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Chemistry 112. Overview of Chapters 1-4. Chapter 1 Highlights. Chemistry is the study of matter, the physical substance of all materials. The building blocks of matter are atoms, which combine to form compounds.
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Chemistry 112 Overview of Chapters 1-4
Chapter 1 Highlights • Chemistry is the study of matter, the physical substance of all materials. • The building blocks of matter are atoms, which combine to form compounds. • The different types of atoms are called elements, which are arranged systematically in the periodic table.
Chapter 1 Highlights (cont) • Atoms are composed of protons, neutrons, and electrons. • All atoms of the same element contain the same number of protons (and electrons) but may vary in the number of neutrons. • The protons and neutrons are found inside the tiny but dense nucleus, whereas the electrons are found in orbitals outside the nucleus.
Chapter 1 Highlights (cont) • The arrangement of electrons in the orbitals is called the electronic configuration and determines the chemistry of an atom.
Chemistry and Matter • Physical Changes versus Chemical Changes • Physical changes involve changes in appearance (i.e., changes in state such as melting). • Chemical changes result in new substances.
The Building Blocks of Matter • Atoms • Smallest representative units of the elements. • Compounds • Different atoms linked together; e.g., H2O.
The Building Blocks of Matter (cont) • Dalton’s Atomic Theory • All matter is composed of indivisible atoms. • All atoms of one element are identical to each other but different than the atoms of other elements. • Compounds are formed when atoms of different elements combine in whole number ratios. • Atoms are rearranged during chemical reactions but atoms cannot be created or destroyed.
The Periodic Table • Used to organize the elements by recurring chemical properties. • Elements in the same vertical column of the periodic table have similar chemical properties and are said to be in the same group or family.
The Atom • Components • Positive protons, negative electrons, and neutral neutrons • Atomic Number • The number of protons in an atom, which determines what element it is • Mass Number • Number of protons + the number of neutrons
The Atom (cont) • Isotopes • Isotopes of the same element have the same number of protons but differ in the number of neutrons. • Atomic Mass • The atomic mass for each element on the periodic table reflects the relative abundance of each isotope in nature.
Models of the Atom • The Plum Pudding Model • Electrons are embedded in a sphere of positive charge. • The Nuclear Model • All of the positive charge is in a tiny central nucleus with electrons outside the nucleus. • This model was developed by Rutherford after his landmark experiment.
Models of the Atom (continued) • Bohr’s Solar System Model • Electrons circle the nucleus in orbits, which are also called energy levels. • An electron can “jump” from a lower energy level to a higher one upon absorbing energy, creating an excited state. • The concept of energy levels accounts for the emission of distinct wavelengths of electromagnetic radiation during flame tests.
Models of the Atom (continued) • The Modern Model • Orbits are replaced with orbitals, volumes of space where the electrons can be found. • The arrangement of electrons in the orbitals is the electronic configuration of an atom, which determines the chemistry of an atom.
Chapter 2 Highlights • Having eight valence electrons is particularly desirable (“the octet rule”). • Atoms form bonds with other atoms to satisfy the octet rule. • The two major types of chemical bonds are ionic and covalent.
Chapter 2 Highlights (cont) • Electronegativity is the ability to attract shared electrons. • The type of bond formed between two atoms depends on their difference in electronegativity. • Ionic bonds form between atoms with a large difference in electronegativity (generally a metal and a nonmetal).
Chapter 2 Highlights (cont) • Nonpolar covalent bonds form between atoms with little difference in electronegativity (generally two nonmetals). • Polar covalent bonds form between atoms with intermediate difference in electronegativity. • There are many ways to depict molecules.
The Octet Rule • Atoms with eight valence electrons are particularly stable, an observation called the octet rule. • Atoms form bonds with other atoms to achieve a valence octet.
Ionic Bonds • Ionic compounds result from the loss of electrons by one atom (usually a metal) and the gain of electrons by another atom (usually a nonmetal). • Ionic bonds arise from the attraction between particles with opposite charges(electrostatic forces); e.g., Na+ Cl-.
Covalent Bonds • Covalent bonds are formed when two atoms share one or more electron pairs. • When two atoms share one pair of electrons, the result is a single bond. • Two shared pairs of electrons is a double bond; three is a triple bond.
Equal Sharing versus Unequal Sharing • When two different kinds of atoms are bonded, the electrons are usually shared unequally. • When a bond exists between two identical kinds of atoms, the electrons are shared equally. • An atom with greater electronegativity has a greater ability to attract shared electrons.
Representing Structures • In a structural formula, atoms are represented by chemical symbols, and bonds are represented by lines. • In a line drawing, any point where lines connect or terminate is understood to be a carbon atom with sufficient bonded hydrogen atoms to achieve the four bonds necessary for carbon.
Chapter 3 Highlights • Reaction equations have with the initial materials (reactants) on the left, followed by a reaction arrow pointing from left to right, and the final materials (products) on the right. • A balanced equation has the same number and kinds of atoms on both sides of the equation.
Chapter 3 Highlights • The relationship between the amounts of reactants and products is the stoichiometry, which comes from a balanced reaction equation. • The SI unit for measuring atoms and molecules is the mole. • In an oxidation-reduction reaction, electrons are transferred from one material (the substance that is oxidized) to another material (the substance that is reduced).
Na + Cl NaCl • Balanced Reaction Equations • Writing a Chemical Reaction • The starting materials, the reactants, are written on the left. • The materials that are produced, the products, are written on the right. • Reactants are separated from products by a horizontal arrow pointing from left to right. Reactants Product
Incorrect H2 + O2 H2O 2 H2 + O2 2 H2O Correct • Balanced Reaction Equations (cont) • Balancing the Equation • The law of conservation of matter states that matter can neither be created nor destroyed in a chemical reaction. • The number and kind of atoms on the left-hand side of an equation must be equal to the number and kind of atoms on the right.
Balanced Reaction Equations (cont) • Stoichiometry • The stoichiometry of a chemical reaction is the relationship between the number of molecules of the reactants and products in the balanced reaction equation. • A reactant present in insufficient amounts is the limiting reagent.
The Mole • The mole is the SI unit of measure to describe the amount of matter that is present. • One mole is equal to 6.02 x 1023 particles (Avogadro’s number). • One mole of an element has a mass that is equal to the atomic mass of that element in grams. • One mole of a compound has a mass that is equal to the molecular/formula mass of that compound in grams.
Stoichiometry Calculations • The units of molar mass are grams/mole. • Moles x molar mass = mass. • Example: 2.0 mol CO2 x 44 g/mol = 88 g CO2 • Mass/molar mass= moles. • Example: 132 g CO2 / 44 g/mol = 3.0 mol CO2
Stoichiometry Calculations • The expected mass of a product or reactant can be calculated for any reaction by using the balanced equation and the molar mass.
Oxidation-Reduction Reactions • Defined • Oxidation-reduction (“redox”) reactions involve the transfer of electrons from one substance to another. • Oxidized substances lose electrons and reduced substances gain electrons.
Oxidation-Reduction Reactions (cont) • The Chemistry of Batteries • Combining a readily oxidized substance with an easily reduced substance can create a battery. • The oxidized material is the anode and the reduced material is the cathode of the battery.
Chapter 4 Highlights • Intermolecular forces hold the molecules of a material together. • Stronger intermolecular forces lead to higher melting and boiling temperatures. • The relative strengths of intermolecular forces generally follow the trend: hydrogen bonds > dipole-dipole interactions > London forces
