PERIODICITY
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Transcript of 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 # ORBITALS # ELECTRONS
S 1 2P 3 6D 5 10F 7 14
Electron Configuration
What period are the follow elements in based on their electron configurations?
1) Nitrogen2) Aluminum3) 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 Metals
• Group 1• Very reactive• 1 valence electron• ns1
• Soft• Silvery
Alkali Earth Metals
• 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 1- charge.
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.