The Periodic Table of Elements

Periodic  Periodic Law  Periodic Table Something periodic occurs at regular or at least generally predictable intervals Periodic law - physical and chemical properties of the elements are periodic functions of their atomic numbers Periodic Table of Elements – a table of the elements, arranged by atomic number, that shows the patterns in their properties; based on the periodic law

Element A pure substance made up of one kind of atom that cannot be broken down into simpler substances by physical or chemical means 92 occur naturally on earth The rest were synthesized (made) by scientists

Dmitri Mendeleev In the 1860’s he devised a periodic table where the elements were ordered by their atomic masses He did this by grouping elements together according to their similarities He found missing gaps that predicted the existence of unknown elements

Why do you think there are question marks here? Image taken from: Mendeleev’s Published Periodic Table of Elements

Mendeleev’s Predictions Although Mendeleev’s Periodic Table of Elements had missing elements or “gaps,” he was able to predict the characteristics of these missing elements because of Periodic Law. Date Predicted 1871Date Discovered 1886 Atomic Mass72Atomic Mass72.6 Density5.5 g/cm 3 Density5.47 g/cm 3 Bonding Power 4 4 ColorDark GrayColorGrayish White “Ekasilicon”Germanium Notice how Mendeleev’s predictions (orange column) were very accurate when compared to Germanium’s actual characteristics (green column)

Henry Moseley In 1914, his work led to a revision of the periodic table by rearranging the elements by their atomic numbers He concluded that the number of protons in an atom is its atomic number We now use a periodic table that uses the atomic number, the atomic mass, and the number of electrons and valence electrons to classify and categorize elements. /

Electrons Typical student: “Mr. Owens, did you say valence electrons? What the heck are valence electrons?” Mr. Owens replies: “Remember that atoms have electrons which control the overall charge of an atom. In a neutral atom, one that is not reactive, the number of protons = the number of electrons (each positive piece has a matching negative piece). Electrons control how, and when, an atom will form a compound.”

Electrons (valence electrons) Here’s how that happens: Electrons fill their electron shells (also called energy levels, or orbitals) from the one closest to the nucleus to the outer shells. In other words, the 1st shell can have 2 electrons, at which point it is full. The 2 nd shell can have up to 8 electrons, and then it is full. The 3 rd shell can have up to 8 (or 18 in some situations), and then it is full; the same with the rest of the shells. The number of shells an atom has is equal to its period (row), and the number of electrons in an outer shell is equal to its family (group or column). More on that a little later..

Electrons (valence electrons) Valence electrons are only the electrons in an outer shell, and are the only ones involved in bonding. Only the ones in the outer shell are valence electrons. Valence electrons

Types of elements There are 3 types of elements: Metals Non-metals Metalloids

Metals Location Found on the left of the zigzag line/staircase on the periodic table (exception  Hydrogen) Chemical Properties Have few electrons in their outer energy level, thus lose electrons easily Physical Properties ductile, good conductors, malleable, shiny, most are room temperature What metal is not a room temperature? Image taken from: lement-Photo-Gallery.--98/Sodium.htm 11 Na Au

Atoms with Few Electrons in their Outer Energy Level Notice: only 1 electron in outer level Notice: only 2 electrons in outer level Na Be 9.012

Non-Metals Location Most found to the right of the zigzag line/staircase on the periodic table Chemical Properties Most have almost full outer energy levels, thus they tend to gain electrons; some have completely full outer level Physical Properties not ductile or malleable, not shiny, poor conductors, most are solid, but some are gas at room temperature Image taken from: Image taken from: 16 S Cl

Atoms with Full or Almost Full Outer Energy Level Notice: 7 electrons in outer level – almost full Notice: 2 electrons in outer level – FULL Notice: 6 electrons in outer level – almost full F O He 4.003

Metalloids Location Border the zigzag line/staircase on the periodic table Chemical Properties Most atoms have ½ (≈) complete set of electrons in outer level Physical Properties have properties of both metals and non- metals (can act like both at times) Image taken from: Image taken from: 5 B Si

Atoms with less than a Complete Outer Energy Level Notice: only 3 electrons in outer level Notice: only 4 electrons in outer level B Si

Important Features of the Periodic Table: Period (Row) each horizontal row of elements on the periodic table FROM LEFT TO RIGHT OR RIGHT TO LEFT How many periods (rows) are on the Periodic Table Of Elements?

Period (Row) Properties Seven periods on a periodic table (numbered from the top down, 1-7) Atomic numbers and atomic masses increase as you move from the left to the right in a period All atoms of the elements in the same period have the same number of orbitals/levels/shells All atoms of the elements in a specific period have that respective number of orbitals/levels –Example Period 1 = 1 orbital Period 2 = 2 orbitals Period 3 = 3 orbitals Etc…

Examples of Period (Row) elements having the same number of orbitals/levels in their atoms In what period (row) do you think these atoms reside? In what period (row) do you think these atoms reside?

each column of elements on the periodic table Important Features of the Periodic Table: Group (Family) FROM TOP TO BOTTOM OR BOTTOM TO THE TOP How many groups (families) are on the Periodic Table Of Elements?

Group (Family) Properties Eighteen groups on the periodic table (numbered from left to right) Atomic numbers and atomic masses increase as you move from the top down in a group (family) Atoms of elements in the same group have the same number of electrons in the outer orbitals/levels of their atoms (known as valence electrons) –Exceptions: Transition elements (3-12) Hydrogen (could be 1 or 17) Helium (actually has 2 valence electrons) Elements in groups usually have similar physical and chemical properties

Examples of Group Elements with the same # of valence electrons 87 Fr (223) 55 Cs Rb K Na Li H How many electrons do each of these atoms have in their outer orbital/level? What group (family) do these elements reside in?

Group (Family) Names Alkali Metals Alkaline Earth Metals Transition Metals Boron Group Carbon Group Nitrogen Group Oxygen Group Halogens Noble Gases

Identify the Element Period 2 – Group 14  Carbon - C Period 5 – Group 2  Strontium - Sr Group 17 – Period 6  Astatine - At Group 4 – Period 7  Rutherfordium - Rf

Using the Periodic Table The boxes that make up the periodic table contain a significant amount of information. To understand this information, it is necessary to refer to the periodic table’s key(s) Atomic Number (Number of protons) Element Symbol (Written with a capital letter or a capital followed by a lower case if two letters ) Atomic Mass (Rounded to a whole number, equals the number of protons and neutrons) 8 O Oxygen ClassColor Metal Non-Metal Metalloid State Room Temp.) Symbol Color Solid Liquid Gas Which class does Oxygen fall into? What is Oxygen’s physical state of matter? Element Name