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: • Made of protons, neutrons, electrons © 2011 Pearson Education, Inc.
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 symbol Mass number Figure 2. 2 © 2011 Pearson Education, Inc.
• Atomic Number = number of protons, which also equals the number of electrons. • Atomic Mass (atomic weight) or mass number = # of protons + # of neutrons. © 2011 Pearson Education, Inc.
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 of chemical bonds: Ionic bonds and covalent bonds. © 2011 Pearson Education, Inc.
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.
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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 charged O sticks to Na+ H sticks to Cl© 2011 Pearson Education, Inc.
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.
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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.
© 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.
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