S ECTION 1: T HE P ERIODIC T ABLE Chapter 19: Elements and their Properties

W ARM -U P Many parts of our lives are affected by repeated patterns. For example, a calendar shows the patterns of weeks. Name some repeated patterns that you see happening all the time.

L EARNING G OALS Explain the composition of the periodic table. Use the periodic table to obtain information. Explain what the terms metal, nonmetal, and metalloid mean.

O RGANIZING THE E LEMENTS In the late 1800s, Dmitri Mendeleev searched for a way to organize the elements. He arranged all of the elements known at that time in order of increasing atomic mass and discovered a pattern.

O RGANIZING THE E LEMENTS All of the elements of the same color show similar properties.

O RGANIZING THE E LEMENTS When we arrange them in rows, similar properties align in the same column.

O RGANIZING THE E LEMENTS Because this pattern repeated, it was considered to be periodic. Periodic Table: a table that arranges the elements by increasing atomic number and by changes in physical and chemical properties.

O RGANIZING THE E LEMENTS Mendeleev’s table was not perfect. Some elements on the current periodic table show decreasing atomic mass from left to right. Henry Moseley arranged the elements based on atomic number instead. We still use this method today!

T HE P ERIODIC T ABLE All of the elements in the pink squares are metals. Ex: Iron, zinc, and copper Most metals are solids at room temperature Shiny, can be drawn into wires, pounded into sheets, and are good conductors

T HE P ERIODIC T ABLE All of the elements in the green squares are nonmetals. Ex: Oxygen, bromine, and carbon Most nonmetals are gases Most are brittle, and are poor conductors of heat and electricity

T HE P ERIODIC T ABLE All of the elements in the purple squares are metalloids. Ex: Boron, silicon, and arsenic Have some properties of both metals and nonmetals Also called semimetals

T HE P ERIODIC T ABLE Vertical columns of elements are called groups or families. Elements in the same group have similar chemical properties. Horizontal rows of elements are called periods. Atomic number increases across a period.

E LECTRON C LOUD S TRUCTURE Electrons are responsible for giving groups of elements similar properties. In a neutral atom, the number of electrons is equal to the number of protons. A carbon atom has 6 protons and 6 electrons.

E LECTRON C LOUD S TRUCTURE Electrons within the electron cloud have different amounts of energy. We model this difference by placing electrons into different energy levels.

E LECTRON C LOUD S TRUCTURE Energy levels closest to the nucleus have lower energy than those in the outer energy level.

E NERGY L EVELS Energy levels are named using the numbers 1-7. Each number corresponds to a row on the periodic table.

E NERGY L EVELS Hydrogen and Helium are in the first row. Their electrons only occupy energy level 1 Hydrogen has 1 electron in this level Helium has 2 electrons in this level

E NERGY L EVELS Each energy level has a maximum number of electrons that it can hold Energy level 1 can hold 2 electrons Energy level 2 can hold 8 electrons Energy level 3 can hold 18 electrons Energy level 4 can hold 32 electrons Once one energy level is filled, electrons start filling the next level.

E NERGY L EVELS It is the number of electrons in the outer energy level that determines the chemical properties of the element. Valence electrons: the electrons that occupy the outermost energy level.

E NERGY L EVELS Even though each energy level can hold a different total number of electrons, the outermost energy level of an atom can only hold up to EIGHT valence electrons.

E NERGY L EVELS All elements in the same group have the same number of valence electrons.

E LECTRON D OT D IAGRAMS Hydrogen, lithium, and sodium all have one electron in their outermost energy level. We can show this relationship by using electron dot diagrams. Electron dot diagram: uses the symbol of the element and dots to represent electrons in the outermost energy level.

E LECTRON D OT D IAGRAMS Practice: draw the electron dot diagram for the following elements: Lithium (Li) Phosphorus (P) Bromine (Br) Argon (Ar) Strontium (Sr) Oxygen (O)

E LECTRON D OT D IAGRAMS The elements in Group 17 have electron dot diagrams similar to chlorine: Because all members of a group have the same number of valence electrons, they all undergo chemical reactions in similar ways.

E LECTRON D OT D IAGRAMS A common property of the elements in Group 17 is that they easily form compounds with elements from Group 1.

E LECTRON D OT D IAGRAMS Sodium and chlorine come together to form sodium chloride.

E LECTRON D OT D IAGRAMS Not all elements will combine readily with other elements. Elements in Group 18 have full outer energy levels. This causes these elements to be relatively unreactive.

C HECK - IN What do all of the elements in a group have in common?