12 Arranging the Elements Ch 12 The Periodic Table 12 Arranging the Elements

Discovering a Pattern Dmitri Mendeleev discovered a pattern to the elements in 1896. First he wrote the names and properties of the elements on cards. Then he arranged his cards in order of increasing mass. A pattern appeared!  Periodic - happening at regular intervals, like days of the week.

Elements with similar properties occurred in a repeating pattern.

Discovering a Pattern Mendeleev predicted that elements yet to be found would fill in the gaps in his table. He was right! Missing element Germanium (Ge) fit into his gap.

Changing the Arrangement Some elements did not fit in the table by increasing atomic mass – so Mendeleev changed his table. 1914 Henry Moseley determined the number of protonsin an element. When the periodic table was arranged by increasing atomic number, all elements fit the table. Periodic Law-Repeating chemical and physical properties of elements change periodically with the elements’ atomic numbers.

The Periodic Table and Classes of Elements Metals – found to the left of the zigzag line Few electrons in the outer energy level All solids at room temp. except Mercury (Hg) shiny ductile malleable good conductors

METALS

The Periodic Table and Classes of Elements Nonmetals - found to the right of the zigzag line almost a complete outer energy level (Group 18 is complete) more than half are gases at room temp. not shiny not malleable not ductile not good conductors (good insulators)

The Periodic Table and Classes of Elements Metalloids – found on the zigzag outer energy level is half full have some properties of metals have some properties of nonmetals sometimes called semiconductors

Decoding the Periodic Table Each square on the periodic table includes: Atomic number Chemical symbol Chemical name atomic mass

Decoding the Periodic Table Period- Each horizontal row of elements Group- Each columnof elements. Elements in the same group have similar properties. Elements in the same period have the same number of electron shells

5.2 Grouping the Elements Group 1 – Alkali Metals Elements in group 1 of the periodic table One valence(electron in the highest occupied energy level) Very reactive because they can easily give away the 1 electron Often stored in oil because they react violently with water and oxygen Soft, silver color, shiny and low density

Group 1 - Alkali Metals Alkali metals in water

Group 2 – Alkaline Earth Metals Elements in group 2 of the periodic table 2 valence electrons Slightly less reactive than alkali metals because it’s harder to give away 2 electrons silver color, higher density

Group 2 – Alkaline Earth Metals Chlorophyll contains Mg; oyster shell, pearl, and cast contain calcium

Group 3-12 – Transition Metals Do not give away electrons as easily as group 1 or 2 1 or 2 valence electrons Shiny, good conductors, higher densities and melting points (except Hg) Some transition metals from periods 6 & 7appear below the table to save space. Elements in each row tend to have similar properties Lanthanides- shiny, reactive metals Actinides- radioactive , or unstable. Elements listed after plutonium do not occur naturally.

Group 13 Boron Group Group 13 Boron Group 4 metals, 1 metalloid 3 valence electrons solid at room temp. Aluminum (Al) is most abundant metal in Earth’s crust reactive

Group 13 Boron Group

Group 14 Carbon Group Group 14 – Carbon Group 4 valence electrons solids at room temp. carbon is needed in body for carbs, fats, and protein.

Group 14 Carbon Group

Group 15 Nitrogen Group Group 15 Nitrogen Group 5 electrons in outer energy level most are solids at room temp. except N N is 80% of the air we breathe, fertilizer

Group 15 Nitrogen Group

Group 16 Oxygen Group Group 16 Oxygen Group 6 valence electrons Reactive Oxygen (O) is 20% air and needed for substances to burn

Group 16 Oxygen Group

Group 17 Halogens Group 17 Halogens 7 valence electrons very reactive Form salts with alkali metals poor conductors

Group 17 Halogens

Group 18 Noble Gases Group 18 Noble Gases All nonmetals 8 valence electrons (except He – 2) unreactive Colorless, odorless gases at room temp.

Group 18 Noble Gases

Hydrogen Hydrogen 1 valence electron reactive,colorless, odorless, explosive reactions w/ oxygen