Introduction to the Periodic Table of Elements Mendeleev In 1869, Dmitri Ivanovitch Mendelev created the first accepted version of the periodic table. He organized elements according to their atomic mass, and as he did, he found that the families had similar chemical and physical properties. Blank spaces were left on the table to add elements that Mendeleev predicted would be discovered. Protons and the Periodic Table Within 15 years, all three elements gallium, scandium, and germaniumwere discovered as Mendeleev predicted they would be. Mendeleev created his table before the discovery of protons. Although Mendeleevs table correctly organized most of the elements, a few elements seemed out of place when organized by atomic mass. In 1913, British physicist, Henry Moseley, discovered that an atoms positively charged nuclear sphere actually contained positively charged particles which he called protons. He found that the number of protons in an atoms nucleus determined the identity of the atom. The number of protons is unique to an atom. The periodic table was then rearranged in order of atomic number Organization of the Periodic Table The periodic table is organized into different sections based on properties of elements. The following slides show some of the different sections that a periodic table has. Color, highlight, or otherwise designate, the different sections on the tables provided in your packet. Periods & Groups/Families Periods are the rows in the periodic table There are 7 periods (rows) Groups/families are the columns in the periodic table There are 18 total groups (columns) Main Group (representative elements) Transition elements Inner transition elements Main group elements are those in groups 1A-8A (or columns 1,2,13-18) Transition elements are those labeled B (columns 3-12) Inner-transition elements are the 2 rows of elements that have been placed underneath the main table. Metals, Nonmetals, Metalloids PropertiesMetalsNonmetalsMetalloids physical shiny (have luster) good conductors of heat & electricity ductile, malleable usually solid at room temperature do not have luster not good conductors of heat or electricity usually a gas or brittle solid at room temperature share physical properties of both metals & nonmetals chemical tend to lose electrons in chemical reactions, and so.. form positive ions Tend to gain electrons in chemical reactions, and so form negative ions LocationTo the left of the stair-step line To the right of the stair-step line Along the stair-step line Stair- step line State of Matter at Room Temperature What elements are liquids at room temperature? What elements are gases at room temperature? The majority of elements are ________ at room temperature. Lets look at specifics: Periods (rows) There are 7 periods in the periodic table Properties (characteristics) change gradually as you go from left to right across a period. This is called periodicity: repeating patterns of gradually changing properties across a period. The periods (horizontal rows) tell how many energy levels (energy shells) an element has. Period 1 has 1 energy level Period 2 has 2 energy levels Period 3 has 3 energy levels And so on through period 7 Period 1 Period 7 Groups/Families (columns) The periodic table has 18 total columns Each column contains a group, or family of elements Columns show a vertical arrangement of elements Columns go up and down (like the columns on the front of a building) Columns are further labeled as A & B group The colored columns are the A groups The white columns are the B groups These labels show that there are chemical similarities among the family members in the group The 18 total columns in the periodic table represent the groups, or families, of elements Put a star over the A groups Groups/Families continued Elements in each group/family have similar chemical and physical properties; just like people share similar characteristics with their family members. Physical Properties: For example, lithium (Li), sodium (Na), potassium (K), and other members of Group IA share physical properties such as; all are soft, white, shiny metals. Chemical Properties: All elements in a group/family have the same number of valence electrons. Li, Na, K & others in group IA have 1 valence electron Valence electrons are the electrons in the outermost energy level of an atom. Valence electrons are where chemical bonding takes place. Valence electrons are transferred or shared when atoms bond together Valence Electrons Valence electrons are the electrons in the outer energy level of an atom. The number of valence electrons an atom has may also appear in a square on the periodic table. We are going to look at characteristics (properties) of some of the major groups on the periodic table Fill in the comparison chart in your packet as you look through the next few slides. hydrogen What does it mean to be reactive? We will be describing elements