Organizing the Elements

 Copper, Silver, and Gold  1700, 13 elements have been identified  Rate of discovery increased..why?   Including hydrogen, nitrogen, and oxygen

Organizing the Elements  Chemists used the properties of elements to sort them into groups.  Dobereiner ( )  Elements were grouped into triads.  Chlorine, Bromine, Iodine

Dobereiner’s Triads  Chlorine, Bromine, Iodine  Physically completely different.  Chemically react similar: react easily with metals.

Organizing the Elements  1869-Mendeleev published his table of the elements.  More than 60 elements  Mendeleev arranged the elements in his periodic table in order of increasing atomic mass.

Mendeleev’s Periodic Table

Organizing the Elements  Based on chemical properties, arranging elements according to atomic mass only produced problems.  Elements that should have been grouped together weren’t, etc.  Mendeleev organized his table before the discover of protons and the assignment of atomic numbers to all of the elements.

Organizing the Elements  1913, Henry Moseley determined an atomic number for each known element.  In the modern periodic table, elements are arranged in order of increasing atomic number.

Modern Periodic Table  7 periods  Periods correspond to energy levels. Increase as the period number increases.  18 groups  Elements within each group share similar properties.  Pattern changes from left to right.

Modern Periodic Table  Periodic Law  When elements are arranged in order of increasing atomic number, there is a periodic repetition of their physical and chemical properties.  Classes of elements: metals, nonmetals, and metalloids.

Metals 80 %  Sodium, iron, copper, any elements appearing in yellow.  Properties of metals:  Conductors of heat and electricity  High luster  Solid at room temp  Ductile  malleable

Metals

Nonmetals  Identified in blue (red)  Neon, carbon, nitrogen, oxygen  Greater variation in properties:  Gases at room temperatures, few are solids like sulfur and phosphorus, and one liquid- bromine. Brittle

Metalloids  Heavy stair step line separating metals and nonmetals. Identified as green (blue).  Metalloids have properties similar to metals and nonmetals.  Alter properties of metalloids by changing the conditions of the metalloids.  silicon

Classifying the Elements Neon

Classifying by Group  Group IA - Alkali Metals  Group 2A – Alkaline Earth Metals  Group 7A- Halogens (Nonmetals)

Classifying by Electron Configurations  Electrons play a key role in determining the properties of elements.  Place elements in groups by the number of elements in the last orbital, or the number of valence electrons.  Noble Gases, Representative Elements, transition metals, and inner transmission elements.

Electron Configuration 1A 2A 3A4A 5A 6A 7A 8A

Noble Gases Group 8A  Inert Gases  8 electrons in last orbit  Helium, neon, argon, etc

Representative Elements  1A-7A  Wide range of physical and chemical properties  Last orbital of electron cloud is not filled

Transition Elements  Group B  Transition Metals- presence of electrons in d orbitals  Displayed in the main body of the periodic table: copper, silver, gold, and iron  Inner transition metals- presence of electrons in f orbitals  AKA: rare earth elements

Electron Orbitals

Electron Sub-orbitals

Energy Levels

Classify by Energy Level  Noble Gases- Orbitals end in p, this will always be filled. Helium (He) will end in s 2  Representative Element- orbitals end in s or p, these orbitals will NOT be filled.  Transition Elements-orbitals end with a combination of unfilled d orbitals and s orbitals.

Periodic Trends  Trends in Size  Atomic Radius-one half of distance between the nuclei of two atoms of the same element when the atoms are joined.  Atomic size increases from top to bottom within a group and decreases from left to right across a period.

Atomic Size

Atomic Radius

Ions  Atom or a group of atoms that have a positive or negative charge  Formed when electrons are transferred between atoms  Positive = cation, written as 1+  Negative = anion, written as 1-

Sodium Ion

Trends in Ionization Energy  Energy required to remove an electron from an atom  Decreases from top to bottom within a group, and increases from left to right across a period.

Trends in Ionization Energy

Trends in Ionic Size