Why is the Periodic Table important to me? • The periodic table is the most useful tool in chemistry. • You get to use it on quizzes and tests! • It organizes lots of information about all the known elements.
Pre-Periodic Table Chemistry … • …was a mess!!! • No organization of elements. • Imagine going to a grocery store with no organization!! • Difficult to find information. • Chemistry didn’t make sense.
Dmitri Mendeleev: Father of the Table • Previous attempts to organize known elements failed to work for all known elements at the time • Russian Chemist and teacher, Dmitri Mendeleev, discovered a way • Found a way to approach the problem when playing his favorite card game, a version of solitaire (organization was the key) • Solitaire…??????
Dmitri Mendeleev: Father of the Table HOW HIS WORKED… • Put elements in rows by increasing atomic weight. • Elements with similar properties were in the same column. • Put elements in columns by the way they reacted.
Mendeleev’s Periodic Table • Periodic Table: an arrangement of elements in columns, based on a set of properties that repeat from row to row
Mendeleev’s Prediction • Table was not complete, not all elements had yet been discovered • He left gaps/spaces in his table for those elements • He was NOT the first to organize the elements in the form of a table • He was the FIRST to offer good explanations for how the properties of an element were related to its location in his table • He used the gaps in his tables to predict properties of undiscovered elements • Other scientists used the predictions to help in their search for undiscovered elements
Evidence Supporting Mendeleev’s Table • The close match between Mendeleev’s predictions and the actual properties of new elements showed how useful his periodic table could be • With the periodic table, chemists could do more than predict the properties of new elements – they could explain the chemical behavior of different groups of elements!!!
The Current Periodic Table • Mendeleev wasn’t too far off. • Now the elements are put in rows by increasing ATOMIC NUMBER!! • The horizontal rows are called periods and are labeled from 1 to 7. • The vertical columns are called groups are labeled from 1 to 18.
PERIODS • Period: A rowin a periodic table of elements (left to right) • To understand the structure of the table, think what happens as the atomic number increases: • Reminder: Atomic Number = Number of Protons • First energy level has ONLY 1 orbital • The 1 e- in a hydrogen atom and 2 e- in a helium atom can fit in this orbital (first energy level) • This is why H and He are in Period 1
PERIODS • Lithium, 1st element in Period 2, has one of its the three electrons in the second energy level • This is why lithium is the first element in Period 2 • Sodium, 1st element in Period 3, has one e- in its third energy level • Potassium, 1st element in Period 4, has 1 e- in its fourth energy level • This pattern applies to ALL the elements in the 1st column on the table
Families (groups) on the Periodic Table • Columns are also grouped into families (or groups). • Families may be one column, or several columns put together. • Families have names (Just like your family has a common last name.)
Groups • Group: A column in a periodic table of elements • Properties of elements repeat in a predictable way when atomic numbers are used to arrange elements into groups
Groups • Periodic Law: the pattern of repeating properties displayed by elements in the periodic table • Elements within a group have similar properties: • Similar e- configurations (see example above – first column of the table) • Electron configuration determines an elements chemical properties
Atomic Mass • Atomic mass is a value that depends on the distribution of an element’s isotopes in nature and the masses of those isotopes.
Atomic Mass Units • Mass of an atom in grams is EXTREMELY small • Scientists came up with an easier way to talk about mass • Chose one isotope to serve as a standard • Scientists assigned 12 atomic mass units (amu’s) to the carbon-12 atom (which has 6P and 6N) • Atomic Mass Unit (amu): 1/12 the mass of a carbon-12 atom
An Example…Isotopes of Chlorine • Chlorine has an atomic number of 17 and an atomic mass of 35.453 atomic mass units • Where does the number 35.453 come from??? • There are two natural isotopes of Chlorine: • Chlorine-35 which has 17 protons and 18 neutrons • Chlorine-37 which has 17 protons and 20 neutrons
It’s a weighted average of the isotopes • Atomic masses come from an average of the isotopes for a given element that exist in nature • The value for atomic mass is known as a “weighted average” • Cl-35 occurs 3 times as often as Cl-37 • Take an average of those numbers: (3 × 35) + (1 × 37) ----------------------------- = 35.453 4
Classes of Elements • Elements are classified as metals, nonmetals, and metalloids.
Metals • Metals: elements that are good conductors of electric current and heat. • Properties of Metals: • Except for mercury, metals are solid at room temperature • Most metals are malleable • Many metals are ductile (can be drawn into thin wires) • Some metals are extremely reactive* (page 135, figure 10) • *Meaning they easily combine chemically with other elements
Transition Metals • Transition Metals: metals in groups 3-12, form a bridge between the elements on the left and right sides of the tables. • Examples: copper and silver • Some of the first elements discovered • Ability to form compounds with distinctive colors (page 137 production of colored glass) • Includes the lanthanide and actinide series (at the bottom of the table)
Nonmetals • Nonmetals: elements that are poor conductors of heat and electric current • Properties opposite those of metals • Low boiling points • Most are gases at room temperature • Nonmetals that are solid at room temperature tend to be brittle (will shatter) • Some very reactive, some not at all, some fall somewhere in between • Fluorine (in Group 17) is the most reactive nonmetal (found in toothpaste)
Metalloids • Metalloids: elements with properties that fall betweenthose of metals and nonmetals • Ability to conduct electric current varies with temperature • Pure silicon (Si) and germanium (Ge) are good insulators at low temperatures and good conductors at high temps.
Variation Across a Period • Across a period from left to right, the elements become less metallic and more nonmetallic in their properties • Most reactive metals on left side • Most reactive nonmetals on the right side (in Group 17) • Period 3 elements (left to right) provide an example of this (page 138, Figure 13)
Hydrogen… • Why is hydrogen (H) on the left side of the table with the active metals? • Hydrogen’s location is related to its electron configuration, not its properties!!!
Patterns of Electron Configuration • Wonder why there are 2 numbering schemes on the periodic table? • When the ‘A’ groups are numbered 1-8, they provide a reminder about the electron configurations of the elements in those groups • The number of an ‘A’ group matches the number of valance electrons in an electron configuration for an element in that group
Valence Electrons • Valence Electron: an electron that is in the highest occupied energy level of an atom • Valence electrons play a key role in chemical reactions • Properties vary across a period because the number of valence electrons increases from left to right • Elements in a group have similar properties because they have the same number of valence electron • Hydrogen is on far left of table because it has one valence electron, just like the rest of the elements in that column
Hydrogen- Yellow • Hydrogen belongs to a family of its own. • Hydrogen is a diatomic, reactive gas. • Hydrogen was involved in the explosion of the Hindenberg. • http://www.youtube.com/watch?v=F54rqDh2mWA • Hydrogen is promising as an alternative fuel source for automobiles.
Alkali Metals- Purple • 1st column on the periodic table (Group 1 /1A) not including hydrogen. • Very reactive metals, always combined with something else in nature (like in salt).
Alkali Metals • Single valence electron • Soft enough to cut with a butter knife. • The reactivity of alkali metals increases from the top of Group 1A to the bottom • Lithium (Li) down through Francium (Fr) • http://www.youtube.com/watch?v=m55kgyApYrY
Alkaline Earth Metals- Brown • Group 2 / 2A on the periodic table. • Reactive metals that are always combined with nonmetals in nature. • Several of these elements are important mineral nutrients (such as Mg and Ca).