Copyright Pearson Prentice Hall Atoms Atoms The study of chemistry begins with the basic unit of matter, the atom. Copyright Pearson Prentice Hall

Copyright Pearson Prentice Hall Atoms Placed side by side, 100 million atoms would make a row only about 1 centimeter long. Atoms contain subatomic particles that are even smaller. Copyright Pearson Prentice Hall

Copyright Pearson Prentice Hall Atoms The subatomic particles that make up atoms are protons neutrons electrons Copyright Pearson Prentice Hall

Copyright Pearson Prentice Hall Atoms The subatomic particles in a helium atom. Helium atoms contain protons, neutrons, and electrons. The positively charged protons and uncharged neutrons are bound together in the dense nucleus, while the negatively charged electrons move in the space around the nucleus. Copyright Pearson Prentice Hall

Copyright Pearson Prentice Hall Elements and Isotopes Elements and Isotopes A chemical element is a pure substance that consists entirely of one type of atom. C stands for carbon. Na stands for sodium. Copyright Pearson Prentice Hall

Copyright Pearson Prentice Hall Elements and Isotopes The number of protons in an atom of an element is the element's atomic number. Commonly found in living organisms: C, H, O, N, P, S Copyright Pearson Prentice Hall

Copyright Pearson Prentice Hall Atoms are Neutral Atoms are neutral because they contain the same number of protons and electrons. Carbon’s atomic number is 6. How many protons are found in one atom of carbon? How many electrons are found in one atom of carbon? Copyright Pearson Prentice Hall

Copyright Pearson Prentice Hall Atomic Mass Atomic Mass: the weighted average of all of an element’s naturally occurring isotopes Usually NOT a whole number because it’s an average We round this number to the nearest whole number to represent its mass number and determine the number of neutrons in an atom of an element. Copyright Pearson Prentice Hall

Copyright Pearson Prentice Hall Neutrons Mass Number: the total number of protons PLUS neutrons in the nucleus of an atom We use the mass number to determine the number of neutrons in an atom. For our purposes, we will round the atomic mass to the nearest whole number to represent the mass number of that isotope. Mass Number – Atomic Number = # neutrons Copyright Pearson Prentice Hall

Copyright Pearson Prentice Hall Elements and Isotopes Isotopes Atoms of the same element that differ in the number of neutrons they contain are known as isotopes. Copyright Pearson Prentice Hall

Copyright Pearson Prentice Hall Elements and Isotopes Because they have the same number of electrons, all isotopes of an element have the same chemical properties. Copyright Pearson Prentice Hall

Copyright Pearson Prentice Hall Elements and Isotopes Isotopes of Carbon Because they have the same number of electrons, these isotopes of carbon have the same chemical properties. The difference among the isotopes is the number of neutrons in their nuclei. 6 electrons 6 protons 8 neutrons Copyright Pearson Prentice Hall

Copyright Pearson Prentice Hall Elements and Isotopes Radioactive Isotopes Some isotopes are radioactive, meaning that their nuclei are unstable and break down at a constant rate over time Copyright Pearson Prentice Hall

Copyright Pearson Prentice Hall Elements and Isotopes Radioactive isotopes can be used: to determine the ages of rocks and fossils. to treat cancer. to kill bacteria that cause food to spoil. as labels or “tracers” to follow the movement of substances within an organism. Copyright Pearson Prentice Hall

Atomic Structure and Models Copyright Pearson Prentice Hall

Copyright Pearson Prentice Hall Atomic Structure Protons and neutrons form the nucleus. The center of the atom Where the mass is located Electrons zoom around the nucleus in orbitals. Electrons are organized in the following way: first orbital: holds two electrons second orbital: holds eight electrons third orbital: holds eight electrons Copyright Pearson Prentice Hall

Copyright Pearson Prentice Hall Valence Electrons Valence electrons are the electrons located in the outermost orbital (valence orbital/shell) of an atom. The number of valence electrons of an atom determines its bonding patterns and chemical properties. We also use the valence electrons to draw the Lewis dot structure of an atom. Copyright Pearson Prentice Hall

Copyright Pearson Prentice Hall Happy Atoms Happy  atoms have either full or empty valence orbitals. Atoms form chemical bonds to make this happen…more on that later…. Copyright Pearson Prentice Hall

Copyright Pearson Prentice Hall Noble Gases Elements located in the right-most column of the Periodic Table are called the Noble Gases. They have completely filled valence orbitals, so they DO NOT bond with other atoms…they are inert, or non-reactive. Copyright Pearson Prentice Hall

Copyright Pearson Prentice Hall Bohr Model Model of the atom most frequently used in science. Determine the number of protons, neutrons, and electrons in the atom. Draw the nucleus. Place electrons into orbitals…do NOT pair until one parking space at each position is filled. Copyright Pearson Prentice Hall

Copyright Pearson Prentice Hall Lewis Dot This is a VERY easy way of representing the structure of an atom. Write the chemical symbol. This represents the nucleus and all electrons EXCEPT the valence electrons. Place the valence electrons around the symbol the same way you would place them in the outer orbital. DONE Easy Peasy, Lemon Squeezy!  Copyright Pearson Prentice Hall

Copyright Pearson Prentice Hall Chemical Compounds Chemical Compounds A chemical compound is a substance formed by the chemical combination of two or more elements in definite proportions. Copyright Pearson Prentice Hall

Copyright Pearson Prentice Hall Chemical Compounds Chemical Formula Water Table Salt Hydrochloric Acid Glucose Copyright Pearson Prentice Hall

Copyright Pearson Prentice Hall Chemical Bonds Chemical Bonds The atoms in compounds are held together by chemical bonds. The electrons that are available to form bonds are called valence electrons. Copyright Pearson Prentice Hall

Copyright Pearson Prentice Hall Chemical Bonds Ionic Bonds An ionic bond is formed when one or more electrons are transferred from one atom to another. These positively and negatively charged atoms are known as ions. Copyright Pearson Prentice Hall

Copyright Pearson Prentice Hall Chemical Bonds Sodium atom (Na) Sodium ion (Cl-) Sodium ion (Na+) Sodium atom (Cl) The chemical bond in which electrons are transferred from one atom to another is called an ionic bond. The compound sodium chloride forms when sodium loses its valence electron to chlorine. Protons +11 Electrons - 11 Charge 0 Protons +11 Electrons - 10 Charge +1 Protons +17 Electrons - 17 Charge 0 Protons +17 Electrons - 18 Charge -1 Copyright Pearson Prentice Hall

Copyright Pearson Prentice Hall Chemical Bonds Covalent Bonds Sometimes electrons are shared by atoms instead of being transferred. Copyright Pearson Prentice Hall

Copyright Pearson Prentice Hall Chemical Bonds A covalent bond forms when electrons are shared between atoms. single covalent bond double bond triple bond Copyright Pearson Prentice Hall

Copyright Pearson Prentice Hall Chemical Bonds The structure that results when atoms are joined together by covalent bonds is called a molecule. Copyright Pearson Prentice Hall

Copyright Pearson Prentice Hall Chemical Bonds Van der Waals Forces When molecules are close together, a slight attraction can develop between the oppositely charged regions of nearby molecules. van der Waals forces Copyright Pearson Prentice Hall