Chemistry Study Guide Midterm PDF

Chemistry Study Guide:​ Each section has a video hyperlinked​ 1/17/25 Matter -​ has both mass and volume (air is matter) Substance -​ Matter that has a uniform and definite composition is called a substance. -​ Ele...

Chemistry Study Guide:​ Each section has a video hyperlinked​ 1/17/25 Matter -​ has both mass and volume (air is matter) Substance -​ Matter that has a uniform and definite composition is called a substance. -​ Elements and compounds -​ Every sample of a given substance ha23ewI s identical intensive properties because every sample has the same composition. Elements 1.​ The purest form of a substance that cannot be broken down into any simpler substances. 2.​ Made up of one type of atom. 3.​ Building blocks are from which all forms of other matter are made. Compounds -​ A compound is a substance that contains two or more elements chemically combined in a fixed proportion. -​ Compounds can be broken down into simpler substances by chemical means, but elements cannot. -​ In general, the properties of compounds are quite different from those of their component elements. -​ Compounds composed of cations and anions are called ionic compounds. Although they are composed of ions, ionic compounds are electrically neutral. -​ A compound composed of covalent bonds is called a molecular compound. Water and carbon monoxide are molecular compounds. Molecular compounds tend to have lower melting and boiling points than ionic compounds. -​ Two atoms held together by sharing a pair of electrons are joined by a single covalent bond. -​ An electron dot structure such as H:H represents Mixtures -​ A mixture is a blend of two or more compounds. -​ Based on the distribution of their components, mixtures can be classified as heterogeneous or homogenous. -​ Heterogeneous Mixtures: a mixture in which the composition is not uniform. Examples include: salad, pasta and sauce, rice and beans, oil and water, etc. -​ Homogenous Mixtures: a mixture in which the composition is uniform. Another name for a homogenous mixture is a solution. Examples include: Kool-Aid, Iced Tea, etc. Chemical Properties -​ The ability of a substance to undergo a specific chemical change is called a chemical property. -​ During a chemical change, the composition of matter always changes. -​ A precipitate is a solid that forms and settles out of a liquid mixture. -​ During any chemical reaction, the mass of the products is always equal to the mass of the reactants. -​ One or more substances change into one or more new substances during a chemical reaction. -​ During a chemical change, there is either a transfer of energy, a change in color, the production of a gas, or the formation of a precipitate. Physical Properties -​ A physical property is a quality or condition of a substance that can be observed or measured without changing the substance’s composition. -​ Physical changes that involve a change from one state to another are irreversible. -​ Cutting hair, filing nails, and cracking an egg are examples of irreversible physical changes. -​ The law of conservation of mass states that in any physical change or change reaction, mass is conserved. Absolute Zero -​ Absolute zero is the lowest temperature possible. At a temperature of absolute zero there is no motion and no heat. Celsius to Zero -​ Absolute zero occurs at a temperature of 0 kelvin, or -273.15 degrees Celsius, or at -460 degrees Fahrenheit. Solids -​ The major types of solids are ionic, molecular, covalent, and metallic. Ionic solids consist of positively and negatively charged ions Liquids -​ A liquid is a matter with specific properties that make it less rigid than a solid but more rigid than a gas. A liquid can flow and does not have a particular shape like a solid. Instead, a liquid conforms to the shape of the container in which it is held. Democritus -​ Democritus believed that atoms were indivisible and indestructible. Dalton 1.​ Dalton’s Atomic Theory States:​ a. All elements are composed of tiny indivisible particles called atoms.  b. Atoms of the same element are identical. c. Atoms of different elements have different masses. d. Compounds are formed by the combinations of atoms of different elements. 2.​ Dalton’s model of the atom looked like solid spheres of matter. Cathode Ray Tube -​ Thomson’s cathode ray tube was a glowing beam that traveled from the cathode (-) to the anode (+). -​ Electrons were discovered as a result of the cathode ray tube. -​ The Plum Pudding Model was created after this, which showed J.J. Thomson’s discoveries on atoms. In the model, electrons were thought of to be stuck in the atoms like raisins in pudding. The electrons were negatively charged while the rest of the atom was positively charged. Gold Foil Experiment -​ Rutherford's gold foil experiment showed: 1.​ The atom is mostly empty spaces. 2.​ All the positive charge and almost all the mass are concentrated in a small region called the nucleus. a.​ Nucleus: tiny central core of an atom and is composed of protons (+) and neutrons (neutral). b.​ Protons: positively charged subatomic particles c.​ Neutrons: subatomic particles with no charge but with a mass nearly equal to that of a proton. Planetary Model (Bohr Model) -​ Bohr’s Model (planetary model)​ 1. Energy levels - the fixed orbital an electron can have based on its energy. 2. Quantum of Energy - the amount of energy required to move an electron from one energy level to another. Wave Mechanical Model (Quantum Mechanical Model) -​ Erwin Schrödinger created the Quantum Mechanical Model (Wave Mechanical Model). -​ The Quantum Mechanical Model determines how much energy an electron can have and how likely it is to find the electron in various locations around the nucleus. Particle Symbol Relative charge Relative mass (mass of proton = 1) Electron e⁻ 1- 1/1840 Proton p⁺ 1+ 1 Neutron n⁰ 0 1 Orbitals -​ Atomic orbitals: a region of space in which there is a high probability of finding an electron. Different atomic orbitals are denoted by letters; S, P, D, and F. S = 1 Orbital ​ ​ S Orbitals are spherical.