Chapter 2 Student Lecture Notes - Introduction to Chemistry PDF

Chapter 2 Atoms, Ions, and Molecules Introduction to Chemistry Learning Objectives Describe the subatomic parts of an atom, including their charges and position in the atom (SLO C) Define chemical element and name the four elements that are the most common in the body (SLO C) Define mole...

Chapter 2 Atoms, Ions, and Molecules Introduction to Chemistry Learning Objectives Describe the subatomic parts of an atom, including their charges and position in the atom (SLO C) Define chemical element and name the four elements that are the most common in the body (SLO C) Define molecule and compound and explain how chemical bonds are formed (compare polar covalent, non-polar covalent, ionic, and hydrogen bonds) (SLO C) Atom Smallest particle of an element that retains the properties of that element Composed of three subatomic particles Protons Neutron Electrons Particle Mass Charge Locatio n Neutron 1 amu No Inside charge nucleus Proton 1 amu Positive Inside nucleus Electron 1/800th Negative Outside proton or nucleus neutron (orbitals) Isotopes Different atoms of the same element Same number of protons and electrons Different number of neutrons Identical chemical characteristics; different atomic masses Atomic mass = protons + neutrons Radioisotopes Contain excess neutrons, so unstable Lose nuclear components in the form of high energy radiation (Alpha particles, Beta particles, Gamma rays) Can be introduced into body to see what happens with those elements Radioactive Iodine Uptake Test Iodine is used by the thyroid gland to make thyroid hormones Radioactive iodine is ingested Thyroid gland is darker in areas where more iodine is taken up Can help locate a thyroid nodule Radioactive Iodine Uptake Test https://www.youtube.com/watch?v=ZTb640Rbq74 Element Pure substance that cannot be separated into simpler substances by physical and chemical means There are 92 naturally occurring elements Elements are organized in the periodic table of elements Periodic Table Organized into columns based on number of electrons in outer shell (valence shell) Each consecutive column has one additional electron in its valence shell Elements in column 8A have a full valence shell Results in chemical stability Helium, neon, chemically inert noble gases Periodic Table Elements tend to lose, gain, or share electrons to obtain complete outer shells with eight electrons Known as the octet rule Compounds Chemical combinations of two or more elements Properties differ from the properties of the elements they are made of Salt (NaCl) is safe to eat, but sodium and chlorine by themselves are not Compounds can be broken down into smaller components by chemical means Classified as ionic or molecular Ionic Compounds Held together by ionic bonds Electrons donated/received Bond forms between a nonmetal and a metal Example: Sodium chloride (NaCl) Cations vs Anions Ions are charged atoms Cations have a positive charge Anions have a negative charge Both are produced from the losing or gaining one or more electrons Molecular Compounds (“Molecules”) Held together by covalent bonds Electrons are shared between atoms of two or more different elements Bond forms between two nonmetals Example: Water (H2O) Covalent Bonds Single covalent bond One pair of electrons shared Double covalent bond Two pairs of electrons shared Triple covalent bond: Three pairs of electrons shared Polar vs. Nonpolar Covalent Bonds Electronegativity is the relative attraction of each atom for electrons Determines how electrons are shared in covalent bonds Nonpolar covalent bond = equal sharing Polar covalent bond = unequal sharing From least to greatest electronegativity hydrogen < carbon < nitrogen < oxygen Polar vs. Nonpolar Covalent Bonds Covalent bonds may be polar or nonpolar Nonpolar molecules contain nonpolar covalent bonds Ex: O-O Polar molecules contain polar bonds Ex: O-H Nonpolar molecules may contain polar covalent bonds, if the polar covalent bonds cancel each other Ex: Carbon dioxide (O-C-O) Hydrogen Bonds Form between polar molecules Usually between hydrogen and oxygen, nitrogen, or fluorine Ex: H-O, H-N, H-F Individually weak bonds, but collectively very strong Helps to influence how water molecules behave