Chem study guide Essay

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Gold and copper have been known for thousands of years
Only 13 elements had been discovered since 1700 as more elements were discovered, chemists realized that they needed a way to organize elements
Chemists used properties of elements to sort them into groups
J.W. Dobereiner arranged elements into triads groups of 3

By the mid-1800s about 17 elements were known to exist
Dmitri Mendeleev – a Russian chemist and teacher
Arranged elements in order of increasing atomic mass
Thus, the first “Periodic Table”
He left blanks for yet undiscovered elements
When they were discovered, he had made good predictions
But, there were problems:
Ex. Te and I,
Iodine weighs less thean tellurium but Tellurium comes before Iodine on the periodic table
Such as Co and Ni; Ar and K; Te and I

In 1913, Henry Moseley – British physicist, arranged elements according to increasing atomic number
The arrangement used today
The symbol, atomic number & mass are basic items included

Many different periodic tables are still used today

When elements are arranged in order of increasing atomic number, there is a periodic repetition of their physical and chemical properties.
Horizontal rows = periods
There are 7 periods
Vertical column = group (or family)
Similar physical & chemical prop.
Identified by number & letter (IA, IIA)

Three classes of elements are: 1) metals, 2) nonmetals, and 3) metalloids
Metals: electrical conductors, have luster, ductile, malleable
Nonmetals: generally brittle and non-lustrous, poor conductors of heat and electricity

Metalloids: border the line-2 sides
Properties are intermediate between metals and nonmetals

Group IA – alkali metals
Forms a “base” (or alkali) when reacting with water (not just dissolved!)
Group 2A – alkaline earth metals
Also form bases with water; do not dissolve well, hence “earth metals”
Group 7A – halogens
Means “salt-forming”

Elements can be sorted into 4 different groupings based on their electron configurations:
Noble gases
Representative elements
Transition metals
Inner transition metals

Noble gases are the elements in Group 8A (also called Group18 or 0)
Previously called “inert gases” because they rarely take part in a reaction; very stable = don’t react
Noble gases have an electron configuration that has the outer s and p sublevels completely full

Representative Elements are in Groups 1A through 7A
Display wide range of properties, thus a good “representative”
Some are metals, or nonmetals, or metalloids; some are solid, others are gases or liquids
Their outer s and p electron configurations are NOT filled

Transition metals are in the “B” columns of the periodic table
Electron configuration has the outer s sublevel full, and is now filling the “d” sublevel
A “transition” between the metal area and the nonmetal area
Examples are gold, copper, silver

Inner Transition Metals are located below the main body of the table, in two horizontal rows
Electron configuration has the outer s sublevel full, and is now filling the “f” sublevel
Formerly called “rare-earth” elements, but this is not true because some are very abundant

Alkali Metals:
Alkali metals all end in s1
Alkaline earth metals all end in s2 really should include He, but it fits better in a different spot, since He has the properties of the noble gases, and has a full outer level of electrons.

1. First ionization energy
2. Ionic size
3. Electronegativity
4. Electron affinity
5. Atomic size
6. Shielding

1. Ionization Energy:
Ionization energy is the amount of energy required to completely remove an electron (from a gaseous atom).
Removing one electron makes a 1+ ion.
The energy