2. The development
3. J.W. Dobereiner
Classified elements into several sets of triads
TRIADS
Li, Na, K
Ca, Sr, Ba
Have similar chemical properties
Properties of the middle element are approximate averages of the
first and third elements
4. J.A.R Newlands
62 elements are already known
law of octaves (increasing atomic mass)
Similar properties: 8th and 1st , 9th and 2nd , 10th and 3rd
5. Dmitri Mendeleev
Together with Lothar Meyer, they published nearly identical schemes
for classifying the elements
Wrote the names of the elements nd its properties in cards and
arranged the cards in various ways.
6. He noticed that a periodic repetition of the properties of the
elements could be observed when the elements were arranged in
increasing atomic masses.
He eventually produced the first periodic table of elements.
7. H.G.J. Moseley
Correctly hypothesized the fundamental property of each elements
the amount of positive charge in the nucleus = Atomic no.
Proposed that the correct way to arrange elements was with the
increasing atomic number
8. The PERIODIC LAW
Basis for the Periodic Table
When elements are arranged in increasing atomic number, heir
physical and chemical properties show a periodic pattern.
9. Reading the periodic table
10. Groups or Families
The arrangement of the elements in vertical columns
Each family has the similar properties
11. Period
Horizontal rows in the periodic table
12. Labeling and naming groups
13. 14. Periodic Trends
15. Metals and Non - Metals
16. Effective Nuclear Charge
The measure of the attraction between the nucleus and the
electron
Also defined by the equation
Zeff = Z S
Wherein,
Z = number of proton in the nucleus
S = average number of electrons that are between the nucleus and
the electron in question
17. 18. Greater Zeff
The greater the attraction between the nucleus and the
electron
The electron are drawn closer to the nucleus
The atomic size is reduced
19. Greater Shielding constant
The lower the Zeff
The lesser the attraction between electrons and the nucleus
20. Electrons in the inner shell (lower n values), effectively
shields the electrons in the outer shell (higher n values)
However the electrons in the same shell do not effectively shield
one another
Example: electrons in the fourth energy level
21. 22. Trend?
Effective nuclear charge increases across any row in the periodic
table.
Effective nuclear charge increases slightly moving down a
family/group
23. Atomic Size
Half of the internuclear distance between adjacent atoms (atomic
radii)
Trend?
Across a period (L-R) = decreases
This is due to the fact that moving from left to right across a
period, the atomic number increases while the shielding factor,
does not significantly increase; therefore, the Zeff increases thus
pulling the electrons towards the nucleus
24. Down a group = increases
Down a group the principal quantum number of the outermost electron
increases
25. 26. Check-up
Arrange the following atoms in order of increasing size:
P, S, As, Se
2. Arrange the following atoms in order of decreasing atomic
radius: Na, Be, Mg
27. Ionic Size
An estimate of the size of an ion in a crystalline ionic
compound
From the relationship between the nuclear size and the atomic size,
the size of the ion relative to its parent atom can be
predicted
28.
Cations are smaller than their parent atom.
When cations form, electrons are removed from the outer
level
Anions are larger than their parent atom
When ions form, electrons are added to the outer level
The increase in repulsion causes the electrons to occupy more
space
29. Isoelectronic series
isoelectronic ions having the same number of electrons
Size decreases as the nuclear charge (atomic number)
increases.
30. Check-up
Arrange the atoms and ions in order of decreasing size: Mg2+, Ca2+,
Ca
Which of the following atoms and ions is the largest ?
S2-, S, O2-
Arrange the ions in order of decreasing size:
S2-, Cl-, K+, Ca2+
31. Ionization Energy
The minimum energy required to remove an electron from the ground
state of the isolated gaseous atom or ion.
First Ionization energy
Energy needed to remove the first electron from a neutral
atom
Second Ionization energy
Energy needed to remove the second electron
The greater the ionization energy, the more difficult it is to
remove an electron
32. 33. Check-up
Referring to a periodic table, arrange the following atoms in order
of increasing first ionization energy.
Ne, Na, P, Ar, K
34. Electron Configuration of ions
When electrons are removed from an atom to form cation, they are
always removed first from the orbitals with largest available
principal quantum number, n.
Example :
Li Li +
35. When electrons are added to an atom to form anion, they are
added to an empty or partially filled orbital
Example:
F F-
36. Check-up
Write the electron configurations for the
Ca2+ ion
Co3+ ion
S2- ion
37. SW
38. Electron Affinity
Energy change that occurs when an electron is added to an
atom
Measures the attraction, or affinity,of the atom for the added
electron
39. Ionization energy vs Electron Affinity
Ionization energy
Measures the ease with which an atom loses an electron
Electron affinity
Measures the ease with which an atom gains an electron
40. 41. 42. 43. Electronegativity
Ability of an atom to attract electrons o itself
44. 45. 46. 47. Worksheet
