Chemistry Unit 2 Review Guide

Chemistry Unit 2 Review Guide Atomic Structure/Theory Various Models and the scientists behind them: o Democritus – Atoms were indivisible and indestructible, but he lacked evidence as to why. o Dalton – Dalton’s model was that atoms were tiny, indivisible, indestructible particles and that each one had a certain mass, size, and chemical behavior that were determined by what kind of element they were. o Thomson – Plum Pudding Model He imagined the atom as a sphere full of an electrically positive substance mixed with negative electrons o Rutherford – The electron in an atom moves around the dense, positively charged nucleus like plants around the Sun; atom is mostly empty space. o Bohr – Electrons arranged in concentric circles or orbits around the nucleus after the planets motion around the sun. Proposed that the electrons in a particular path have a fixed energy that prevents them from collapsing onto the nucleus. Major experiments done to and their findings: o Thomson’s Cathode Ray Thomson found that a cathode ray is deflected by electrically charged metal plates. A positively charged plate attracts the cathode ray. Thomson knew that opposite charges attract and like charges repel – hypothesized that a cathode ray is a stream of tiny negatively charged particles moving at high speed. Thomson named the particles corpuscles; later they were named electrons. o Milikan’s Oil Drop Suspended negatively charged oil droplets between two charged plates. Changed voltage on the plates to see how this affected the droplet’s rate of fall. Charge on each oil droplet =- 1.60 x 10-19 coulomb Using the charge value and Thomson’s charge-to-mass ratio of an electron – calculated electron’s mass. Relative charge = -1 Actual mass = 9.11 x 10-28 g o Rutherford’s Gold Foil Narrow beam of alpha particles directed at a very thin sheet of gold foil. Most alpha particles went straight through the gold foil or were slightly deflected. Small fraction of the alpha particles bounced off the gold foil at very large angles. Some alpha particles bounced straight back toward the source. Atom is mostly empty space – explaining lack of deflection of most of the alpha particles. All the positive charge and almost all of the mass are concentrated in a small region – accounting for the large deflection of some of the particles. Nucleus = the tiny central core of an atom and is composed of protons and neutrons. What does an atom’s atomic number tell us? The number of protons in the nucleus of an atom of an element. What does an atom’s mass number tell us? The actual mass of a proton of neutron. What are isotopes? Atoms that have the same number of protons, but different number of neutrons. Why is atomic mass considered an average? It is a weighted average mass of the atoms in a naturally occurring sample of the element. How do you calculate the atomic mass of an element? Multiply the mass of each isotope by its natural abundance expressed as a decimal, and add the products. Electron Configurations What are the three rules for writing the electron configurations of elements? 1. Aufbau Principle 2. Pauli Exclusion Principle 3. Hund’s Rule How do you write the longhand configuration, Noble Gas configuration, and orbital diagram for any given atom? Longhand configuration: Use the electron orbital filling Noble Gas configuration: Look at previous Noble gas and use regular configuration to fill remaining electrons Orbital Diagram: Fill in levels of orbital diagram Periodic Table Know the following people and how they contributed to the organization of the elements: Dobereiner, Mendeleev Dobereiner created a Periodic Table grouped into triads in 1829 Mendeleev arranged the electrons in order of increasing atomic mass in 1889. How is the modern periodic table organized? How does this differ from Mendeleev’s periodic table? The modern periodic table was organized by increasing atomic number. Mendeleev organized it by increasing atomic mass. Period law? When elements are arranged in order of increasing atomic number, there is periodic repetition of their physical and chemical properties. Characteristics of metals, nonmetals, metalloids and where they can be found on the periodic table. Metals 80% of elements are metal Solid at room temperature Malleable Nonmetals Gases at room temperature Some are solid (phosphorus, sulfur) and tend to be brittle Bromine is liquid Metalloids Properties similar to metals and nonmetals Behavior of these can be controlled by controlling the conditions Names and characteristics of Group 1, 2, 17, 18 elements Group 1: Alkali metals Group 2: Alkaline earth metals Group 17: Halogens Group 18: Noble Gases What are the trends among elements for atomic size? Atomic radius decreases from left to right within a period. Atomic radius increases from top to bottom within a group. How do ions form? Ions are formed when an atom either gains or loses electrons. A normal atom has equal numbers of protons (positively charged) and electrons (negatively charged). When an electron is lost, the resulting ion is now positively charged. Most metals are prone to losing electrons. If an atom gains an electron, the resulting ion is negatively charged. Nonmetals tend to gain electrons. What are the trends among elements for first ionization energy, ionic size, and electronegativity? Ionization energy: Ionization energy increases from left to right in a period. Ionization energy decreases from top to bottom in a group. Ionic Size: Atomic size increases from top to bottom in a group. Atomic size decreases from left to right in a period. Electronegativity: Electronegativity increases from left to right in a period. Electronegativity decreases from top to bottom in a group. Key terms to know: Atomic radius, Ion, Cation, Anion, Ionization energy, electronegativity Atomic radius: One half the distance of two atoms. Ion: An ion is an atom or molecule in which the total number of electrons is not equal to the total number of protons, giving the atom a net positive or negative electrical charge. Cation: An atom or molecule, which is positively charged. Anion: An atom or molecule, which is negatively charged. Ionization energy: The amount of energy required to remove an electron from a neutral atom in its gaseous phase. Electronegativity: A chemical property describing an atoms ability to attract and bind to electrons. Powered by TCPDF (www.tcpdf.org)