​ P = 3 Orbitals ​ ​ P Orbitals are dumbbell-shaped.​ D = 5 Orbitals​ F = 7 Orbitals -​ Four of the 5 D orbitals have the same shape but different orientations in space. ​ ​ a. D orbitals are shaped like clover leaves. ​ ​ b. The number and kinds of atomic orbitals depend on the energy sublevels. Electrons: e⁻ -​ Negatively charged subatomic particles. Neutrons: n⁰ -​ Neutrally charged subatomic particles. Protons: p⁺ -​ Positively charged subatomic particles. Atomic Number ​ Another video* -​ The number of protons in the nucleus of an atom. -​ The atomic number (number of protons) never changes in a chemical reaction. Energy Levels Principal Energy Type of Sublevel Number of Total # orbitals Max. # of Orbitals per level Electrons 1 S 1 1 2 2 S​ 1​ 4 8 P 3 3 S​ 1​ 9 18 P​ 3 D 4 S​ 1​ 16 32 P​ 3​ D​ 5​ F 7 Valence Electrons -​ Valence electrons are the electrons in the highest occupied energy level of an element's atoms. -​ Electron dot structures (Lewis Dot Diagram) are diagrams that show valence electrons as dots. -​ The Octet Rule: in forming compounds, atoms tend to achieve the electron configuration of a noble gas. -​ Atoms of metals tend to lose their valence electrons, leaving a complete octet in the next-lowest energy level. -​ An atom’s loss of valence electrons produces a cation or a positively charged ion. -​ The gaining of negatively charged electrons by a neutral atom produces an anion. An anion is an atom or group of atoms with negative charges. Ions -​ An ion is an atom or group of atoms that has an electric charge. -​ A polyatomic ion, such as NH₄⁺, is a tightly bound group of atoms that has a positive or negative charge and behaves as a unit. -​ Some ions called polyatomic ions are composed of more than one atom. -​ The Stock System and The Classical Method are two forms of naming the ions of transition metals. Excited State -​ Excited State means the electron has absorbed energy and moved to a higher energy level.​ Atomic Mass -​ Weighted average mass of the atoms in a naturally occurring element sample.  -​ Atomic mass unit (amu) - one-twelfth of the mass of a carbon-12 atom. For example:​ Carbon has two stable isotopes: Carbon-12, which has a natural abundance of 98.89%.​ Carbon-13, which has a natural abundance of 1.11%.​ ​ (12 x 0.9889) + (13 x 0.0111)​ 11.8668 + 0.1443 ​ ​ 12.0111 —> meaning it’s closer to carbon-12. Atomic Emission Spectra -​ When atoms absorb energy, electrons move into higher energy levels. -​ These electrons then lose energy by emitting light when they return to lower energy levels. ​ ​ a. Ground State: electrons occupy the lowest energy level. ​ b. Excited State: the electron has absorbed energy and moved to a higher energy level. -​ Frequencies of light emitted by an element separate into discreet lines to give the AES of the element. Periodic Table -​ Each row is called a period. -​ Each period starts with a metal on the left and ends with a noble gas. -​ The number of the period refers to the highest energy level occupied by each element in the period. -​ Each vertical column is called a group. -​ The Group Number is related to the number of valence electrons for each element in the group. -​ In Groups 1 and 2, the Group Number equals the number of valence electrons. -​ In Groups 13, 14, 15, 16, 17, and 18, the second digit equals the number of valence electrons. -​ Noble Gases (Group 18) - These elements all have 8 electrons in their outermost energy level. a.​ These elements are generally unreactive. b.​ This property is very important in chemical bonding. Atomic Radius -​ The distance between the two nuclei (look for the atomic radius in Table S) Metalloids -​ Hybrid between metals and nonmetals. -​ INCLUDES: Boron (B), Silicon (Si), Germanium (Ge), Arsenic (As), Antimony (Sb), Tellurium (Te), Polonium (Po), Astatine (At). Alkali Metals -​ Are Group 1  -​ Tend to be very reactive, because they want to get rid of one valence electron. -​ Hydrogen is not an Akali Metal, but the rest of the group is. Halogens -​ Any element in Group 17. -​ Also very reactive, because they only need to gain one electron to have 8 valence electrons. Group Number -​ For Groups 1 to 2 and 13 to 18, you can take the last number of the group to determine how many valence electrons they have. Formation of Ions * -​ To create an ion, atoms gain or lose electrons. Two types of ions can be created due to the gain and loss of electrons, they are called cations and anions. Those atoms that lose electrons are called cations due to the overall positive charge on the atom. Metals * -​ Metal will lose its valence electrons to reach the configuration of a noble gas. -​ They are malleable, so they can be bent into different shapes. -​ On the left side of the periodic table. -​ Atoms of metals tend to lose valence electrons to complete octets in the next-lowest energy level. Nonmetals -​ Gain electrons to gain 8 electrons like the noble gases. -​ Few are solid, and one is liquid (bromine). -​ Atoms of some nonmetals tend to gain electrons or share electrons with another nonmetal to achieve a complete octet Ionization Energy -​ The amount of energy required to remove an electron from an isolated atom or molecule. -​ Check Table S, under the fourth column. -​ Metals tend to have a higher ionization energy. Electronegativity -​ How strong an element will pull to attract electrons towards itself. -​ Usually, the bottom part of the Periodic Table tends to have more electronegativity. Ionic Bonds -​ When you have a metal, forming a bond with a nonmetal. -​ The electrostatic forces that hold ions together in ionic compounds are ionic bonds. -​ The charge would be neutral.  -​ When creating ionic bonds, the configuration on the metal would become how many non-metal atoms are needed to create a balanced ionic bond. Balancing Equations -​ To write a balanced chemical equation, first write the skeleton equation. Then use coefficients to balance the equation so that it obeys the law of conservation of mass.