THE PERIODIC TABLE Organizing the Elements
Jan 19, 2016
THE PERIODIC TABLEOrganizing the Elements
Organizing the Elements
Copper, Silver, and Gold 1700, 13 elements have been
identified Rate of discovery increased..why?
1765-1775 Including hydrogen, nitrogen, and
oxygen
Organizing the Elements
Chemists used the properties of elements to sort them into groups.
Dobereiner (1780-1849)
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 Configuration1A
2A 3A 4A 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 s2
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