Tour of the Periodic Table (Chapter 6) Dr. Walker Objectives • Describe the historical development of the periodic table • Name the groups of the periodic table and describe their properties • List elements that are diatomic • Differentiate elements based on periodic trends History • First periodic table created by Dmitri Mendeleev – Arranged elements by increasing atomic mass, which caused mistakes – Was incomplete, but pattern predicted existence of elements found later • Current periodic table created by Henry Moseley – Arranged by increasing atomic number Mendeleev’s Periodic Table The columns are called groups or families. Groups have similar physical and chemical properties. Periodic Law • When elements are arranged in order of increasing atomic numbers, their physical and chemical properties show a periodic pattern. • Elements in the same groups have the same general physical and chemical properties because of their similar number of valence electrons. • Periodicity is regularly repeating patterns or trends in the chemical and physical properties of the elements arranged in the periodic table. More About Periodic Law • Valence Electrons – Electrons in the outer shell of an atom – Determines chemical properties Determining Valence Electrons • How do we determine valence electrons? – Valence electrons = last number of group number – Examples • Sodium – Group 1 = 1 valence electron • Boron – Group 13 = 3 valence electrons • Chlorine – Group 17 = 7 valence electrons • Nitrogen – Group 15 = 5 valence electrons Determining Valence Electrons • We can also get valence electrons from the electron configuration • Superscripts for highest energy level are valence electrons • Includes s AND p electrons – Examples • Sodium – 1s22s22p63s1 = 1 valence electron – There is one electron in the third energy level • Boron – 1s22s22p1 = 3 valence electrons – There are three electrons in the second energy level • Chlorine – 1s22s22p63s23p5 = 7 valence electrons – There are seven electrons in the third energy level Determining Groups • Each group has a distinctive electron configuration – ns2np2 = 4 valence electrons = Group 14 • 1s22s22p2 = carbon • 1s22s22p6 3s23p2 = silicon • 1s22s22p63s23p6 4s23d104p2 = germanium Determining Valence Electrons • What about the transition metals (groups 3-12), actinides, and lathanides? – We don’t worry about these elements – These elements can use electrons from d and f orbitals, which we won’t deal with Groups of the Periodic Table • Group 1-Alkali Metals • Physical Properties – Soft – Low melting points – Low densities • Chemical Properties – Explodes in water – Tarnish rapidly in air Groups of the Periodic Table • Group 2 - Alkaline Earth Metals • Physical Properties – Soft • Chemical Properties – React well with hot water – Strong reducing agents Groups of the Periodic Table • Groups 3-12 - Transition Metals • Physical Properties – High density – High melting point – Magnetic Groups of the Periodic Table • Metalloids – Diagonal Elements beginning with Boron • B, Si, Ge, As, Sb, and Te • Physical Properties – Semi-conductors • Chemical Properties – Act like metals when they react with non-metals – Act like non-metals when they react with metals Groups of the Periodic Table • Group 17 – Halogens • Physical Properties – increase in density as you go down the column – colored (yellow-green to brown to black) • Chemical Properties – Form salts with elements from alkaline metals – Exist as diatomic molecules – Form acids with hydrogen Groups of the Periodic Table • Group 18 - Noble Gases • Physical Properties – Colorless – Odorless – Tasteless • Chemical Properties – chemically inert (do not react) – full valence shell Hydrogen • Why is this separate? – Since it only has one electron, it is placed with group 1 – Doesn’t possess any chemical similarities with alkali metals – Physical Properties • Colorless, Tasteless, Odorless – Chemical Properties • Inflammable • Highly reactive • Exists as diatomic molecule Diatomic Molecules • Some elements exist as diatomic molecules – Exists as TWO atoms covalently bonded to each other • Mostly top right of periodic table • H2, N2, F2, O2, I2, Cl2, Br2 – ClIF H BrON Not in guided notes! Inner Transition Metals • Otherwise known as lanthanide and actinide series or “f-block” elements – Some not found in nature (primarily actinides) The