according to their reactivity. Reactivity increases vertically as you go down a group because the valence electrons contain more energy & are farther away from the nucleus making them more readily available for bonding. Elements that are reactive bond easily with other elements to make compounds. Some elements are only found in nature bonded with other elements. What makes an element reactive? An incomplete valence electron level. All atoms (except hydrogen & helium) want to have 8 electrons in their very outermost energy level (This is called the rule of octet.) Atoms bond until this level is complete. Atoms with few valence electrons lose them during bonding. Atoms with 6, 7, or 8 valence electrons gain electrons during bonding. Hydrogen Hydrogen is in a class of its own. The hydrogen square, sits atop Family 1A, but it is not a member of that family. Chemical properties: Hydrogen has only one energy level Hydrogen has only one valence electron, making it a very reactive element. Physical properties: It is a nonmetal It is a gas at room temperature. Metalgroups Alkali Metals Group 1A Chemical properties: Most reactive of all metals Are never found as free elements in nature. They are always bonded with another element. Must be stored in oil to prevent a reaction with moist air. Atoms of the alkali metals have one valence electron. Physical properties: Soft (clay-like), shiny, ductile, malleable, good conductors Alkaline Earth Metals - Group 2A Chemical properties: They are very reactive, but not as reactive as Group 1 Are never found as free elements in nature. They are always bonded with another element. They have two valence electrons. Physical properties: Soft, shiny, ductile, malleable, good conductors Transition Elements (groups 3-12) Chemical properties: Not as reactive as group 1 & 2 are often found in nature as individual elements (do not have to be combined with other elements) Physical properties: Usually a hard solid, ductile, malleable, good conductors, shiny, colorful These elements are located in the middle of the periodic table between the A groups (columns 1,2 & 13-18). They are labeled as B groups They are called transition elements because they are considered to be changing gradually (transitioning) from the group 1 & 2 elements to the group elements. These elements are metals that you are the most familiar with like: copper, iron, nickel, platinum, gold, silver and zinc Inner transition elements (elements at bottom of table) These elements fit into the main table in periods 6 & 7 between groups 3 &4. They are pulled out to save room. Sometimes called rare earth elements Chemical properties: Many inner transition elements are radioactive & are not found in nature Physical properties: Usually hard, ductile, malleable, good conductors Transition Elements or Rare Earth Elements Lie below the main body of the periodic table The thirty rare earth elements are composed of the lanthanide and actinide series. One element of the lanthanide series and most of the elements in the actinide series are called trans-uranium, which means synthetic or man-made. Mixed Groups (named for the 1 st element in the group) Boron Group Carbon Group Nitrogen Group Oxygen Group Boron Family Group 13 (3A) Chemical properties: Atoms in this family have 3 valence electrons. This family includes the most abundant metal in the earths crust (aluminum). Physical properties: This family includes a metalloid (boron), and the rest are metals. Elements have a mix of physical properties Carbon Family: Group 14 (4A) Chemical properties: Atoms of this family have 4 valence electrons. The element carbon is called the basis of life. There is an entire branch of chemistry devoted to carbon compounds called organic chemistry. Physical properties: This family includes a non-metal (carbon), metalloids, and metals. Carbon exists in many forms including: diamond and graphite Nitrogen Family: Group 15 (5A) Chemical properties: Atoms in the nitrogen family have 5 valence electrons. They tend to share electrons when they bond. (covalent bond) Physical properties: The nitrogen family is named after the element that makes up 78% of our atmosphere. This family includes non-metals, metalloids, and metals. Oxygen Family: Group 16 (6A) Chemical properties: Atoms of this family have 6 valence electrons. Most elements in this family share electrons when forming compounds. (covalent bond) Physical properties: Oxygen is the most abundant element in the earths crust. Group contains gases and metalloids Halogen Family: Group 17 (7A) Chemical properties: have 7 valence electrons they are the most active non-metals. They are never found free in nature. Halogen atoms only need to gain 1 electron to fill their outermost energy level. Halogen means salt-former. They react with alkali metals (Group 1 elements) to form salts. Physical properties: Elements in this group include: gases, solids and a liquid