrogen, and hydrogen compose 96% of living matter.

Atom

Smallest unit of matter that retains the properties of an element.

Subatomic Particles

Protons, neutrons, and electrons that make up an atom.

Proton

Positively charged particle located in the nucleus of an atom.

Neutron

Neutral particle located in the nucleus of an atom.

Electron

Negatively charged particle that orbits the nucleus of an atom.

Atomic Number

Number of protons in an atom.

Mass Number

Protons plus neutrons in an atom.

Isotope

Variant of an element with a differing number of neutrons.

Radioisotope

An isotope whose nucleus decays spontaneously, emitting radiation.

Electron Energy Level

The specific energies that electrons can have when occupying energy levels around the nucleus.

Valence Electrons

Electrons in the outermost shell of an atom.

Covalent Bonding

The sharing of valence electrons between atoms.

Electronegativity

Attraction of a particular atom for the electrons in a covalent bond.

Ionic Bonding

Bonding that occurs when one atom strips an electron from another, resulting in charged ions.

Cation

A positively charged ion.

Anion

A negatively charged ion.

Weak Bonds

Bonds that are important in living matter, often reversible.

Hydrogen Bonds

A weak bond formed when a hydrogen atom covalently bonded to an electronegative atom is attracted to another electronegative atom.

Van Der Waals Forces

Weak attractions between molecules due to transient local partial charges.

Chemical Reaction

Making and breaking of chemical bonds; rearranging matter.

Inert

A substance that is not chemically reactive.