Name Chemistry-PAP. Notes: Periodic Table and Periodic Trends

Transcription

1 Name Chemistry-PAP Period I. History Notes: Periodic Table and Periodic Trends Dmitri Mendeleev ( ) Russian professor Gathered a wealth of data on all chemical elements known at the time noticed similarities in properties when known elements were arranged in order of increasing atomic created first table in which he placed elements with similar properties into the same groups left spaces in table to allow for discovery of Inductive reasoning is the use of detailed facts to form a general principle or model (going from specific to general). How did Mendeleev use inductive reasoning? Deductive reasoning is the use of a general principle or model to draw specific inferences (going from general to specific). How did Mendeleev use deductive reasoning? Mendeleev placed the elements in order of atomic mass to create his table, but he was forced to break the order a few times to preserve the patterns he had discovered. Something was not quite right, but it would take further scientific discovery to shed light on the problem. Henry Moseley ( ) scientist working with Work using x-ray spectroscopy led to definition of atomic as the number of in the nucleus of the atom. Realized that Mendeleev s table is actually arranged by increasing atomic Was killed in action in WWI at the age of 27. Isaac Asimov once wrote, "In view of what he [Moseley] might still have accomplished... his death might well have been the most costly single death of the War to mankind generally." [ Periodic Law: the physical and chemical properties of the elements are functions of their atomic. 1

2 ** Use your Gallery Walk notes to help you fill in pp. 2-3! ** Modern Periodic Table the is an arrangement of elements in order of their atomic numbers so that elements with similar physical/chemical fall in the same column II. Elements of the Periodic Table the electron of an atom s energy level governs the atom s chemical properties 1. Organization horizontal rows are called vertical columns are called and correspond to the element s electron config 2. s-block elements groups and and the element Group 1 has configuration known as metals (except hydrogen, a nonmetal) color enough to cut with knife VERY! (most reactive metals on table) not found in nature (only in compounds) typically stored in oil to prevent with air and water Group 2 has configuration called metals harder,, stronger than alkalis also very, but not as much as alkali metals not found in nature 3. d- block elements Hard, silvery, solid (except Hg) metals that have a density also known as metals less than alkali and alkaline earth metals Examples of d-block elements: 2

3 4. p-block elements all elements of Groups except also known as elements (along with s-block) contains, nonmetals, and have properties of metals and non-metals Group 17 called most reactive strong and will burn Group 18 called Not chemically (inert) Have configuration All have 8 valence electrons except, which is still stable because it has a filled outer energy level. 5. f-block elements the and sublevels are being filled these elements have very unpredictable electron configurations Also known as the transition metals 6 th period f-block elements are called the series (rare earth elements) 7 th period f-block elements are called the series The actinides are all (unstable nuclei) Most actinides are also (do not occur in nature) Useful definitions: Metal: a substance that conducts heat and electricity, is shiny and reflects many colors of light, and can be hammered into sheets (malleable) or drawn into wire (ductile). Metals lose electrons to form cations (positive ions). All solid at room temperature except mercury. About 80% of the known elements are metals. Nonmetal: a substance that is a poor conductor of heat and electricity, is brittle or waxy or gaseous, and is not malleable or ductile. Nonmetals gain electrons to form anions (negative ions). About 20% of the known elements are metals. Metalloid: An element with some metallic and some nonmetallic properties. Semiconductors. They are boron, silicon, germanium, arsenic, antimony, tellurium, and polonium. 3

4 III. Periodic Trends Keep these 3 factors in mind when considering periodic trends: 1. Nuclear charge Whenever a is added to the nucleus, it creates a stronger pulling the in to the nucleus even more. Nuclear charge increases across a period Comparison of nuclear charge: (compare K to Br) 2. Shielding Effect When an is added to the atom (each new on the periodic table), you are adding a between the nucleus and the electrons. As energy levels are added, the atom becomes in radius. The pull of the for the electrons is decreased, because not only are there more, but the valence electrons are also now from the nucleus. It is easier to a valence electron as energy levels are added. Diagram of the shielding effect: (compare Li to K) 3. Octet Rule will lose, gain or share so they can achieve the electron configuration of the closest. As elements get to the noble gases on the periodic table (further to the ), the greater the attraction they have for electrons. Elements on the side of the periodic table want to lose electrons, so they will not have a great for electrons. 4

5 Trends in the Properties of the Elements A. Atomic Radius Atomic radius can be thought of as the distance from the center of the nucleus to the edge of the electron cloud, but it is officially defined as one-half the distance between of two like atoms in a molecule Ex: diagrams of H 2 and O 2 measured in picometers (pm), m or Angstroms (A), m atomic radius indicates relative or size of the atom 1. Group trend Atomic radius generally as you move down a group. This is mainly due to succeeding being filled. 2. Periodic trend Atomic radius generally as you move across a period from left to right. This is mainly due to increasing. B. Ionic Radius A positive ion is known as a. It is a metal atom that has electrons. A negative ion is known as an. It is a nonmetal atom that has electrons. Ex: Na and Na + F and F - 5

6 Positive ions are always smaller than the neutral metal atoms from which they were formed. When metal ions form, typically the outer energy level will be emptied, resulting in an overall smaller electron cloud. Also, the excess of protons compared to electrons draws the remaining electrons in closer. Ex. Which is larger, Na or Na+? Circle one. Negative ions are always larger than the neutral nonmetal atoms from which they were formed. There is more repulsion in the cloud due to the added electrons, therefore making it spread out, but there are no extra protons to pull it closer. Ex. Which is larger, F or F? Circle one. 1. Group trend Ionic radius (for both cations and anions) generally as you move down a group. This is mainly due to succeeding being filled. 2. Periodic trend Cation radius generally as you move across a period from left to right. This is mainly due to increasing. The same trend is observed for anions across a period, for the same reason. Note that overall, anions within one period are larger than the cations within one period. This is due to the fact that cations have lost an energy level. C. Ionization Energy Ionization energy is defined as the amount of energy required to remove an from a gaseous atom, producing a (a positively-charged ion). Na (g) kj Na + (g) + e - (energy) 1. Group Trend Ionization energy as you move down a group. This is mainly due to the. 2. Periodic trend Ionization energy as you move left to right across a period. This is mainly due to increasing and the octet rule. 6

7 The energy required to remove the first outermost electron is called the ionization energy. To remove the second outermost electron is called the ionization energy, and so on. Element First IE (kj/mol) Second IE (kj/mol) Third IE (kj/mol) Li Be F Ne Note the sharp increase for the second IE for Li and for the third IE for Be. Why? D. Electronegativity Electronegativity is defined as the tendency for atoms of an element to attract bonding when they are chemically combined with atoms of another element. Ex: H 2 O 1. Group trend Electronegativity as you move down a group. This is because the from the nucleus is. 2. Periodic Trend Electronegativity as you move left to right across a period. This is mainly due to increasing and the octet rule. 7

8 Electronegativities of the Elements Note: Noble gases have no electronegativity because they don t attract electrons at all. Think of the octet rule. IV. Summary of Periodic Trends With your teacher s help, summarize the trends on the periodic table using arrows and labels. 1 Group 1 2 Periodic Table