Download periodicity

PERIODICITY
SC4b. Compare and contrast trends in the
chemical and physical properties of elements
and their placement on the Periodic Table
The Periodic Table
• Started by Dmitri Mendeleev – arranged by
atomic mass
– Wrote out info known about 63 elements on cards
– Arranged by similar properties
– Predicted existence of 3 unknown elements
– w/I 4 years, 2 had been discovered
• Since Mendeleev, evidence has supported that
the arrangement of elements should be based
on the elements atomic number (# of protons)
Periodic Law
• Periodic Law – the physical and
chemical properties of the elements
are periodic functions of their
atomic numbers.
• Periodic Law allows properties of
elements to be predicted based on
their position in the periodic table.
The Periodic Table
• Period – horizontal row across the PT
– Elements in a row have the same number of major
energy levels
– i.e. A Row 4 element has 4 major energy levels
• Group – vertical column in the PT
– Elements in the same group have the same # of
valence electrons
– Valence e-’s are the outermost, bonding electrons
(always in the S and P orbitals)
By the NUMBERS
Based on the Noble Gases He, Ne, Ar,
Kr, Xe, and Rn, is there a repeatable
pattern of atomic numbers?
A: 2, 8, 8, 18, 18, 32
The Periodic Table
• Chemical and Physical
properties
– Vary across a period
– Similar down a group
• Elements are either
solids or gases (only 2
liquid elements at room
temperature, Hg & Br)
METALS
• Metals – majority of the PT (78 %)
– Properties include high conductivity, high density,
solid at room temp., malleable, ductile, and
lusterous.
• Primarily belong in sublevels S, D, and F.
METALLOIDS
• Metalloids – have properties b/w metals and
non-metals; small portion (7 %)
NON-METALS
• Non-metals – make up right side of PT (15%)
• Properties include being non-conductive, low
density, mostly gases at room temp., brittle,
non-lusterous
• 7 non-metals form DIATOMIC (2 atoms)
molecules when pure elements
Quantum Numbers
• The Principal Quantum Number (n)
– Main energy level
• Sublevels (s, p, d, f)
• The principal quantum number is followed by
the sublevel and the number of electrons
within the sublevel
Sublevels
SUBLEVEL
S
P
D
F
# ORBITALS # ELECTRONS
1
3
5
7
2
6
10
14
Electron Configuration
What period are the follow elements in based
on their electron configurations?
1) Nitrogen
2) Aluminum
3) Calcium
Valence Electrons
Valence Electrons
• electrons in the highest
energy level of atoms of
an element
• Each element in a group
has same # of valence
e-’s
• Electrons available to be
lost, gained, or shared
in bonding
Group
# of Valence e-’s
1
1
2
2
3-12
Varies b/w 1,2,3
13
3
14
4
15
5
16
6
17
7
18
8
Group Names
•
•
•
•
•
•
•
Alkali metals – group 1 of the PT
Alkaline Earth metals – group 2 of the PT
Transition Metals – groups 3-12 of the PT
Halogens – group 17 of the PT
Noble gases – group 18 of the PT
Lanthanides – elements 58 – 71
Actinides – elements 90 - 103
Groups 1 & 2
Alkali Earth Metals
Alkali Metals
•
•
•
•
•
•
Group 1
Very reactive
1 valence electron
ns1
Soft
Silvery
•
•
•
•
•
•
Group 2
Reactive
2 valence electrons
ns2
Soft
Silvery
Halogens
• Group 17
• Most reactive group of elements
• Why? They have 7 valence electrons and want
1 to have a full octet
• Based on electronegativity values
• Have an electron configuration of ns2 np5
• Fluorine has the greatest Electronegativity
Noble Gases
•
•
•
•
•
Group 18
8 valence electrons
ns2 np6
Not reactive
All gases
PERIODICITY
SC4a. Use the Periodic Table to predict
periodic trends including atomic radii,
ionic radii, ionization energy, and
electronegativity of various elements.
Periodic Trends
• Atomic Radius
• Electron Affinity
• Ionic Radius
• Ionization Energy
• Electronegativity
Atomic Radius
• Atomic radius  ½ the distance b/w the
nuclei of identical atoms that are bonded
together
• Radii decrease across a period
• Radii increase down a group
Electron Affinity
• Electron affinity – the amount of energy
absorbed when an electron is added to an
isolated gaseous atom to form an ion with a 1charge.
Cl(g) + e-  Cl- (g)
EA = -349 kJ/mol
Electron Affinity
Ionic Radius
• Cation – a positively charged ion (i.e. Na1+)
• Anion – a negatively charged ion (i.e. F1-)
• Ionic radius increases from right to left across
a period and increases from top to bottom
down a group.
Ionization Energy
• Ionization Energy - energy needed to
remove 1 e- from a neutral atom
• Increases from bottom to top in a group.
• Increases from left to right across a
period.
Electronegativity
• Electronegativity is a measure of the relative
tendency of an atom to attract electrons to
itself when it is chemically combined with
another atom.
• Elements w/ HI Electronegativity’s
(nonmetals) gain electrons to form anions.
• Elements w/ LOW Electronegativity’s (metals)
often lose electrons to form cations.