Noble Gases: Group 18 (8A) Chemical properties: Noble Gases are extremely un-reactive. They are unreactive because their outermost energy level is full. They have 8 valence electrons except helium (has 2) Because they do not readily combine with other elements to form compounds, the noble gases are called inert Physical properties: Are all colorless gases All the noble gases are found in small amounts in the earth's atmosphere. Periodicity Periodicity is the phenomenon in which certain chemical and physical properties of atoms occur in regular and predictable situations. properties change gradually and predictably A period, is a row of elements in the periodic table whose properties change gradually and predictably as you move from left to right across a period There are 7 periods (rows) on the periodic table. The elements in a period are not alike in properties. In fact, the properties change greatly across every given row. This is what we call, periodicity. Reading the periodic table is analogous to reading a paragraph. You read from left to right, top to bottom and there is a period after each sentence (or row in this case). Examples of Periodicity (gradual changes in properties across the periods (rows) atomic radii decreases atomic radii increases The diagram to the right shows some of the general trends in periodicity as we look from left to right, and up and down, on the periodic table. Elements & the Periodic Table Science has come along way since Aristotles theory of Air, Water, Fire, and Earth. Scientists have identified 92 naturally occurring elements, and created about 26 others. Elements The elements, alone or in combinations, make up our bodies, our world, our sun, and in fact, the entire universe. The most abundant element in the earths crust is oxygen. A Map of the Elements The periodic table is analogous to a map. The geography or placement, of each element, gives important information about that element We read the periodic table from left to right & from top to bottom The table is arranged by increasing atomic numbers Whats in a square? Different periodic tables can include various bits of information, common bits include: atomic number atomic mass symbol number of valence electrons state of matter at room temperature. Key to the Periodic Table Elements are organized on the table according to their atomic number, usually found near the top of the square. The atomic number refers to how many protons an atom of that element has. For instance, hydrogen has 1 proton, so its atomic number is 1. The atomic number is unique to that element. No two elements have the same atomic number. Atomic Number This refers to how many protons an atom of that element has. No two elements, have the same number of protons. Bohr Model of Hydrogen Atom Electron Cloud or Wave Model Recall the 2 most used models of atomic structure: Bohr Model: Used to diagram an atoms structure Shows electrons in specific orbits (paths) Electron Cloud Current theory Based on probability of where electrons may be located Also referred to as the wave model Electron Cloud Model: Current model theory aka: Wave Model Current model theory Based on Quantum Mechanics: States that regardless of what we know about a particle, we can only predict its location based on high and low probabilities. The high & low predictions create a wave, with crests (high probability) & troughs (low probability) Wave Model shows a cloud of electrons around the nucleus Atomic Mass Atomic Mass refers to the amount of matter in the atom. It is calculated by adding the number of protons with the number of neutrons. atomic mass = protons + neutrons This is a helium atom. What is its atomic mass? (protons + neutrons) = ______ What is its atomic number? Number of protons = ________ Atomic Mass Unit (AMU) The unit of measurement for an atom is an amu. It stands for, atomic mass unit. One amu is equal to the mass of 1 proton. Neutrons are slightly larger than protons; however, we say they also have a mass of 1 amu. Atomic Mass Unit (AMU) There are 6.02 X or 600,000,000,000,000,0 00,000,000 amus in one gram. (Remember that electrons are 2000 times smaller than one amu)!! Atomic Mass and Isotopes All atoms are neutral, meaning they have the same number of electrons as they do protons. However, atoms of the same kind can have differing numbers of neutrons. These are called the atoms isotopes. The atomic mass number, indicates the weighted average atomic mass of an atom and its isotopes. Organic matter is made of C- 12 C-13 is used by plants & medical research C-14 is radioactive, used for carbon dating stable unstable Symbols All elements have their own unique symbol. It can consist of a single capital letter, or a capital letter and one or two lower case letters. The 1 st letter is ALWAYS a capital letter The following letters are ALWAYS lower case letters. C Carbon Cu Copper Common Elements and Symbols The Element Key