Getting to know the Periodic Table

Before getting to know the periodic table Drawing Bohr Models and electron dot diagrams

Bohr Model of the Atom Neils Bohr developed a model of the atom in which the electrons orbit the nucleus in fixed orbits like the planets orbiting the sun. We now know that rather than fixed orbits the electrons move about the nucleus in an electron cloud. The electron cloud has energy levels just as Bohr’s model did. Each energy level has a specific number of electrons it can hold. The first energy level can hold two electrons, the second energy level can hold 8 electrons, and the third energy level can hold 18 electrons. The formula 2n2 where n is the energy level can be used to determine how many electrons any energy level can hold. There is only a maximum number of electrons an energy level can hold there is no minimum.

Bohr Model of the Atom - A representation of all the electrons of an atom Determine the number of electrons a particular element has - #electrons = #protons Draw a small circle - this represents the first energy level of an atom and it can only hold 2 electrons Draw dots on this first circle to represent electrons (no more than two) If the atom has more than 2 electrons (total) draw a second circle to represent the second energy level. It can hold a maximum of 8 electrons. Add dots to represent the additional electrons. Continue drawing increasingly larger circles and adding dots for electrons until you have one dot for each electron in the atom. The total number of dots on all the circles should equal the total number of electrons in the element.

Electron dot diagrams Also known as Lewis dot diagrams or Lewis structures Are a representation of an atom’s valence electrons Valence electrons are those electrons located in an atoms outermost energy level They are the electrons involved in bonding

Determine the number of valence electrons, this can be done using the electron configuration or by memorizing based on the atom’s group Draw the element’s symbol Place one dot for each valence electron around the symbol There will never be more than 8 dots

N

Periodic Table Arrangement The periodic table is arranged by increasing atomic number. It is also divided into periods and groups.

Periods Horizontal rows are called periods.

Periods The period number corresponds to the number of energy levels an atom in that period has. Example: all elements in period 3 (the turquoise) have three energy levels

Groups Vertical columns are called groups.

Groups/Families Groups are also called families. All elements in the same group have the same number of valence electrons. Elements with the same number of valence electrons have similar properties. Since they have similar properties they are in the same family.

Groups/Families The groups have specific names. There are 5 you must remember: Group 1 elements are the alkali metals.

Alkali Metals 1 valence electrons Extremely reactive Reactivity increases from top to bottom Like to give up electrons http://www.youtube.com/watch?v=wY0afMI4Jgc http://www.youtube.com/watch?v=YvSkXd_VVYk http://www.youtube.com/watch?v=pPdevJTGAYY

Groups/Families Group 2 elements are the alkaline earth metals.

Groups/Families Groups 3 – 12 are the transition metals.

Groups/Families Group 17 are the halogens (sometimes called halides).

Halogens 7 valence electrons Highly reactive Like to gain electrons http://www.periodicvideos.com/videos/009.htm

Groups/Families Group 18 are the noble gases.

Groups/families All elements in the same group have the same number of valence electrons. Group 1 elements have 1 valence electron. Group 2 elements have 2 valence electrons. Group 13 elements have 3 valence electrons. Group 14 elements have 4 valence electrons. Group 15 elements have 5 valence electrons. Group 16 elements have 6 valence electrons. Group 17 elements have 7 valence electrons. Group 18 elements have 8 valence electrons.

Metals/Nonmetals/Metalloids The periodic table is divided into metals, nonmetals, and metalloids. The metals are located to the left of the dark stair stepped line. The nonmetals are located to the right of the dark stair stepped line. The metalloids are located along the stair stepped line.

Metals/Nonmetals/Metalloids The metals are colored gray. The metalloids are colored blue. The nonmetals are colored beige.

Metals Metals are: Shiny General hard Malleable Good conductors of heat and electricity Most are solids at room temperature http://www.periodicvideos.com/videos/026.htm

Nonmetals Nonmetals are: Brittle if solid Most are gases Not good conductors http://www.youtube.com/watch?v=wmC8Dg4n-ZA

Metalloids Have properties of metals and nonmetals. http://www.periodicvideos.com/videos/033.htm

Periodic Trends: atomic radius Atomic radius is an indication of atom size It is actually half of the distance between 2 adjacent nuclei

Atomic Radius Trend

Atomic Radius The inner 2 electrons shield the outer electrons from the pull of the nucleus and atoms get larger as you go down a group. And you add an energy level as you go down. As you go across the periodic table from left to right atoms get smaller because adding additional protons and electrons increases the attraction between the nucleus and electrons

Electronegativity The ability of an atom to attract electrons Fluorine is the most electronegative element

Electronegativity

Ionization energy The energy required to remove an electron.

H He Li Be B C N O F Ne Na Mg Al Si P S Cl Ar K Ca Ga Ge As Se Br Kr