rows are called periods. The period number matches the principle energy level of the element. Periodic Trends • Atomic Radius: Measure of the distance between radii of two identical atoms of an element. • Ionization Energy: The energy required to remove an electron from an atom in its gaseous state • Electronegativity: Measure of the attraction of an atom for electrons in a bond. Atomic Radius Across periods: Radius size decreases due to increased nuclear charge Down a group: Radius size increases to due higher number of occupied shells Ionization Energy • The energy required to remove an electron from an atom in its gaseous state Electronegativity Electronegativity: The tendency of an atom to attract electrons to itself when chemically combined with another element. The halogen group has the highest electronegativity of the families. The first period has the highest electronegativity. Question • If electronegativity increases to the right, why don’t the noble gases have the highest electronegativity? Question • If electronegativity increases to the right, why don’t the noble gases have the highest electronegativity? – Electronegativity involves atoms in a bond. Noble gases DO NOT BOND! Therefore, no electronegativity value Nuclear Shielding • Outer shell electrons feel less effect of the positive nucleus because of the inner shell electrons. • The nuclear shielding effect is constant within a given period and increases within given groups from top to bottom. Shielding Trends • Shielding is equal among elements in the same period Chemical Reactivity • Reactivity refers to how likely or vigorously an atom is to react with other substances. • Metals and nonmetals have their own trends (can’t be easy….can it?) Not in textbook, but on SOL (figures!) From http://www.pleasval.k12.ia.us/highschool/teachers/hoffmanjoshua/Chem%20PDF/Chem%20Unit%203/PeriodicTrendsReading.pdf Chemical Reactivity - Metals • Increases as you go down – As you go down valence electrons are further from the nucleus – Further from the nucleus, easier to get rid of • Decreases left to right – Further to the right, more electrons to get rid of – Takes more energy to do this Not in textbook, but on SOL (figures!) http://edtech2.boisestate.edu/lindabennett1/502/Periodic%20Table%20e%20config/PTable_trends%20around%20table.html Chemical Reactivity - Nonmetals • Decreases as you go down – Higher elements have more electronegativity – The more they “hog” electrons, the faster they react • Increases left to right – The closer you are to filling an octet the more reactive it is – Noble gases don’t count – their octet is full, so they don’t react Chemical Reactivity https://jahschem.wikispaces.com/file/view/Reactivity_Trends.jpg/211822562/Reactivity_Trends.jpg Review • What group is chemically unreactive? • What is the Periodic Law? • Give three diatomic elements. • What group consists of elements that explode in water? Review • What group is chemically unreactive? • Noble gases • What is the Periodic Law? • When elements are arranged in order of increasing atomic numbers, their physical and chemical properties show a periodic pattern. • Give three diatomic elements. • H2, N2, F2, O2, I2, Cl2, Br2 • What group consists of elements that explode in water? • Alkali Metals Review • Of F, B, and O, which is the most electronegative element? • Of F, B, and O, which element has the largest radius? • Of Rb, Na, and K, which element has the largest shielding effect? Review • Of F, B, and O, which is the most electronegative element? • Fluorine (farthest right) • Of F, B, and O, which element has the largest radius? • Boron (farthest left) • Of Rb, Na, and K, which element has the largest shielding effect? • Rubidium (lowest on periodic table) Terms to Know • Mendeleev (name) Inner Transition Metals • Moseley (name) Diatomic elements • Valence electrons Atomic Radius • Alkali metals Electronegativity • Alkaline earth metals Ionization Energy • Transition metals Nuclear Shielding • Metalloids • Halogens • Noble gases Skills To Master • Determining diatomic elements • Determining valence electrons from their position on the periodic table, by group name, and by electron configuration • Classifying elements by their group name • Arranging elements according to their periodic trends – Electronegativity – Atomic Radius – Shielding – Reactivity .