Basic Chemistry and Properties of Water Matter anything

Basic Chemistry and Properties of Water • Matter: anything that occupy space and has mass • All solids, liquids, and gases • All living and nonliving things are composed of atoms © 2011 Pearson Education, Inc.

Atoms • Atoms: The basic unit of matter • Atoms contain: • Sub-atomic Particles:

Atoms Continued: • Protons: have a positive charge, found in the atomic nucleus • Neutrons: are neutral and found in atomic nucleus • Electrons: have a negative charge and orbit the nucleus in shells • Atoms form Elements: • Elements are pure substances consisting entirely of one type of atom • example H 2 = hydrogen, O 2 = oxygen © 2011 Pearson Education, Inc.

• All the elements are listed in the periodic table Atomic number Element

• Atomic Number = number of protons, which also equals the number of

Elements and Isotopes • Elements: are pure substances consisting of entirely one type of atom. • Example: H = Hydrogen, Na = Sodium • Isotope: atoms of an element with the same number of protons but a different number of neutrons. • Example: isotopes of carbon, nonradioactive Carbon 12 (C 12) has 6 electrons, 6 protons, and 6 neutrons. • Carbon 13 (C 13) nonradioactive has 6 electons, 6 protons and 7 neutrons. • Radioactive Carbon-14 (C 14) has 6 electrons, 6 protons, and 8 neutrons. © 2011 Pearson Education, Inc.

Carbon-12 and Carbon - 13 © 2011 Pearson Education, Inc.

Electrons and Electrons Shells • • • Orbit the atomic nucleus at fixed distances Negatively charged Orbits called shells In order to become stable, they fill their shells First shell is full with 2 electrons The last or valence shell holds 8 electrons © 2011 Pearson Education, Inc.

How atoms interact to form molecules • Atoms can interact with one another when the outermost shell of an atom is not at full capacity • Example: Carbon has 4 electrons in outmost shell but can hold eight. This will allow carbon to share up to 4 electrons. © 2011 Pearson Education, Inc.

• Atoms of the four elements most abundant in life First electron shell (can hold 2 electrons) Outermost electron shell (can hold 8 electrons) Electron Hydrogen (H) Atomic number = 1 Carbon (C) Atomic number = 6 Nitrogen (N) Atomic number = 7 Oxygen (O) Atomic number = 8 Figure 2. 7 © 2011 Pearson Education, Inc.

Atoms Interact • Atoms interact with one another according to two basic principles. 1. Atoms do not interact if the outermost electron shell is completely full or empty. Example: Noble gases are stable because full outer shells. 2. Atoms do react with other atoms when the outer shell is only partially full. Example: Carbon © 2011 Pearson Education, Inc.

Chemical Bonds • Atoms in compounds are held together by chemical bonds. • Types

Chemical Bonds • Valence Shell Electrons: Atoms want to be stable like the noble gases, so they want full shells. The first shell fills with 2 and the rest with 8 electrons. • Ionic Bonds: formed when one or more electrons are transferred from one atom to another. They are held together by electrical attractions between positive and negative charges. Example: Formation of sodium chloride (Na. Cl) © 2011 Pearson Education, Inc.

Ionic Bonds: Sodium Chloride Sodium gives up an election to chlorine and thus becomes a sodium ion with a positive charge. Chlorine accepts an electron becomes the chloride ion and has a negative charge. (form sodium chloride held together with ionic bond – ionic bonds are weak) © 2011 Pearson Education, Inc.

Covalent Bonds • Covalent Bonds: A chemical bond between atoms that share electrons • When atoms share 2 electrons it is a single bond • Sharing 4 electrons is a double bond. © 2011 Pearson Education, Inc.

Covalent Bonds and Ionic Comparison Figure 2. 9 © 2011 Pearson Education, Inc.

The Structure of Water • Studied in isolation, the water molecule is deceptively simple – Its two hydrogen atoms are joined to one oxygen atom by single covalent bonds H H O Unnumbered Figure 2. 2 © 2011 Pearson Education, Inc.

• But the electrons of the covalent bonds are not shared equally between oxygen and hydrogen. This is called a Polar-Covalent Bond. – This unequal sharing makes water a polar molecule ( ) ( ) Figure 2. 11 a © 2011 Pearson Education, Inc.

• The polarity of water results in weak electrical attractions between neighboring water molecules – These interactions are called hydrogen bonds ( ) ( ) Hydrogen bond ( ) ( ) ( ) (b) Figure 2. 11 b © 2011 Pearson Education, Inc.

Hydrogen Bonds Water molecules carry slight charges Electrons favor O over Hydrogen H bonds form between O of one and H of another + – H H + O + H – + O H + Hydrogen Bonds © 2011 Pearson Education, Inc.

Water’s Life-Supporting Properties • The polarity of water molecules and the hydrogen bonding that results explain most of water’s lifesupporting properties – Water’s cohesive nature – Water’s ability to moderate temperature – Versatility of water as a solvent © 2011 Pearson Education, Inc.

The Cohesion of Water • Water molecules stick together as a result of hydrogen bonding – This is called Cohesion Microscopic tubes – Cohesion is vital for water transport in plants Figure 2. 12 © 2011 Pearson Education, Inc.

• Surface Tension is the measure of how difficult it is to stretch or break the surface of a liquid – Hydrogen bonds give water an unusually high surface tension Figure 2. 13 © 2011 Pearson Education, Inc.

Cohesion and Surface Tension among Water Molecules © 2011 Pearson Education, Inc.

Adhesion and Capillary Action Adhesion: Attraction between water molecules and different surfaces. Capillary Action: Ability of a liquid to flow against gravity and rise in a narrow thin tube. © 2011 Pearson Education, Inc.

Water as the Solvent of Life • Because water is polar and has both positive and negative poles, it works well as a solvent – When salt is put into water, the positive charged hydrogen ends of water are attracted to the negatively charged chloride ions (Cl-) – Negatively charged oxygen ends of water surround the positively charged sodium ions (Na+) – Sodium and chloride ions are surrounded, crystals separate Ion in solution Salt crystal Figure 2. 16 © 2011 Pearson Education, Inc.

Na. Cl Dissolved by Water Na. Cl is ionicly bonded Water is polar and

Acids, Bases, and p. H • Acid – Acids have greater amount of H+ ions then pure water and have a p. H < 7 – Pure water has a ph of 7, neutral • Base (Alkaline) – Has less H+ ions and more OH (hydroxide ions)then pure water and has a p. H > 7 © 2011 Pearson Education, Inc.

Oven cleaner Household bleach Household ammonia Basic solution Milk of magnesia Seawater Human blood Pure water Neutral solution Urine Tomato juice Grapefruit juice Acidic solution Lemon juice; gastric juice p. H scale Figure 2. 17 © 2011 Pearson Education, Inc.

• Buffers are substances that resist p. H change. Help maintain a solution at a relatively constant p. H. They are weak acids or bases that can react with a strong acids or base to prevent sudden p. H changes. – They accept H+ ions when they are in excess – They donate H+ ions when they are depleted • Buffering is not foolproof – Example: acid precipitation Figure 2. 18 © 2011 Pearson Education, Inc.