Elements & The Periodic Table

Forces within an atom… 1) Electromagnetic force Opposite charges attract protons (+) attract electrons (-) Like charges repel protons (+) repel protons (+) electrons (-) repel electrons (-) This holds the electrons in their energy levels

Forces within an atom… 2) Strong force Cancels out the electromagnetic force Holds the protons together along with the neutrons in the nucleus The attraction between the particles that make up the protons and neutrons (quarks) are stronger than the force of repulsion (like 2 body builders playing tug of war) Only works when the particles are close enough together The neutrons help to separate the protons from each other so that they do not feel as strong of a repulsive electromagnetic force http://www.youtube.com/watch?v=UkLkiXiOCWU

Periodic Table The Periodic Table was “invented” by Dmitri Mendeleev around 1870 At the time there were only about 65 elements discovered Multiple chemists had determined the properties of these elements (i.e. relative masses, chemical activity, physical properties) but there was no systematic way of organizing the elements

Periodic Law Mendeleev noticed that certain groups of elements had similar properties He found that when he listed the elements in order of increasing relative mass those similar properties reoccurred in a pattern Periodic Law: When elements are arranged in order of increasing relative mass, certain sets of properties recur periodically

The First Periodic Table Mendeleev organized elements in a table Mass increased from left to right Elements with similar properties in same vertical columns He was able to predict properties of elements that had not been discovered yet

The Modern Periodic Table Elements are listed in order of increasing atomic number (not relative mass like Mendeleev’s) Elements are still grouped according to common properties

Location of Metals, Non-Metals, Metalloids The Periodic Table is split by the “stair-step” line On your Periodic Table: Draw in the stair-step line

Location of Metals, Non-Metals, Metalloids, & Transition Elements Metals are located on the LEFT of the stair-step line Non-Metals are located on the RIGHT of the stair-step line Metalloids are located next to the stair-step line (B, Si, Ge, As, Sb, Te, At) Transition Elements are located in the SHORT columns On your Periodic Table: Write in Metals, Transition Elements, Metalloids, and Non-Metals on the top next to each section

Properties of Metals Physical Properties Chemical Properties Have luster (shininess) Conduct heat and electricity Ductile (can be made into wires) Malleable (can be hammered into sheets) Chemical Properties Tend to be electron donors (lose electrons) Many corrode (react with water or air) Precious metals (gold and silver) are not very reactive

Properties of Non-Metals Physical Properties Generally the opposite of metals May be solid, liquid or gas at room temperature Have much lower densities and melting points than metals Chemical Properties Tend to be electron acceptors (gain electrons) Noble Gases (Group 18) do not react with other elements

Properties of Metalloids Metalloids have properties of both metals and non-metals

Properties of Transition Elements Transition elements are located in the short columns (#3-12) Properties are more difficult to predict Number of valence electrons can vary because the electrons shift or “transition” from one energy level to the other

Properties of Rare Earth Elements Rare Earth Elements are the 2 “removed” rows (on the bottom of your Periodic Table) These rows fit between Lanthanum (La # 57) and Hafnium (Hf #72) and Actinium (Ac#89) and Rutherfordium (Rf#104) Many of these are man-made elements The bottom row (#90-#103) are called the Actinoids- these are all radioactive

Groups on the Periodic Table Elements are listed in groups (families) Groups are represented in each vertical column (up and down)

Patterns within a Group 1) All elements in the group have the same number of valence electrons (in the tall columns) and therefore the same charge (we’ll talk more about this during bonding) Valence electrons are the electrons in the outermost electron energy level On your Periodic Table: Number each column (1-18) *Your book numbers each tall column with an A after the number and each short column with a B after the number *Note: The transition metals (short columns) do not necessarily follow these rules, but the elements in the tall columns do!

Patterns within a Group: METALS 2) Metals become MORE reactive as you move DOWN a group and the ATOMS become LARGER (top to bottom) The larger an atom is, the further those valence electrons are from the nucleus, and the easier it is to remove those valence electrons

Patterns within a Group: NON-METALS 3) Non-Metals become LESS reactive as you move DOWN a group and the ATOMS become LARGER (top to bottom) Non-metals tend to GAIN electrons when they undergo chemical changes so it becomes more difficult to gain electrons when the atom is larger because the electromagnetic force is not as strong the further you get from the nucleus

Main-Group Elements Elements in the tall columns (1,2, 13-18) Group 1: Alkali metals very reactive, especially with water! Group 2: Alkaline Earth metals fairly reactive, but not as much as alkali metals Group 17: Halogens most reactive non-metals Group 18: Noble Gases non-reactive (have full valence shells) Other Main Groups: named according to element at the top of their column

Periods on the Periodic Table Elements are also listed in periods Periods are represented in each horizontal row (left to right)

Patterns within a Period 1) All of the elements within the same period contain the same number of electron energy levels 2) Elements become LESS metallic as you move from left to right 3) Atom size DECREASES as you move left to right As you move left, the electromagnetic force increases between the protons and electrons, pulling the energy levels in “tighter” On your Periodic Table: Number the Periods 1-7

Noble Gases Group- Not Reactive More Reactive More Reactive Noble Gases Group- Not Reactive http://www.chem1.com/acad/webtext/atoms/atpt-6.html