Atoms & Properties of Water Sections 2.1 & 2.2
2.1 Atoms, Ions, & Molecules Key Concept: All living things are based on atoms and their interactions.
Living things consist of atoms of different elements. Atom: the smallest basic unit of matter Element: one type of atom
An atom has a nucleus and electrons. The nucleus has protons and neutrons An energy level is an area around the nucleus where electrons are located
Compounds A compound is made of different elements bonded together. Example: Water (H 2 O) Carbon dioxide (CO 2 )
Ions form when atoms gain or lose electrons. Positive ions: formed when atoms lose electrons Negative ions: formed when atoms gain electrons
Ionic bonds Ionic bonds form between oppositely charged ions due to electrical attraction
Covalent bonds A covalent bond forms when atoms share a pair of electrons. Molecule: atoms bonded together by covalent bonds
2.2 Properties of Water Key Concept Water’s unique properties allow life to exist on Earth.
Life depends on hydrogen bonds in water. Water is a polar molecule. Polar molecules: molecules that have slightly charged regions Nonpolar molecules: molecules that do not have a slightly charged region
Hydrogen bonds are responsible for three important properties of water. 1.High Specific Heat: a lot of heat energy is need to increase the temperature of water 2.Cohesion: water molecules stick to each other 3.Adhesion: water molecules stick to other things
Many compounds dissolve in water. A solution is formed when one substance dissolves in another. A solution is a homogeneous mixture. Solvents dissolve other substances Solutes dissolve in a solvent
Polarity “Like dissolves like.” Polar solvents dissolve polar solutes. Nonpolar solvents dissolve nonpolar solutes. Polar substances and nonpolar substances generally remain separate (think of oil and water)
Some compounds form acids or bases. Acids release a hydrogen ion when they dissolve in water; have a high hydrogen ion (H + ) concentration and a low hydroxide ion (OH - ) concentration pH: 0 to less than 7
Neutral solutions have an equal amount of hydrogen (H + ) and hydroxide (OH - ) ions pH: 7 (seven)
Bases remove hydrogen ions from a solution; have a low H + concentration and a high OH - concentration pH: greater than 7 to 14