The Periodic Table
Dmitri Mendeleev(1834 – 1907)
•He organized elements into the first periodic table
•He arranged elements by increasing atomic mass
Henry Moseley(1913)
•He arranged elements according to atomic number rather than atomic mass
•The modern periodic table is arranged by atomic number
Periodic Law
The periodic law states that
there is periodic repetition of chemical and physical properties of elements
The Modern Periodic Table
There are 18 groups (columns up and down)
The group A’s (the tall columns) are called representative elements
•The group B’s (the middle columns) are called transition metals
There are seven periods(rows across the periodictable)
Metals are to the LEFT of the zig-zag line (except hydrogen!)
Metals in yellow
Nonmetals are to the RIGHT of the zig-zag line
nonmetals in red
Metalloids
•Metalloids are those elements ON the zig-zag line
Metalloids border the zig-zag line
Now . . .YOU fill in the chart using your book!
Metals
•solid at room temperature
•shiny (have luster) and smooth
•good conductors of heat and electricity
Metals
•malleable – “bendable” (can be pounded into sheets)
•ductile - can be pulled into wires
Metals
•react with acids
•mercury (Hg) is the only LIQUID metal
Nonmetals
•generally gases or brittle, dull looking solids at room temperature
•poor conductors of heat and electricity
•Bromine (Br) is the only LIQUID nonmetal
Metalloids
•sometimes called semimetals
•metalloids have properties of both metals and nonmetals
Metalloids
•silicon and germanium are two of the most important metalloids (they’re used in computer chips and solar cells)
Trends of the Periodic Table
Periodic LawIf elements are organized according to atomic number, their properties will repeat periodically
Four Periodic Trends:
1.Atomic radii
2.Ionic radii
3.Electronegativity
4.Ionization energy
Atomic RadiusThe atomic radius basically tells you the size of the atom. It is half the distance between two nuclei of identical atoms bonded together.
radius
The trend: atomic radii DECREASE across a
period•Why?
•Each time a positive proton is added to the nucleus, the negative electrons feel a greater attraction to the positively-charged nucleus and get “pulled in” tighter
Decreasing – getting smaller!
Trend: atomic radiiINCREASE down a group
•Why?
•electrons are added to higher and higher energy levels as you go down
Atomic radii DECREASE down a group!
The farther the electrons from the nucleus, the larger
the atomic radii!!!!!
Try these . . .
1.Which element has the larger atomic radius: C or F?
carbon
2.Which element has the smaller atomic radius: Ar or Kr?
argon
Ionic Radii
•Is basically the size of an ion or half the distance between the nuclei of two ions bonded together
What is ion???
Ionic Radii
•Ion – an atom with a charge (+ or - )
•An ion is formed when atoms lose or gain electrons
•What happens to an atom if it LOSES an electron?
it loses a negative charge so it becomes POSITIVE
Na +1
•A positively charged ion is called a cation
Na +1
Positive ions (cations) are smaller than the atoms they come from because they lose electrons making the atom smaller.
Na Na +1
•What happens to an atom if it GAINS an electron? It gets more negative
(so it has a negative charge) Cl -1
A negatively charged ion is
called an anion.
Cl -1
Negative ions (anions) are LARGER than the atoms they come from because they gain electrons – making the atom LARGER!
Cl -1 Cl
The trend:
•See the board
Remember . . .
•all atoms want a full octet (8 valence electrons)
•atoms with 1 valence electron will give up that electron VERY QUICKLY to become stable
example: •sodium has one valence electron: 1s22s22p63s1 •if sodium gives it away, then the configuration will be:
1s22s22p6
•sodium will have a full octet
•atoms with 7 valence electrons will hold on to those electrons VERY TIGHTLY
•they try to get one more and become stable
Ionization Energy•The amount of energy needed to remove an electron
•think of it as: how tightly an atom holds on to its electrons
The trend:•ionization energy INCREASES across a period
•Why?
•the more valence electrons an element has, the more difficult it is to remove them!
The trend:•Ionization energy DECREASES down a group
•Valence electrons in higher energy levels are NOT held as tightly because they are farther from the nucleus
•Therefore, it is easier to remove an electron that is farther from the nucleus
Try these . . .
•Which has a higher ionization energy: Na or Cl
Chlorine •Which has a lower ionization energy: Li or O
Lithium
Electronegativity
•The ability of an atom to attract electrons to itself
The Trend: electronegativity
INCREASES across a period •Why?•atoms are trying harder to attract electrons to get a full octet
The trend: electronegativity
DECREASES down a group
•Why?
•it is harder to hold on to the electrons that are farther away from the nucleus
Try these . . .
•Which element is more electronegative? F or Br
Fluorine•Which element is more electronegative? B or Ca
Boron
Finished!