Chapter 2 (Campbell's Biology in Focus)

==Matter== is anything that takes up space and has mass
==An element== is a substance that cannot be broken down into other substances by chemical reactions
==A compound== is a substance consisting of two or more different elements combined in a fixed ratio
==Essential elements== are natural elements that an organism needs to live a healthy life and reproduce
==Trace elements== are required by an organism in only minute quantities

The three main parts of an atom are
- neutrons
- protons
- electrons
The unit of measurement for atoms and subatomic particles is a ==dalton==
Different atomic forms of the same element are called ==isotopes==
A ==radioactive isotope== is one in which the nucleus decays spontaneously giving particles and energy
==Potential energy== is the energy that matter possesses because of its location or structure

electrons are found in different electron shells
The chemical behaviour of an atom depends mostly on the number of electrons in its outermost shell
- These electrons are called ==valence electrons== and are found in the ==valence shell==

Attractions between atoms are called ==chemical bonds==
A ==covalent bond== is the sharing of a pair of valence electrons by two atoms
Two or more atoms held together by covalent bond constitute a ==molecule==
The attraction of a particular atom for the electrons of a covalent bond is called its ==electronegativity==
A ==nonpolar covalent bond== is when electrons are shared equally because two atoms have the same electronegativity
A ==polar covalent bond== is when an atom is bonded to a more electronegative atom, the electrons will therefore not share equally

Two resulting oppositely charged are called ==ions==
Positively charged results in a ==cation==
Negatively charged results in an ==anion==
A ==hydrogen bond== is formed when there is a noncovalent attraction between hydrogen and an electronegative atom
==Van Der Waals interactions== occur when atoms get just close enough that a few electrons in their valence shell (electron cloud) touch

The making and breaking of chemical bonds leading to changes in the composition of matter are called chemical reactions
The point at which the reactions offset one another exactly is called ==chemical equilibrium==
The unequal sharing of electrons and water’s V-like shape make it a polar molecule.
The phenomenon of the ==cohesion== of water molecules is due to hydrogen bonds
==Adhesion== is the clinging of one substance to another
==Surface tension== is a measure of how difficult it is to stretch or break the surface of a liquid
Anything that moves has ==kinetic energy==
The ==specific heat== of a substance is defined as the amount of heat that must be absorbed or lost for 1g of that substance to change its temperature by 1C
==The heat of vaporization== is the quantity of heat a liquid must absorb for 1g of it to be converted from the liquid to the gaseous state
==Evaporative cooling== occurs because the hottest molecules, (those with the greatest kinetic energy) are the ones most likely to leave as a gas

==A solution== is a liquid that is a completely homogeneous mixture of two or more substances
==A solvent== is the dissolving agent of a solution
==The solute== is the dissolving agent of a solution
==An aqueous solution== is one in which the solute is dissolved in water, water is the solvent
A ==hydration shell== is formed when there’s a sphere of water molecules around each dissolved ion
Any substance that has an affinity for water is said to be ==hydrophilic==
Substances that are nonionic and nonpolar are ==hydrophobic==
==Molarity== is the number of moles of solute per liter of solution
==An acid== is a substance that increases the hydrogen ion concentration of a solution
A substance that reduces the hydrogen ion concentration of a solution is called ==a base==